Charging voltage for LifePO4 4S pack?

CarsonGrey

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May 23, 2020
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Wondering if someone can answer this question or point me to an article.

I have a 4s/5p pack built from K2 26650 LifePO4 batteries. It has a simple Chinese BMS.essay writer

I have a Li-Ion charger (16.8V/3A)that I've used to charge a 4s/8p pack built with 18650's. Can I use this charger to charge the 4s/5p LifePO4 pack?

Thanks!
 
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daromer

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No.

4s life should generally not be charged above 3.65 * 4 = 14.6V.
 

jonyjoe505

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if you can get a buck converter (about 10 dollars) you can use that to to reduce the voltage of your charger down to 14.6 volts, it be a cheaper method then getting a new charger. I use these buck converters to charge all my lifepo4 and li-ion battery packs. The output volts and amps are fully adjustable.
The only reason not to use the 16.8 charger is that bms have been known to fail.
300 watt buck converter.jpg
 

Engineer34

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@jonyjoe505 will this buck converter or minghe 7210a will cause any problem at Lifepo4 in long term ?
I tought Lifepo4 does not like to be under stress and likes to be not charged when it is full.

My Lifepo4 pack is 8s 60Ah Pouch cells. This giant Ebike battery will be charged by a small 80W 17V Solar panel mounted on
Bike with Minghe 7210A. So i dream i will never need to grid charge bike again. I set charging voltage to 27.6V(3.45V) but even
after this voltage Minghe or your Buck converter will not stop it self right ?
 

Engineer34

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For my case i dont have BMS. Ming He input solar panel ( or maybe an adaptor later ) output is battery. And battery directly connected to
Ebike controller. No BMS. BMS at Ebike is almost always on its own battery.
What do you think ?
 

Redpacket

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For my case i dont have BMS. Ming He input solar panel ( or maybe an adaptor later ) output is battery. And battery directly connected to
Ebike controller. No BMS. BMS at Ebike is almost always on its own battery.
What do you think ?
You will damage your batteries 100% certain.
Solar panel will overcharge batteries. You must have charge controller like this:
Solar panel > charge controller > battery > ebike controller, etc
 

Engineer34

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Solar. panel connecter to Ming He charge controller. Charge controller connected to Battery. Battery connected to Ebike battery poles.
Is that what you mean ? @Redpacket
 

Engineer34

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I made like you advised.
Now my question is.
Ming he set maximum 27.6V maximum. And this is very safe for Lifepo4/per cell 3.45V Max.
But it will not cut charging. It will always give 27.6V even it is full. Is that so bad for batteries ?
 

OffGridInTheCity

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From what I've read.... 3.45v/cell seems a little 'too safe' as I don't see how the cells will ever get charged due to the extremely flat charge/discharge curve of Lifepo4 - e.g. essentially flat from what I read. So the charger won't know to pump in current and unless you track ah(s) in/out - you won't even know the SOC to any degree of accuracy - could be 40% or 60% - who knows? I'll be interested to read any comments on this.
 

Redpacket

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It's a trade off between maximum possible capacity & getting into the part of the curve where it starts to jump up.
The SoC is tracked apparently quite well by both batrium & a Victron BMV, don't have issues there.
With my LiFePo4 banks, "full charge" seems to be good when CV charged to 3.45V & held there until the sun goes down.
The current ramps down to hovering around zero after about 30-45 mins there. IMHO this is when it's "full".
If I try to raise the voltage much, eg to 3.55V/cell the pack becomes unstable & some cells start rising more than I want fast.
I tried allowing the batrium system to top balance this but it was always too unstable for my liking (because charge current is much greater than balance current).
I've been running it at 3.45V for about 3 years now & it's been very stable & when (rarely) drained to low % SoC, the monitoring systems are telling me I am getting my 100% range (or as close as I'm willing to let it get down there!).
I'll accept 95% capacity for longer battery life :)
 

daromer

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3.5 i whats considered long time run of LiFePo4. Max is often 3.65.
Yes LifePo4 raise quickly when above 3.3V often or slightly higher when they are degraded.
 
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