LiFePO4 batteries in series with out balancing them first (8 cells) to power up BMS

dgd4040

New Member
Joined
Apr 8, 2021
Messages
15
I am waiting for my bench power supply to arrive. I want to power up the BMS and check out the Bluetooth interface and all the setting.
The batteries range from 3.222V to 3.314V. I don't foresee any problem connecting the batteries in series as a 24V pack and connecting the BMS to become familiar with it? I am not going to charge or discharge the pack.
Anything I am missing? the batteries should be fine in series
Thanks
 

FilterGuy

What, me worry?
Joined
Nov 26, 2019
Messages
4,456
Location
Los Gatos CA
I am waiting for my bench power supply to arrive. I want to power up the BMS and check out the Bluetooth interface and all the setting.
The batteries range from 3.222V to 3.314V. I don't foresee any problem connecting the batteries in series as a 24V pack and connecting the BMS to become familiar with it? I am not going to charge or discharge the pack.
Anything I am missing? the batteries should be fine in series
Thanks
No problem at all. In fact, I like building the battery and charging till the BMS hits a high cell voltage and shuts down. This quickly pre-charges the cells so it will not take as much time to top balance them.

 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
131
I skipped the top balance entirely this summer with my 4 Luyuan cells. I initially installed the $20 60a/30a non-bluetooth Daly. I just upgraded due a mis spec of my system having 45a of charge to an Overkill/JBD. All cells were within one hundredth of a volt at install.

A top balance is necessary with sub par cells, but may not be with a true grade A. I don't know how long it took to balance, but it wasn't more than a couple of months and I presume it was close to begin with per my voltmeter measurements.
 

alcook62

Don't Be A Casualty - Cut the Cord
Joined
Jan 27, 2021
Messages
35
Location
Wyoming, USA
I am waiting for my bench power supply to arrive. I want to power up the BMS and check out the Bluetooth interface and all the setting.
The batteries range from 3.222V to 3.314V. I don't foresee any problem connecting the batteries in series as a 24V pack and connecting the BMS to become familiar with it? I am not going to charge or discharge the pack.
Anything I am missing? the batteries should be fine in series
Thanks
As stated by @FilterGuy, perfectly fine. I've been running my 24v system for six months now and have never top-balanced my system. My cells run from 7-8mv to as much as 38mv out of balance with just a Heltec active balancer maintaining them. I guess I got lucky and my 8 cells were closely matched when I got them. I am NOT trying to talk you out of the top-balance process. I still will do it eventually, if nothing else just to see how close I can get my battery to balance.
 

wholybee

Solar Addict
Joined
Feb 11, 2021
Messages
364
Measuring voltage as received is useless for determining balance. The voltage will be very close until the cells are >95% charged and at 3.4V or more.

There is nothing wrong with connecting them to the BMS without top balancing first. You can even charge them to test that the BMS functions, and do a capacity test to find out how out of balance they are. The only thing "wrong" with cells not being in balance is that your lose usable capacity until they are balanced. If you do a capacity test and are happy with the results, you could skip top balancing. Although, you will certainly improve the capacity by balancing them.
 

smoothJoey

mumble...
Joined
Nov 30, 2019
Messages
9,315
I am waiting for my bench power supply to arrive. I want to power up the BMS and check out the Bluetooth interface and all the setting.
The batteries range from 3.222V to 3.314V. I don't foresee any problem connecting the batteries in series as a 24V pack and connecting the BMS to become familiar with it? I am not going to charge or discharge the pack.
Anything I am missing? the batteries should be fine in series
Thanks
If those are new commodity cells I would note the voltage range of the cells.
Doesn't mean there is a problem but usually they come pretty within 3.29-3.3 volts.
Why do yours have a ~100mv spread when <10mv is typical?
 

dgd4040

New Member
Joined
Apr 8, 2021
Messages
15
I did get one battery what was a lower voltage then the rest. the vent cap was a different colour then then rest too. Once I get everything I will be able to fully test and document each cell.
Thanks for the info everyone. I look forward to get this pack up and running and into the trailer :)
 
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