Lifepo4 charging question going to float too soon

[toothy]

Hello All,

I installed 400Ah of CALB CA400's on the 3rd of July so I know less than nothing. I set the 3 Classic 200's Firmware 2096 and 2097 as follows.

Absorb 53.2V for 5 minutes
Float    52.8 

It seems when the voltage gets to 52.8 it kicks to absorb and goes to float 5 minutes later and never hits the absorb voltage. They are in follow me but  end amps set on WBJR to 0 and no check mark in box.

What else could cause them to kick to float without reaching the absorb V?

Thanks
Wade

[justinbowser]

I have 800 AH @24V LiFePo4 and my battery supplier recommended that I set "Bulk" to 29.2V, "Absorb" to 29.2V, and "Float" to 27.5V.  Although I currently have the WBJR installed with ending amps at 2A I seem to remember they said to set absorb for something like 6 or 8 minutes.  Watching my 200SL switch from bulk to absorb to float it follows what I have programmed. 

Your voltage values sound a bit low compared to what was recommended for my 24V bank.  Are you using values supplied by battery manufacturer?

[toothy]

Hello,

The 29.2 is right at the 3.65V per cell and I think will be very bad for longevity.  Yes, my settings are conservative but that's OK to start with while getting stuff figured out. I did try to push them up, but at around 55v I was getting bad divergence in the cells as reported by the BMS.

CALB didn't seem to have specific charge recommendations. I think the closer you stay to 50% SOC the longer they will last, so I'm staying off the ragged edge.

[boB]

You have multiple (2 or more)  Classics on this battery bank ?

To be in Absorb, at least one of the charge controllers must get up to that set voltage.  After that, the Absorb timer can keep counting even if it drops below that set point voltage by a couple of tenths of a volt.   This MAY be because one of the controllers are at a couple of tenths of a volt above the other controller.

If that is the case, then you should still be OK.  With a bunch of series batteries, that 1 or 2 or maybe 3 tenths of a volt will not matter as much.

A Fluke meter may help see what is really going on.

[toothy]

Hello boB,

3 Classic 200's all set at the same absorb V. I've Fluked them out with 3 Fluke meters to the best of my ability with the jumpyness of a system in use. I'm in float and throwing out any weird spikes from something kicking on or whatever. There are 16 cells in one string with a BMS that agrees fairly closely with the Flukes more or less, it is a Chinese Chargery BMS...

I would 100% agree that to go to absorb at least 1 controller has to see the bulk voltage reach the absorb setting. That is not what is happening, it seems that 1 controller, or more, sees the float setting of 52.8 and kicks it to absorb and starts the timer. It has always worked fine with my 1350Ah FLA's and my 16 Aquions stacks but the absorb/float differential was much greater than for the Lithium. I've forced it to do this numerous times to watch the voltages.

I guess since you didn't mention something there is no other little trick that I'm missing. I did a VMM already, I guess I'll try a FW update, I'm a little shy about those since I bricked one years ago from that.

Thanks for your help
Wade

[boB]

I think that bricking a Classic is a thing of the past now since Matt has seemed to fix the uploading software for the PC.

Even an older Classic should be able to be resurrected if it had not been upgradeable years ago.

Will have to think about....     " it seems that 1 controller, or more, sees the float setting of 52.8 and kicks it to absorb and starts the timer."

[justinbowser]

The 29.2 is right at the 3.65V per cell and I think will be very bad for longevity. 

This was the battery manufacturer recommendation, maybe it has something to do with the internal BMS?  Seems trange to me that CALB would not provide any guidance on charge voltages...

[toothy]

boB,

The magic smoke was a long time ago and I wasn't the only one. You sent me a new one so all was well!!! The new FW looked quite different when I downloaded it yesterday. Don't let the magic smoke out of the top knot over this!

Calb does list a max charge voltage of 3.65 but for max life I don't think it is wise from what I've read. Maybe the internal BMS takes care of all of that. It would certainly be safer If I wasn't allowed near any settings!

[ClassicCrazy]

Lithium batteries go from absorb to float really quickly. Of course that was when I was using ending amps and  no bms.
Your BMS is probably kicking in and then it is different than the Classic would be doing normally on a lead acid.

Larry

[australsolarier]

set bulk to 3.5V and absorb to 3.35V.

in any case above 3.4V there is hardly any more capacity to be gained. it is absolutely not worth the shortening of the lifespan. and keep in mind not all cells have perfectly parallel voltages in absorb. even with a good BMS.