Question about charging batteries

[deeznutz206]

I apologize in advance if this is a stupid question. ?

I am using K2 Energy LiFePo4 26650 cells @ 3200 mAh in my battery pack that I built. The specs for these cells say that the max charging rate for each is 3.2 amps. My battery pack is in a 4s12p configuration (48 cells).

My question is, can I charge at a higher rate, say 5 amps, because I am charging a whole pack or do I still have to charge at 3.2 amps so that I don't damage the cells and decrease its performance life?

 

[dwh]

The 4 in series would create a string of 12.8v (if they are 3.2v ea.) but doesn't change the 3.2a limit.

The 12 series strings in parallel doesn't change the voltage but does increase the amperage.

So the max would be 3.2a x 12.

 

[deeznutz206]

The 4 in series would create a string of 12.8v (if they are 3.2v ea.) but doesn't change the 3.2a limit.

The 12 series strings in parallel doesn't change the voltage but does increase the amperage.

So the max would be 3.2a x 12.

Thanks for the reply. So if I'm understanding your post correctly, technically the pack can be charged at 38.4 amps (3.2x12) , not that I would do that.

Can anyone else confirm this just so that I can have a second opinion/input? My charger goes up to 10 amps and I am going to charge the pack at 10 amps if the consensus says it is safe.

 

[dreadlocks]

I confirm, your parallel multiplier is what you use against individual cells max amps to determine pack max amps..

10A is safe.. each battery will be getting ~0.8A each as long as everything is balanced & wired correctly.

 

[deeznutz206]

I confirm, your parallel multiplier is what you use against individual cells max amps to determine pack max amps..

10A is safe.. each battery will be getting ~0.8A each as long as everything is balanced & wired correctly.

Thanks guys! No more waiting for 10hrs to get the pack charged up!

 

[john61ct]

Did not read the other posts.

3.2Ah capacity per cell, so *12 for pack = 38.4Ah

Ideal for longevity would be 0.3-4C so 13-15A

Max fast charging IMO 0.8C or 30A, but only in very warm temperatures.

 

[deeznutz206]

Did not read the other posts.

3.2Ah capacity per cell, so *12 for pack = 38.4Ah

Ideal for longevity would be 0.3-4C so 13-15A

Max fast charging IMO 0.8C or 30A, but only in very warm temperatures.

Got it! Thanks!

 

[john61ct]

Lower rate the better if plenty of time.

And definitely in cool temps, lotsa damage pushing current into cold cells

 

[deeznutz206]

Lower rate the better if plenty of time.

And definitely in cool temps, lotsa damage pushing current into cold cells

Yep. Settled on 8 amps instead of 10 amps. Still faster than the 3.2 amps I was previously charging them at ?

 

[john61ct]

10-13A would be no problem at all long as they aren't cold.

 

[Chorky]

10-13A would be no problem at all long as they aren't cold.

I'm curious what the definition of 'cold' is... and at what point one would want heat pads for batteries to warm them up, or a fan to cool them off

 

[john61ct]

Each model battery will have its minimum "no charging anywhere near this temp or instant scrap" spec.

In truth you usually can charge at a **very** low C-rate around 0°C

But in general, being conservative I'd start pre-warming below 10° if going over 0.1C

25° should be fine for 0.2-3C

Faster charging than this, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30° first to maximize longevity.

Of course in many contexts people just take the hit, if they're even aware of the issue.

 

[Photobug]

I'm curious what the definition of 'cold' is... and at what point one would want heat pads for batteries to warm them up, or a fan to cool them off

I believe its below freezing and the biggest problem with them is only charging while cold. I believe it is around 25F. Relion makes a "Low Temp" series of batteries that has a work around for this.

LiFePO4 Batteries | RELiON

LiFePO4 Batteries

relionbattery.com

 

[Chorky]

Each model battery will have its minimum "no charging anywhere near this temp or instant scrap" spec.

In truth you usually can charge at a **very** low C-rate around 0°C

But in general, being conservative I'd start pre-warming below 10° if going over 0.1C

25° should be fine for 0.2-3C

Faster charging than this, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30° first to maximize longevity.

Of course in many contexts people just take the hit, if they're even aware of the issue.

Very interesting, thanks for your response. I feel like I've heard this now on a different thread I made months ago. Anywhoo...I dont consider freezing (0 C or 32F for us Americans ) to be very 'cold'. If this in fact be the case, then I would think most batteries wouldn't last a winter, especially for diesel rigs... Interesting though nonetheless as last year I had considered battery heaters even just for the starting batteries when out in well below 0 temps. I wonder though, how many in this forum actively use battery heaters... It doesnt seem to be discussed much.

 

[Chorky]

AAAnnnd I just realized this was for lithium, correct? if so, my question probably doesn't stand for standard batteries..... Oops...