52V Battery wont charge past 80%

J_R_X

10 µW
Joined
Jun 8, 2020
Messages
5
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
 
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.
 
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-battery-checker.html?queryID=76e275a620295925dcbcd94372dfc7bc&objectID=72617&indexName=hbk_live_magento_en_us_products

Cheaper 6S
https://hobbyking.com/en_us/hobbykingtm-battery-medic-system-2s-6s.html?queryID=efb27bdd0cbd2f2c2ba229445127c637&objectID=38766&indexName=hbk_live_magento_en_us_products

Even Cheaper 6S
https://hobbyking.com/en_us/battery-monitor-2-6s.html?queryID=64421c3569d3bc342419ac870df56aaf&objectID=37197&indexName=hbk_live_magento_en_us_products

6 pages on search
https://hobbyking.com/en_us/batteries-chargers/battery-accessories.html#q=&idx=hbk_live_magento_en_us_products&dFR%5Bwarehouses%5D%5B0%5D=USA&dFR%5Bwarehouses%5D%5B1%5D=Global&dFR%5Bwarehouses_stock_data%5D%5B0%5D=USA%7C1&dFR%5Bwarehouses_stock_data%5D%5B1%5D=USA%7C2&dFR%5Bwarehouses_stock_data%5D%5B2%5D=USA%7C3&dFR%5Bwarehouses_stock_data%5D%5B3%5D=Global%7C1&dFR%5Bwarehouses_stock_data%5D%5B4%5D=Global%7C2&dFR%5Bwarehouses_stock_data%5D%5B5%5D=Global%7C3&hFR%5Bcategories.level0%5D%5B0%5D=Batteries%20%2F%20Chargers%20%2F%2F%2F%20Battery%20Accessories&is_v=1
 
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.
 
markz said:
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 said:
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.
 
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