24c LiFePO4 Battery Storage/Discharge

[Whitty21]

Hi all,

We are working on setting up a 24v solar system at our off grid cabin this spring. We are typically there on long weekends for 3-4 nights.

So the batteries will be stored in 2 different ways. Off an on for 1-2 months during may-October, then be brought home for the winter and stored Nov-April.

My question is, should we leave the batteries connected to solar all summer? There will be no load at the cabin, and have the charge voltage set to 3.35 or 3.45 per cell. Or leave the batteries full, or near full and disconnect from the system entirely?

Also, our batteries (Redodo) state for long term storage at 40-50% SOC. In the fall, it will be easy to just disconnect the PV array and use up whatever we need to 40%. However Redodo states that it should be cycled to full every 3 months when in storage. Is that all that necessary provided the discharge isn't concerning? I dont believe there is a way to turn of the BMS.

If one was to do a charge cycle, how would be best to do it? With them being 24v and my inverter being a 7 hour drive away?

Thanks in advance

 

[MisterSandals]

My question is, should we leave the batteries connected to solar all summer?

Ideally I would want things powered down and disconnected when not there. The question would be whether the batteries would have enough power upon arrival and whether the solar would charge them to make the batteries usable.

 

[Whitty21]

Ideally I would want things powered down and disconnected when not there. The question would be whether the batteries would have enough power upon arrival and whether the solar would charge them to make the batteries usable.

Would you worry about a higher SOC than 50% for 1-2 months? We have 400ah to run a small camp, so we dont need it full, but a cloudy weekend may pose an issue

 

[MisterSandals]

Would you worry about a higher SOC than 50% for 1-2 months?

I would charge it up pretty high before leaving. If it was at 100%, i'd probably drain it down a smidge for a feel good and not any good reason. Just sitting they will self discharge down to 3.35 to 3.45Vpc pretty quickly.

The BMSs will pull them down too. If possible, i might even disconnect those. Left on their own, there is no stopping the BMSs from using power.

I'd be very comfortable with all of this.

The worst would be to hold them with continual charge at an elevated charge.

 

[OffgridMatty]

I have a similar setup and situation. I've only had the cabin for a year and a half so far. The first year I used the system all summer and never turned it off. The batteries have no trouble keeping the charge at 90-100% even with a small fridge running. The first winter we didn't know what to expect. I knew I had to turn the system off due to not being able to charge below freezing/ We use the cabin a few weekends during the winter so there was on issue with having enough charge during our stay. I did bring the batteries home between stays and charged with a 24v charger from Signature Solar. That process got old really quick. This winter I turn the system off between visits. I have my Growatt AIO charger/ inverter connected to my generator and top off the batteries when needed so I always come back with at least a 75% charge. It has worked well so far with that procedure. It stinks that the Lifepo4 batteries can't charge in the cold, but the other advantages outweigh that negative.

 

[MisterSandals]

I have my Growatt AIO charger/ inverter connected to my generator and top off the batteries when needed so I always come back with at least a 75% charge.

So this is all up and running and the generator automatically starts up to charge the batteries, even when you are not there?

 

[OffgridMatty]

No, I have it shut down when not there in the winter. I run the generator for a few hours before we leave after a weekend stay to make sure we arrive with enough power for our next visit. It usually gets to 75% SOC and I have two 24v EG4 batteries in parallel at 5.1kwh each. In the summer, I let the solar charge when away as we get plenty of sun and the only load is my small refrigerator and the AIO. It's a basic set up, but seems to work well so far.

 

[740GLE]

No, I have it shut down when not there in the winter. I run the generator for a few hours before we leave after a weekend stay to make sure we arrive with enough power for our next visit. It usually gets to 75% SOC and I have two 24v EG4 batteries in parallel at 5.1kwh each. In the summer, I let the solar charge when away as we get plenty of sun and the only load is my small refrigerator and the AIO. It's a basic set up, but seems to work well so far.

Sounds like the ideal set up for an off grid build.

Any idea a how many KWhr you use over a weekend?

 

[OffgridMatty]

Sounds like the ideal set up for an off grid build.

Any idea a how many KWhr you use over a weekend?

I don't have any tracking programs running. I can say it's usually 30% of my total, so about 3kwh in the winter. In the summer it seems less due to extra light and great solar charging of the battery all day.