Switching to lithium

[Dads2vette]

Been using this system for 8-9 years, I had dates wrong last time I posted, and it's time to switch to lithium batteries. I need some help here and am looking for the same voltage and ah while switching to lithium. I'm off grid and the system will not be used as often as I will be using this as a seasonal place. Major appliances are a full size fridge and small window A/C unit at 5000 btu's. I am looking at the new batteries will did a video on 2/21/25, the "Dumfume" LiFePO4 200ah or 300ah models. How many would I need? I've been getting different numbers online.



Current system:
Specs:
6 REC 280 watt (30 Volt 8.9 amp panels)
1 96 Amp Midnite classic150 solar charge controller
1 Box w/250 amp inverter disc. 83 Amp GFCI & 80 Amp charge disconnect breakers
8 Rolls Surrette S-480 6 volt 372 AH batteries
1 3000 watt 24 volt Aims inverter with 40 Amp charger
1 30 amp knife disconnect for A/C side of inverter to feed house system

Thanks,
Dave

 

[yabert]

8 Rolls Surrette S-480 6 volt 372 AH batteries

This is roughly 17.8 kWh of energy, but as lead acid can't give entire Ah when discharge under 20h and because it's not good to discharge lead acid to much, you have way less than that.
Let say you have 10 kWh usable.
With LFP battery, at 24V (25.6V) it represent 394Ah as LFP can use 100% capacity.
So you should have similar or better performance from 400Ah battery.

BUT, be sure to buy 24V battery and not use two 12V in series.

 

[chrisski]

Your pack is 24 volts and 744 ah correct (8 X 6 volt 372 ah setup 4S2P)?

Since 372 Ah is usable, I agree 400 ah would be good, but that gives you more than you asked for, so 300 Ah would give you about the same usable energy since Lithiums can be drained more than 50%.

 

[Dads2vette]

Your pack is 24 volts and 744 ah correct (8 X 6 volt 372 ah setup 4S2P)?

Yes, that is correct.

 

[Steve777]

A couple of other considerations:

Sounds like you are looking to replace your old batts with the same capacity. If you are satisfies with how the old batts worked, that's great, but if you ever wished for more capacity (or plan on adding any new loads), now is the time to increase the AH.

And you should consider that LFP batteries have some limitations vs L-A (and benefits too), mostly around temperature. If the batts will be used in environment which sees cold temps (<32F), that needs to be taken into account. For example a remote cabin that you visit occasionally that sees cold tempsin winter, you may show up and find your batteries are too cold to power anything (at least until they are warmed). May not be a concern for you in AZ, but something to be aware of...

 

[Dads2vette]

A couple of other considerations:
And you should consider that LFP batteries have some limitations vs L-A (and benefits too), mostly around temperature. If the batts will be used in environment which sees cold temps (<32F), that needs to be taken into account. For example a remote cabin that you visit occasionally that sees cold tempsin winter, you may show up and find your batteries are too cold to power anything (at least until they are warmed). May not be a concern for you in AZ, but something to be aware of...

I live in Northern AZ. Yearly temp swings are lows in the low teens and highs in the winter around 110 in the summer. Biggest concern I've had in the past is freezing pipes or water pump. I have a temperature switch that kicks on at 40 degrees that lights a 100 watt light bulb. That keeps everything warm enough so that the don't freeze. Friends have been using that method in there pump houses in Western NY for decades. Gets much colder for much longer times there.

Thanks

 

[Steve777]

I live in Northern AZ. Yearly temp swings are lows in the low teens and highs in the winter around 110 in the summer. Biggest concern I've had in the past is freezing pipes or water pump. I have a temperature switch that kicks on at 40 degrees that lights a 100 watt light bulb. That keeps everything warm enough so that the don't freeze. Friends have been using that method in there pump houses in Western NY for decades. Gets much colder for much longer times there.

Thanks

Used to live in upstate NY and remember the light bulbs in the pump house.

Just something to think about. If it is getting cold enough to freeze/burst your water pipes, you may find that LFP batts won't be able to supply power for that 100W bulb, without some planning (like a batt heater or the like).