Canister light li-Po or Li-Fe - what discharge protection

[txaggie08]

I've been building drone from 2" to 1100mm octos for years, I'm just curious what over discharge protection yall might be using in your conversions?

I've got a diverite canister with a dead nimh pack, was going to make the switch. I could do a 3s4p setup with protected 18650 cells, but it would be simpler to use some form of inline overdischarge protection

Just curious what yall are using, the ones I use aren't really effective, they're designed to work with rc equipment.

 

[broncobowsher]

I've been looking for something for some other projects as well.

 

[fmerkel]

Not sure you really NEED it. I've ended up taking apart a few different packs of friends that weren't working right, none very old or used hard. In each case the cells were fine. All meet nearly new specifications when tested individually. The battery management system had gone bad. Re-assemble the packs using balance taps like RC and they are fine now.

In my own canister the protection is built into the light head. It flashes when it gets too low. OTOH, it's not really needed as you'd have to be pretty unaware to not see how dim the light was getting just before protection kicked in. I don't bother with protected cells for my single cell lights for the same reason, they become obviously dimmer.

I do have one commercial (Tenergy 2S2P) pack for that canister that has a BMS. That one is apparently been OK, at least the pack works, and charges appropriately. I have not stripped the shrink wrap to check if the cells are staying in balance. As long as it's working and behaving I'm good to let it ride.

 

[txaggie08]

The current bad pack is NiMh, and while I can take it apart and probably find the cells, I think they're both showing their age. I'd much rather convert the cans to probably LiFe( not like I don't have the charger to do it, I'm running 4s2p 15ah batts on my big bird.)

I'm just not confident on lithium with no lvs. Had to many fires in the past with lipo, makea me nervous lol!

 

[dm9876]

@txaggie08

Probably I'm telling you how to suck eggs, but ...

your typical RC hobby BMS is monitoring only with no intervention (no cutoff etc). maybe a buzzer or perhaps telemetry back to the transmitter at best. I guess your looking for something with mosfet to actually cut the flow of current and protect the cells. There are plenty of options, just google "3s pcb" as an example. heaps of options for 1s, 2s, 3s even up to 13s is pretty available. depending on which model you choose will have different options to cut out based on per-cell low voltage / high voltage / pack high current discharge / charge etc. Maybe less available options for LiFePo4 but still plenty.

I don't really know about which ones are good or bad, but cheapo BMS do have a bad rep of murdering cells so do your research

Worth browsing the likes of https://banggood.com etc

 

[fmerkel]

Lipo is not Li-on. Decent cells are pretty safe unless you abuse the hell out of them or are an idiot.
LiFe is safer, lower voltage, and you'll need more cells....but I'd suspect you know that. Personally I've given up on that chemistry, at least for now. Good Li-on are much better density and are completely safe if you stay with known brand names from reputable sources.

 

[kelemvor]

As long as your lipos are 4.2v/cell then you can use a standard lithium protection circuit. Same circuit that's used for li-ion such as 18650. Just keep in mind you need a protector circuit for each cell rather than one for the whole pack.

They cost almost nothing on amazon. Here's a few:

Strip form factor 5 units for $4 ($0.80ea) free shipping (no prime) Amazon.com: Baoblaze 5 Pieces 1S 3.7V 3A Li-ion 18650 Lithium Lipo Battery Protection Board Module, Overcharge Overdischarge Overcurrent Protection: Home Audio & Theater

I guess you'd have to order two of those as you'll need 6 units for a 3s2p pack. It would be fine for a 2s2p pack though.

I don't use protection circuits on lipo cells, but everything I use lipo in has a built-in protection circuit already (my drone's pdb or the charger for example). You can always add one to your light just to prevent over-draining.


I'm not sure if you're talking about using your RC batts in a light or if you're talking about using regular 18650 in an RC. The latter won't work too well. Standard 18650's don't put out nearly enough current.. at least the ones I've got don't. I don't see any reason why you couldn't use a pack from an RC in a dive light...

 

[txaggie08]

Lithium- anything will explode from over discharge. 18650's are what have caused quite a few disfiguring explosions from vapes, both from overdischarge and over draw incidents unfortunately. I'm using 18650s in my fpv goggles, and for the external power source on my big drone's gimbal, but not as primary packs anywhere, as stated, they're really not rated for it( most good ones are rated to what...2 or 3c?)

I'm in the same boat with LI-FE, except in my transmitters. They lower voltage means a 2s pack is much closer in that application. I also have a charger that will charge 6s @10amps, so I could fast charge, but they're not quite there. I may do a 3s2p 18650 pack that i can pull cells from for this, most of the hobby batteries I have now days are either huge, or quite small for what I'm doing, and I have several projects using them outside of just RC.

I've just seen enough bad lipo and lithium batt experiences that I'm....cautious.

Years ago, when Li-Po first made its appearance. I had a low voltage shutoff that was soldered inline of the supply to the esc on cars and aircraft. It read voltage via the balance lead, and would kick a small relay off if the voltage passed a threshold. It's been long enough since I had an esc or electronics system that didn't monitor voltage I don't remember who made it.

 

[tbone1004]

Batteryspace makes high quality packs designed to drop right into those canisters, better off just buying one of those.

 

[txaggie08]

I don't see anything but nimh pack from them