Refrig motors & Inverters

[rotorgoat]

I have a small bar type fridge that shows 120VAC and .8A operating load. I hooked up a watt meter inline with household current and start up is about 270 watts then down to 75 watts after about 15 seconds and stays at that load while running. When I plugged it into a pure sine wave inverter (300 watts with 600 surge) it trips the inverter about 2 times then resets and starts the fridge motor but the load on the watt meter stays in the 255 range for about 2 minutes then trips the inverter again. Any ideas as to what's happening here? Do I need a larger inverter? I previously tried it with a modified sine wave inverter of about the same capacity but it would not start up at all -- thus I went to a pure sine inverter.

 

[Mr RB]

It sounds like you need a larger inverter and/or better wiring between the battery and inverter.

 

[Tedfred]

I do refrigeration work. RV’s have air conditioners that runs off of inverters and have similar problem. I’ll assume that the little bar type frig. has a standard refrigerator system but only cut down a bit. Refrigerator compressor motor can draw up to 10 times the running current at start up. Amp meter and watt meters often don’t read the total peak watts/amps. To add to the problem, if you unplug the frig and then plug it right back in, The compressor will not start under the heavy head pressure. It takes about 5 minuets for the system to equalize. After that the compressor will start. But back to the stalled compressor. The stalled compressor draw very heavy current. It is called lock rotor current(LCR). If this heavy current is left unattended it will destroy the compressor. But a limit switch in the electrical system takes over and click off for a minuet or two. It then retries again, and again until the system restarts.
Also that same frig should be quite happy running on square wave 60 cycle inverters. I only had 1 frig that would not run on the square wave. Be would run most of the time if put into the barm. I never was able to figure that one out.
P.S. some compressors have the (LRC) stamp on the side of the compressor.
Also there might be (but not likely) an easy start up kit that might just make the different

 

[rotorgoat]

Thanks, I'll start with trying a new battery although I had a 6 amp charger hooked to the battery during my testing. If that doesn't show any promise I'll move to a larger inverter. The advice on modified sine wave was great as those are considerabley cheaper. My idea of keeping the inverter as small as possible was due to the efficiency factor of the inverter as most reccommend operating them near their rated limit. I figured that a 300 w/ 600w surge would handle the start up. I guess that's kind of a moot point if you can't get it running to begin with.

 

[Tedfred]

This may or may not help, but there are refrigerators that have compressors that run on DC current, so they have almost no start up current. There are several types, the voce-coil type, vibrator type compressor, Brushless DC Hermetic Compressors. You might fine one used for in around $100.00. They are not easy to find, so you will have to look around a bit. But it will be cheaper then buying an inverter. Also your frig will run longer on a single battery charge

 

[magickaldan]

Your charger can only supply 12*6=72 watts, assuming your using a 12v inverter. So try hooking it up to a battery with the correct size wiring and see what happens. Also try at least a 20A/H battery. Fully charged car battery should more than easily run it.

 

[rotorgoat]

Your charger can only supply 12*6=72 watts, assuming your using a 12v inverter. So try hooking it up to a battery with the correct size wiring and see what happens. Also try at least a 20A/H battery. Fully charged car battery should more than easily run it.

I guess I should have clarified my test setup better. I had the charger on the car battery which was hooked up to the inverter. I'm using the wiring that came with the inverter (18 inches of #4 wire) which should be more than sufficient for this load.