Refer running on inverter

[TexstarBob]

I have been experimenting with a setup that would allow me to run a small 1.7 CF refrigerator on an inverter while traveling. Maybe some of you guys have already tried this and can save me from wasting any more time/money on persuing this. The refrigerator is a compressor unit that is rated at 1.2A, 83W @ 115V. Doing a few calculations, it seemed possible to get 10-12 hours of run time on this unit from a 115ah battery. My first discovery was that the Aims 400W modified sine wave inverter I purchaced would not run it at all. The appliance technical service dept said it was because of the modified sine wave while Aims technical service blaimed it on the excessive surge of the appliance which they said could be as much as 12 times the running amperage (seems a little high to me). I checked the actual power usage of the refrigerator and found it runs at 1.5A and has a surge of ~7A or 800W for less than .5 sec. Since the 400W inverter had a rated surge capability of 1200W, I decided to go with the opinion of the appliance tech dept and purchased an Aims 300W pure sine wave inverter which is advertised as being capable of handling a 1000W surge. The first one I recieved blew it's fuse instantly before even plugging in the refrigerator. I can give more info on this for those that are interested, but I found THEINVERTORSTORE.COM to be less than compliant when it comes to replacing faulty products. Long story short . . . I purchased another one and returned the faulty one at my expense. The second one turned on and seemed to work fine, but went into overload as soon as the refrigerator turned on. I don't know what the surge capacity actually is on this inverter, but it is less than 800W and certainly less than the 1000W advertised. Aims technical service now tells me you should never surge an inverter over it's rated capacity. So my question is . . why call it a surge CAPABILITY if it's not capable of handling it? My next quest will be to install a hard start capacitor on the refrigerator which (here we go with manufacturer claims again . . .) should cut the surge amperage in half or possibly less.

[Q]

I have two 4 cubic foot refrigerators, a Sanyo and a Magic Chef. I've run them both on a Black and Decker 400 watt inverter (made by Vector) but not at the same time. They're both currently running on a single $69.00 1000 watt Xantrex inverter I bought at Costco a few years ago.

Since my house is off grid and photovoltaic solar powered I prefer to use refrigerators that don't have the heaters used in automatic defrost units. While on vacation I leave the refrigerators running on the 1000 watt inverter and turn off the main 3000 watt inverter.

There have been no problems running these refrigerators on the "modified sign wave" inverters over several years.

Q

[madjack]

Bob...something is very wrong...either the Aims inverters are way past crap or the fridge is...the only thing you need a pure wave inverter for is VERY sensitive electronics...a fridge should not fall into that category...the surge on the fridge shoud be in the 3a to 6a and is so momentary that, it should make no difference...I have a 500watt mod-sine inverter by Vector that, while I haven't tried a small fridge on it, I have run a full sized box fan and 13"tv/vcr combo on, at the same time with no problem...what size wire do you have feeding the inverter...keep in mind that the 12VDC amperage draw(from the battery) will be 10 times what the 120VAC amperage output(to the fridge) will be...
madjack

[Alphacarina]

I checked the actual power usage of the refrigerator and found it runs at 1.5A and has a surge of ~7A or 800W for less than .5 sec

Wondering how you measured this?

The actual, instantaneous startup surge is nearly impossible to measure as the load begins to decrease as soon as the compressor begins to turn . . . . probably after just a few milliseconds - It's many times higher on compressors than it would be on any fan motor . . . . even a fan motor which uses the same number of running amps as the compressor. Fan motors are inductive start while compressor motors are capacitor start

I would bet that your actual surge is probably in the 1500 watt range for the first 5 or 10 milliseconds and that knocks most inverters flat before they can even get the compressor turning. You know the fridge is fine . . . . it runs great off the grid, doesn't it?

You CAN buy a 12 volt compressor and replace the 120 Volt one in the icebox and run it straight off the batteries with no inverter needed - Boaters frequently use that approach

http://www.rparts.com/Catalog/Major_Components/compressors/Danfoss/danfoss.asp

Don

[TexstarBob]

I think I'll have to try another brand of inverter. The Aims brand is leaving me less than satisfied with their products and their service department is not very helpful. The units don't seem to have the capacity as advertised. I would not recommend using theinverterstore.com. The refrigerator is almost new and runs fine on shore power. I measured the power usage of the refrigerator with a digital amp meter that had a data hold feature. It showed the maximum amperage to be 7.01A. The time I just estimated, but figured since it was less than one second, that probably wasn't the problem.

[TexstarBob]

Mad Jack,
You were right. I bought a Vector modified sine wave inverter to try out with the refrigerator and it worked fine. I ran it for 10 hrs on battery power alone. The waterbottles I put inside the freezer unit were frozen solid and the battery still had 12.46 volts.

Don, thanks for the tip on the 12v compressors. If the compressor gives out on the fridge, I may look into that, but since they are rather pricey, I think I'll keep working on the inverter solution for now. It looks like I may have it licked. I was looking for a solution for keeping food cold while on-the-road without having to deal with ice and water. Engle coolers are nice and would suit my needs, but are rather expensive. 2 and 3 way RV refrigerators are a big investment also. 115 volt compact refrigerators are so cheap and plentiful, I figured that would be the solution if I could make it work. I think I'll still try adding a hard-start kit to the compressor. These cost about $20 and reportedly enhance the performance of the refrigerator . . making it run more efficienlly and start with a reduced power surge. Hopefully that would extend the battery charge.

[Alphacarina]

While a hard start kit will allow you to run the fridge with a smaller inverter (because it starts it with less of a spike) it won't change the overall power consumption of the fridge any - Since you have an inverter which runs it fine now, I would save the $20 and use to to connect the battery in your tear to your tow vehicle so it recharges as you drive

The big 'energy killer' to any standard refrigerator is that all the cold falls out whenever you open the door - Most all units designed to be run off a battery are top loading, so you can reach in and get a soda without dumping all the cold and having to start the cooling process all over again after every opening of the door

Perhaps you could remount your compressor (turn it 90 degrees) so you can lay the little fridge down on it's back and make it a top loader? - THAT would save you a bunch of battery power

Don

[TexstarBob]

Perhaps you could remount your compressor (turn it 90 degrees) so you can lay the little fridge down on it's back and make it a top loader?

Don

Good idea Don. Looks like there may be enough room to re-mount the compressor. I like the chest units better anyway because you don't have to worry about stuff falling out when you open the door. Samsung makes a few small chest type refrigerators like the SKRA0742BU, but so far, I haven't found them available anywhere.

[mikeschn]

Which Vector did you buy?

I tried the HF 1000 Watt, and it just beeped at me. Wouldn't run my 2.7 cft fridge at all.

Mike...

Mad Jack,
You were right. I bought a Vector modified sine wave inverter to try out with the refrigerator and it worked fine. I ran it for 10 hrs on battery power alone. The waterbottles I put inside the freezer unit were frozen solid and the battery still had 12.46 volts.

Don, thanks for the tip on the 12v compressors. If the compressor gives out on the fridge, I may look into that, but since they are rather pricey, I think I'll keep working on the inverter solution for now. It looks like I may have it licked. I was looking for a solution for keeping food cold while on-the-road without having to deal with ice and water. Engle coolers are nice and would suit my needs, but are rather expensive. 2 and 3 way RV refrigerators are a big investment also. 115 volt compact refrigerators are so cheap and plentiful, I figured that would be the solution if I could make it work. I think I'll still try adding a hard-start kit to the compressor. These cost about $20 and reportedly enhance the performance of the refrigerator . . making it run more efficienlly and start with a reduced power surge. Hopefully that would extend the battery charge.

[TexstarBob]

I bought the Vector 750 Watt inverter. I got it wired up for the trip to Petit Jean and it ran the refrigerator fine all the way there and back. It still had ice in the ice compartment after 11 hours of driving and the battery charge never got below 75%. I have a 1.7 cf refrigerator, but I think most compact refrigerators up to 4.4 cf use the same compressor. I assume they all take about the same wattage, but the larger ones run longer.