question

tex260z avatar image
tex260z asked

LiFePO4 balance

Hi Guys,

Just wondering on what constitutes "balanced" when it comes to LiFePO4 batteries.

As you can see from the attached pics I have one cell slightly lagging behind the other three in all states of charge. However, the little balancer I am using runs to four digits, on my multi-meter they all look exactly the same, so how close is good enough! The balancer does actually balance the pack, but it goes out of balance pretty shortly after with some use.

Lithium Battery
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6 Answers
wkirby avatar image
wkirby answered ·

I like to keep mine within 10mV of one another.

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kai avatar image kai ♦ commented ·

There's a subjective "close enuff" factor in any particular value :)

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vicrvusr avatar image
vicrvusr answered ·

My active balancer doesn't do much better than what you're showing. Like WKirby I like to see less than 10mV difference which it seems you have.

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tharbarn avatar image
tharbarn answered ·

With that little a difference it could be slightly more resistance in the cable or connector.

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tex260z avatar image
tex260z answered ·

Cheers, thanks for that.

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tex260z avatar image
tex260z answered ·

Yes, so considering Off Grid Garage Andy's latest video today, I would like to ask, something along the same lines.

I have an active balancer for my 4S 200 amp Hr. LiFePO4 battery pack, said balancer has the facility for an activation switch (as shown in the video), as I don't really want to buy a new BMS, can anyone advise how I could used either my Bluesmart 75/15 MPPT regulator or the (networked) BMV712, to control the balancer?

I would like it to switch on when the battery is fully charged as suggested, and I would be interested to know what happens when it is actually balanced?

Any suggestion welcomed.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
KISS unless there is a problem, there is no need to do anything.


With my 300ah cells I use an active and shunt type cell balancers. Always on.

During the night and in the fat part of the battery SOC, the cells are within 2mv, active balancer running, (not transferring energy tho).

When the battery goes into absorb at 14v, the cells are within 10mv of each other while still being charged at 30a.

At the end of absorb (20 mins) the charged current has dropped to 3a. Cell voltage differential has risen to 30mv. My battery gets fully charged every second day on average. I doubt my balancers ever do much.

For myself l leave my active balancer running always. It works for me.

YMMV.

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tex260z avatar image tex260z klim8skeptic ♦ commented ·
Hi, so you saw the "Off grid garage" video demonstration about how permanently connected balancers actually put cells out of balance?
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tex260z avatar image
tex260z answered ·

Built a new 33Ah LiFePO4 26650 4S battery based solar charging system for my 60 litre portable fridge, piggy backed the Flying capacitor active balancer to my ISDT BG-8S meter so I can see cell voltages, all seem s to work well. test shows the balancer never switches off, so just plugging it in occasionally as needed.

piggy-backed-cell-balancer-10.jpgpiggy-backed-cell-balancer-11.jpg


portable-fridge-solar-power-system-4.jpg

portable-fridge-solar-power-system-5.jpg

portable-fridge-solar-power-system-6.jpg


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