Time to replace defective and potentially dangerous absorption fridge

[gondolaguy]

(07-10-2013 00:58)davidmbrady Wrote:  Corey,

I'll take a swing at it.

There's a chap on some forum I read somewhere who reports real world data for the RF197 of 12 amps at 120VAC for initial compressor start which ramps down to 1.3 then 1.0 after a minute or so. Then there's a 3.5 amp draw at 120VAC for the defrost cycle which runs for 15 minutes, but he didn't report how often it runs only that these high efficiency fridges need to stay on top of the defrost, so let's assume it runs every 6 hours.

That means the steady state AH (at 12V) draw is 23hrs * 1A * 10 = 230AH at 12V, but the compressor doesn't run continuously. Let's assume the compressor runs 50% of the time, so divide the steady state AH by 2 to get 230/2 = 115AH.

Next we have the defrost cycle. The defrost cycle runs for 15 minutes 4 times a day, so we have 1hr * 3.5A * 10 = 35AH.

Next we have the compressor startup current of 12A. Let's assume it quickly decays to 1A in around 2.5s and it does this once every 2 minutes. This means for every other minute there's a 2.5s period where the current draw averages 6A. That's 0.5 hours per day of compressor startup decay which gives us 0.5hrs * 6 * 10 = 30AH

Our grand total is steady state + defrost + compressor startup = 115 + 35 + 30 = 180AH consumed in a 24hr period.

There's a bunch of assumptions here including the duty cycle of the compressor which depends how often the doors are open, and the ambient temperature.

Our Lifelines have a capacity of 210AH * 6 = 1260AH, but we can only drain them down to 50% Depth of Discharge (DOD) so effective AH is 630.

To restore your batteries to full capacity you need to put back 180AH.

According to the Lifeline Technical Manual for AGM batteries. The recharge time to restore 180AH is (DOD*Battery Bank Capacity / Rated output of Charger) + 2 hours. In this case we have 180/1260 = 14.3% DOD, so our charge time is (0.143 * 1260 / 280) + 2 = 2 hours and 40 minutes.

The person who reported the real world numbers said he gets thru the night with a drain of around 75AH.

So probably fair to say, with new batteries, you'd easily get 4 boondock days before needing a recharge? That works fine for me.

Wonder how the dual compressor technology helps/hurts the equation?