LifePo4 Charge Performance

[otrfun]

Thinking seriously about replacing our two GC2's with a pair of 100ah LifePo4's. Hearing a lot of chatter about how lithiums accept a charge much quicker than lead cells.

Very familiar with how our GC2's charge after being discharged to 50%. It typically takes our 45a converter 2.5 - 3.0 hours to charge them from 50% to ~90% (at 14.4v).

Assuming a pair of 100ah LifePo4's were discharged to say, 10-20%, roughly how long would it take a 45a converter to charge two 100ah LifePo4 batteries to 90-95% assuming the converter remained at 14.4v the entire time?

Thanks!

[BFL13]

https://en.wikipedia.org/wiki/Car_tailfin#/media/File:Cadillac1001.jpg

[RickLight]

Mentioning your charger. I do hope it's lithium compatible, so you can charge to full. That's the real reason I got a new one!

[BFL13]

BFL13 wrote:

otrfun wrote:
OP here. Appreciate everybody's replies!

Really likin' the fact LifePo4's can accept full charge current for most of the charge cycle. I'm thinking our 45a converter will suffice with two 100ah LifePo4's for the time-being. If we can charge two 100ah LifePo4's from 10-20% to 90-95% in approx. 3 hours I think we'll be fine. That's approx. 150ah being placed back in the LifePo4's which is approx. double the ah we'd get into our two GC2's in 3 hours.

Looking forward to this LifePo4 upgrade!

150/45 = 3 hrs 20 minutes
45 x 3 = 135 AH

Best you can do with two GC2s is a 40-90 = 50% of C20, = 115 AH from a pair of 230 GC15s

that would be 40-80 at 45 = 92AH/45 = 2 hours, plus an hour to do the 80-90 with tapering amps =23 AH so :

115 AH takes 3 hours with a pair of GC2s
135 AH takes 3 hours with a pair of LFPs

BUT when you really want LFPs no matter what, you can call 135 twice 115 if you like. 🙂

[BFL13]

Duplicate

[otrfun]

OP here. Appreciate everybody's replies!

Really likin' the fact LifePo4's can accept full charge current for most of the charge cycle. I'm thinking our 45a converter will suffice with two 100ah LifePo4's for the time-being. If we can charge two 100ah LifePo4's from 10-20% to 90-95% in approx. 3 hours I think we'll be fine. That's approx. 150ah being placed back in the LifePo4's which is approx. double the ah we'd get into our two GC2's in 3 hours.

Looking forward to this LifePo4 upgrade!

[RickLight]

LiFePo can be discharged to 0%, as defined by it's own BMS!

Reliable manufacturers rate their products in real world terms. Whatever point the BMS shuts off power is likely 10-20% of capacity. The important part is getting the amp hours you pay for.

[pianotuna]

theoldwizard1 wrote:

First, understand that LiFePO4 can be discharged much deeper, down to about 10% State of Charge. Therefore, it will take more energy to recharge them.

Second, depending on the brand of LiFePO4 batteies you buy, some do and some don't have built in charge controllers. Reality is, you are going to need a new charger to get optimal performance and life from your batteries.

The new "trend" is to buy individual cells (directly from China; up to 280Ah per cell) and build your one "battery pack". This will save you hundreds of $$$ ! For charging, use a MPPT solar charge controller and connect it to a "dumb" 15V-20V DC power supply.

Since they can be discharged to a recommended 20% (most that I've seen, but not all), it does take longer--but the extra capacity does mean less frequent generator running.

Could you elaborate on "For charging, use a MPPT solar charge controller and connect it to a "dumb" 15V-20V DC power supply."

[theoldwizard1]

otrfun wrote:
Assuming a pair of 100ah LifePo4's were discharged to say, 10-20%, roughly how long would it take a 45a converter to charge two 100ah LifePo4 batteries to 90-95% assuming the converter remained at 14.4v the entire time?

First, understand that LiFePO4 can be discharged much deeper, down to about 10% State of Charge. Therefore, it will take more energy to recharge them.

Second, depending on the brand of LiFePO4 batteies you buy, some do and some don't have built in charge controllers. Reality is, you are going to need a new charger to get optimal performance and life from your batteries.

The new "trend" is to buy individual cells (directly from China; up to 280Ah per cell) and build your one "battery pack". This will save you hundreds of $$$ ! For charging, use a MPPT solar charge controller and connect it to a "dumb" 15V-20V DC power supply.

[BFL13]

Yes, as the EDIT tried to get in there. I should not have got so testy anyway, sorry Rick.

AFAIK LFPs do not go from 0-full though, but down to 10%. So that needs to be in any comparison of AH.

The OP can get "faster charging" with no tapering just by doing 40-80s instead of 50-90s with his 45 amper. The tapering is on the 80-90 part. So no difference in gen time for the 88AH. (The 6s won't suffer by going to 40 that most RVers would ever notice for number of lifetime cycles)

Just getting a higher amp converter is not so simple. You need a generator that can run it, so eg, a 2000w is limited to 60 amps and a 2200 to about 75 amps. A PF corrected 100 amper might run on a 2200, haven't tried it.

80 amps and higher without PF correction need 20 amp (120v) circuits and plugs. The gens need a 20 or 30 amp receptacle or a 15/20 type, that some don't have.

[StirCrazy]

BFL13 wrote:

RickLight wrote:
Different brands can charge and discharge at different rates.

My 3 Lion Energy UT1300 can each discharge at 150A and charge at 100A but prefer 45A. I upgraded my charger to a lithium rated one and went to 75A. Even at 45A it's just over 2 hours from 0 to full.

The beauty is that the charging rate doesn't slow down as they fill, like all lead acid based. Their "internal resistance" is much lower so the last 10% is as fast as the rest.

Those are 105 AH batts, so 3 x 105 = 315AH/75 amps = 4.2 hours
315/45 = 7 hours

So "even at 45A it's just over 2 hours from 0 to full"---where on Earth did you get that from?????????? 😞

EDIT-- 105/45 = 2.33 hours

I think he was talking about just 1.

Steve

[Itinerant1]

Looking at the link pianotuna posted it does sum it up correctly in the "Lifepo4 battery charging profile" section where it states "... the advantage of Lifepo4 battery is that the rate of charge can be much higher, making the charge time much faster".

If your charger isn't larger than it's not a whole lot faster other than the long absorb stage that lead needs and lfp doesn't.

[BFL13]

RickLight wrote:
Different brands can charge and discharge at different rates.

My 3 Lion Energy UT1300 can each discharge at 150A and charge at 100A but prefer 45A. I upgraded my charger to a lithium rated one and went to 75A. Even at 45A it's just over 2 hours from 0 to full.

The beauty is that the charging rate doesn't slow down as they fill, like all lead acid based. Their "internal resistance" is much lower so the last 10% is as fast as the rest.

Those are 105 AH batts, so 3 x 105 = 315AH/75 amps = 4.2 hours
315/45 = 7 hours

So "even at 45A it's just over 2 hours from 0 to full"---where on Earth did you get that from?????????? 😞

EDIT-- 105/45 = 2.33 hours

[RickLight]

Officially they are 105AH like most group 27 units.

[pianotuna]

Rick are those 100 amp-hours each? Sounds like a great system.

[time2roll]

Yes I was thinking about four hours. Consider going to a 90 amp converter and do it in two. Solar should also perform better if you are inclined.