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How to Balance and Series Connect 12V LiFePO4 Batteries

One of the comments on Youtube is an important one:

Folks: Not all batteries are rated for putting 4 in series. Be sure to check how many in series your particular brand & model can support.

As will mentioned in the video, the FETS in the battery BMS has to be rated for the full series voltage of the string of batteries.

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A question for @Will Prowse: In the video you say to charge the batteries individually before putting them in series. Do you see anything wrong with putting them all in parallel and charging them all at once?
 
One of the comments on Youtube is an important one:



As will mentioned in the video, the FETS in the battery BMS has to be rated for the full series voltage of the string of batteries.

------------------------------------------------------

A question for @Will Prowse: In the video you say to charge the batteries individually before putting them in series. Do you see anything wrong with putting them all in parallel and charging them all at once?
You can. But I've run into issues, such as current sharing and voltage sensing circuit of charger cutting off before one pack is full.

Individually charging with the same charger will ensure a perfect charge. This way beginners can never screw it up. There are so many variables to putting in parallel and wiring them up. I'd rather stick to the method that anyone can do and ensure perfect balancing every single time.

If I do a long term system with 12V packs in series, I always charge individually. I've done that for years, and it's the only way I've found to get a good charge.

Raw cell top balancing is different. Large bus bars, power supply etc. Just probe the voltage, charge a few times, then wait for it to settle and charge a little bit more to get final absorption. But not the same with packs because they have a BMS.
 
Individually charging with the same charger will ensure a perfect charge. This way beginners can never screw it up. There are so many variables to putting in parallel and wiring them up. I'd rather stick to the method that anyone can do and ensure perfect balancing every single time.
How about using the charger built into my All-In-One unit? I plug it into 120 volts and program the charge function and charge 1 at a time.
 
How about using the charger built into my All-In-One unit? I plug it into 120 volts and program the charge function and charge 1 at a time.
If you can charge them individually with 12V to a set absorption value, absolutely. That would work great.
 
How about using the charger built into my All-In-One unit? I plug it into 120 volts and program the charge function and charge 1 at a time.
That works fine if your inverter is for 12V batteries, but it is for 48V batteries that would be a problem..... I assume it is for 48V batteries since we are talking about building a 48Volt system.
 
That works fine if your inverter is for 12V batteries, but it is for 48V batteries that would be a problem..... I assume it is for 48V batteries since we are talking about building a 48Volt system.
Nope, mine is 24 volts but I'm thinking the same principles should apply. Correct me if I am wrong.

So ultimately I will need a dedicated charger, as will many who read this thread. Tonight's search has come up with this as the best product so far. Any suggestions would be appreciated though.

www.expertpower.us/collections/lifepo4-chargers/products/epc1220-20a-1
 
I also like the fact that you made a thread for the video.
There really should be a sub forum that is just for your videos and each one should have it's own thread.
That is the way Dave Jones does it and it seems to work really well.
 
Like the thread/video concept. Keep ‘em coming Will.
 
One of the comments on Youtube is an important one:



As will mentioned in the video, the FETS in the battery BMS has to be rated for the full series voltage of the string of batteries.

------------------------------------------------------

A question for @Will Prowse: In the video you say to charge the batteries individually before putting them in series. Do you see anything wrong with putting them all in parallel and charging them all at once?
Why is this? Doesn't the FET only see the voltage from 1 battery?
 
Doesn't the FET only see the voltage from 1 battery?
No. When the FET turns off, the voltage of the whole string is across the FET.

The diagram below represents the FET as a switch. Notice that when the FET Turns off (Opens), it will see the voltage of the full string, just like a disconnect switch would.

1645812163546.png
 
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