Running dorm fridge with inverter

[MCDenny]

I have a Lil Snoozy with the standard Magic Chef 3.6 cu ft 110vac dorm style fridge. The manual doesn't say but IIRC the "running" power draw is around 70 watts, maybe less. Who knows what the starting current really is. I figured 6X when I sized the inverter.

I have a Samlex 600 watt (900 surge) true sine wave inverter, 12v 220 ah battery bank and short 4 gage cables connecting the inverter to the battery.

Everything was new last summer. Used the fridge for a three night trip in Sept and it started fine with the inverter. Tried it in December and it won't start, inverter displays current overload error every time. Thought maybe it would work better after it had been run on shore power and here in warm Florida. No dice. Fridge works fine on shore power.

Inverter is working fine recharging running computer chargers, even a soldering gun.

Any thoughts? Anyone used a 'hard start kit' (essentially a big capacitor) wired to the motor windings?

[honda03842]

We had a magic chef and it started marginally with an 800 watt inverter, non-sine wave in our case. It worked fine with a 1200 watt non-sine. It's the starting current with compressors, starting is much greater

[cpaharley2008]

Maybe try getting it chilled on ac and then hooking up to dc and see if it works, then you know it is the start up pull.

[steve dunham]

Originally Posted by honda03842

We had a magic chef and it started marginally with an 800 watt inverter, non-sine wave in our case. It worked fine with a 1200 watt non-sine. It's the starting current with compressors, starting is much greater

The starting current of a motor NOT under load is 400% to 600% of the motors FLA . A motor starting under load has a starting current of 700% to 1200% of the motors FLA . A fan motor is an example of a motor not started under load , the load picks up as the fan speed increases .An air conditioner ,air compressor and refrigeration equipment are examples of motors started under load . (Against head pressure) and have high inrush currents at times reaching the point of LRA. The NFPA allows 1400% of the FLA in Art 430 of the code for hard starting motors. Your inverter may have internal protection that sees the starting current of the refrigerator as a short circuit.

[deryk]

Contact lil snoozy and ask them what size inverter you need, they should know for a fact since they offer the fridges to be run off of your batteries.

deryk

[David Tilston]

You could go buy a 12VDC compressor fridge. Use your inverter to run toys.

[cpaharley2008]

I think Lil snoozy, like the EggCamper uses 12v refers which run directly off battery without an inverter. I maybe wrong with LilSnoozy but I know EggCamper is that way. Using an inverter to convert 12v to operate a 120v appliance is not as efficient as using a direct 12v appliance.

[David Tilston]

Since the Norcold 12VDC fridges run on 3A, (36W @ 12 VDC) They are already about half the power. Since the inverter can't be 100% efficient the power draw will only go up.
Your battery can easily supply the 1400% of full load starting current.

[MCDenny]

Thanks for the quick replies.

Snoozy doesn't offer the inverter, they expect the fridge to run only on shore power.

My puzzlement is that the inverter would start the fridge last fall but not now.

I realize I should have gotten a bigger inverter but here I am with a $200 600 watt unit.

I tried running it for a while n shore power then switching to inverter - didn't work.

A 12v / 110v fridge is about ten times the cost of the $150 fridge I already have.

Hoping against hope there is a solution using my existing fridge and inverter

[deryk]

I spoke with lil snoozy and he said they use a real efficient ac powered unit... I agree an efficient 12 volt unit would be wiser.

deryk

[rabbit]

I precool a 2.7cu.ft. Dorm fridge on AC and then power it on the road thru 1500watt true sine wave on a 6' 1/0awg leash. I have roughly half your amp hour capacity and extended runs of greater than 16 hours aren't possible without solar battery charging and are sketchy with it so its use is usually confined to hookup situations. I have not tried a "hot" start and cool down of the fridge from battery/inverter. This method of cool down is, I suspect, a big battery drawdown due to sustained compressor runtime. Too bad Snoozy doesn't see fit to spec and/or provide a system operational "portal to portal."

jack

[David Tilston]

Originally Posted by MCDenny

Thanks for the quick replies.
A 12v / 110v fridge is about ten times the cost of the $150 fridge I already have.

My local wrecker sells RV fridges for $25. I have purchased an RM36E propane fridge from them, and it works. The last fridge I found was an older 12VDC compressor unit. If I had a use for it, I would have purchased it.

[honda03842]

McDenny
I bought a $59 non-sine wave 1200 watt inverter at a black and decker outlet store. It powered everything from TV to fridge.

We've used it in our Sunline trailer and have since moved it to our SCAMP

[honda03842]

Jack,
If one is off the grid, propane is really required and some of the best spots are off the grid.

One way we extended the run time was to charge the batterys from the tow vehicle while driving, keeping the fridge really cold while driving and the battery charged

During our cross Labrador trip with a dorm fridge we carried a 1000 watt generator $120.00. The gen was only 1 foot on a side and weighef 40lbs

[MCDenny]

It's been about a week since I last tried the fridge on the inverter. I just tried it again and what do you know it beeped but started!

Inverter plus running fridge takes 9.2 amps at nominal 12v.

I guess my inverter is just on the ragged edge.

[rabbit]

Norm, I have propane. My combination of AC compressor fridge and Coleman upright ice chest is working fine for my needs. For me a 3-way is a no-way. I suspect there are more owners of older 3-ways who carry an "auxilliary" ice chest than will admit it. There are some that will. I would love to have a 6-900$ trailer refrigerator but don't choose to spend the money. I'm sure you understand.

jack

[honda03842]

Jack
The reason I bought the dorm style was cost of the 3 way, afterall we were only keeping our little trailer for the 2 month across Labrador trip.

Oops, that trip has turned into 3 trailers and 5 years.

We stll have the fridge and generator

As to coolers we've learned to live within the confines of our small Scamp fridge. We don't like to carry coolers, pets and the like though many RVers do

[David Tilston]

I may be beating a dead horse, but older working 3-way fridges are available. I would not pay more then $100 for one, but I have got them for free as well. At one point I had three spare RM211's. I sold one, one is a hot swap-able spare, and the other is now a bone yard. I also have a Spare RM36E I got for $25 at the wreckers. I found, but did not purchase an older Norcold 12 VDC compressor fridge at the wreckers as well.
We do have a portable 12 VDC solid state cooler in the van. It keeps the snacks and drinks cool while we drive.

[glamourpets]

A fridge compressor needs a lot of extra power to get it going. Would the addition of a capacitor give the inverter a little extra boost it needs to get the fridge running? Perhaps this is a way to get the existing fridge and inverter to work more reliably together. A capacitor can react much faster than a battery. It will provide that sudden extra kick needed to the compressor going. Usually these capacitors are sold for car audio, but there is no reason they can't be used in other applications. Thoughts?

Car Audio Capacitors | Stereo Capacitors

[MCDenny]

The capacitor noted above is for a 12v dc load. My problem is the fridge motor drawing too much 110Vac from the inverter. I have plenty of 12v capacity and short fat cables connecting the battery to the inverter.

Anybody know if the theory would work for AC?

The hard start kits, I think, are just caps somehow wired to the motor windings.