Lithium end charge

[Wdeertz]

I recently swapped out my FLA batteries with LiFePo batteries. I’m loving the battery bank performance while out cruising but have a question while under shore power. I currently have my Magnum inverter/charger set to go to silent mode once the batteries are at 100% charge. This results in the batteries continually going between 100% and 80% when the rebulk charge cycle restarts at 26.6v (about once every 24 hrs). I know LiFePo batteries don’t like to be stored long term at 100% hence why I choose the silent mode at the end of the charge cycle rather than a float of 27.2v.

My question is if I cycle 20% of the battery capacity every day then over a 60 day shore excursion I’ve effectively done 12 full charge cycles. The LiFePo are supposedly rated for a minimum of 3000 cycles so maybe I’m splitting hairs but would it be better to have the charge cycle end with a 27.2v float charge at a minimal amps?

 

[Delfin]

I recently swapped out my FLA batteries with LiFePo batteries. I’m loving the battery bank performance while out cruising but have a question while under shore power. I currently have my Magnum inverter/charger set to go to silent mode once the batteries are at 100% charge. This results in the batteries continually going between 100% and 80% when the rebulk charge cycle restarts at 26.6v (about once every 24 hrs). I know LiFePo batteries don’t like to be stored long term at 100% hence why I choose the silent mode at the end of the charge cycle rather than a float of 27.2v.

My question is if I cycle 20% of the battery capacity every day then over a 60 day shore excursion I’ve effectively done 12 full charge cycles. The LiFePo are supposedly rated for a minimum of 3000 cycles so maybe I’m splitting hairs but would it be better to have the charge cycle end with a 27.2v float charge at a minimal amps?

There's some evidence LFP batteries will develop memory and that by short cycling them you may be reducing overall capacity. I've managed my bank by drawing it down 70 - 80%, then recharging. Three years and they still have original capacity. IMO it is also a good practice to periodically charge to 28.8 - 29.2 vdc with an absorption period of 30 minutes.

 

[twistedtree]

I've done two LFP systems at this point and I float both of them at 3.35 volts per cell which is 26.8V for a 24V system. That maintains them around 80%, and prevents gratuitous cycling. If they spend a lot of time on shore power, you could dial it down to 26.6V.

 

[Rossland]

I've done two LFP systems at this point and I float both of them at 3.35 volts per cell which is 26.8V for a 24V system. That maintains them around 80%, and prevents gratuitous cycling. If they spend a lot of time on shore power, you could dial it down to 26.6V.

That is my advice too. My boat is now in long term storage on shore power, and my lithium batteries are being floated at 13.38 V., but once a week, the charger briefly bumps this up to 13.45V.

As far as the number of cycles, I don't think you need to be concerned. The 3000 estimate probably refers to taking the batteries down to a fairly deep discharge, 20% or something like that. Ask your battery manufacturer.

 

[Wdeertz]

Thanks for all the replies. I wasn’t aware of any possible memory effect for lithium if they are short cycled. I can adjust my rebulk voltage so the batteries draw down more before the bulk/absorb cycle restarts. The rated 3000 cycles is 100% to 0% which is so many a few cycles here and there while on shore power shouldn’t be a concern.

I think cycling through a charge cycle every few days is better than leaving on a nominal float charge. Thanks again.