12 volt Refrigerator

3 tons wrote:
Starting with only two 100a/h batteries (assuming wet cells), only gives you 100a/h usable for all your needs…Solar might augment, but with only two 64w panels, even the best harvest might only result in about 6.5 amps, then add to that the refer door seemed to be opening occasionally (ugg!!), and I think you were hitting the ‘sweet spot’ for failure… In this case I would have definitely gone with LPG, and I believe your trusty vendors were chock full of optimistic advice…This is why (per my previous…) having a substantial battery and solar set-up is critical, particularly the battery - this is why I said 400a/h Lithium, due to Li’s deeper depth of discharge, and the vagaries of solar to carry you over to the ‘next productive’ harvest cycle…And with a decent amount of solar, a few amps of harvest is often possible even with full cloud cover…While on the Oregon coast (with 660w solar) I was recently able to get about 6-7amps with full cloud cover and even a small amount of drizzle, admittedly not a whole lot but still enough over a time to ‘increase’ my 400a/h Lithium by a welcome 8% SOC…

I have a pal that has a 9 cu/ft (Danfoss comp) double door refer that runs fine with only two 100a/hr of Lithium and 400w MPPT solar (recently upgraded to 800w - fine for Nevada), and know of another fella that has a 7 cu/ft compressor refer (don’t recall the make), 460a/hr lithium and 400w of solar with no issues…So to achieve true LPG liberty, expect the devil is in the details ($$)…

3 tons

200amp-hr @ 12v will result in around 1200w-hr of usable power (2400w-hr total) assuming you start from 100% charge and they are in good shape.

At 50w when the compressor is in operation, that's about 24hr of run time at 100% duty cycle. Assuming a more typical 50% duty cycle, that's around 48hr or about 600w-hr per day.

2 - 64w panels (128w total) will generate about 500w-hr per day.

Assuming no other loads, you are probably OK for a long weekend.
- End of 1st 24hr, you've used 600w-hr and put 500w-hr back in leaving a net of 1100w-hr.
- End of 2nd 24hr, you've used 1200w-hr and put 1000w-hr back in leaving 1000w-hr
- End of 3rd 24hr, you've used 1800w-hr and put 1500w-hr back in leaving 900w-hr

But in reality, the systems aren't 100% efficient and you may use a bit more or generate a bit less, so by the 3rd 24hr period, it's going to be condition dependent.
- If it's a cool sunny weekend, you might be near full on the batteries.
- If it's a hot muggy overcast weekend, you might be running a bit low for the 2nd day.

Always good to have a fall back charging method rather than way overbuild the system so it can handle anything.

PS: This assumes you have no other electrical loads other than the fridge...and why it's good to do a general energy audit rather than look at a single component.