What Type of Inverter Needed to Run ARB Fridge 120VAC (1 Viewer)

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the 12VDC side of my ARB fridge crapped out. while i am sorting that out, (and hopefully able to get it fixed) the fridge runs fine on 120VAC.
so i need a small inverter.
do i need a pure sine wave inverter or can i use a less expensive modified sine wave type?
the fridge controller is a Danfoss 101N0500 but i can't seem to find input power requirements online.
any input appreciated...
thanks, Mark
 
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Modified sine will work just fine. No need for a pure sine. You should buy an inverter enough for your highest
power usage, not just for the fridge.

Don't know what size ARB fridge you have, but mine is a 63 qt and barely draws 1 amp an hour.
 

sdnative

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The fridge will draw over 5A @ 12V DC when the compressor is running. So ~60W. The duty cycle is about 20% depending on ambient conditions and insulation so you end up with 1Ah per hour. Considering inverter loses I would use a 100W inverter minimum. Pure sine wave inverters are cheap these days, no reason to get a modified sine wave.
 

e9999

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of course, the inverter would have to support the normal running power, but more than that, it has to be able to handle the starting current surge. That can be a lot more than the former. I don't know about your motor, and unfortunately, that is not that easy to measure, but perhaps you can talk to the manufacturer tech support to find out. If it were me, if I didn't know the numbers, and considering how cheap inverters are now, I'd go at least several times the nominal running power. And even then, the details of the inverter construction could matter because the short-term inrush current can be quite large (IOW, it can fry stuff).
 
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I haven't measured but I'm thinking there's little inrush current. The Engel has a pretty sophisticated compressor (no motor per se) control circuit. The compressor is basically a piston connected to a coil. The controller controls coil current to control piston speed and amplitude. I would think they a have "soft start" feature in there but once again I'm guessing.
 
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The fridge will draw over 5A @ 12V DC when the compressor is running. So ~60W. The duty cycle is about 20% depending on ambient conditions and insulation so you end up with 1Ah per hour. Considering inverter loses I would use a 100W inverter minimum. Pure sine wave inverters are cheap these days, no reason to get a modified sine wave.
thanks, i will find a small ~300W or so that fits on the back of the center console. i have power there and install will be easy.
any brand you would recommend?
 

sdnative

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thanks, i will find a small ~300W or so that fits on the back of the center console. i have power there and install will be easy.
any brand you would recommend?

I haven't shopped for inverters for years so not sure what is good these days. I have an older Zamp 300W that has been great, but it seems to be discontinued. I was actually surprised to see this model is still selling for over $100. Seems like 300W is about the smallest you can get.

If you just need it to power the fridge in a pinch, probably any of the high rated ones on amazon would work. May want to check craigslist, ebay, etc as well.

If you want to make more of an investment and keep it long term consider a unit from the major players like Magnum, Xantrex, Victron, Samlex, etc ( I am probably missing some).

Another thought: have you tried contacting ARB about replacing the power supply in the fridge? I would guess this is pretty easy. You may even be able to find replacement parts on ebay.
 
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yeah, the control board/power supply is replaceable and likely the problem as the compressor is working fine. the Danfoss part is available on ebay but cost more than an inverter.
i will likely do both. get an inverter now so the fridge is working (gotta love prime shipping) and figure out what is needed to fix the fridge so the 12VDC works.
 
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after a little research, i went with this 300W Samlex.
it got great reviews, holds the sine waveform under load, is quite, way under rated, etc....
i couldn't find anything decent in the $100 range. most have a crap waveform that just falls apart under light load, let-alone full rating or above, they are loud, pull current without any load...
i will put it on the scope tomorrow (prime shipping :) ) when i get it to verify specs but this appears to be a solid inverter.
thanks for all the input.
 
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sdnative

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That looks like a nice one! You should be happy with it.

I know you already have a solution, but another thing to consider if you just need to power the fridge is a factory Toyota inverter (with plug and pigtail). Mine is rated at 120W, but some are up to 400W I believe. Probably modified sine wave but should work for a fridge.
 
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uhmm... well i guess i could look for a Toy inverter from someone parting out a newer vehicle, but think the Samlex will work out ok.
 
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e9999

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1FZ, if you have access to a scope and a shunt, it'd be great to see what you can measure at motor startup
 
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1FZ, if you have access to a scope and a shunt, it'd be great to see what you can measure at motor startup

i will put the inverter on my scope to check the sine waveform (just to satisfy my curiosity), but it would actually be easier to use my DC power supply and to record voltage/amps during start-up, but it is a non-issue. the in-rush current will never exceed the surge rating of the Samlex which is 500W. The ARB fridge uses a Danfoss control and compressor unit which (i believe) is 3-phase and soft start. there is tons of info on this refrigeration system on the interwebs if you want to do the research. but, a 300W inverter (with 500W surge) can easily power the compressor.
 
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i checked out the inverter today and it seems to be pretty solid.
easily powers the fridge and sine wave looks really nice. i don't really know if a chunky sine wave would hurt the fridge, but at least i don't have to worry about it.
here is the wave on the scope. yellow is utility grid power and magenta is the Samlex.

DS1Z_QuickPrint4.jpg
 

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