Burnt BMS (Pics included) Please help?

[Watchamacallit]

Yes thats correct. I've put the multimeter to 20 vdc and i'm seeing anywhere between 0.00-0.02 difference between each pair.

Just to be sure, this is a different set of measurements than previously done?

I'm checking, because the results are definitely different than 3.4-3.5v per cell, and it makes a difference to whether the cells are healthy / balanced or not.

Only a couple of hundredths of a volt difference, that is pretty well balanced for a typical ebike pack (especially if there aren't any balancers on the BMS).

A tenth of a volt, however....

Measuring using the balance lead (so negative on b0, red to b1/b2/b3 etc) and the increase is around 3.49-3.47 between each one.

So for example, readings were:
3.47,
6.96
10.45
.. etc

Not sure if i'm doing it right or if that increment even matters, but thought i'd bring it up just in case.

Curious but why does it state in the title "constant current" ? Is this just reffering to CC/CV charging?

If you mean the " 40A constant discharge current " in the item name at the top right, then that matches this spec further down (and also in the attached chart)

Brand Name: LiRooter
Certification: CE
Accessory Type: Battery Accessories
Origin: CN(Origin)
Model Number: Lirooter14S001
Application: for 13S or 14S 48V Lithium Ion Battery Protection
Function: with full set of protection
Dimension: 90*57*9mm
Constant discharge current: 40A
Constant charge current: 10A

Which would mean it can handle a continuous load of 40A pulled from the battery by the controller/motor system, if necessary. That's good in that it means it probably won't heat up as much under the smaller load you'll use it under (the actual limiting is done by your controller).

Similarly, it can handle as much as 10A continously for charging, so it should also run cooler there, too.

But the best part of their page is that they give you complete specs of how the BMS works; all it's limits and shutdown conditions. Makes it easier to troubleshoot problems, and more predictable behavior (because if the system shuts off when none of these limits are in play, something else is wrong).

Ah ok great, thanks for the clarification - i was a bit worried at first as i thought it ONLY output 40a continually, meaning the moment i plugged it in and up to a motor it would wizz off at full speed and/or blow up lol (Which is hugely impractical for the intended use of course, but sometimes i do like to assume the worse lol)

The battery is only going to be powering a few higher wattage buck converters (12v, x2 5v etc), fairly powerful LED lights and a magic pie edge motor (pulls around 30a absolute maximum for brief periods) so compared to most people I dont think i really stress these batteries.

[amberwolf]

Measuring using the balance lead (so negative on b0, red to b1/b2/b3 etc) and the increase is around 3.49-3.47 between each one.

So for example, readings were:
3.47,
6.96
10.45
.. etc

Not sure if i'm doing it right or if that increment even matters, but thought i'd bring it up just in case.

Not sure what you mean by "that increment".

You may already be testing and recording the right information, but I'll go into more detail just so you can be sure:

The thing you are testing is the cell voltages. Those do matter. So does the difference between them. You're not looking for an average difference, you're looking for the actual exact difference, because the bigger the difference in voltage, the bigger the difference in the groups' charge state (whcih may mean a difference in capability, or capacity, etc).

So what you want to measure and record is each cell group voltage. Doing this at the BMS pads for the balance connector, starting from the BMS B- wire if the most negative wire of the balance connector isn't equal to B-. (if it is equal, then reading from B- to most negative balance pad will read 0v; anything else should indicate there is a cell group there, and that the most negative balance pad is the positive of that group, and you need to record that voltage as well).

You can measure by keeping the black meter lead on the B- wire, and moving the red lead to each solder pad of the balance connector in turn, starting at the most negative one and ending at the most positive one. But you have to set the meter to 200vdc for this (because otherwise you can only get a few cells in before you're at a higher voltage than the meter can read at 20vdc and it then gives you it's "out of range" reading), which is less precise*** than the 20vdc mode you can use if you measure by moving the leads together as pairs instead, so that when you move the red lead to the next pad, you then move the black wire to the one you moved the red lead from.

That will instead give you an actual list of voltages, starting at "cell group 1" which is the most negative, that doesnt' require any calculations to determine.

As noted before, tenths of a volt difference between any cells is bad. A couple of hundredths, not so much.


***it may not matter about precision (number of decimal places) because the meter may not actually be that accurate...but if the display is a 4-digit then you only get one decimal place for a 200vdc range, which is not enough to really tell cell state (need at least two decimal places, which you would still get in a 20vdc range for a 4-digit meter). If it's a 5-digit meter, then you do still get 2 places even at 200vdc range.

If you use autoranging it will just switch to the higher mode when necessary, but the readings in that mode will have less decimal places, and can't necessarily be directly compared with those made at the lower range. (the more accurate (better at measuring) the meter, and the more precise (more decimal places) the meter is, the less difference this makes).

Ah ok great, thanks for the clarification - i was a bit worried at first as i thought it ONLY output 40a continually, meaning the moment i plugged it in and up to a motor it would wizz off at full speed and/or blow up lol (Which is hugely impractical for the intended use of course, but sometimes i do like to assume the worse lol)

Ah; i see the misconception: a battery doesnt' force current into a controller/motor. The motor places an electrical load on the controller based on the physical load on the motor, which then pulls more current from the battery to help the motor overcome it's load.

The battery is only going to be powering a few higher wattage buck converters (12v, x2 5v etc), fairly powerful LED lights and a magic pie edge motor (pulls around 30a absolute maximum for brief periods) so compared to most people I dont think i really stress these batteries.

Unfortunately it isn't a comparison between others' use of similar batteries that matters for how a battery behaves; it's the actual load on it vs it's actual condition.

So, for example, even though I have packs on my trike that are made of EIG cells the same as one of the Zero motorcycles used, and some other EVs I can't recall the names of, the performance of mine won't be nearly the same, even though I put a lot less load on them than those EVs, mostly because the ones I have are old, and well-used.

However, it is likely that you aren't loading yours heavily, probably not even pushing them a little, as far as the cells' capabilities.

The problem you ran into is the BMS, heat, and having nowhere for the heat to go.

[velias]

just buy a speedict BMS, it is well documented and supported and high quality relative to ebay noname ones.
www.speedict.com

[Watchamacallit]

Ok, so i got the BMS today from Aliexpress (The ones previously recommended)

Took my time wiring it up, B- first, then C-/P-, then the more difficult balance leads.

It was actually far easier than i anticipated, i was more nervous than anything else especially doing the balance leads but overall, it went very smoothly without issues. (I also measured the balance leads wires to ensure they were connected in order before connecting to the BMS)

However, an issue has cropped up.

Firstly, the BMS appeared dead, flicking the switch on and off did nothing. There was a voltage reading from the charge socket of 30v (even though the battery is at 45v)

I then disconnected the balance leads, and reconnected them which then made it spring to life. Battery was on fully (45v at discharge port) but, oddly, seemed to be switched on regardless of weather the battery switch on the side was on or off!

I then disconnected the balance leads again, and verified the switch itself wasn't faulty - it was working fine and as intended, so i reconnected it all back up.

Now it's doing the same thing again, just reading around 30v at the charging port, and, if i remember correctly, around 1v at the discharge connector, with no change with the switch on or off.

Any thoughts? I'm confident that nothing has been shorted or damaged because i was extremely careful. I'm guessing some sort of protection measure has been triggered and it's just a case of resetting it. That or maybe the cells are too unbalanced for it and it's disabling itself to stop use? ( presumably a charge cycle will resolve?)

[Chalo]

If any one cell is outside the permissible voltage range, the BMS will cut off. Confirm what that range is by referring to the BMS spec sheet, and then measure the cell voltages you have. If they're all in the allowable range, then either you wired something up incorrectly or the BMS isn't working.

[Watchamacallit]

If any one cell is outside the permissible voltage range, the BMS will cut off. Confirm what that range is by referring to the BMS spec sheet, and then measure the cell voltages you have. If they're all in the allowable range, then either you wired something up incorrectly or the BMS isn't working.

Ok, just did further testing.

Each cell has a difference of about 0.01v, so they're fine (3.490 - 3.500 usually)

I connected a charger and the bms sprung to life again. I then disconnected the charger and switched the battery off.

in a switched off state, the charging port has about 20v at it, with the switch on, it has the main battery voltage (45v)

however, still regardless of the switches state, it still gives out 45v at the discharge port. So the switch must work as turning it on and off changes the chart ports voltage (20v off, 45v on) but the discharge port stays at 45v regardless?

is something wrong here? Could it just be like a "phantom" voltage like before that would dissappear with a small load?

edit-
It does, it just oddly takes a while. I hooked the battery up to a inverter and ran a small 250w load off that. switched the battery off while running and it took nearly a minute to deplete and switch off.

edit 2
Ok, so it is acting odd. I left it switched off for about a day, go back to it and find the full 45v from the discharge port without touching the switch at all.

I did order two, so i think i will swap out the bms for the other to see if the second one has a similar issue.

[Watchamacallit]

OK so something is definitely up with these two replacement BMS's from ali express.

upon connecting the first one (as mentioned post above) i had that weird behavior where it appeared to initially work, but then voltage was being supplied regardless whether it was on or off (BIG problem too, as obviously causes arching when plugging it into a load) - it didn't seem like a "ghost" voltage either as it would happily power a load for minutes on end and not immediately dissipate.

...Then randomly, it would work intermittently - eventually turn itself off, then not come on!

This was also installing it exactly in the order of B-, P-, C- and then balance cables so im confident it wasn't anything on my part (their difference being <0.01v, and it rises in the correct increments between banks)

So i figure "ok, the BMS is faulty or some protective circuit has kicked in and im not sure how to reset - i'll just install the second instead."

Installed the second one, no issues. turn it on, 48v at discharge, turn it off, it turns off. Great! Test it under a continual 750w load - perfect! it even runs INSANELY cool. fantastic.

I Then decide to fully charge the pack and monitor it closely. charges absolutely no issues - and again, very low temperature @ 5amp charge. fantastic.

Once fully charged, I check balance lead voltages and there's still only a <0.01v difference across all cells. Great.

turn it on.........Nothing. nothing from discharge, and only 1.5v from charge port.

LED/power indicator also says flat. (1 red light)

It recieves a charge fine. but it wont turn on. There appears to be a voltage at the discharge but it varies in voltage (43v or so) just really odd.

So back to intermittent behavior just like the first it seems. wth?

I put it back on charge, thinking it might "wake" it. Nope.

I disconnect balance lead, and reconnect. It "springs" to life again (LED indicators light up to full) then suddenly down to single red light. it now reports 54v at discharge regardless as to whether the battery is ON or OFF, it'll also power a 15w 5v converter without issues in this state. What gives?

I've included pictures, as i'm very confident i've been careful in assembly of both attempts and there's just something weird about these BMS's. Can anyone provide any thoughts?

pics below:
https://imgur.com/a/C2RXaJH