Hey guys,
I have the D140 10s BMS wired to a 5p10s VTC6 pack charging with a standard evolve 42V charger.
My problem is that it won’t allow a full charge (stops charging @40.5V and the light goes green)
The pack also doesn’t stay in balance.
All cells where balanced with in 0.01V when I built the pack, have skated about 40km with top up charges here and there.
Cell levels at a “full charge” (green light shown on the charger) 40.5V.
–battery negative–
*4.05v
*4.04v
*4.05v
*4.04v
*4.03v
*4.16v
*4.02v
*4.02v
*4.04v
*4.04v
–battery positive–
Wondering what my next move should be?
I was thinking to discharge cell 6 down to the rest of the pack and see if it keeps in check with the rest after a skate.
Hoping someone can point me in the right direction as I have used $5 aliexpress BMS with more success in the past.
is you bms warm/hot when battery is just laying around unplugged?
can you somehow check output voltage on your charger? if its normal 5.5x2.1mm, you can stick one multimeter probe inside hole and second on outer cylinder, just be very careful to not short anything.
it could be that you charger output is 40.5v and bms won’t start balancing until battery is full. Don’t hold my word for it, because I got answer from bestech that bms should balance cells all the time, even when battery is not full.
@tinp123 good idea, yep, I have a few spare charging jacks to test, only problem is I think k if there is no load the charger doesn’t deliver the voltage? I’ll rig a test up tonight and see what I find and report back👍
Nothing I noticed. Periodically checked it during the first charge up and it didn’t get warm.
Checking cells now. Hoping there is a dead one, which is an odd feeling but it might explain the problems, although not why all other cells are 0.2v bellow where they should be at full charg6🤔
I don’t think there is dead one. difference in voltage would be much bigger. probably just one cell has higher resistance than others, thats why there is slight difference in voltages. OR bms does that on purpose - discharges slowly one group.
If I were you, I would balance groups and do maybe 2-3 charging cycles and then check voltages again. If they drift again I would replace bms.
This is a great application for a DC clamp-style ammeter - you can check each BMS balance wire for current draw without disconnecting anything. Having one has saved me a lot of trouble in the past.
Mine is a Uni-T UT210E, and it’s fantastic for the price ($25-50).
A word of warning for anyone planning to acquire a clamp meter! Most clamp meters, especially older ones, are AC ONLY. Make sure the meter specifically states “DC Clamp” or similar.
Ok,
So I balanced things up as best I could.
–battery negative–
*4.11v
*4.10v
*4.10v
*4.10v
*4.09v
*4.17v
*4.09v
*4.09v
*4.10v
*4.10v
–battery positive–
Still getting 41v and the light on the charger goes green
Not anything odd other than all of the voltages being higher than the rest of the pack (and in general, the fact that it will only charge to 41v)
I did find one cell that showed 3.6V then 4.15V - flicked around for a little. Had the same internal resistance as the others.
Marked it and replaced it with a new cell charged to the same voltage.
I was thinking to wire up another 10s BMS I have laying around. https://s.click.aliexpress.com/e/4CaqTUw8
It’s just a cheap one off aliexpress which I didn’t use because I thought the bestech would give me less trouble
If I’m honest I wanted to be sure it wasn’t something else causing it because stripping and soldering balance leads is one of my least favorite jobs.
I’ll go for a skate tomorrow, get a partial cycle or 2 through it and check again.
I’d say that one of the P groups has either a dead cell or a bad connection. Specifically the 6th group. What is happening is under charge voltage, that group is hitting 4.20v and the bms is cutting off the power to avoid overcharging that group. Dropping back down to 4.17 is just the voltage dropping back after charging and is pretty normal for those cells.
Tl:Dr - Your 6th P group has a dead cell or bad connection to one of the cells and there is nothing wrong with your charger or BMS (they are operating as intended).
@Friskies thanks for that!
I’m hoping with a few cycles and the cell I replaced things settle in to a pattern and then I can just enjoy the board
It’s all back together and ready for a carve tomorrow morning.
I’ll monitor the overall voltage on the vesc app, see if it’s discharging is making sense to the wh consumed and do a balance check after a few sessions.
With the meter set to DC amps in the lowest range it has (mine has ranges from 2A to 200A), zero the meter (the DC range drifts a little) and then clamp it around one balance wire at a time and check the reading. They should all read zero when the BMS isn’t balancing. If one reads higher then the rest, then that may be causing one of your cell groups to drain - I had this happen because one of the balance transistors on my BMS was damaged. I was able to replace it without needing a whole new BMS, and before it killed my pack.
Seems pretty balanced except the first one which is off by around 0.005V (correct me if I’m wrong but that does not seem like a huge difference). Going to try charging it to full again and hopefully it’ll successfully go up to 4.2V per p group this time.
