How bad is 75a charger on a 100bms bat? 12v 200ah 2560wh lifepo4

nschizzano

How much life will it take off a new lifepo4 bat witch charging it this fast? 75a charger from the Yamaha gasoline generator on a 100a bms lifepo4 bat. 12v bat. 200ah/2560wh

The battery company does recomend 40a charger but it's sort of slow to charge

Does anyone know the charging time math? It's a 200ah bat. So 200amp charger, charges it in 1 hour? 100amp charger charges it in 2 hours? 50 amp charger charges it in how long?

Dave Angelini

I have seen alot of damaged LFP batteries from people who charge and discharge too fast.
Really hard to make economic sense for using LFP if you do not follow the manufactures specs!
The math is really in the algorithm the BMS uses. This is the reason that really good batteries recommend you use closed loop charge/discharge. Closed loop can easily charge 30% faster and safer!

nschizzano

Okay great comment. Yeah I should probably just stick to spec. I've been with that idea from the start but now I'm looking at all the options and learning everything I can. I also want to keep everything Litime brand so it ensures compatability and assitance from the LITIME service department. I have Litime MPPT and LITIME battery, I was going to get their 40a LITIME charger, but I kept hearing the fan is louder than anything. I also don't really mind charging it for 5hrs, it won't even be 5hrs because that's 0 to 100 and I would be charging it from 10 or 20 percent to 80 or 90 percent. 

But also the majority of its charge will be at 1 or less amps up to 16.6 amps from the 200 watt 12v PV's & MPPT. So it will be picking up a nice lower to medium low charge from the MPPT & panels

BB.

Lithium Ion batteries typically have a very flat charging curve from beginning to near 100% State of Charge... So, they should draw 100% of the charger's rated current (assuming charging voltage is correctly set, good heavy/short copper wiring, etc.)...

Unlike FLA batteries which tend to "throttle down on current draw" as they exceed 80% State of Charge...

I Like to suggest charging between 20% and 80% State of charge for best Lithium battery life (others here think I am too conservative)... Yes, they will work fine if you go from 5% to 100%--But it is at the expense of cycle life (at least in my humble opinion).

You can ask the battery mfg and get their "take" on optimum charging/discharging practices.

-Bill

Dave Angelini

I think you can easily unbalance the cells in a battery bank by not charging to 100% monthly/weekly at a minimum.  An unbalanced bank often does not show up for several years at which point you may have permanent damage. This is expressed as State of life on a quality battery. It can be also used for logging in a warranty dispute.

Most of these disputes favor the manufacturer BTW😉

Wheelman55

…but doesn’t the bms do that?  Meaning keeping charge above zero and below 100%?

The Disco AES batts that we use have a capacity of 7.5kw with only 6.6kw usable. 

Dave Angelini

 Yes and no. Yes a BMS limits charge and protects at the bottom, but the user has to provide enough charge source to get a battery to 100%.  By limiting charge as Bill was saying, on some LFP, you are not allowing the BMS to do it's other job and keep the cells in balance. I get his point on cycles but tend to stay with the spec that the warranty is based on.

You should write me as I do not go into AES specifics here. Just trying to generally be of help!

Horsefly

The max charge rate from manufacturers of pretty much all LiFePO4 cells is 1C. So for the OP's 200Ah 12V battery, that should mean the maximum charge rate is 200A. The manufacturers own tests actually do charge and discharge at that rate. However, charging (or discharging) repeatedly at that high of a rate will shorten the life of your battery. Besides, with a 100A BMS it will probably cut of charging / discharging once you get up to 100A. 

75A is not all that high for a 200Ah LiFePO4 battery. I probably would feel comfortable charging at that rate.

Unlike Lead Acid batteries, LiFePO4 doesn't really care if it never gets to 100% SoC.  There are some folks that have been using their LiFePO4 cells for approaching 10 years and never charge them more than about 80-90%. For me the problem is that most coulomb counting battery meters need to get to 100% now and then to maintain a good reference of how full the battery is. So if you have a battery monitor you probably will want to get to 100% periodically.

Note that charging to 100% SoC is that the same as charging to the max voltage of 3.65V per cell. You can charge at a voltage of 3.45V up to 3.55V per cell and eventually the charge current will drop to nearly zero at which point the cells are actually full. As the current is dropping down the BMS is balancing the cells, which is good. 

Bottom line: Set your bulk / absorption voltage to 3.5V per cell (14V for your 12V battery). You'd probably be fine charging at 75A, but if for some reason the manufacturer explicitly says 40A max, I'd stay with it. If you charge source has a tail current setting, set it to something below 10A (0.05C for your battery). 

Dave Angelini

I know the store here has had problems with people not getting a full charge on system type batteries.
( not talking about individual cells) I am not involved with DIY batteries but agree if you get the bank up to 56V (typical for 48vdc commercial banks that NAZ sells) and float about 53.6v, you will probably have long life.

Two of the damaged battery banks (10K$+) were the BMS did not get to the right voltage unless it was at 99% Soc. The State of life was low because it could not be balanced anymore. It was toasted from undercharging. It was very well logged in the BMS for warranty.

The OP wants a faster charge on a battery make I have never heard of so I would defer to the manufacturer. If he bought it from the store here, he would have excellent support!