question

Sportswagoneer avatar image

Taking optimum care of LiFePo batteries on boats and RV’s. Storage mode and timer?

I have a standard drop-in 3x100Amps LFP bank. During the week and some weekends the boat is docked and plugged into shore power. There’s also a solar panel of 114W nominal (MPPT) on deck. Use a Cerbo to monitor, constant VRM connection. I can see the MPPT going through a full cycle of bulk-absorption-float every day even if the shore power charger maintains long term float.

Whats the problem?

From my experience with electric cars (EVs), I know that allowing Lithium batteries to sit for longer periods at very high (or very low) SOC is quite detrimental to cycle life. I understand that LiFePo4 may be more robust but still think the default charging to 100% seems less than optimal. (Have set the absorption duration from MPPT at 5min to minimize that at least.) At the same time, I certainly do want maximum SOC when cruising.

Idea:

A separately configurable “storage mode” for LFP batteries - as opposed to the normal “active mode”. This could work like this: A storage voltage or SOC (I.e. 50-70%) is set. This requires the charger/inverter to override the MPPT so that no unit will exceede the storage level. A timer/date and target SOC for active mode can be set so that the inverter/charger will charge to that level based on the timer. (Every n’th charging could be to 100% with 2 hrs. absorption to allow for cell balancing.) Normal minimum temps (>5°) secures long term winter storage.

I really don’t know if I’m trying to solve a non-problem here - but as more users become familiar with EVs I suspect these concerns will become more commonplace - so it would be great to either clarify this - or to implement a solution.

Lithium Batterybattery charging
10 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
snoobler avatar image
snoobler answered ·

It's expecting nightly discharge since it's designed that way. Charger shuts off at night. Wakes up in morning, sees voltage is below absorp, bulks, absorps, floats. It's behaving exactly as it's designed to do.

In reality you are trying to solve a non-problem. LFP is way more tolerant than NMC, BUT I get it. I like it my way too. :)

Disable charger in battery settings when away. Turn it back on when you need it. That's essentially the same effort as selecting a "storage" mode option.

If you want it enabled as a backup in case grid goes down because you have a load that might pull it down, set absorp to same as float voltage. It will wake up every day and immediately float when grid is up, or if grid goes down, it will do a quick bulk/absorp/float and keep the battery in a healthy operating range for both storage and use.


Share
10 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.