Generators

[david]

[quote source="/post/7013/thread" timestamp="1424393241" author="@sandroad"]Anyway, I'm intrigued by the very low usage of the fridge! At our cabin we have an older Dometic 6 cu ft that is propane or AC. When on AC it draws 185 watts during the on cycle. I guess the DC powered fridges have a motor driven compressor that's super-efficient if it draws less than an amp. That gives me hope for our future solar power. Of course the daily power usage of a fridge depends on how often it's opened too! [/quote][p]Merlin:[/p][p]
[/p][p]Almost no RV fridges use a compressor. They use an ammonia/water (typical in the old days but I am not sure today, might be something else) absorption refrigeration cycle. This cycle uses heat (in any form- AC power or propane but not DC) to boil the ammonia solution which separates the ammonia from the water. The ammonia is then cooled and condensed by convection to the outside. I am not sure if there is a fan to help cool it but I don't think so for RV units. The liquid ammonia then evaporates in a coil inside the refrigerator to cool it.  The evaporated ammonia is reabsorbed into the water which completes the cycle.[/p][p]
[/p][p]Other than possibly a fan, there are no moving parts.[/p][p]
[/p][p]So the fridge uses propane or AC power to boil the solution. The only use for DC is to power the fan (if there is one) and operate the controls- the biggest power draw being the DC solenoid valve that controls the propane flow. That is why an RV fridge running on propane uses very little DC power.[/p][p]
[/p][p]In absolute efficiency terms they are lousy. But propane is a cheap source of heat so it is used for RV fridges.[/p][p]
[/p][p]A 12 V compressor refrigeration system such as used on boats might take only 4 amps at 12 volts to run the compressor. That means it uses 48 watts DC vs the 185 watts AC draw for the absorption cycle. Boats and sailboats in particular can't use the absorption cycle because it needs to be fairly level to work properly. Sailboats are not always level.[/p][p]
[/p][p]David
[/p]

[daplumbr]

Thanks! Just what I needed to know. I assume that means my 3-way fridge is using propane for the heat source even when on the DC mode and the DC is just running a fan? 

I do have a separate, 40 qt. portable cooler made by Waeco (now owned by Dometic) that runs on either AC or DC. Either power source runs a small, very efficient oscillating compressor that runs the refrigeration cycle. We've used that car-camping for a while it's wonderful to not have to deal with ice. It runs fine off the 12 VDC outlet in the the car. We won't be using that in the Camplite (too small a capacity), but we may use it as an aux freezer in the car? 

[charliem]

[quote source="/post/7016/thread" timestamp="1424397465" author="@sandroad"]Thanks! Just what I needed to know. I assume that means my 3-way fridge is using propane for the heat source even when on the DC mode and the DC is just running a fan? 

I do have a separate, 40 qt. portable cooler made by Waeco (now owned by Dometic) that runs on either AC or DC. Either power source runs a small, very efficient oscillating compressor that runs the refrigeration cycle. We've used that car-camping for a while it's wonderful to not have to deal with ice. It runs fine off the 12 VDC outlet in the the car. We won't be using that in the Camplite (too small a capacity), but we may use it as an aux freezer in the car? 

[/quote][font size="3"]No, the smaller three way fridges use a 12V heating element when running on DC. The 3.7 cu ft Dometics suck 8-9 Amps on 12V. That's why you never run on 12V unless the TV engine is charging the TT battery. It will suck the battery dry in no time. There are 12V DC fridges with small compressors [/font][font size="3"]like your Waeco[/font][font size="3"] that take about 4A as David mentioned. They work well, but are small and a bit noisy in a quiet cabin. However, they too will eat a battery after a while.
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