View Full Version : running a fridge off an inverter setup?
03-27-2013, 07:33 AM
I am in the middle of setting up my new 6x12 competition trailer. I have picked up a 3000watt inverter and will get 2 large deep cycle batteries. This will be used to run my pellet pooper and some LED lights, etc.
Ideally, I would like to run a standard fridge (maybe fridge only, no freezer) in the trailer as well, but don't want to run a generator if possible. Comp power provided will be used to smart charge the batteries.
I have read the AC motors on the fridges do not like being run off inverters. I also understand the initial start up burst of the motor could be up to 5x the average power consumption of the fridge and you need an inverter capable of handling the surge.
Who here is succesfully running a fridge off an inverter? And what kind of run time are you seeing (what capacity batteries)? Even if the fridge takes a beating, they are cheap used appliances on kijiji, craigs list, etc. Versus a three way fridge or continously buying ice.
03-27-2013, 07:54 AM
The old style inverters didn't put out a very good sine wave. It was much closer to a square wave and motors don't like the DC component of square waves. Today's inverters are far superior with distortion being very often less than 5%.
What you are hearing is correct about intial surge of a refregerator starting up. The initial impedance of a refridgerator is highly capacitive which presents a very low impedance at startup. This produces a very high peak inrush current. Once that inrush is overcome, the impedance will go up and the current will drop accordingly.
A 3000 watt inverter of at least decent quality should be sufficient. That works out to around 26 amps which should handle the inrush of the fridge.
My concern would be running the fridge/inverter off of two deep cycle (group 27?) batteries. They won't last very long at that type of load. I would look at a crossover switch to move the fridge over to shore power once you've arrived at the site or home and only use the batteries while traveling. You could even use some 12vdc from your tow vehicle to run the inverter if you set it up correctly with an isolator.
Hope some of this helps,
03-27-2013, 09:43 AM
Thank you for the quick and detailed reply.
Another quick question on charging the batteries while towing.
I am planning to hook the 'charge lead' from the 7 pin trailer wire to the batteries (thank you for your suggestion on using the isolator, should I also place an inline fuse by the postive of the batteries in the trailer), but what about grounding the circuit? The negative side needs to be grounding to complete the circuit for charging while driving, but 2 questions: 1) what about the inverter running while the batteries are grounded (will this effect the inverter at all) and 2) what about when I arrive onsite and remove the tow vehicle charge and want to hook up the smart charger, the batteries will already be grounded, does this matter?
03-27-2013, 11:11 AM
I have done it. Honestly, by the time you do all the investment, et al. You are better off buying an LP fridge. Ive got a nice inverter and 2 massive marine batteries for sale!
03-27-2013, 11:56 AM
Yes, use the power lead on the 7-pin trailer connector. You tow vehicle should already have a fuse on the power lead, if it was wired from the factory. However, it never hurts to add additional protection with seperate fuses/breakers at the batteries.
For the DC grounding. I didn't ground my lights, appliances, etc. to the trailer frame. In my opinion (and only my opinion), the trailer frame is not a good reliable ground return. I ran dual lead that I purchased at Home Depot that already has a protective sleave built onto it. That way all power & returns are dedicated and come back to a terminal strip that connects to the battery posts. The terminal strip also connects to the 7-pin trailer/tow connector. That way I am assured of proper current paths. I can take a picture of it if you like.
For AC, I do ground (the green wire) the trailer frame. That puts my trailer frame at earth potential as soon as I plug in. But the breaker panel and outlets are wired exactly the same way as a normal house outlet.
03-27-2013, 12:41 PM
Thank you a pic would be great for clarification.
Will work for bbq
03-27-2013, 02:11 PM
X2 on the LP fridge.
Be aware that the current draw on the AC side may only be 25 amps (peak) but on the DC side it will draw about 250 amps (peak). So size the primary wires accordingly and protect the wiring at the power source (fuse at battery, size fuse according to wire size).
Yea, I was going to suggest LP before Scottie and Paul beat me to it. RV's with inverters often have 2 deep cycle batteries. RV's with a fridge hooked to the inverter have 6 to 8 batteries. That should tell you everything you need to know.
EZ Freeze, Crystal Cold, etc. There are a bunch of propane refrigerators made for (and sometimes by) the Amish and people with remotely located homes or hunting cabins. Propane refrigerators have to be kept strictly level. RV fridges (Dometic, Norcold) could probably be rigged for a comp trailer, and would probably handle bouncing around during travel a little better.
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