Charging schemes for LiFePO4

[Jd1]

Originally Posted by Maine Sail

Please elaborate ....

[Maine Sail]

Originally Posted by Jd1

Please elaborate ....

You already have the cells, I really should not have to..

The BMS relays are not for charge management they are for bank protection / insurance. All your charge sources should be programed for the LFP banks safe charging range and dialed in specifically for the LFP bank. Then, if there is a failure in one of your charge systems, the relays can do their job at protecting the bank.

This is like smashing up your car every time you want a new one. Your insurance policy is not your ticket to a new car, but you are using it as such. Your BMS is not the proper way to manage your charge sources but you are trying to use it as such.. They should all manage themselves. The insurance is there as, well..... insurance. By using the BMS as your charge management system you have no additional level of protection.

I feel you seem to be losing the forest for the trees.... Forget the lead acid bank and focus on the LFP and how to keep it safe and happy. Really what we are looking at is $2000.00 worth of LFP cells vs. $100.00 +/- of LA battery....... I certainly know where I would focus my efforts...

Once you've nailed the LFP bank and programming all charging sources to self manage and also nailed the BMS then you figure out what to do about the LA bank.... Really not a lot to think about.... On a C-36, I owned one, an LA bank is only really necessary as a reserve bank (yes another insurance policy). It can sit there for months with no charge if you choose an AGM or GEL.. A GEL will do fine at LFP voltages.

The biggest use for my LA reserve battery is in the winter when the LFP bank is not on board. The rest of the time it sits there and minds its own business. Every now and then I charge it by combining it with the LFP bank...

It seems like you are under thinking the LFP and over thinking the LA battery.. If you design your system correctly you will not need the LA battery. Keep it as added insurance but like your car insurance just keep it updated, so its there when or if you should ever need it, and that is all you'll need.

[Jd1]

Actually I am spending very little time on thinking about the lead acids. I have however been reading a lot about lithiuns and everything I have read (and still remember) says that lithium does not need any special charge steps. You just connect a charge source and disconnect it when the battery is at the desired voltage (at the bottom of the upper knee). Since my alternator is running at 14.4V in bulk mode this should be perfectly fine.
Also, using the House Power BMS, you have the signals for HVC and LVC which are used to control the charge and load relays as well as the main contactor relay which is the insurance policy.
I invite you to describe your system setup for alternator charging (only source in my setup) and how you keep everything going. A listing of your 614 parameters as used for lithium would probably be appreciated by a lot of folks as well (me included).

[RichardE]

I think this is the appropriate thread for posting this info. I am not a sailor, but an RVer. I have a 1000 aH 13 VDC nominal battery bank built from 4 Balqon cells. The bank is fitted with a Housepower BMS and Junsi Cell Logger. I am running a Magnum full sine 2800 with the Magnum ME-ARC remote control. I also have the Magnum Battery Monitor Kit (BMK) which uses a resistor and shunt to monitor current in and out of the bank.

My needs in an RV are quite different than the Cruiser will need so my setup may not be applicable to what you need at all. I am just providing data for one to ponder.

I set the charger up as a Custom in the programming. That allowed me to set the charge voltage to 13.8, Max amps 250. I also set the charger to stop at 90% SOC. I bought the Magnum specifically so I could use this feature to stop the charge. When the charge is finished, I programmed the charger to Silent, meaning there is no float voltage. Right now I have the charger programmed to recharge when the bank reaches 12.4 volts, but I am seriously considering raising that to around 12.8.

I have the low battery cutout for the inverter set to 12.2 V.

Here is my thinking. I only have the BMS as an insurance policy. My intent is to set the charger parameters to operate well within the HVC and LVC of the BMS. If I use the charger correctly the BMS never activates.

I will primarily use the shore power or generator to charge the bank as needed.

I am not fretting about the mix of Lead Acid batteries for the chassis and LiPo for the house because I have a remotely activated merge solenoid that only connects the two banks IF I chose to. If I chose to charge the LiPo's with the alternator( 250amp Leece Neevile) then I can, but have to monitor the voltage and return amperage on the LiPo's. I can use the merge switch to help crank the engine if needed, or to charge the house batteries while driving.

The battery bank has been in use for a little over a year. The cell to cell variation is less than 0.005 V. They were bottom balanced by the original owner, and have not been manually balanced since. The charger typically charges at about 125 amps maximum, so this is just another data point that fractional charging and discharging somewhat negates the need for full time individual cell monitoring of the BMS.

I realize that I am not getting the maximum benefit of the LiPos, but I don't need to. The bank is oversized for my needs, and I don't go off grid for more than a few days at a time.

[RichardE]

I have raised the voltage at which the above bank recharges. I now have it set for 13.0 V. This operates the bank from 30 to 90% DOD giving me 600 Amp hours of use and operating well within the extremes.

[Patriot58]

To evm1024

I also have Winston FP 700Ah cells in my house bank but have a cell that is failing. Do you know a US source for the cells since Balqon seems to have disappeared?

[evm1024]

Originally Posted by Patriot58

To evm1024

I also have Winston FP 700Ah cells in my house bank but have a cell that is failing. Do you know a US source for the cells since Balqon seems to have disappeared?

Sorry, I don't know a source. I got mine from Balqon before they went totally dark here in the US.