| Re: How to disconnect my Norcold refrigerator from A/C 120v [message #317254 is a reply to message #317246] |
Tue, 09 May 2017 11:22   |
A Hamilto
Messages: 4508
Registered: April 2011
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A Hamilto wrote on Tue, 09 May 2017 08:25RF_Burns wrote on Tue, 09 May 2017 05:59...You may be better to consider running the fridge off an inverter into its 120V input. The swing motor and transformer will run cooler and quieter. It also possible an aftermarket inverter will be less drain on the battery than the built-in chopper inverter.
http://www.bdub.net/Refrigeration_in_the_GMC.pdf Its a slow day, so I was thinking about how to really make this fridge energy efficient. IIRC, someone powered one with an inverter and wired the thermostat to turn the inverter on and off. The inverter eventually failed, probably because it didn't like being turned on and off multiple times a day.
But in that line of thought, there is nothing wrong with running the fridge off 12VDC all the time. Because it will get power from the engine alternator through the isolator and through the house battery when underway, from the converter through the house battery when on shore power or the Onan (neither of those will not deplete the house battery) and from the battery when neither of those is available.
Now the most efficient way to run the fridge off 12VDC is to replace all the electrical stuff with a 100VA 12VDC-to-24VAC 60Hz inverter. I have found such a thing on the 'net (IIRC was around $300, but they do exist). Wire it: 12VDC to the inverter, inverter output to compressor. If you put the thermostat at the 12VDC input, you run the risk of failing the inverter because they are probably not made to be switched on and off dozens of times a day. If you put the thermostat between the inverter and the compressor, you have the 0.1A idle current to the inverter even when the fridge is not running. But it will still be quite a bit more efficient than OEM.
If you want to use a 12VDC-to-120VAC inverter, you will get more efficiency if you replace the existing multiple winding transformer with a 100VA 5:1 transformer. Again, just remove all the existing electrical stuff and install the new stuff. Same consideration for where the thermostat goes. Closer to the compressor means more idle energy gets lost, if installed at the 120VAC input it will switch the inverter on and off dozens of times a day and the inverter might not last. Thermostat between the inverter and the transformer will jolt the compressor with a high voltage from the transformer when the thermostat switches on. But between the transformer and the compressor means the transformer is wasting a bit just because that's what they do. Not a lot, but it might be a consideration.
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