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52V Battery wont charge past 80%

Posted: Nov 22 2020 1:41pm
by J_R_X
Built this summer 14s5p, maybe has had 20x+ cycles and worked flawlessly. Last 3 charges stopped at 55.5-56V.
https://www.aliexpress.com/item/32922633046.html
https://www.aliexpress.com/item/32997105784.html
That's the charger and 40A bms. On charger able to change power output (2A-12A) but not final charge voltage like on luna chargers.
All 14 blocks appear to be balanced (3.99V+/-) and the welds are solid. Tried another plastic 4A charger, same result.
What could be causing this behavior?
Is there anything I can do short of replacing the bms and seeing if that'll fix the issue?
Thanks

Re: 52V Battery wont charge past 80%

Posted: Nov 22 2020 5:45pm
by john61ct
See if you can find another charge source to borrow, test to see if it's the BMS.

And test your charger on a different battery or a dummy load, see if it will reach its intended setpoint.

Re: 52V Battery wont charge past 80%

Posted: Nov 22 2020 7:02pm
by markz
Throw a digital multimeter on the open voltage and another for current measuring and see what happens when it starts to charge the battery. Then it'd be nice to see what each string is doing to try and find a weak string. Hobbyking sells these, this happens to be an 8S
https://hobbyking.com/en_us/bg-8s-smart ... s_products

Cheaper 6S
https://hobbyking.com/en_us/hobbykingtm ... s_products

Even Cheaper 6S
https://hobbyking.com/en_us/battery-mon ... s_products

6 pages on search
https://hobbyking.com/en_us/batteries-c ... ies&is_v=1

Re: 52V Battery wont charge past 80%

Posted: Nov 22 2020 7:24pm
by Balmorhea
If you have a charger that won't go above 58.8V under any circumstances, then charge the battery directly from its leads, bypassing the BMS.

If it takes and holds a charge at a higher voltage, then your problem is the BMS.

It should go without saying, but if you conduct this experiment, do it in a location where a fire would be acceptable.

Re: 52V Battery wont charge past 80%

Posted: Nov 23 2020 2:10pm
by J_R_X
markz wrote:
Nov 22 2020 7:02pm
Throw a digital multimeter on the open voltage and another for current measuring and see what happens when it starts to charge the battery. Then it'd be nice to see what each string is doing to try and find a weak string. Hobbyking sells these, this happens to be an 8S
When it's below 80% it charges normally, takes whatever amps you're putting in and stays in balance. At the mentioned voltage just stops taking charge. Input current doesn't slowly decrease, just cuts out.
Balmorhea wrote:
Nov 22 2020 7:24pm
If you have a charger that won't go above 58.8V under any circumstances, then charge the battery directly from its leads, bypassing the BMS.

If it takes and holds a charge at a higher voltage, then your problem is the BMS.

It should go without saying, but if you conduct this experiment, do it in a location where a fire would be acceptable.
Was thinking about doing that, I'm 99% sure it's the bms, just curious as to why it decided to start doing that. Almost like it's been reprogrammed for lower cutoff.