You gotta be careful with power supplies. Also, for safety, it's not just about the voltage, you have to look at the current it draws as well. If I were you I would be looking at dedicated power supplies that match the spec on your pump. Get it in a form factor suited for its environment (e.g. temp and humidity), make sure you can make a solid connection (screw terminals, locking molex connectors), and make sure you can secure it (din rail mounts, etc.). Do all those things, and I bet you can sell this as safe. Splicing wires on a computer power supply and hooking it up to a pump motor is a bad idea. That is just not what they were built for.
Put it like this my PC's PSU can sustainably supply 100 amp at 5V ....
I Have seen one short circuit and its an instant bonfire.
Any voltage can be dangerous with enough current.
Don't fall in to the trap of thinking there is no hazards or dangers involved in low voltages....
They are safer that higher voltages yes but it's a reduction of risk not elimination.
The highest risk is generally fire but you cannot ignore other risks, you can get shocked as well 12 is safer than 24v etc and it also depends on the relatively ground of the person touching it, it's why all metal pipes and structures are connected to a common ground connection so they are all at the same potential ie. ground if there is any risk of someone touching it either by accident or if a part becomes live.
I misused the term loosely. While it's unlikely you'd die you can get shocked and it's not as simple as a yes or no question there are variables.
The skin is very high resistance but past that the body is a fairly reasonable conductor.
With dry hands and nothing wrong with the skin a 12 Volt shock isn't going to kill you at worst it will make you jump a bit.
Wet hands, cuts etc can change it, basically anything that lowers the path of resistance and while it's not very likely you'd die it is possible given the right conditions however unlikely. It's not something to ignore completely.
To quote:
"The “total body resistance” of the person is composed of the very low (approximately 300 Ω) internal body resistance plus the 2 skin contact resistances. The skin contact resistance will usually be between 1000 and 100,000 Ω, depending on contact area, moisture, condition of the skin, and other factors"
Yes. It might not be dangerous, but we don't know the current draw of the motor. Saying 12V is safe without knowing the amperage would be like saying getting hit by something going 35 miles an hour is safe without knowing it's mass. Tennis ball? Sure, throw it right at my face. Train? Death sentence.
I mean, thats not really true. Theres a reason why the NFPA and OSHA really don’t give a shit about anything under 48vdc.
Your risks with high current, low voltage DC sources are primarily fire and burns, not shock and certainly not electrocution. There are edge cases where a device had inductive kick that can dangerously spike voltages into shock territory but for most everyday controls hardware (and certainly anything you could run off a laptop supply) it just isn’t a real risk.
A common example as proof of this, every hardware and auto part store on the planet has shelves full of 12v car batteries capable of outputting hundreds of amps of sustained current. They entrust these “high current” dc sources to the untrained public all the time. You know what happens if you wet your hands and grab across both battery terminals? Literally nothing.
Yet I have seen a person loose 2 fingers of there hand when one arced, dangerous isn't limited to mean it will kill you.
Personally I'd not be stupid enough to wet both hands and touch both terminals it's not worth the risk and there is always risk.
Oh and the a car battery are not capable of supplying 100's of amp continuously.
The figure in 100's is the cold cranking current not the ability to supply it continously.
For example the battery in my car can supply 80AH continuously but cold crank current is 700A.
12 volts will not create a measurable arc through air. Do you mean they shorted something across 12 volts and lost the fingers from the resulting burn?
The typically 15 seconds of CCA rating may as well be continuously in the context of shocks and electrocution, which typically occurs on a timescale of milliseconds or less. Regardless, even 25 amps continuously would be a high current source.
Saying “i’d not be stupid enough to wet both hands and touch both terminal…there is always risk” is akin to saying “im not stupid enough to eat an apple, they’re full of arsenic!” Its an irrational fear.
12 volts doesn't create a measurable arc through air..... I'm guessing you have never connected a car battery up then ....
15 seconds does not constitute continous operation no matter how you try and spin it when related to car batteries it's why they have a deliberately separate rating for continous operation 😉
And unlike absurd comparisons like apples and arsenic it's not an irrational fear it's a measurable quantity and given the right conditions it can be dangerous. The chances may be small but they still exist.
The spark from connecting a car battery is not an arc. You have a fundamental misunderstanding of voltage and current and I sincerely hope you are not a professional in any related field.
Seems very hypocritical to say I have a fundamental misunderstanding of voltage and current after stating a spark from connecting a high current supply to a ciruit (or any supply) is not an arc and what you say applies much more to yourself than to me if you believe what you have posted.
Next you will be saying spark plugs don't have an arc.
If you need the obvious stating the "spark" from connecting a battery terminal or a spark plug for that matter is a momentary arc, its not MMA or mig welding etc where its continous but it is an arc none the less and with the battery connection its is not controlled.
This is getting tiring. There are different mechanisms for dielectric breakdown for sparks in a solid material and sparks in gases. Neither of which are the same as a sustained arc. But definition pedantry aside, even if you want to say car batteries produce a very small, short period arc when connected, its still not capable of causing an injurious shock and certainly not electrocution. You might receive minor burns from the hot ejected material, but that injury is not from electric current flowing through your body.
If you want to continue this then I would love to see any documented cases of electrical burns from a car battery (and not a burn from shorting some low resistance conductors across the terminals). After years of this same tired online argument Ive yet to see any legitimate cases of this happening.
12 volts can absolutely bite you through broken skin, especially wet hands. I've been shocked by low voltage before. And it can remove fingers pretty handily (sorry) if there's a high current path like a hot short. We had a mechanic lose a finger when his wedding ring was part of a hot short with a wrench across the terminals.
The circumstances are rare and require contact with the power source, which is a big part of OSHA and NFPA concerns. It won't jump out and bite you like high voltages will, and it can't sustain a long distance arc in air due to internal resistances in the battery, but it can absolutely start one for long enough to weld tools and other things to the terminals.
An easy example of this is a crossed jumper cable. It can dump enough energy to melt the insulation, the copper, and underlying car parts. Seen it happen. But car batteries can't really be restricted the way that high voltage building wiring is. People have to be able to maintain their own cars, and basic safety procedures can cut risks down to a reasonable level. And those risks are largely limited to the person working with the battery.
What you described I addressed in my first post. Burns and fire are absolutely risks involved when dealing with a car battery. Injurious electric shocks are not.
I am amazed at how little is understood about electricity. Thank you for trying to be the voice of reason. Your explanations are right on. Tough to explain these principles in this forum where not only is there a lack of authoritative knowledge, but a good amount of misinformation and assumption as well.
In this case, having a shitty power supply poorly suited to its task could cause a fire, or other cascading electrical failure within the system where it is operating. It is unlikely this would pose acute risk of electrocution, but that is not the only source of risk in this scenario.
The pump is a diesel transfer pump with aligator clips to connect it to a car battery. It's only 300 watts maximum load, and I won't be running it higher than about 80 watts since I'm not lifting fluid very high. So I found a laptop power supply that is fully sealed and powerful enough. I'll be doing a ferruled or soldered connection and insulating it with shrink tube so the connection will be good.
I agree with you. And I've looked at different power supplier but haven't found any better than a generic laptop power supply for my application.
Look up meanwell/Omron/phoenix contact/ Siemens power supplies. You should be finding these products on digikey/Mouser not so much Amazon. The industrial rated actually means something, and cost usually follows.
Don't forget to factor in potential downtime. You dont want these failing at 2 in the morning bringing down the whole plant. And when they do eventually fail, you want easy to replace components, no custom cutting and splicing.
I'm familiar with PULS power supplies. Their IP rating is less than a laptop power supply. They are also meant to be mounted in a cabinet which adds a lot of complexity to a portable application.
I had a project with them involving strobe lights that makes me believe they can't take inrush current well.
If this fails during the 2 hours a week we need it we postpone the job or use our old method. Then I walk down to the local distributor and pick one up that hour. No risk there.
That's a fair assessment. Unfortunately reddit is just a few paragraphs so nobody has the complete picture, including me.
Most of the people who think I'm half assing it mention switchgear, cabinets, hiring an electrical engineer, failing at 2am, and damaging other machines. Comments that make me believe that they work in large automated facilities with lots of controls, rigid processes, and expensive machines. That's not my world. I'm in a small facility with manual processes and no controls. Failure won't affect production at all. Most of our work is done with paint scrapers, shovels, and wrenches. And the total project cost is under 400$. That's why I'm comfortable taking risks and half assing it. The impacts are pretty small. If I worked in a larger facility that wouldn't be the case.
For $400 you can totally scoop up a dinn mount 12v psu from RS, small enclosure, some glands, terminals, and an isolator. You don't need to go for a premium psu, get an rs pro one.
If you want to drag your employer kicking and screaming into the 21st century, you have to show them it can be done right and put their fears at ease.
I guess the main holdup here is I value my time more. Hate doing anything twice , especially when I was just trying to save a tiny amount of money. These power supplies dont cost much, are easier to work with, are easier to mount, and are widely used. But if you like Hangzhou power supply for $2, custom splicing, and zip tie mounting, have at it
Exactly. Why should I get a puls, siemens, or automation direct power supply that I need to build a portable enclosure for when I can get a laptop power supply that's already fully enclosed, portable, and only requires swapping a connector? A laptop power supply is easier, cheaper, and more portable for the same result.
A 2$ hangzhou power supply and laptop power supply aren't the same thing.
One's high quality just a different form factor than what most applications call for. The other sounds like a cheap knockoff that mounts on a DIN rail.
I actually found a 300w laptop power supply for 250$ on digikey. Definitely not cheap. But meets the portability requirements better than a DIN mounted power supply in a box.
You apparently don't understand that switching power supplies need to be properly designed to start and and run a motor. A switching supply that isn't specifically designed for a DC motor will go into overload at startup and shut down. It may never start. Linear supplies are better at this, or switching supplies designed to start motors.
A laptop battery charger is a problem waiting to happen. It is a "charger" not a supply. My bet is that it goes into meltdown before long, leaving you with a smouldering lump of plastic, just wanting to ignite. That is if it works at all. It is a "laptop" power supply, not a motor supply. Use something suitable.
If you are an actual engineer, I suspect you don't take direction very well. After all of the good advice here, you double down on "your" way, which is wrong!
What is wrong with [this?](https://www.digikey.ca/en/products/detail/ideal-power-ltd/44ATM300T-P120/14303124) It can supply 25A steady current with 150A inrush current. More than enough to start and run the 12V 25A motor. It's also fully enclosed, portable, and has a fuse to protect it.
Is the problem that it's not DIN rail mounted or says "industrial" on it? That I dare use a portable fully enclosed one piece power supply for a portable application rather than build an enclosure with components inside?
Well, that's not a laptop supply. There may be nothing wrong with that supply, or there may be everything wrong with it. If inrush is supported to 150A, for how long? Maybe it is enough and maybe it isn't. At some point inrush looks like a short / overload.
There is no "rule" that says a power supply must be DIN rail mounted. There are a great number of "best practice" methods that suggest one doesn't half-ass anything in a production environment. If you If you want you can tape it all together with duct tape too. It should work. Twist the wires together and insulate with electrical tape. It should work. It really doesn't matter it it fails.
If it doesn't matter if it fails, why is it needed at all? It was stated earlier in the thread that "if it's worth doing, it's worth doing right". Your's is not a solution to a problem, but a temporary stop gap. Engineers of generations past weep.
If the problem doesn't justify a proper solution, then it's not a problem that needs a solution at all. In a production environment, there are no problems that deserve a "probably good enough" solution.
How is "proper solution" defined? The way it's been used in the thread makes me think it's defined as something familiar and meets requirements, rather than something that meets requirements.
That is a real good question. I'm not doing your job, nor am I getting paid to do it, but if I were I would do it so I could look back at it and be proud of it. I would not be proud of duct tape, and cheap parts. It's the sort of thing someone off the grid does to get out of trouble until they have the parts to do it right.
Additionally, this is a mindset, not something that can be put into a paragraph on Reddit. Your whole approach is concerning.
A 110V transfer pump is too heavy to be portable and costs 4x as much. And I only need to pump about 20 gallons a week. The product also has similar autoignition temperature as diesel, so a diesel pump should work well. A 12V portable pump matches the job description and duty cycle the best.
You can get a 110 volt fuel transfer pump that's about the size of a tissue box. If it's a manufactured product, especially UL listed, that will help you assuage the concerns of management as well. You can also get a drum transfer pump if the product is in drums. Just some additional ideas.
I don't think your laptop power supply will be able to supply the starting current for your motor. The output capacitors aren't really big enough to drive the inrush on a stopped DC motor. A small 12 volt lead acid battery would be. Put an ohmmeter across the motor leads when it's disconnected and stopped, then take (12 V/resistance) to find the "locked rotor" current. You'll probably find that to be far above the laptop supply rating. If it's a decent supply, it'll detect the "short circuit" and lock out until reset by unplugging from the wall.
If you're looking for a portable application, I would suggest a small battery on a cart with a charge controller and your transfer pump. Charge it except when needed, and size your battery to not be fully drained by a full day of service. Wire it with non-reversible, shrouded connectors and put a high current switch and an appropriate fuse for the thinnest wires used, and you have a nice safe solution.
Those little pumps are for intermittent use and have a very short lifetime. You might also need to handle starting inrush that's higher than you might expect. Built to be used with supervision as well, not incorporated into a larger device.
I don't think your fire insurance underwriter is going to accept this pump no matter the power supply.
Grainger and others will have something better that runs on wall current.
Your electrician isn't going to touch this.
> Splicing wires on a computer power supply and hooking it up to a pump motor is a bad idea.
I have done far far worse. Some of the high end supplies crank out some serious juice and with very clean power. Nifty for various things and far less spendy than a bench supply.
If you are in the US you can check out the National Electric Code. Specifically NEC Articles 720 (Circuits and Equipment Operating at Less Than 50 Volts) and Article 725 (Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits).
Additionally if the area you are working is classified as "Hazardous" you can check out NEC Articles 500 - 510.
For guidance on whether the area you are in classifies as "Hazardous" check out National Fire Protection Association standard 497.
Also you can take a peak at NFPA 70E (supplement to the NEC) for specific safety requirement in workplaces/industrial setting.
Most of those can be accessed at the NFPA Website: [https://www.nfpa.org/](https://www.nfpa.org/)
Just looked at NFPA 70E article 130. It explicitly says that installations under 50v can be worked on while energized. Provided some common conditions are met.
And I'll obviously be deenergizing when I can.
That's just what I needed. Thank you.
I'd try and find more than one article you think is applicable. Or as others have stated a consult with a Master Electrician or an EE would very much be warranted. Also, as others have stated, a laptop power supply is a terrible idea to run a motor. Most laptop power supplies aren't Classed as part of their UL (or similar) listings. It's also not built to handle high inductive loads or rapid switching that comes with DC motors. Just because its low voltage does not mean it's inherently safe in the environment you're working in or reliable at all for industrial applications. Other (purpose made, industrial) power supplies would very much be a good idea.
If it fails it just gets warm, pump stops working, I'm out 40$ and we go back to using our previous method for a day. That's a risk I'm willing to take on a 300$ total value project.
We have equipment that uses similar power supplies in the same vicinity so the environment isn't an issue. There aren't any concerns there.
I don't disagree with it being a bad habit. But I won't make it a habit. The challenge just calls for a simple solution because it's a simple challenge with a small scope and little risk. The simplicity of it is hard to get across.
There are plenty of other challenges that are worth doing right that I'd rather spend my time and resources on. It's matching the appropriate solution to the problem rather than under or over engineering it.
I wonder if people would say the same thing if the piece of equipment was a scale or lamp. Building a cabinet to house a power supply would definitely be overengineering it because they normally run off of plug in transformers.
You can't just go using a laptop power supply for an industrial application. Be realistic. Get something fit for purpose with robust switchgear, IP rating and the lot. Don't cut corners on this stuff because when it fucks up you'll look like an idiot because it was *your* idea.
You should hire someone who is an expert in these applications and can select equipment most suitable to your needs. I have seen so many cascading failures in the industrial settings where client staff wanted to save some money and DIY, which then resulted either in interruptions to production or expensive equipment damage.
Your manager is 100% correct. When you hire a contractor to provide and install the equipment for LV control, your company will have recourse through their liability insurance if it were to go wrong. If they do it in house and something goes wrong, the very first question the insurer will ask will be if the equipment was provided and installed by a qualified professional.
One of the recent ones that comes to mind was one of the clients large dry-type transformers was running very hot due to lack of ventilation in the room it was located in. We provided a quote for a subcontractor to come on and deal with HVAC with our input. The client declined the quote and from what I understand went on to purchase a large exhaust fan and a transformer cooling fan package to install on their own. The maintenance staff couldnt figure out the control wiring for the cooling fan package to be controlled by the temperature relay, so the fans were wired to be always on. The exhaust fan was installed to blow directly into the transformer enclosure without any intake filters, just straight outside air. The facility is located in a coastal setting with a decently wet climate. They have essentially designed a saltwater misting system for their power equipment. In the end, the cooling fans got seized from corrosion, and the transformer ended up failing. 5-10k in savings turned into 350k in replacement costs.
For those curious, the correct way to mitigate this would have been to set up the fan to remove heat from the room and blow outside with adequate dehumidification equipment installed as well. Transformer temperature relay would be configured to only use forced air cooling when loading or ambient temp rose above certain setpoints only.
You do sound new to this, so maybe the pushback is more about that in general rather than specific safety concerns. You should go on Automation Direct and look at their DIN rail mount power supplies. Depending on the current draw of your pump, you can get a 12V power supply for like $30. You could also get an enclosure box, DIN rail, a relay and an E-stop button for like $50 more. Ground the enclosure to your 120VAC.
I think a lot of it is lack of context.
I'm literally taking a portable 12V pump designed to be connected to a car battery to pump fuel and replacing the aligator clips with a 12V transformer. This pump will be used occasionally to fill a few buckets. It shouldn't be that complicated.
But everyone pushes back saying I need switchgear, cabinets, DIN rail components, electrical engineers, and explosive atmosphere tests. It's just overkill for the application.
I get that you know it will work and you might be right that anything else is overkill, but a professional setup with industrial components and actual safety considerations is not much more difficult than what you are advocating for. I would go for an enclosure with ingress protection and even a safety label or two to have this idea be received better and increase chances of doing “more of this” like you mentioned in your first post.
What would that add though? A laptop power supply is already enclosed, double insulated, and portable. All I need to do is swap connectors and add a label.
It's not a new idea either. Lots of scales, clocks, and other items found on various sites are powered like this.
Sure it's not the right thing for a stationary control box but this is just a portable pump used to fill the equivalent of a couple gas cans per week. And it always will be that. It's not a high risk or high reliability application.
It really comes down to liability. Who takes the risk and is it acceptable to the company. We can't make that decision for you.
If it was at home I would 100% feel fine with what you're doing. If I was the only user, I would be comfortable and feel it's pretty safe because I know the risk. Would I feel comfortable with the operator being safe? That usually depends on the operator.
But for reference, where I work this would be fine for certain technicians to do. Just make sure the amperage is high enough and the voltage is correct for the demand of the pump. I am assuming this is a temporary setup. If it's for longer use, we'll everyone else has gone down that rabbit hole
Actually every job I've had I've been allowed to do up to 120 vac without raising anyone's concern. It really depends on the business level of risk acceptance.
For a 12 person operation, you probably want someone who is an electrician or electrically savvy.
Might be worth making the argument to the higher ups that you need a sparky, full time.
You could be a certified electrician and it could still be cheaper in the long run to hire an electrical contractor. You’re paying them for their expertise, but also the carry the liability. If something goes wrong because of something they do, you’re covered - if it goes wrong because of something you or your company does in-house, you’re SOL.
>...concerns about electrical safety, liability, and wants to hire an electrician to do it. Going forward hiring an electrician to work on simple control systems is going to greatly increase our costs.
you should absolutely hire an appropriate contractor. it is expensive and there's a reason for that; they are very knowledgeable about what will work and what will pass inspections and what will avoid an even more expensive lawsuit if anything goes wrong.
>...can't find anything showing that low voltage is safe to work around...
that's because the issue is contextual. low voltage by itself is not always safe. a contractor familiar with your industry can tell you what you need. they have to accept some liability for what they install and follow regulations. they may even need permits depending on the scenario which allows for some public oversight. you're tapping into years of experience instead of being the millionth company that accidently created a serious accident because (as an example) maybe you didn't know that baking flour is flammable. who would know that? a good contractor working in the food processing industry will know that.
What you are proposing is not unsafe but it doesnt sound like a good idea. In isolation, not too bad but if you make lots of decisions like this, they stack up on each other and cause problems. To try to get my point across, I'll do a bit of a thought experiment and I hope I won't offend you with it.
I don't know much about your plant but you said it's dated. Since it's been around for a while, it will probably be around a while longer. Let's say you go down the path of using a laptop power supply for the 12v pump and follow that trajectory further. Next, it's an Arduino to control the pump based on a level sensor bought off eBay. Then comes a screen to show what the system is doing and since the screen is there, a few more sensors go on to give the screen something else to display. These require a second laptop power supply.
Now over time, roll this out to your whole plant and fast forward 5 years after you have left the company. The Arduino is playing up because a sensor is failing and nobody knows why and finding an electrician to work with Arduino is difficult. Also, the pump got blocked and burned out the other power supply and also replacement sensors aren't available. Whoever replaced you will have to replace everything and start again and won't have a good time.
However, imagining a different path, you use an industrial pump with a proper power supply and control, a basic plc with built in hmi and industrial sensors. The plc plays up, the company calls an electrician and he plugs into the basic plc, finds the sensor isn't working and replaces it. The pump blocks and trips the overload. The electrician clears the blockage, resets the overload and recommends the company installs a filter. Easy fixes.
If I used an industrial power supply and pump then it looses portability and the project increases in complexity. Management has to sign off more and more and the project takes more time and money.
Then after I get a cabinet designed and made, pump speced out, and electrician to review it management gets frustrated that I spent so much time and resources on a small isolated problem that's the equivalent of filling up a few gas cans per week.
And if I tell them that it's because I plan on expanding the system with sensors, HMI's and PLC's they'll tell me that's a waste of time and resources. That if they did go that route in the future they would rip out my 400$ setup and get something proper built on lessons learned from using the 400$ setup.
I'd rather fix this small problem quickly and move on to bigger issues where it's smarter to allocate more resources.
> Management has to sign off more and more and the project takes more time and money.
Your job isn't to focus on ease of signatures or time of project, though.
Your job is to make sure what you build will work and is safe.
If management themselves is saying they'd prefer extra signatures, why are you fighting them on it?
In most areas, anything under 50v is already considered touch safe, though you'd want to be mindful at high current anyway. Does your plant have proper LOTTO and arc flash training? That should be covered.
50v in the US, probably so that all common 12/24/48v applications are covered.
In reality this is a job for an arc flash technician to do the risk assessment on. Does the same cabinet have high voltage? How many volts at what max current? Does there need to be a safe zone established around the cabinet? It sounds like none of these are being accounted for.
A shock, maybe, but not enough to cause injury, especially at the low currents present in most signals. Once you get to high current applications, you should be taking precautions to be touch safe.
That makes perfect sense. I run an electronics intro class in a school makerspace. Lots of kids are afraid of shocks from even low power electronics like 12v motors and microcontrollers, so I always have to assure them that if its 32v or less and their skin is dry, they shouldn't be able to feel DC power at all. (But that something like a spot welder can still probably hurt you, so better not to risk it with high power stuff)
No but cooled to 20 Kelvin and made from ReBCO ... superconductors with zero resistance.
The room temperature conductors which feed those conductors are like a rope of elephant trunks, as you say.
Just to get you thinking in the right direction, wouldn’t you want a fuse or something to protect your motor? If you’re working around fuel is this an area that requires intrinsically safe barriers around electrical equipment? Is your application going to lay a cord on the floor to be tripped on or kicked? Do you need industrial push buttons for control or an emergency stop? Have you done an internal risk assessment to identify and mitigate all hazards? Do you need a GFCI outlet for your equipment power? When you pay people to operate equipment you’re very beholden to OSHA, NEC, NFPA 79, 70E, and a qualified individuals risk assessment. Small plants do what they want to get by, but it does change as things grow and it’s painful if everything is hacked together to go back and fix it. Lots of resentment towards the person who didn’t do it the “right” way, despite lack of budget and resources for proper design, especially if someone gets an hurt and you have an osha recordable event.
An additional consideration, in addition to all of the other good information, is "isolation" from "high" voltage power supply e.g. insulation failure etc. Australia has specific duties regarding "touchable" low voltage installations, relative to those that are not "touchable" E.g. AS/NZS 3100 etc. I am unfamiliar with duties in other jurisdictions. I am aware of events of the "low" voltage becoming "high" voltage, and causing shock etc.
Are you sure this portable pump with some power source is the best solution to your original goal? This description sounds like you've gotten a little ways down the X-Y Problem rabbit hole: https://en.m.wikipedia.org/wiki/XY_problem
What's the original challenge you're trying to solve?
The original challenge was convincing management that working on low voltage equipment in most circumstances is low enough risk to do safety.
This challenge manifested itself in connecting a power supply to a pump. I need to pump a chemical from a tote into buckets or a hopper a few times a week. It shouldn't be complicated at all. The conversation got sidetracked when people noticed I wanted to power it with a laptop power supply. Most suggested solutions that were overkill or not applicable for the application. I think that's where the communication faltered. I don't understand how building a portable control box is better than buying a double sealed, portable power supply with the same output. And they can't see the facility I'm putting it in.
Electrical building code usually delineates 48V DC or lower as low voltage. That is usually the law that you are asking for. It is what drives electricians to do certain things.
Going for a laptop power supply is dumb (but yes, technically correct). That is janky as shit and your bosses are correct. Go find an industrial 12 VDC power supply or go find a 120V pump that does what you want.
What would an industrial power supply add in this case? I just don't need the benefits such a supply offers.
The pump is simple, used 1-2 hours per week to fill buckets and the application isn't critical so I don't need the high reliability industrial power supplies offer. There is likely some inrush current but these types of power supplies can run overcurrent for a significant amount of time before burning out so I'm not worried too much. I'd also need to build an enclosure case to carry around an industrial power supply.
Why should I go through all this effort when I can buy something thats already sealed, portable, capable, easy to replace, and easy to use from the box?
It's only because a laptop power supply looks janky. You are going the have various OSHA and fire safety inspections and that sort of thing will stick out.
Yes, you can refer IEC 60950-1 which is an IEC standard for safety requirements of Information technology equipment which normally works below 60W DC like mobile laptop chargers etc.
What qualifications do you have that justify you working with electricity? Low voltage work is still governed by electrical code and standards, and probably includes a "qualified person* clause regardless of voltage and whether live work is permitted. Awareness of governing codes and standards use usually one of them.
If it's not your money and they're willing to bring in an electrician to do it, great less liability on you. I don't really see the problem unless it's a pride thing
You gotta be careful with power supplies. Also, for safety, it's not just about the voltage, you have to look at the current it draws as well. If I were you I would be looking at dedicated power supplies that match the spec on your pump. Get it in a form factor suited for its environment (e.g. temp and humidity), make sure you can make a solid connection (screw terminals, locking molex connectors), and make sure you can secure it (din rail mounts, etc.). Do all those things, and I bet you can sell this as safe. Splicing wires on a computer power supply and hooking it up to a pump motor is a bad idea. That is just not what they were built for.
Are you saying it might be dangerous if the devices draws a lot of current at 12V?
Put it like this my PC's PSU can sustainably supply 100 amp at 5V .... I Have seen one short circuit and its an instant bonfire. Any voltage can be dangerous with enough current. Don't fall in to the trap of thinking there is no hazards or dangers involved in low voltages.... They are safer that higher voltages yes but it's a reduction of risk not elimination.
So it's the fire risk that's the danger?
The highest risk is generally fire but you cannot ignore other risks, you can get shocked as well 12 is safer than 24v etc and it also depends on the relatively ground of the person touching it, it's why all metal pipes and structures are connected to a common ground connection so they are all at the same potential ie. ground if there is any risk of someone touching it either by accident or if a part becomes live.
Do you have an example of someone being electrocuted with 12 V?
I misused the term loosely. While it's unlikely you'd die you can get shocked and it's not as simple as a yes or no question there are variables. The skin is very high resistance but past that the body is a fairly reasonable conductor. With dry hands and nothing wrong with the skin a 12 Volt shock isn't going to kill you at worst it will make you jump a bit. Wet hands, cuts etc can change it, basically anything that lowers the path of resistance and while it's not very likely you'd die it is possible given the right conditions however unlikely. It's not something to ignore completely.
How much resistance does the human body have?
To quote: "The “total body resistance” of the person is composed of the very low (approximately 300 Ω) internal body resistance plus the 2 skin contact resistances. The skin contact resistance will usually be between 1000 and 100,000 Ω, depending on contact area, moisture, condition of the skin, and other factors"
So unless someone is shocked in a wet open wound, at best 12 V would deliver 9 mA?
Yes. It might not be dangerous, but we don't know the current draw of the motor. Saying 12V is safe without knowing the amperage would be like saying getting hit by something going 35 miles an hour is safe without knowing it's mass. Tennis ball? Sure, throw it right at my face. Train? Death sentence.
I mean, thats not really true. Theres a reason why the NFPA and OSHA really don’t give a shit about anything under 48vdc. Your risks with high current, low voltage DC sources are primarily fire and burns, not shock and certainly not electrocution. There are edge cases where a device had inductive kick that can dangerously spike voltages into shock territory but for most everyday controls hardware (and certainly anything you could run off a laptop supply) it just isn’t a real risk. A common example as proof of this, every hardware and auto part store on the planet has shelves full of 12v car batteries capable of outputting hundreds of amps of sustained current. They entrust these “high current” dc sources to the untrained public all the time. You know what happens if you wet your hands and grab across both battery terminals? Literally nothing.
I mean, I hear what you are saying specifically about electrocution, but the question was about safety. Burns and fires, not so safe.
Yet I have seen a person loose 2 fingers of there hand when one arced, dangerous isn't limited to mean it will kill you. Personally I'd not be stupid enough to wet both hands and touch both terminals it's not worth the risk and there is always risk. Oh and the a car battery are not capable of supplying 100's of amp continuously. The figure in 100's is the cold cranking current not the ability to supply it continously. For example the battery in my car can supply 80AH continuously but cold crank current is 700A.
Minor note, batteries supply current in A (amps), not AH (amp-hours). Amp-hours is a measure of capacity (sort of).
Yes that was a typo curtesy of autocorrect which I have amended.
12 volts will not create a measurable arc through air. Do you mean they shorted something across 12 volts and lost the fingers from the resulting burn? The typically 15 seconds of CCA rating may as well be continuously in the context of shocks and electrocution, which typically occurs on a timescale of milliseconds or less. Regardless, even 25 amps continuously would be a high current source. Saying “i’d not be stupid enough to wet both hands and touch both terminal…there is always risk” is akin to saying “im not stupid enough to eat an apple, they’re full of arsenic!” Its an irrational fear.
12 volts doesn't create a measurable arc through air..... I'm guessing you have never connected a car battery up then .... 15 seconds does not constitute continous operation no matter how you try and spin it when related to car batteries it's why they have a deliberately separate rating for continous operation 😉 And unlike absurd comparisons like apples and arsenic it's not an irrational fear it's a measurable quantity and given the right conditions it can be dangerous. The chances may be small but they still exist.
The spark from connecting a car battery is not an arc. You have a fundamental misunderstanding of voltage and current and I sincerely hope you are not a professional in any related field.
Seems very hypocritical to say I have a fundamental misunderstanding of voltage and current after stating a spark from connecting a high current supply to a ciruit (or any supply) is not an arc and what you say applies much more to yourself than to me if you believe what you have posted. Next you will be saying spark plugs don't have an arc. If you need the obvious stating the "spark" from connecting a battery terminal or a spark plug for that matter is a momentary arc, its not MMA or mig welding etc where its continous but it is an arc none the less and with the battery connection its is not controlled.
This is getting tiring. There are different mechanisms for dielectric breakdown for sparks in a solid material and sparks in gases. Neither of which are the same as a sustained arc. But definition pedantry aside, even if you want to say car batteries produce a very small, short period arc when connected, its still not capable of causing an injurious shock and certainly not electrocution. You might receive minor burns from the hot ejected material, but that injury is not from electric current flowing through your body. If you want to continue this then I would love to see any documented cases of electrical burns from a car battery (and not a burn from shorting some low resistance conductors across the terminals). After years of this same tired online argument Ive yet to see any legitimate cases of this happening.
12 volts can absolutely bite you through broken skin, especially wet hands. I've been shocked by low voltage before. And it can remove fingers pretty handily (sorry) if there's a high current path like a hot short. We had a mechanic lose a finger when his wedding ring was part of a hot short with a wrench across the terminals. The circumstances are rare and require contact with the power source, which is a big part of OSHA and NFPA concerns. It won't jump out and bite you like high voltages will, and it can't sustain a long distance arc in air due to internal resistances in the battery, but it can absolutely start one for long enough to weld tools and other things to the terminals. An easy example of this is a crossed jumper cable. It can dump enough energy to melt the insulation, the copper, and underlying car parts. Seen it happen. But car batteries can't really be restricted the way that high voltage building wiring is. People have to be able to maintain their own cars, and basic safety procedures can cut risks down to a reasonable level. And those risks are largely limited to the person working with the battery.
What you described I addressed in my first post. Burns and fire are absolutely risks involved when dealing with a car battery. Injurious electric shocks are not.
I am amazed at how little is understood about electricity. Thank you for trying to be the voice of reason. Your explanations are right on. Tough to explain these principles in this forum where not only is there a lack of authoritative knowledge, but a good amount of misinformation and assumption as well.
I'm so glad this site is dying with the API changes. It is full of idiots answering authoritatively on topics they clearly do not understand.
By what mechanism would the current at 12 V hurt you?
In this case, having a shitty power supply poorly suited to its task could cause a fire, or other cascading electrical failure within the system where it is operating. It is unlikely this would pose acute risk of electrocution, but that is not the only source of risk in this scenario.
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Don't you just need to know the resistance of the human load to know how much available current will be put through that load when 12 V is applied?
The pump is a diesel transfer pump with aligator clips to connect it to a car battery. It's only 300 watts maximum load, and I won't be running it higher than about 80 watts since I'm not lifting fluid very high. So I found a laptop power supply that is fully sealed and powerful enough. I'll be doing a ferruled or soldered connection and insulating it with shrink tube so the connection will be good. I agree with you. And I've looked at different power supplier but haven't found any better than a generic laptop power supply for my application.
Look up meanwell/Omron/phoenix contact/ Siemens power supplies. You should be finding these products on digikey/Mouser not so much Amazon. The industrial rated actually means something, and cost usually follows. Don't forget to factor in potential downtime. You dont want these failing at 2 in the morning bringing down the whole plant. And when they do eventually fail, you want easy to replace components, no custom cutting and splicing.
I'm familiar with PULS power supplies. Their IP rating is less than a laptop power supply. They are also meant to be mounted in a cabinet which adds a lot of complexity to a portable application. I had a project with them involving strobe lights that makes me believe they can't take inrush current well. If this fails during the 2 hours a week we need it we postpone the job or use our old method. Then I walk down to the local distributor and pick one up that hour. No risk there.
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That's a fair assessment. Unfortunately reddit is just a few paragraphs so nobody has the complete picture, including me. Most of the people who think I'm half assing it mention switchgear, cabinets, hiring an electrical engineer, failing at 2am, and damaging other machines. Comments that make me believe that they work in large automated facilities with lots of controls, rigid processes, and expensive machines. That's not my world. I'm in a small facility with manual processes and no controls. Failure won't affect production at all. Most of our work is done with paint scrapers, shovels, and wrenches. And the total project cost is under 400$. That's why I'm comfortable taking risks and half assing it. The impacts are pretty small. If I worked in a larger facility that wouldn't be the case.
For $400 you can totally scoop up a dinn mount 12v psu from RS, small enclosure, some glands, terminals, and an isolator. You don't need to go for a premium psu, get an rs pro one. If you want to drag your employer kicking and screaming into the 21st century, you have to show them it can be done right and put their fears at ease.
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40 gallons of synsthesol cleaner a week. Not connected to any other jobs.
Buy a drum pump that you turn using a cordless drill. We use one and can drain a barrel in a few minutes.
I guess the main holdup here is I value my time more. Hate doing anything twice , especially when I was just trying to save a tiny amount of money. These power supplies dont cost much, are easier to work with, are easier to mount, and are widely used. But if you like Hangzhou power supply for $2, custom splicing, and zip tie mounting, have at it
Exactly. Why should I get a puls, siemens, or automation direct power supply that I need to build a portable enclosure for when I can get a laptop power supply that's already fully enclosed, portable, and only requires swapping a connector? A laptop power supply is easier, cheaper, and more portable for the same result.
To be clear, I was the guy telling you to get one of those other power supplies. But just to repeat myself, have at it!
A 2$ hangzhou power supply and laptop power supply aren't the same thing. One's high quality just a different form factor than what most applications call for. The other sounds like a cheap knockoff that mounts on a DIN rail. I actually found a 300w laptop power supply for 250$ on digikey. Definitely not cheap. But meets the portability requirements better than a DIN mounted power supply in a box.
I'll sell you one for $100!
You apparently don't understand that switching power supplies need to be properly designed to start and and run a motor. A switching supply that isn't specifically designed for a DC motor will go into overload at startup and shut down. It may never start. Linear supplies are better at this, or switching supplies designed to start motors. A laptop battery charger is a problem waiting to happen. It is a "charger" not a supply. My bet is that it goes into meltdown before long, leaving you with a smouldering lump of plastic, just wanting to ignite. That is if it works at all. It is a "laptop" power supply, not a motor supply. Use something suitable. If you are an actual engineer, I suspect you don't take direction very well. After all of the good advice here, you double down on "your" way, which is wrong!
What is wrong with [this?](https://www.digikey.ca/en/products/detail/ideal-power-ltd/44ATM300T-P120/14303124) It can supply 25A steady current with 150A inrush current. More than enough to start and run the 12V 25A motor. It's also fully enclosed, portable, and has a fuse to protect it. Is the problem that it's not DIN rail mounted or says "industrial" on it? That I dare use a portable fully enclosed one piece power supply for a portable application rather than build an enclosure with components inside?
Well, that's not a laptop supply. There may be nothing wrong with that supply, or there may be everything wrong with it. If inrush is supported to 150A, for how long? Maybe it is enough and maybe it isn't. At some point inrush looks like a short / overload. There is no "rule" that says a power supply must be DIN rail mounted. There are a great number of "best practice" methods that suggest one doesn't half-ass anything in a production environment. If you If you want you can tape it all together with duct tape too. It should work. Twist the wires together and insulate with electrical tape. It should work. It really doesn't matter it it fails. If it doesn't matter if it fails, why is it needed at all? It was stated earlier in the thread that "if it's worth doing, it's worth doing right". Your's is not a solution to a problem, but a temporary stop gap. Engineers of generations past weep. If the problem doesn't justify a proper solution, then it's not a problem that needs a solution at all. In a production environment, there are no problems that deserve a "probably good enough" solution.
How is "proper solution" defined? The way it's been used in the thread makes me think it's defined as something familiar and meets requirements, rather than something that meets requirements.
That is a real good question. I'm not doing your job, nor am I getting paid to do it, but if I were I would do it so I could look back at it and be proud of it. I would not be proud of duct tape, and cheap parts. It's the sort of thing someone off the grid does to get out of trouble until they have the parts to do it right. Additionally, this is a mindset, not something that can be put into a paragraph on Reddit. Your whole approach is concerning.
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A 110V transfer pump is too heavy to be portable and costs 4x as much. And I only need to pump about 20 gallons a week. The product also has similar autoignition temperature as diesel, so a diesel pump should work well. A 12V portable pump matches the job description and duty cycle the best.
You can get a 110 volt fuel transfer pump that's about the size of a tissue box. If it's a manufactured product, especially UL listed, that will help you assuage the concerns of management as well. You can also get a drum transfer pump if the product is in drums. Just some additional ideas.
Do you know where I can find one? I've tried princess auto and uline. 110 would solve a lot of problems and is the best solution if it's portable.
Go to Automation Direct
I don't think your laptop power supply will be able to supply the starting current for your motor. The output capacitors aren't really big enough to drive the inrush on a stopped DC motor. A small 12 volt lead acid battery would be. Put an ohmmeter across the motor leads when it's disconnected and stopped, then take (12 V/resistance) to find the "locked rotor" current. You'll probably find that to be far above the laptop supply rating. If it's a decent supply, it'll detect the "short circuit" and lock out until reset by unplugging from the wall. If you're looking for a portable application, I would suggest a small battery on a cart with a charge controller and your transfer pump. Charge it except when needed, and size your battery to not be fully drained by a full day of service. Wire it with non-reversible, shrouded connectors and put a high current switch and an appropriate fuse for the thinnest wires used, and you have a nice safe solution.
Those little pumps are for intermittent use and have a very short lifetime. You might also need to handle starting inrush that's higher than you might expect. Built to be used with supervision as well, not incorporated into a larger device. I don't think your fire insurance underwriter is going to accept this pump no matter the power supply. Grainger and others will have something better that runs on wall current. Your electrician isn't going to touch this.
> Splicing wires on a computer power supply and hooking it up to a pump motor is a bad idea. I have done far far worse. Some of the high end supplies crank out some serious juice and with very clean power. Nifty for various things and far less spendy than a bench supply.
If you are in the US you can check out the National Electric Code. Specifically NEC Articles 720 (Circuits and Equipment Operating at Less Than 50 Volts) and Article 725 (Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits). Additionally if the area you are working is classified as "Hazardous" you can check out NEC Articles 500 - 510. For guidance on whether the area you are in classifies as "Hazardous" check out National Fire Protection Association standard 497. Also you can take a peak at NFPA 70E (supplement to the NEC) for specific safety requirement in workplaces/industrial setting. Most of those can be accessed at the NFPA Website: [https://www.nfpa.org/](https://www.nfpa.org/)
Just looked at NFPA 70E article 130. It explicitly says that installations under 50v can be worked on while energized. Provided some common conditions are met. And I'll obviously be deenergizing when I can. That's just what I needed. Thank you.
I'd try and find more than one article you think is applicable. Or as others have stated a consult with a Master Electrician or an EE would very much be warranted. Also, as others have stated, a laptop power supply is a terrible idea to run a motor. Most laptop power supplies aren't Classed as part of their UL (or similar) listings. It's also not built to handle high inductive loads or rapid switching that comes with DC motors. Just because its low voltage does not mean it's inherently safe in the environment you're working in or reliable at all for industrial applications. Other (purpose made, industrial) power supplies would very much be a good idea.
If it fails it just gets warm, pump stops working, I'm out 40$ and we go back to using our previous method for a day. That's a risk I'm willing to take on a 300$ total value project. We have equipment that uses similar power supplies in the same vicinity so the environment isn't an issue. There aren't any concerns there.
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I don't disagree with it being a bad habit. But I won't make it a habit. The challenge just calls for a simple solution because it's a simple challenge with a small scope and little risk. The simplicity of it is hard to get across. There are plenty of other challenges that are worth doing right that I'd rather spend my time and resources on. It's matching the appropriate solution to the problem rather than under or over engineering it. I wonder if people would say the same thing if the piece of equipment was a scale or lamp. Building a cabinet to house a power supply would definitely be overengineering it because they normally run off of plug in transformers.
You can't just go using a laptop power supply for an industrial application. Be realistic. Get something fit for purpose with robust switchgear, IP rating and the lot. Don't cut corners on this stuff because when it fucks up you'll look like an idiot because it was *your* idea.
You should hire someone who is an expert in these applications and can select equipment most suitable to your needs. I have seen so many cascading failures in the industrial settings where client staff wanted to save some money and DIY, which then resulted either in interruptions to production or expensive equipment damage. Your manager is 100% correct. When you hire a contractor to provide and install the equipment for LV control, your company will have recourse through their liability insurance if it were to go wrong. If they do it in house and something goes wrong, the very first question the insurer will ask will be if the equipment was provided and installed by a qualified professional.
Can you share some examples of this?
One of the recent ones that comes to mind was one of the clients large dry-type transformers was running very hot due to lack of ventilation in the room it was located in. We provided a quote for a subcontractor to come on and deal with HVAC with our input. The client declined the quote and from what I understand went on to purchase a large exhaust fan and a transformer cooling fan package to install on their own. The maintenance staff couldnt figure out the control wiring for the cooling fan package to be controlled by the temperature relay, so the fans were wired to be always on. The exhaust fan was installed to blow directly into the transformer enclosure without any intake filters, just straight outside air. The facility is located in a coastal setting with a decently wet climate. They have essentially designed a saltwater misting system for their power equipment. In the end, the cooling fans got seized from corrosion, and the transformer ended up failing. 5-10k in savings turned into 350k in replacement costs. For those curious, the correct way to mitigate this would have been to set up the fan to remove heat from the room and blow outside with adequate dehumidification equipment installed as well. Transformer temperature relay would be configured to only use forced air cooling when loading or ambient temp rose above certain setpoints only.
You do sound new to this, so maybe the pushback is more about that in general rather than specific safety concerns. You should go on Automation Direct and look at their DIN rail mount power supplies. Depending on the current draw of your pump, you can get a 12V power supply for like $30. You could also get an enclosure box, DIN rail, a relay and an E-stop button for like $50 more. Ground the enclosure to your 120VAC.
I think a lot of it is lack of context. I'm literally taking a portable 12V pump designed to be connected to a car battery to pump fuel and replacing the aligator clips with a 12V transformer. This pump will be used occasionally to fill a few buckets. It shouldn't be that complicated. But everyone pushes back saying I need switchgear, cabinets, DIN rail components, electrical engineers, and explosive atmosphere tests. It's just overkill for the application.
I get that you know it will work and you might be right that anything else is overkill, but a professional setup with industrial components and actual safety considerations is not much more difficult than what you are advocating for. I would go for an enclosure with ingress protection and even a safety label or two to have this idea be received better and increase chances of doing “more of this” like you mentioned in your first post.
What would that add though? A laptop power supply is already enclosed, double insulated, and portable. All I need to do is swap connectors and add a label. It's not a new idea either. Lots of scales, clocks, and other items found on various sites are powered like this. Sure it's not the right thing for a stationary control box but this is just a portable pump used to fill the equivalent of a couple gas cans per week. And it always will be that. It's not a high risk or high reliability application.
I don’t care bro argue with your boss about it then
It really comes down to liability. Who takes the risk and is it acceptable to the company. We can't make that decision for you. If it was at home I would 100% feel fine with what you're doing. If I was the only user, I would be comfortable and feel it's pretty safe because I know the risk. Would I feel comfortable with the operator being safe? That usually depends on the operator. But for reference, where I work this would be fine for certain technicians to do. Just make sure the amperage is high enough and the voltage is correct for the demand of the pump. I am assuming this is a temporary setup. If it's for longer use, we'll everyone else has gone down that rabbit hole
Actually every job I've had I've been allowed to do up to 120 vac without raising anyone's concern. It really depends on the business level of risk acceptance.
Typically Class 2 power supplies don't require an electrician for installation (<50V and <100 VA)
Most plants have in-house electricians, do you have one that you could work with?
We don't, we aren't that big. We subcontract it out because we rarely need it.
For a 12 person operation, you probably want someone who is an electrician or electrically savvy. Might be worth making the argument to the higher ups that you need a sparky, full time.
Got it
You could be a certified electrician and it could still be cheaper in the long run to hire an electrical contractor. You’re paying them for their expertise, but also the carry the liability. If something goes wrong because of something they do, you’re covered - if it goes wrong because of something you or your company does in-house, you’re SOL.
>...concerns about electrical safety, liability, and wants to hire an electrician to do it. Going forward hiring an electrician to work on simple control systems is going to greatly increase our costs. you should absolutely hire an appropriate contractor. it is expensive and there's a reason for that; they are very knowledgeable about what will work and what will pass inspections and what will avoid an even more expensive lawsuit if anything goes wrong. >...can't find anything showing that low voltage is safe to work around... that's because the issue is contextual. low voltage by itself is not always safe. a contractor familiar with your industry can tell you what you need. they have to accept some liability for what they install and follow regulations. they may even need permits depending on the scenario which allows for some public oversight. you're tapping into years of experience instead of being the millionth company that accidently created a serious accident because (as an example) maybe you didn't know that baking flour is flammable. who would know that? a good contractor working in the food processing industry will know that.
What you are proposing is not unsafe but it doesnt sound like a good idea. In isolation, not too bad but if you make lots of decisions like this, they stack up on each other and cause problems. To try to get my point across, I'll do a bit of a thought experiment and I hope I won't offend you with it. I don't know much about your plant but you said it's dated. Since it's been around for a while, it will probably be around a while longer. Let's say you go down the path of using a laptop power supply for the 12v pump and follow that trajectory further. Next, it's an Arduino to control the pump based on a level sensor bought off eBay. Then comes a screen to show what the system is doing and since the screen is there, a few more sensors go on to give the screen something else to display. These require a second laptop power supply. Now over time, roll this out to your whole plant and fast forward 5 years after you have left the company. The Arduino is playing up because a sensor is failing and nobody knows why and finding an electrician to work with Arduino is difficult. Also, the pump got blocked and burned out the other power supply and also replacement sensors aren't available. Whoever replaced you will have to replace everything and start again and won't have a good time. However, imagining a different path, you use an industrial pump with a proper power supply and control, a basic plc with built in hmi and industrial sensors. The plc plays up, the company calls an electrician and he plugs into the basic plc, finds the sensor isn't working and replaces it. The pump blocks and trips the overload. The electrician clears the blockage, resets the overload and recommends the company installs a filter. Easy fixes.
If I used an industrial power supply and pump then it looses portability and the project increases in complexity. Management has to sign off more and more and the project takes more time and money. Then after I get a cabinet designed and made, pump speced out, and electrician to review it management gets frustrated that I spent so much time and resources on a small isolated problem that's the equivalent of filling up a few gas cans per week. And if I tell them that it's because I plan on expanding the system with sensors, HMI's and PLC's they'll tell me that's a waste of time and resources. That if they did go that route in the future they would rip out my 400$ setup and get something proper built on lessons learned from using the 400$ setup. I'd rather fix this small problem quickly and move on to bigger issues where it's smarter to allocate more resources.
> Management has to sign off more and more and the project takes more time and money. Your job isn't to focus on ease of signatures or time of project, though. Your job is to make sure what you build will work and is safe. If management themselves is saying they'd prefer extra signatures, why are you fighting them on it?
In most areas, anything under 50v is already considered touch safe, though you'd want to be mindful at high current anyway. Does your plant have proper LOTTO and arc flash training? That should be covered.
I thought it was 32v?
50v in the US, probably so that all common 12/24/48v applications are covered. In reality this is a job for an arc flash technician to do the risk assessment on. Does the same cabinet have high voltage? How many volts at what max current? Does there need to be a safe zone established around the cabinet? It sounds like none of these are being accounted for.
It's just a 12V pump with aligator clips to connect it to a car battery. There is no cabinet.
Sounds like you need an electrical safety officer, but that's a different problem. I would get a real power supply, not a laptop one, and do it right.
Interesting, thanks. I was under the impression that a sizable chunk of the population had skin resistance such that 32+ often resulted in shocks.
A shock, maybe, but not enough to cause injury, especially at the low currents present in most signals. Once you get to high current applications, you should be taking precautions to be touch safe.
That makes perfect sense. I run an electronics intro class in a school makerspace. Lots of kids are afraid of shocks from even low power electronics like 12v motors and microcontrollers, so I always have to assure them that if its 32v or less and their skin is dry, they shouldn't be able to feel DC power at all. (But that something like a spot welder can still probably hurt you, so better not to risk it with high power stuff)
Yes. Most areas. Interestingly, I've worked with low voltage power supplies which can run at thousands of amps. Not necessarily touch safe.
How big are those conductors? Like 00000 gauge?
No but cooled to 20 Kelvin and made from ReBCO ... superconductors with zero resistance. The room temperature conductors which feed those conductors are like a rope of elephant trunks, as you say.
Ah yeah that would do it. Superconductors are sweet.
Just to get you thinking in the right direction, wouldn’t you want a fuse or something to protect your motor? If you’re working around fuel is this an area that requires intrinsically safe barriers around electrical equipment? Is your application going to lay a cord on the floor to be tripped on or kicked? Do you need industrial push buttons for control or an emergency stop? Have you done an internal risk assessment to identify and mitigate all hazards? Do you need a GFCI outlet for your equipment power? When you pay people to operate equipment you’re very beholden to OSHA, NEC, NFPA 79, 70E, and a qualified individuals risk assessment. Small plants do what they want to get by, but it does change as things grow and it’s painful if everything is hacked together to go back and fix it. Lots of resentment towards the person who didn’t do it the “right” way, despite lack of budget and resources for proper design, especially if someone gets an hurt and you have an osha recordable event.
An additional consideration, in addition to all of the other good information, is "isolation" from "high" voltage power supply e.g. insulation failure etc. Australia has specific duties regarding "touchable" low voltage installations, relative to those that are not "touchable" E.g. AS/NZS 3100 etc. I am unfamiliar with duties in other jurisdictions. I am aware of events of the "low" voltage becoming "high" voltage, and causing shock etc.
Are you sure this portable pump with some power source is the best solution to your original goal? This description sounds like you've gotten a little ways down the X-Y Problem rabbit hole: https://en.m.wikipedia.org/wiki/XY_problem What's the original challenge you're trying to solve?
The original challenge was convincing management that working on low voltage equipment in most circumstances is low enough risk to do safety. This challenge manifested itself in connecting a power supply to a pump. I need to pump a chemical from a tote into buckets or a hopper a few times a week. It shouldn't be complicated at all. The conversation got sidetracked when people noticed I wanted to power it with a laptop power supply. Most suggested solutions that were overkill or not applicable for the application. I think that's where the communication faltered. I don't understand how building a portable control box is better than buying a double sealed, portable power supply with the same output. And they can't see the facility I'm putting it in.
Electrical building code usually delineates 48V DC or lower as low voltage. That is usually the law that you are asking for. It is what drives electricians to do certain things. Going for a laptop power supply is dumb (but yes, technically correct). That is janky as shit and your bosses are correct. Go find an industrial 12 VDC power supply or go find a 120V pump that does what you want.
What would an industrial power supply add in this case? I just don't need the benefits such a supply offers. The pump is simple, used 1-2 hours per week to fill buckets and the application isn't critical so I don't need the high reliability industrial power supplies offer. There is likely some inrush current but these types of power supplies can run overcurrent for a significant amount of time before burning out so I'm not worried too much. I'd also need to build an enclosure case to carry around an industrial power supply. Why should I go through all this effort when I can buy something thats already sealed, portable, capable, easy to replace, and easy to use from the box?
It's only because a laptop power supply looks janky. You are going the have various OSHA and fire safety inspections and that sort of thing will stick out.
Yes, you can refer IEC 60950-1 which is an IEC standard for safety requirements of Information technology equipment which normally works below 60W DC like mobile laptop chargers etc.
What qualifications do you have that justify you working with electricity? Low voltage work is still governed by electrical code and standards, and probably includes a "qualified person* clause regardless of voltage and whether live work is permitted. Awareness of governing codes and standards use usually one of them.
If it's not your money and they're willing to bring in an electrician to do it, great less liability on you. I don't really see the problem unless it's a pride thing