"it monitors the temp inside the freezer and cuts power when it's at a certain temperature". Lets call the "No Power" state resting, and the "Running Power" active. If your box is full of ice bags in tubs, the box will be in "No Power" until all the Ice Melts and the temp rises to your Johnson setting. If your box is full of hot rocks in a tubs, the "Running Power" will stay on till the rocks have cooled to the Johnson setting. How much Power does your freezer draw when it is in the "Running Power" state (I mean measured). Your usage should equal the measured requirement (volts and amps) x the time you are in the Running State. This should be straight forward.
The variable should be caused by what is in the box and what status it is in. Also what Johnson Setting is chosen (or what is built in as a temp setting). If you know the voltage the device uses when in the Runnning State, then I would sit down and time the running state length and frequency of the runs for a couple of hours to see what the load really is.
Just my 2 cents.
thanks rch
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So based on the 300wh per day I had read, /very/ roughly 300wh/12v=25ah per day used by the fridge. Not including inefficiencies or inverter draw, etc.. Also I wasn't sure how much of an effect the startup draw would have since it's high amperage but brief - but I didn't expect to be using more than 50ah per day total.
Are you asking out of curiosity or because you thought my logic was flawed?Leave a comment:
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What I did was a typical chest freezer to fridge conversion using a johson control's thermostat. How that works is it monitors the temp inside the freezer and cuts power when it's at a certain temperature. When the temp rises again it reconnects power. So there is really no idle time or resting amps.
Used a killawatt for the other measurements though...
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I think you need to check your amp requirements for when the freezer is at rest (no compressor running) and when you compressor kicks in for a cooling cycle. I suspect that your 80 watts may be "at rest" between cooling cycles. Your issue could be as simple as accounting for the additional load when the compressor kicks in to maintain the freezer thermostat set temperature.
I am new to solar, but, not freezers. Put a Kill A Watt on the freezer plug, then read your resting amps. Turn down the thermostat till the compressor kicks in and see what your amps are. This may show where your amps are going.
Just my 2 cents. rchLeave a comment:
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12v solar and chest freezer to fridge conversion - what went wrong?
I was off grid for about 6 weeks over the summer and got tired of buying ice, so I picked up a 7 cubic foot chest freezer and ordered a johnson controls thermostat. I heard similar setups draw about 300 wh per day, and I measured mine between that and 500 wh per day. The startup draw of the fridge was 800w and it ran at 80w. I started with one 100 ah battery, which i figured would be OK as long as there was plenty of sun and I could use a generator on the cloudy days. Also used a 250w panel. The battery was ending up very dead by morning, so I added a second battery and then a third (taken from another small solar system that I was using for something else). I was still seeing very surprising results like being below 50% by morning, meaning I lost over 150 ah over night. Also surprising was that the batteries could be floating by noon, which should be impossible too. Some troubleshooting showed my sunforce 1000w inverter was drawing 1.5 amps at idle, so that had to go. I replaced it with a xantrex 1000w, which could only start my fridge when the batteries were fully charged. I also upgraded to a MPPT charge controller because by that point I was committed and why not throw a few hundred more bucks at it. I think the weak point in the system was the batteries - this was meant to be a quick and dirty system so I used Walmart 24DC marine, deep cycle batteries. Since everything else /should have/ worked, if the batteries were the problem can someone explain why and why there seemed to be a disparity between the amp hours used/remaining and the voltage of the battery bank? Thanks!
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