Smallest Inverter needed?

[Singing Land Cruiser]

Hello all, what is the smallest inverter I can use for an 11.2 amp refer. We hardly ever boondock and just want to keep the food cold. Thank you all. M&C

[Just Dallas]

Removed

[NewbeeMC9]

If you check into turning off the Defrost Heaters while you are on Inverter you may be able to get by with less inverter or at least the batteries may last longer.

[Singing Land Cruiser]

It's 11.2 start up then around 4.5 to 5.5 running. M&C

[Dreamscape]

11.2a X 120V = 1344W plus another 10~20% for overhead would be a good 1750 - 2000 watts

2000 watts has been recommended, I agree. You need one that size when she starts up on load.

[Singing Land Cruiser]

So a 750 / 1500 peek should work for the frig only? M&C

[JackConrad]

We tried a 750 watt for our 1st house type refrigerator and it would not start the refrigerator.  We then tried a 1000 watt with same results. Both of these were cheap inverters only (no built-in charger). We then bit the bullet and bought a Heart-Interface 2500 watt with a built-in charger.  It runs everything we need to run off the inverter.  YMMV  Jack

[TomC]

Jack's suggestion is a good one.  I also have a Trace 2500 inverter/charger.  While they are not cheap, it does keep the batteries up and running-so much so, I disconnected the alternator from my generator and just use the inverters charging.  Good Luck, TomC

[Singing Land Cruiser]

Hi Jack, thanks for the tip. "?" Did you have the 750 hooked to anything else or pluged str to the refer? M&C 

[JackConrad]

Hi Jack, thanks for the tip. "?" Did you have the 750 hooked to anything else or pluged str to the refer? M&C 

Both of the smaller inverters were connected directly to the house batteries and the refrigerator was plugged directly into the inverter.  AC waveform from these small (cheap) inverters may have been part of the problem, I never looked at the waveform on an ocilliscope.  Jack

[robertglines1]

I tried the Modified sign wave 3000 and it did not do the job...I understand the True sign wave will do the job...like the one Jack is talking about...just my past experience....now I just keep the door closed and it doesn"t melt the icecream for 8 hours...run generator for about 1/2 hr and it has already cycled off as cold enough...go to bed at 10pm get up at 9am icecream still good...spent 3 days dry camping and just used gen when needed,going down road just start up once and awhile...just my observation...the true sign wave units are pricey.and require a battery bank..

[Sean]

Sorry for jumping in late here...

You really want a true sine wave model to run a refrigerator.  MSW units will require more power (so must also be a higher-rated unit), and both the compressor motor and the inverter will heat up more.  Ultimately you will destroy the compressor, and in the meantime, the compressor will have to run much longer duty cycles, not only to overcome the energy shortfall, but also to remove the excess heat caused by the MSW wave form.

Also, motor starting capability is not something that you can assume just from the surge rating of the inverter.  You really want to get the motor starting spec from the manufacturer, in HP.  That said, if you have truly measured the starting current of the fridge, a SW inverter with a surge rating of about 115% of this current will most likely work.  11.2 amps, BTW, sounds low to me; if that's the nameplate rating I would not trust it -- you need to measure with a peaking wattmeter or ammeter.

I would guess that when all measurements are accounted for, the smallest unit that will work is a true sine 1,000-watt continuous, 2,000-watt peak unit.  However, that's just a guess, and depending on how hard your compressor starts, even that might not be enough.  Adding a hard-start cap to the compressor might help.

-Sean
http://OurOdyssey.BlogSpot.com