As a recap: I just received my aliexpress Black and Decker 40v battery that weight-wise alone feels like a junk : ( So I'm actually still looking for a decent 36v/40v tool battery that has battery build-in BMS. If anyone can point me to a distinct battery package I'd be more than happy : )
Experiences with 36V tool battery as drive battery
- Thread starter SuperHans
- Start date
Whichever battery you get, you MUST check that it cuts off at the correct LVC. As said by people above, many such tool batteries do not have LVC nor charge controls in the battery, even though they might have some sort of BMS, Instead those things are in the charger or the tool. The only way to be sure is to test. It's especially dangerous to put two in series without those controls in place..
People say it works for them, but that doesn't mean it works for you. It can be done, but you need to do it right and test that your system has the necessary LVC, HVC and charge controls in place.
Thanks for pointing that out! Safety and usability are my main concerns : ) I just opened the battery to see whether it has some BMS and hoping to find even some part number that helps me to look up this particular circuit. It looks like it is a BMS, but I cannot find any specific details. I post a photo, maybe some of you can tell from the ICs being used whether it's legit?! @d8veh : how would I test LVC, HVC and charge controls?!
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The BMS is built for that battery, so everything (in a quick glance) that comes up for it's p/n on the edge of the board just says it's for that battery. (google itself finds zero results for the full term, and only shows results for the battery p/n that is a subset of the characters of the BMS p/n). I didn't read them beyond summaries, so there could be other info
The only way to tell if it's "legit" is to test it's functions, by making sure it disconnects the cells from the outside world in normal usage upon LVC (during discharge turns off when battery is empty), upon HVC (during charge when battery is full), and upon things like overheating and overcurrent situations (which you may have to create artificially).
The basic parts necessary to do the functions appear to exist on the board, but whether they actually do them (are designed to under the conditions you want to use them under, and actually function under those conditions) must be tested.
Note also that conditions that can damage the BMS like overcurrent, or seriesing them so that higher voltages than designed are placed on the FETs when they turn off, usually damage the FETs in a way that leaves them *always on*, so that the BMS can no longer protect against anything. It's a silent failure, in that outside the battery there's no signal to you this has happened, unless you do test for HVC, LVC, overcurrent, etc. to be sure the battery does indeed shut off under those conditions. (that kind of test for this failure isn't a one-time thing, it'd be a regular test if you need to be certain it is working).
The only way to tell if it's "legit" is to test it's functions, by making sure it disconnects the cells from the outside world in normal usage upon LVC (during discharge turns off when battery is empty), upon HVC (during charge when battery is full), and upon things like overheating and overcurrent situations (which you may have to create artificially).
The basic parts necessary to do the functions appear to exist on the board, but whether they actually do them (are designed to under the conditions you want to use them under, and actually function under those conditions) must be tested.
Note also that conditions that can damage the BMS like overcurrent, or seriesing them so that higher voltages than designed are placed on the FETs when they turn off, usually damage the FETs in a way that leaves them *always on*, so that the BMS can no longer protect against anything. It's a silent failure, in that outside the battery there's no signal to you this has happened, unless you do test for HVC, LVC, overcurrent, etc. to be sure the battery does indeed shut off under those conditions. (that kind of test for this failure isn't a one-time thing, it'd be a regular test if you need to be certain it is working).
It's not a normal BMS. It only has B+ and B-. An ebike one has P- and often C- for the switched charge state controls. It would also have a few MOSFETs to do the switching, so I'd say that it doesn't have all the necessary controls.
