I have a Norcold N811 reefer, 2 way unit (120 volt or propane.) I know it uses the absorption type of refrigeration, but are there any motors in it at all?
I want to use an inverter for it for when we are on the road. The nameplate on the unit states it's 2.5 amps, 300 watts @120 volts. The manufacturer's web site shows a slightly higher rating of 3.0 amps @120 volts. Called Norcold, absolutely no help there.
Is it safe to assume that at a minimum, a 400-500 watt inverter would be fine, if there are no inductive (motor) loads?
Also, it appears the unit's controls are 12 volt. Do I need a pure sine inverter or will a modified sine wave unit be sufficient? I assuming the 120 volts is just for the heater.
Yes, a 400-500 watt inverter will work. But you do realize there will be no savings in what you suggest. You alternator will be required to produce in excess of 25 amps more, which imposes more load on your engine, increasing fuel use. Thus off setting any savings in propane costs. No free energy. If you are uncomfortable with using propane while driving, then go for the inverter.
I can only say that I had an older unit, that was gas/electric and ran it on the inverter a couple of times when I ran out of gas. I got about two hours on the battery with the inverter. It wasn't a pure sine wave. It's only heating a heating element, which doesn't require a full sine. The control circuit still drew on the battery. The alternator put out more then enough to keep the battery up when I was going down the road. JM2Cents Bill
It's too bad it doesn't have a 12 volt option, that would save a step. There are usually no motors in it, unless there is an air fan of some sort inside. The 120 VAC option uses an electric heater to replace the propane flame. Pure resistive heaters are fine on modified sine wave, if less efficient. These days pure sine wave inverters are coming down in price fast, and can be used for more things without issue, so I would keep that in mind. I'd personally think about other loads like microwave, coffee maker, etc. But I think your analysis of this is correct. I'd look for a 500 watt inverter as the minimum choice.
Your are right, not about saving energy, but just getting off the tank while we are underway. I could probably swing something like this, use up some of those HD gift cards I have laying around:
Polishnurse wrote: I can only say that I had an older unit, that was gas/electric and ran it on the inverter a couple of times when I ran out of gas. I got about two hours on the battery with the inverter. It wasn't a pure sine wave. It's only heating a heating element, which doesn't require a full sine. The control circuit still drew on the battery. The alternator put out more then enough to keep the battery up when I was going down the road. JM2Cents Bill
I only have a single battery in the RV, maybe should add a second to increase run time. I'm thinking if the reefer and food in it is already down to temp, how much is the thing going to run anyway.
If I can go with modified sine wave, that would save quite a bit of $$$ towards a second battery.
johnvb wrote: a single battery in the RV, maybe should add a second to increase run time.
If I can go with modified sine wave, that would save quite a bit of $$$ towards a second battery.
I'd do that. Someday you're going to stop for a bite and forget your refer is on inverter.
I'd get the PSW. Inverters are very handy devices, and sooner or later you'll find something else to run which may not like MSW. And if you go too cheap on the msw, that's just more problems like overheating.
My 300w GoPower sine wave inverter has run my Dometic fridge for an extended period when needed.
400w to 600w MSW inverter should be fine. It will pull close to 30 amps from the battery when cycled on. MH will provide the amps pretty easy.... a trailer you will get maybe 10 amps from the tow vehicle. Two batteries should get you at least 4 to 6 hours run time. As long as you plug in at the destination, no worries.
Just a heating element and no motors in these absorbtion fridges.
OK, so now that I know I'm on the right track...What would be the proper way to hook this thing into the existing power supply to the reefer?
Thinking I could add some sort of DPDT switching relay, with a 120 volt coil, that when energized from the shore power, opens the 120 volt relay contacts power source from the inverter. And closes the contacts of 120 volt power source from the shore power to the reefer. (used to be an HVAC tech so know a little about controls ). Obviously want to do the switching on the high voltage side, for lower amps. Sound Kosher?
Either that or just a manual switch, which I know I would forget sooner or later to hit.
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