| Electronics > Projects, Designs, and Technical Stuff |
| PV in a RV running a refrigerator with some SLA batteries - sanity check |
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| DTJ:
--- Quote from: jmelson on January 10, 2019, 08:11:37 pm ---There are all sorts of scrambled units in the OP. 6 A x 12 V * .17 duty factor is 12.24 W average, * 24 = 294 Watt-Hr per day. Assuming some of the load is powered direct (without storage) then maybe that needs 100 - 150 W-Hr of storage. 150 W-Hr storage at 12 V is 12.5 A-Hr. Now, of course, most batteries are rated to near zero, so you don't want to drain your battery that far down. Depending on how good the MPPT tracking works on your charge controller will determine whether you can charge the batteries fully every sunny day. Don't forget to include a fudge factor for cloudy days. And, a 6 A x 12 V refrigerator is going to be a Peltier cooler, not a compressor type. Look for the most efficient one you can get, it will save you a lot of problems making this all work. Jon --- End quote --- Hi Jon - it's definitely a compressor unit. From my limited experience the Peltier units are little more than coolers and don't work well as a refrigerator. To clarify, from the Waeco spec sheet the power needs are "6A @ 17% duty". This gives 6A x 24 hr x 0.17 = 24.8Ahr per day. |
| james_s:
--- Quote from: jmelson on January 10, 2019, 11:02:27 pm ---Yes, indeed, a compressor would have to be really AWFUL to be worse than Peltier. I'd never heard of compressor refrigerators with only a 72 W power draw! Great stuff is being made. Jon --- End quote --- My fullsized domestic fridge only draws 140W (measured) while it's running, I'd expect most small dorm and RV fridges to draw considerably less than that, 72W doesn't sound too unreasonable. Fridge efficiency went up quite a bit at some point due largely to improved insulation. |
| georges80:
I run a 50qt ARB danfoss based fridge. Previously (for 30+years I'd run a Engel). Fed from a dual battery system in my 4wd which charges both batteries while driving and splits to a main and aux when parked. The aux powers the fridge. And yeah, a modern ARB draws maybe around 4A while running, so around 50 - 60W. I first bought a solar panel in the early 80's charge the aux for fridge use. So, quite few years experience with this kind of usage. I run a nominal 80W panel that I can position to face the sun. I run a Victron mmpt (bluetooth paired) controller (check them out - fairly inexpensive and good quality/performance). I've camped in 37C (100F) and higher temps and the panel + 80ahr lead acid can easily keep up with 24 hour demand. One of these days I'll upgrade to a 120-140W panel (they are so cheap in oz). These modern fridges are very efficient even in hot climate (just keep the fridge in the shade and provide a decent airflow path for the compressor radiator). This kind of setup is very popular in oz and panels are quite inexpensive. Put some money into the controller and into the battery. Consider that if your panel is in the 100W (or more range) then you will collect around 6A or more per hour during sunshine part of the day (call it 8 hours). So even on an average day you are in the 50a.hr range being collected. Seems nuts to have a 20a.hr or even 40a.hr battery with near 200W for the OP's setup. Very unbalanced system. In cooler weather a danfoss equipment compressor will be running maybe 1/6 or even less of the time, so less solar collection due to some cloud cover will be compensated by lower a.hr draw each 24 hours. Anyhow, I recommend you do some more calcs to figure out real a.hr usage in the weather you plan to camp and match the battery capacity to make good use of the harvested a.hr from the solar panel. Finally, keep the fridge full (more efficient), don't open it unnecessarily, refill drinks etc early in the morning (or before driving) so that it can be cooled while the engine/alternator/solar is running - versus refilling in the evening and camped. cheers, george. |
| Teledog:
Off topic perhaps..? Why not a propane fridge? KISS? |
| NiHaoMike:
--- Quote from: Teledog on January 12, 2019, 05:44:40 am ---Off topic perhaps..? Why not a propane fridge? KISS? --- End quote --- The absorption cycle is something like 1/5 the efficiency of a good compressor refrigeration cycle. Now I wonder if it might be possible to take advantage of thermal storage. Maybe keep bottles of very pure (distilled) water inside and adjust the temperature so it just barely freezes during the day, relying on the fact that the water in the food is going to be much less pure and would freeze at a lower temperature. |
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