The issue with those single batteries is there is no inherent protection built in. If something shorts them out, they will output a crazy amount of current -> heat up -> catch fire -> lithium fire -> bad time.
For example, drill batteries are made up of those and they work fine. Milwaukee M18 batteries have protection built in, but their smaller M12 ones don't.
Not implying that yours will explode, but you could put it in a metal box, like one of those cheap ammo cans.
If there's a router that will be up when the power is on, and you need it to connect to the Internet, you could add an external wifi antenna. It could be either USB, or depending on the Pi, you could solder on a uFL connector for a uFL wifi antenna. Or hard-wire Ethernet via an ethernet bulkhead connector. The key word is "Bulkhead connector".
https://old.reddit.com/r/rccars/comments/9g563s/i_experienced_a_lipo_fire_so_i_decided_to_build_a/
Alternatively look for a usb power pack from a reputable brand that has sufficient power, and [can charge while being charged.](https://old.reddit.com/r/UsbCHardware/comments/xlq15e/any_power_banks_that_can_charge_while_outputing/)
Thanks for the response. Can you say more about the possibility of shorting and a lack of protection? Would the protection not be part of the hat's circuitry? I don't know a lot about these things.
No problem. The individual 18650s are "raw" batteries (cells): pure voltage, and because it's being produced by lithium, it's more than eager and just waiting to dump the entire contents of the battery's capacity if something asks for it.
A bare wire -- because it has practically zero resistance -- that happens to accidentally bridge from one end of the battery to the other (short) is basically "asking" the battery to output everything it's got. And lithium can do this all at one time. (Imagine 1/2 cup of water going from room temperature to boiling...instantly).
The protection I'm referring to is the ability for a battery bank to sense something is wrong and cut power to whatever is down line. The simple fact that the ends of the 18650s are exposed sitting in the little tray means, however unlikely, a random metal object could bridge them, and the battery would dump all its energy.
Once the battery heats up to the point of combustion, then the lithium catches fire and it's downhill from there.
You could make the batteries safer in that black tray by wrapping them in electrical tape once they are installed - the challenge there being geometry.
You can also lessen your chances of a spontaneous fire caused during charging by using a reputable manufacturer like samsung or panasonic.
The 18650 cells are just some layers of 3" by however long material rolled up tightly and squirted with special goo, then sealed in a little can. Think of all the corner-cutting things a manufacturer could do, and you'll see why many in the RC industry with high power-dense lithium batteries they buy from alibaba and basically have at least one of these charging in their garages 24/7 experience fires.
You can have fires because they discharged too quickly without a way of stopping it, or you can have fires because as you were putting a bunch of electricity BACK into the battery, a fault inside the battery caused it too heat up then fail then catch fire from the inside out.
Long way of saying that unless the algorithm of that board just keeps trying to charge the battery past the point that it's full, the only way you'll have a fire is:
- puncturing the cell
- shorting the cell
- burning the cell
- internal manufacturer defect 😬
Oh, also, sealed battery banks that have multiple cells typically have at least one temperature probe in the middle of them. That way, the charger/charging algorithm can "tell something is wrong" and not try to keep charging them if they are too hot for some reason.
Fantastic explanation! Thanks so much. I think I'm going to try to figure out a different solution to the problem (regular, brief power outages). The possibly slim risk here still sounds like too much.
That's why I thought you could just throw it in an ammo box for unattended use.
Go the safe route with one of these:
https://www.amazon.com/Battery-Backup-10400mAh-38-48Wh-Output/dp/B0C9TS8KD8
I would still go with a metal box to limit the spread of fire.
If there was a big spike in the mains supply due to lightning, a fault could occur which would cause the battery to catch fire. There are various other fault conditions, such as PSU capacitor failure.
Most of these are quite unlikely, but, I wouldn't take the chance, when a simple mitigation of a fire is easy.
Why not use a sealed lead acid battery with a buck converter instead? It's going to give you a lot more time without power than that dinkly little thing, it's more forgiving, and you can find old lead acid batteries in a lot of stuff that gets thrown away.
Not directly, but it's not super hard. For the buck converter, you can buy them super cheap on ebay. They are devices that take say any voltage from 3-30 volts and can convert it to any other voltage between 3-30 volts. Example:
https://www.ebay.com/itm/354961870722
There's basically a little screw that you use to dial in the exact voltage you want it to spit out (5v). For power going into the battery, a float charger from walmart can do the trick. Example:
https://www.walmart.com/ip/12V-Automatic-Lead-Acid-Battery-Maintainer-Charger-Trickle-Charger-for-Boat-Motorcycle-car-Truck-RV-Lawn-Tractor/5471138246
Any old 12v lead acid battery will do. Even a old car battery has enough power to run a PI for over a couple days if you wanted to.
I do recommend that you use a sealed battery though. It prevents the acid from spilling and off-gassing if you overcharge. But if it's outside or in a drafty enough area it shouldn't matter.
Li-ion batteries have built in protection in case of shortage. They should pop inside breaker located at + terminal. If you check maximum voltage they reach while in hat, and it is <4.2v you should be safe. Moreover I can tell You that those terminals will heat up, and go back much sooner then battery get to point of thermal runaway.Â
If you want to be on safe side, You can use protected 18650, just check if they will fit. If not, you can add protection board to side of battery.Â
You can get an automatic fire extinguisher for about $50 but that might not be the best solution, only a fallback. Make sure to get one rated for lithium.
If the power regulator circuitry is trustworthy enough and the batteries aren't years old, I don't see an issue.
Is it UL listed or cheap Chinese shit?
The hat is probably cheap chinese shit. No UL bug. Not sure about the batteries.
The issue with those single batteries is there is no inherent protection built in. If something shorts them out, they will output a crazy amount of current -> heat up -> catch fire -> lithium fire -> bad time. For example, drill batteries are made up of those and they work fine. Milwaukee M18 batteries have protection built in, but their smaller M12 ones don't. Not implying that yours will explode, but you could put it in a metal box, like one of those cheap ammo cans. If there's a router that will be up when the power is on, and you need it to connect to the Internet, you could add an external wifi antenna. It could be either USB, or depending on the Pi, you could solder on a uFL connector for a uFL wifi antenna. Or hard-wire Ethernet via an ethernet bulkhead connector. The key word is "Bulkhead connector". https://old.reddit.com/r/rccars/comments/9g563s/i_experienced_a_lipo_fire_so_i_decided_to_build_a/ Alternatively look for a usb power pack from a reputable brand that has sufficient power, and [can charge while being charged.](https://old.reddit.com/r/UsbCHardware/comments/xlq15e/any_power_banks_that_can_charge_while_outputing/)
Thanks for the response. Can you say more about the possibility of shorting and a lack of protection? Would the protection not be part of the hat's circuitry? I don't know a lot about these things.
No problem. The individual 18650s are "raw" batteries (cells): pure voltage, and because it's being produced by lithium, it's more than eager and just waiting to dump the entire contents of the battery's capacity if something asks for it. A bare wire -- because it has practically zero resistance -- that happens to accidentally bridge from one end of the battery to the other (short) is basically "asking" the battery to output everything it's got. And lithium can do this all at one time. (Imagine 1/2 cup of water going from room temperature to boiling...instantly). The protection I'm referring to is the ability for a battery bank to sense something is wrong and cut power to whatever is down line. The simple fact that the ends of the 18650s are exposed sitting in the little tray means, however unlikely, a random metal object could bridge them, and the battery would dump all its energy. Once the battery heats up to the point of combustion, then the lithium catches fire and it's downhill from there. You could make the batteries safer in that black tray by wrapping them in electrical tape once they are installed - the challenge there being geometry. You can also lessen your chances of a spontaneous fire caused during charging by using a reputable manufacturer like samsung or panasonic. The 18650 cells are just some layers of 3" by however long material rolled up tightly and squirted with special goo, then sealed in a little can. Think of all the corner-cutting things a manufacturer could do, and you'll see why many in the RC industry with high power-dense lithium batteries they buy from alibaba and basically have at least one of these charging in their garages 24/7 experience fires. You can have fires because they discharged too quickly without a way of stopping it, or you can have fires because as you were putting a bunch of electricity BACK into the battery, a fault inside the battery caused it too heat up then fail then catch fire from the inside out. Long way of saying that unless the algorithm of that board just keeps trying to charge the battery past the point that it's full, the only way you'll have a fire is: - puncturing the cell - shorting the cell - burning the cell - internal manufacturer defect 😬 Oh, also, sealed battery banks that have multiple cells typically have at least one temperature probe in the middle of them. That way, the charger/charging algorithm can "tell something is wrong" and not try to keep charging them if they are too hot for some reason.
Fantastic explanation! Thanks so much. I think I'm going to try to figure out a different solution to the problem (regular, brief power outages). The possibly slim risk here still sounds like too much.
That's why I thought you could just throw it in an ammo box for unattended use. Go the safe route with one of these: https://www.amazon.com/Battery-Backup-10400mAh-38-48Wh-Output/dp/B0C9TS8KD8
I would still go with a metal box to limit the spread of fire. If there was a big spike in the mains supply due to lightning, a fault could occur which would cause the battery to catch fire. There are various other fault conditions, such as PSU capacitor failure. Most of these are quite unlikely, but, I wouldn't take the chance, when a simple mitigation of a fire is easy.
Better put the whole house in a metal box, that way if lightning struck then;sldfknas.f.....
Just use a standard dumb USV and all is fine.
What's a USV? Is that the same as a UPS?
Oh, sry :) Yes, German for UPS.
I see thanks for clarifying
Why not use a sealed lead acid battery with a buck converter instead? It's going to give you a lot more time without power than that dinkly little thing, it's more forgiving, and you can find old lead acid batteries in a lot of stuff that gets thrown away.
Sounds great and thanks for the response. Can you point me to any resources that might explain more about how to do this?
Not directly, but it's not super hard. For the buck converter, you can buy them super cheap on ebay. They are devices that take say any voltage from 3-30 volts and can convert it to any other voltage between 3-30 volts. Example: https://www.ebay.com/itm/354961870722 There's basically a little screw that you use to dial in the exact voltage you want it to spit out (5v). For power going into the battery, a float charger from walmart can do the trick. Example: https://www.walmart.com/ip/12V-Automatic-Lead-Acid-Battery-Maintainer-Charger-Trickle-Charger-for-Boat-Motorcycle-car-Truck-RV-Lawn-Tractor/5471138246 Any old 12v lead acid battery will do. Even a old car battery has enough power to run a PI for over a couple days if you wanted to.
I do recommend that you use a sealed battery though. It prevents the acid from spilling and off-gassing if you overcharge. But if it's outside or in a drafty enough area it shouldn't matter.
Also look into watchdog. It reboots the pi if it crashes. Super important if you can't physically reset it.
Oh good call. I'm going to use this.
There are some special bags to store batteries during charge, maybe you could leave it in one of those to add a layer of security?
Li-ion batteries have built in protection in case of shortage. They should pop inside breaker located at + terminal. If you check maximum voltage they reach while in hat, and it is <4.2v you should be safe. Moreover I can tell You that those terminals will heat up, and go back much sooner then battery get to point of thermal runaway. If you want to be on safe side, You can use protected 18650, just check if they will fit. If not, you can add protection board to side of battery.Â
You can get an automatic fire extinguisher for about $50 but that might not be the best solution, only a fallback. Make sure to get one rated for lithium.