Daly BMS 100 A 4S did not cut off cell at 3.73 V while charging

rush

New Member
Joined
Apr 28, 2021
Messages
3
I recently built a 100-Ah 4S battery using batteries from batteryhookup.com. The BMS is a Daly 100-A unit (J05A-CG30, specifically marked LiFePO4 on the product listing and the case) from Amazon. It is marked 100 A/50 A charging on the case. It doesn't support bluetooth (d'oh!) or low-temp disconnect so I have ordered an Overkill Solar 120-A BMS, but I expect that it will take several weeks to arrive.

I top balanced the batteries and discharged them to about 30% capacity to get an initial functional test. Next I charged them at a 0.15-0.2C rate until the BMS cut off charging. The battery took 76.5 Ah and 1038 Wh. So far, so good.

As soon as charging completed, I tested the cell voltages. I measured the cells immediately at the end of the charging cycle and found one cell at 3.73 V. That was disconcerting. I was under the impression that an LFP BMS should disconnect charging when any cell reaches 3.65 V.

The cell voltages settled fairly quickly but they were nowhere near balanced after charging. I'm not sure what to make of that, but it's really a separate problem I think. After 90 minutes, these were the cell voltages (BMS still connected):

Cell 13.35 V
Cell 23.557 V
Cell 33.553 V
Cell 43.483 V
That's a 227-mV (huge) delta between the highest and lowest cells.

Three hours after charging ended:
Cell 13.447 V
Cell 23.496 V
Cell 33.484 V
Cell 43.453 V
That's a 49-mV difference between the highest and lowest cells.

Interestingly, that first cell was also the lowest before I did the top balancing.

In summary, I'm interested in comments on the disconnect voltage question and the cell balance after charging. I would greatly appreciate any links or references to supporting data.

Thanks.

Rus
 

Diysolar123

Photon Sorcerer
Joined
Feb 28, 2021
Messages
675
and another contestent has now played the favorite game of many...
"what happens when you buy the best of the worst BMSs"!!

notice the specs on that daly you linked:
BMS protect battery charge voltage: 3.75V.
BMS protect battery discharge voltage: 2.2V.
Continuous charging current: 50A.
Continuous discharging current: 100A.
Balance voltage: 3.7V.

these are cheap and better than nothing to protect from a catastrophic oops...
its better than nothing.
it will not protect well
it will not balance anything
 

rush

New Member
Joined
Apr 28, 2021
Messages
3
and another contestent has now played the favorite game of many...
"what happens when you buy the best of the worst BMSs"!!

notice the specs on that daly you linked:
BMS protect battery charge voltage: 3.75V.
BMS protect battery discharge voltage: 2.2V.
Continuous charging current: 50A.
Continuous discharging current: 100A.
Balance voltage: 3.7V.

these are cheap and better than nothing to protect from a catastrophic oops...
its better than nothing.
it will not protect well
it will not balance anything
Thank you for your witty and informative response. Sometimes the specs are right in front of your face . . ..
 
Top