Can anyone tell me How long the 6 cubic ft Dometic absorption refrigerator could run on one 20 lb tank of Propane and/ or how long the the Norcold would run on 2 x 100 AmpHour Lithium batteries fully charged if it was storming or my spot was heavily shaded and the solar panels were not bringing in significant energy? Trying to figure out if if I would have issues keeping my food cold with a compressor refrigerator if I couldn't be in direct sun for an extended period of time and how long the batteries would last.
It's probably something that could be calculated given that the Norcold pulls 3.4 amps but I don't fully understand that yet. I will attempt it here anyway and see if anyone can verify my calculations or point me in the right direction if it's wrong.
If I don't let the batteries go below 30% that would be 70 Ah each or 140 Ah total, so 140 Ah/3.4 A = 41.2 hrs and longer if I had solar power coming in. Can anyone tell me if I'm calculating that correctly?
@Mark Christopherson: I think you are right about that, my compressor does not run continuously, And, depending on how often I go into the refrigerator, (and how hot the desert is where i am camping) the duty cycle is really low. I have never measured it. but its much less than 25%. my expedition trailer (with 45qt compressor fridge) doesn't even have solar panels. only one type 34 AGM battery, and I can go well into the second week, before I need to see about charging the battery.
Those power Watt Hours, and current Amp Hours need to be divided by the duty cycle. to get a valid comparison. Otherwise, those numbers are for with the door propped open continuously. Which is a really silly state, your food wont stay fresh if you leave the door open.
Using your numbers...
Refrig.
3.4 amp/hrs x 120V = 408 Watt/hrs.
408 x 24 = 9792 watts/day.
Solar (low 1 panel case)
1- 190watt @ 50%=95 Watt/hrs.
95 x 8hrs = 760 watts/day.
9792-760 = 9032 watts required/day from batteries.
2- 100amp LiFeP04 Batts=140 amp/hrs.
140 x 120 = 16,800 watts total.
16,800 ÷9032= approx 1.8 days between recharges if nothing else is used.
Propane will last more than 11-12 days depending on conditions.