LifeP04 voltage drop after fully charged...

[General_Lee]

Hi Guys, I have two battery pack Prismatic LiFeP04 (15ah 24s) in parallel = 30ah 76.8 nominal. I use Cycle Satiator charger set to reach 86volt for charging my pack.
When the pack is full, the charger keep the pack fully charged.
When I unplug the charger, the voltage begin to drop slowly until 84v. This is normal or not? It is better to set the charger at 84v? instead of 86v? I not want to break my pack.

I tried without BMS and same thing.

thanks. 8)

 

[dustNbone]

I think this is normal for LiFePo4. Mine (16s 20Ah A123) charges up to 60V and drops down to around 58 almost immediately after the charger is removed. It's been doing that since it was new, and the battery performs wonderfully. I wouldn't worry about it.

 

[dmwahl]

It's totally normal, although I don't fully understand the chemistry behind it. You can set the charger voltage lower, but you're unlikely to notice much difference other than slower charging when it nears full and maybe marginally improved life. The amount of energy actually absorbed once the cells get above 3.5V is minimal.

 

[General_Lee]

OK thanks, if you have the same phenomena, is probably normal

 

[dogman dan]

Lifepo4 tolerates a slight overcharge far better than other lithium types.

So they routinely overcharge a bit, which forces a great balance on the cells every cycle. Your pack is full at 84v,, the rest is surface charge, which only sticks if the pack is brand new.

Later on, as your capacity drops, "full" will be 83v, then 82, and so on. at 79v you pack is about at it's end, only holding 3.3v per cell.

You can set your satiator to 84 if you wish, but your bms may not function to balance the pack till a higher voltage. So at the least, charge to 86 from time to time. If you want to undercharge, to extend lifespan,, you can charge to 3.4v per cell. But once in a while charge to 86 and then use the battery immediately to keep it from sitting around fully charged.

Ideal use pattern might be this,, ride it, charge to 80%,, then in the am,, finish the charge and use the battery in an hour or two. minimize the time it ever spends fully charged.

 

[General_Lee]

Lifepo4 tolerates a slight overcharge far better than other lithium types.

So they routinely overcharge a bit, which forces a great balance on the cells every cycle. Your pack is full at 84v,, the rest is surface charge, which only sticks if the pack is brand new.

Later on, as your capacity drops, "full" will be 83v, then 82, and so on. at 79v you pack is about at it's end, only holding 3.3v per cell.

You can set your satiator to 84 if you wish, but your bms may not function to balance the pack till a higher voltage. So at the least, charge to 86 from time to time. If you want to undercharge, to extend lifespan,, you can charge to 3.4v per cell. But once in a while charge to 86 and then use the battery immediately to keep it from sitting around fully charged.

Ideal use pattern might be this,, ride it, charge to 80%,, then in the am,, finish the charge and use the battery in an hour or two. minimize the time it ever spends fully charged.

If I set the Satiator at 86v, when the battery come fully charged, the Satiator will keep the pack fully charged until I unplug it. In this condition, is not good for the battery? Because often I start the charge at evening and unplug at morning. Depending how many it is discharged to reach full charge, the satiator take around eight hours (4amp).

If the pack stay some hours fully charged before to unplug it and go to take a ride, like you write is not a problem?

Maybe I can set the Satiator to 3 or 2 amp to take more long time...

Thats why I was asking if is better to set the Satiator to 84v instead 86v. But I understand your explanations. 8)

 

[999zip999]

I charge my lifepo4 24s to 84v it will settle a little. No bms 4yrs old still works great. I would set charger to 84v and monitor cell balance. Does it still balance ? I like a set of sense wires for ez checking 4 - 6s sense wires. What kind of lifepo4 cells are you using at what amps.

 

[dogman dan]

Change your charge voltage easy with the satiator. Only if you are flogging the pack will it really need a balancing charge every single cycle.

So you can just charge to 84 most of the time, or even less.

What I do a lot with my lipo packs,, I charge to 90% only if I will ride the next morning. In the morning, I put back on charge a few min for the last 10%. If I know the ride will be short, I just ride off charged to 90%. I'm stuck with the choices half, 90%, and full with my charger. But with a satiator, you can do whatever you want.

If I won't ride till late morning, I start the charge in the morning.

But if you wish to,, charge your pack to full and balanced every night. Lifepo4 is more tolerant of this than other chemistries.

At some point you just have to say,, "I'm using this in the real world, and I need to just get up and hop on and go." Retired guys like me can dork around with stuff to get a few extra cycles from a pack. Your time might be a lot more valuable than that battery.

 

[General_Lee]

ok thanks, I put a picture about one of my pack, I have two like this. I don't know the brand, I bought it from (sun-thing28). I'm satisfied about this pack, I can ride easily 60 km with speed 55 Km/h (arround 35ah) but I'm not sure the quality. I hope I can use it some years like this :?

I checked all individual cells and all is perfectly balanced.

 

[999zip999]

Be careful that thing is alive so do be very careful. Sometimes you only get one mistake. Slight compassion is good. You can run thoes cells to 40amp with 30ah of capacity. Higher capacity equals more possible amps The bms I don't know it's rating.

 

[General_Lee]

Be careful that thing is alive so do be very careful. Sometimes you only get one mistake. Slight compassion is good. You can run thoes cells to 40amp with 30ah of capacity. Higher capacity equals more possible amps The bms I don't know it's rating.

BMS is 80 amp capability (supposed) and my controller can reach 48 amp.

 

[999zip999]

Im confused you brought two 24s 15ah sunthing packs each has a 80amp bms paralleled to a 24s15ah with its own 80amp bms 80amp peak ? Or does it have one bms ?

 

[General_Lee]

Im confused you brought two 24s 15ah sunthing packs each has a 80amp bms paralleled to a 24s15ah with its own 80amp bms 80amp peak ? Or does it have one bms ?

Each pack have one BMS, I connect the packs in parallel for have 30 amp total. Sunthing can't ship 72v 30 amp only, too heavy, he need to split them and ship separately.

One pack have: 24s 15amp X2 = 30amp.

 

[999zip999]

Amp hour or ah. Not amp or a. A battery that big should have little stress.