Voltage difference

yycwrangler · May 2, 2024

Quick question just charged both my new 100ah batteries today. Smart charger took the lifepo4 batteries up to 14.6v. I then connected them in parallel and when I checked they were now readin 13.7 volts. Why the change when they just came off the charger and no loads on the. There connected together to balance them out

sunshine_eggo · May 2, 2024

yycwrangler said:
Quick question just charged both my new 100ah batteries today. Smart charger took the lifepo4 batteries up to 14.6v. I then connected them in parallel and when I checked they were now readin 13.7 volts. Why the change when they just came off the charger and no loads on the. There connected together to balance them out

LFP is similar to lead acid in that you have to charge to a higher voltage than the operating voltage. When charging is removed, voltage settles.

Recommend you put them on the charger while in parallel.

yycwrangler · May 3, 2024

sunshine_eggo said:
LFP is similar to lead acid in that you have to charge to a higher voltage than the operating voltage. When charging is removed, voltage settles.

Recommend you put them on the charger while in parallel.

Thank you. I did charge both individually to 14.6 volts

upnorthandpersonal · May 3, 2024

yycwrangler said:
Thank you. I did charge both individually to 14.6 volts

You can go lower than that. 14.6V is 3.65V per cell. It doesn't have to be that high: 3.5V per cell is ok too, which is 14V pack voltage.

yycwrangler · May 3, 2024

sunshine_eggo said:
LFP is similar to lead acid in that you have to charge to a higher voltage than the operating voltage. When charging is removed, voltage settles.

Recommend you put them on the charger while in parallel.

I will in the future..What I read was the initial charge for new batteries be done individually, then connected and allowed to balance

sunshine_eggo · May 3, 2024

yycwrangler said:
Thank you. I did charge both individually to 14.6 volts

Yes. I read that. You should still put them on the charger while in parallel. Simply paralleling them doesn't do as much for balancing as an applied current.

yycwrangler · May 3, 2024

sunshine_eggo said:
Yes. I read that. You should still put them on the charger while in parallel. Simply paralleling them doesn't do as much for balancing as an applied current.

Good to know. Will do that today. Can I ask you what you run your batteries down to before charging.?

caddnima · May 3, 2024

I believe they call it charging voltage and resting voltage.

TomC4306 · May 3, 2024

I use 55.6 (13.9), 60 minute absorption, and 49 (12.25) as my operating voltage range.
There is very little usable capacity outside this range

sunshine_eggo · May 3, 2024

yycwrangler said:
Can I ask you what you run your batteries down to before charging.?

I only have a couple of 12V LFP, and they're for experimental purposes. If necessary, and I had the means to "jump start" them if they entered low voltage discharge protection, I wouldn't hesitate to run them down to BMS cut-off; however, for routine use, 12V.

From the testing discussed here:

LFP full charge @ 3.4V/cell

Thought I'd try a little something on a cheap 12V I've been testing... Charge to 20A @ 13.6V (3.4V/cell), 2A tail current. When testing at cell level and dealing with testers that don't have separate sense leads, lead resistance plays a big role, and I would typically observe cells get charged...

diysolarforum.com

This is an example of a discharge to empty

As you can see a 12V cut off utilizes the vast majority of the battery capacity without triggering protection.

Voltage difference

yycwrangler

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sunshine_eggo

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yycwrangler

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upnorthandpersonal

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yycwrangler

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sunshine_eggo

Happy Breffast!

yycwrangler

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caddnima

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TomC4306

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sunshine_eggo

Happy Breffast!

LFP full charge @ 3.4V/cell

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