Blackout back up planning.

[bonnie]

I am in the middle of trying to design a lithium battery backup system to run my 4.4 cf dorm fridge and my truck frig/freezer (used as a freezer) during the coming summer blackouts/brownouts.

If I figured correctly dorm fridge will take 3.8 amps if it runs for the entire hour. The truck fridge freezer says 4.5 max use per hour. So, worst case would be 8.3 amps. 8 hrs of darkness would mean 66.4 amps before charging.

I’m looking at getting a lithium battery/charger. I have a 1500w inverter and a renology 150 w monocrystaline (sp) Solar panel.

The battery and the charger will handle pass through charging.

Here’s the various labels and info:





The truck frig info is in the second col.

Am I correct in thinking a 100ah battery is the smallest I can go? Thanks in advance.

Bonnie S.


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[S. Heisley]

Am I correct in thinking a 100ah battery is the smallest I can go?

If you plan for that 66 Amp blackout, you'll need to have an extra 30% left over to keep from possibly damaging a standard battery. That would take it pretty close to 100 Amps, especially if you want lights, etc. Of course, if you use a LIFEPO4 lithium-type battery, you can empty the charge without hurting it so might be able to get away with less. Also, if you have solar panels and an inverter, you might get away with a smaller battery. Others will chime in, I'm certain. I look forward to what others write and learning what you finally decide on.

Best Wishes!

[bonnie]

Thank you!


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[featherliteCT1]

Bonnie,

You are asking the right questions. But the learning curve is a bit steep and the answers come slowly because new questions keep popping up as we seek each answer. Here is a link to a series of web pages that I have found most useful in obtaining answers to basic solar system questions. Hope you like math!
https://www.explorist.life/diy-campervan-solar

[Pmullen503]

The fridge says 1.4 amp at 115v. That converts to 13.4 amp at 12 volts assuming 100% conversion rate at the inverter. You hopefully aren't running the dorm fridge continuously. Let's just guess 25% duty plus inverter inefficiency gets you to around 4 Ah so around 100 Ah for just the fridge per day. Same guesses for the truck cooler so about 1.2 Ah or another 30 Ah per day.

25% duty cycle is probably the high end, especially if you are trying to limit how often you are going in and out of the fridge and cooler. So 100Ah usable power is in the ball park.