Off Grid LifePo4 Battery storage/standby modes

[ianganderton]

I was thinking about options for storing batteries while they are not being used or when full storge is not required. E.g cabin uninhabited, campervan/RV in storage, a yacht is on its mooring

My understanding is a LifePo4 battery prefers to 'live' around 80% for maximum life

Batteries need maintaining and some resources my need to stay on, e.g. yacth's have bilge pumps, cabins and RV's may have a fridge or heater that needs to stay on

I was thinking of ways to easily change settings and thought 2 solar controllers would be an option. One set for full charge, one set for a storage/standby/ maintenance charge profile



Would the right place to put a relay be on the cables from the PV array?

 

[Ampster]

That sounds like a good plan. I don't know the specifics of those charge controllers. I know there is a sequence to boot them and I think it starts with connecting the battery first. You may wish to test my hypothesis.
Incidentally I do the same thing with my EVs. Fortunately there is a slider on the screen which allows me to set the percentage charge.

 

[gnubie]

smartsolar, bluetooth integrated, controllable via smartphone. Simply set up a user defined charge profile or two and toggle between them or built in preset and user defined. IMO two controllers is just a waste of money.

If you can sail a boat and do the configuration of two controllers with relays and switches, changing the settings via a smartphone would be a walk in the park.

 

[Fred S]

If you can find an inexpensive spdt relay that is rated for the max amps that the scc will draw, and is rated for the array's max DC voltage, then what you drew should work fine. I've found in the past that relays get expensive above about 32vdc contact rating. I think they make spdt-style solid state relays, but I assume they are pretty expensive too. You could use a spdt switch and put two ssr's at the junction where you drew the single relay (one ssr for each scc). Again, being on the array side of the scc, the needed Vdc ratings may limit your relay options.

The mechanical relay's N.C. path would be used for the "battery storage" mode, so that no power would be drawn by the coil during storage. I assume that the main controller would draw insignificant power from the battery while there is no PV input, but I would test that to be sure.

 

[tictag]

I agree with @gnubie, no need for two SCCs, just set absorption = float voltage when you leave, raise it when you return. Simple.

Your battery will never fully discharge because the SCC will be powering your loads during the day and the float voltage will trickle charge it if required i.e. if they discharged at all over night.