BMS Battery Problems!

[Drywax3d]

HI Guys,

I have a problem just recently I bought a couple of kits from BMS Battery they are
36V 9AH battery with a Q100H motor and all the gubbins.
I made up 1 of the bikes with no problems still works well today.
The problem started a couple of weeks ago when I built up the second bike.
The kit works well but the battery wont take a charge Ive checked all the fuses etc all in tact
Good battery rests at 41.6V
Bad battery rests at 35.6V

Ive bypassed the BMS to charge it up to 41V which works up until the battery drops to 35/36V
I think it may be the BMS as all cells have the same 4.1V even when it drops below the threshold

Needless to say Ive contacted BMS on multiple occasions and had no response I will not be using them in the future Ive seen more effective chocolate fireguards.

any thoughts,

Thanks Rich

 

[Drywax3d]

this is the bms

https://bmsbattery.com/bmspcm/566-7s-10s-13s-lithium-ion-bms-for-linicomn-bms-pcm.html
does anyone know how to test if these are any good without using a pc?

 

[trex]

you need to check the cell pack first.
Pull the balance leads out, check the voltage between battery - and each wire, you should read 4.1V, 8.2V,... 41V
If one of the block is too much out of balance, your BMS won't charge the cells.

 

[Deleted member 4366]

It's not really practical to repaira BMS. All you can do is chek the soldder joints visually with a magnifing glass.

One check worth doing is that the voltage from the sensor wires is appearing on the PCB. That will eliminate the connector as a cause.

 

[Drywax3d]

ok I'm getting there! the battery is 12.5AH its 10S type I believe.
5 in parallel 10 in series 50 batteries in total
Voltages are as follows 4.1, 8.3, 8.8???, 13, 17.2, 21.4, 25.6, 29.8, 34, 38.2
so the anomaly is in the 3rd string which is around 0.5v and 0.6v

Faulty cell or are the connections bad?

 

[trex]

faulty cell or cells in third string. You need to isolate and charge each cell individually with something like a imax B6 to see which cell is not working properly.

 

[Drywax3d]

As much as I'm enjoying the educational aspect of this problem these kind of things highlight the problems of dealing with poor Chinese engineering and dealing with the Chinese in general. Reality is it needs to go back to the vendor but as they only get in touch to add more P&P to your order I doubt that's going to happen.

Rant over I've looked at the balance charger but it only does 6S I've been looking at some 10s ones which makes sense to me if I'm going to continue along the E-Road.

on a separate note I was going to start up a little business based on these kits but that's out of the window now as trying to get a reasonably priced supplier with quality seems to be nigh on impossible!
I am however going to carry on with my custom stuff as you can see below with my 1000w 48v orange and cream electric dream!
hence getting a 10s charger may end up being more beneficial than the 6s (although the low price is tempting)
and 1 final poke at BMS BATTERY the wheel came damaged for the custom build again with no kind of response from them!

anyway best start stripping that pack down

 

[Nealh]

The 3rd string may be due to a bad solder/wire joint or could be bad tab welding ? So a bit of investigating needed. 1st thing I would do is charge the string up, for charging individual cell strings I use an old 5a phone charger with the connector end cut off and a pin soldered to each wire after checking the polarity you can stick these in the correct position on the BMS loom and charge manually, just keep an eye on the voltage so no more then 4.2v. By charging manually if they keep the charge you will then know its a wiring/connection problem or even a duff BMS rather then a duff cell string.

 

[Drywax3d]

I've managed to get the cells up to 3.1v and so far there holding at that I'm going to leave them over night to see if the drop any V's! the BMS is disconnected at this point so if they drop then I'm guessing a bad cell however If the voltage holds I'll reconnect the bms and see if that has an effect.
Also I have had a response from BMS Battery and there on holiday of course Chinese New Year!

 

[awol]

I've managed to get the cells up to 3.1v and so far there holding at that I'm going to leave them over night to see if the drop any V's! the BMS is disconnected at this point so if they drop then I'm guessing a bad cell however If the voltage holds I'll reconnect the bms and see if that has an effect.
Also I have had a response from BMS Battery and there on holiday of course Chinese New Year!

I would take them to nearer 4.1 to match the other strings as the bms may struggle to balance the pack with a string down so low.

 

[Nealh]

Agree with Awol as soon as you reconnect BMS and charge again the BMS on reaching HVC with high cells will stop charging leaving the low cells still out of balance. Hopefully they won't bleed back in which case you can charge again to 4.1 and then reconnect the BMS, so far so good at least they are accepting a charge.

 

[Drywax3d]

Hi Guys,

Just a quick thanks for all your help its been a steep learning curve but I'm getting there!
So the batteries now appear to hold there charge until I plug the BMS back in then it rapidly discharges the cells. I've decided to hold off pulling the individual cells apart until I hear back from china which should be tomorrow! but I will keep you posted as to the solution if any!

Thanks

Rich Hu5h

 

[Deleted member 4366]

It takes very litlle charge to change the cell voltage a lot when the cell is below 3.1v. You need to get that group up to 4.2v like the others before you can assess whether they're draining throuh the BMS.

Each channel has a bleed resistor, which is normally the first component after the connector. You can see them all lined up across the BMS. I think they're in the range of 100 ohms. A transistor or other logic device opens a path to ground through each one when it's cell-group goes over something like 4.1v. The path closes at 4.1v. That's how it does the balancing. The charger charges the cells to 4.2v, then they bleed down to 4.1v, which gives the lower ones a chance to catch up the higher ones.

It's possible that the bleed resistor on that low channel is stuck open.