# 12V inverter for small 7cu ft freezer?



## HermitJohn (May 10, 2002)

I'd still like either a Lister diesel or small diesel Japanese tractor to power a 1800rpm generator head. The seller of that little Kubota I mentioned in another thread kept changing his mind as to price and whether he really wanted to sell it at all, so forget that for now. Dont need to deal with crazy people.

But still being without electric service since ice storm, I am thinking more about emergency use. A 5.5hp Honda clone plus automotive alternator which I already have seem better short term strategy right now. I found info on 12V circuit to power standard 40watt fluoresent tube, my laptop has 12V adapter. Its my little freezer that is the riddle. Lot of conflicting info, some saying sure no problem with inverter, some say it has to be up to 10 times the watt rating of the freezer, some say use a pure sine wave inverter only. Prices all over the place from under $50 to several hundred. Its not like I can try one, take it back and try another. Sure probably most of the brands are made by two or three factories out of china unless maybe some high dollar one made here or to more exacting standards anyway.

I am mostly thinking future, right now contents of my freezer and refrigerator already out on compost pile. And the light is thing I miss most and that I can apparently do without an inverter. Bright light and laptop and I am in high cotton.... Now if it were summer I would be hurting for want of functional room fans.


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## Explorer (Dec 2, 2003)

I have a sine and modified sine wave inverter. My small 10 cuft freezer runs fine on either. I have been told here that the motor will not last as long with a modified sine wave, but I don't know for sure. My freezer pulls about 80 watts when running. The thing that surprised me is how much it runs even turned down to about 1/4 and it is in an unheated building.

I ran two 20" box fans all last summer using the modified sine without any apparent problems.


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## HermitJohn (May 10, 2002)

Explorer said:


> I have a sine and modified sine wave inverter. My small 10 cuft freezer runs fine on either. I have been told here that the motor will not last as long with a modified sine wave, but I don't know for sure. My freezer pulls about 80 watts when running. The thing that surprised me is how much it runs even turned down to about 1/4 and it is in an unheated building.
> 
> I ran two 20" box fans all last summer using the modified sine without any apparent problems.


So what size inverter did you need for your freezer? I've not found firm answer in my reading. Have you found brand of inverter matters?


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## Explorer (Dec 2, 2003)

I don't have the meter to measure start-up current draw, but I would expect it is less than 400 watts for a freezer that pulls about 80. I am using 1000 watt inverters, but also running other things at the same time. Something like this should work (?):

http://www.donrowe.com/inverters/150_800_watt.html

I also would expect some difference between manufactures in motors used and that would make a difference. I have found there are very few answers to some questions, so I experiment a lot.


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## Jim-mi (May 15, 2002)

Motors running on Mod Sine run hotter so there for shortening life.
The box fans . . well ya . . self cooling...........

Hermit can you find some currant requirements on that freezer .? 
Probably best to not go under 1k on the inverter . . .give it plenty of head room to start it.
The 'Conserve' chest freezer that I have will certainly let me know when it starts . . . and I've got a 4500 watt inverter. . . .I have never tried to measure its inrush currant.


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## artificer (Feb 26, 2007)

When I go out to the off-grid property next, I'll try and remember to put the kill-a-watt on our 5.4cu ft freezer. I remember it taking around 100watts to run, and that would drop to 80 something after a while. I seem to remember it taking 400 watts (900w?) if you cut power, and it tried to restart too soon. It would cycle off, and a while later try to restart.

The first time this freezer is run, it takes all day to get down to freezing. I don't know what the long term power usage will be, but its high to start with. The freezer is a cheap import.

There are differences in quality of "modified sine-wave" inverters. Some are basically almost a square wave. If you buy a cheap Harbor Freight special, expect to get that. If you get one of the charger/inverters, they tend to have more segments in the square wave, so they are closer to a sine wave. It boils down to: the more you pay, the better (mostly) you get. 

If I ever get enough batteries and big enough inverter to power the well pump and freezer, I'll probably make sure its a true sine wave inverter.

So... to answer your questions, maybe...

Starting watts on my freezer is (I think) 4x the running watts. Inverters have a peak as well as a running watts. The peak is typically 2x the running watts, so a 400watt inverter will briefly supply 800 watts. A monster fridge/freezer should take less than 400 watts. If you take half of that for a small unit, 200 watts, multiply by 4 to get 800 starting watts. Based on this SWAG, I wouldn't get an inverter less than 500watts. The 1000watts Jim-mi mentions would be better, since it will have extra capacity. If your power blips, and the compressor locks up due to the high pressure in the lines, it can supply the full starting power long enough for the compressor current sensor to trip. You probably wouldn't blow the inverters fuse, or trip its overcurrent protection on the inverter.

For occasional use (the week you've been without power) I would probably buy a good modified sine wave inverter. I'd say it would be over $100 for a 1000watt unit. Longer life of the freezer isn't too much a concern if you only use the inverter a week or two a year, as long as it doesn't burn out the compressor in a short amount of time.

I have a 1000watt inverter in our conversion van out in the parking lot. If I get a chance, I'll pull it into the shop today, and get an o-silly scope shot of the waveform. This inverter was about $70 a few years ago.

Michael


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## HermitJohn (May 10, 2002)

Ah, electric back on this morning. Been reading lot about 12V inverters. Sort of a crap shoot. Tripp-lite seems to be one of more reliable brands. See what shows up. If one is patient and does ones homework, one gets the best deal. 

I did find couple websites saying that adapting an automotive muffler to a small engine quiets it considerable. Way back when somebody made a little putt putt car with lawn mower engine and did that, looked funky. I never tried it but be worth a shot, have few doner mufflers in my car parts stash I am sure.

Am sure my little freezer simular power needs to artificers'. 

I even have an old 5000 watt inverter out in one of old cars I picked up along the way back in 80s, never used it but suppose to work. Unfortunately it was 24V I think. Maybe also not so efficient as modern ones. Also out in the old car sure rats have had their way and it most likely is no good anymore.


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## artificer (Feb 26, 2007)

Just shot a pic of the o-silly scope on my Vector 1000w inverter. Its a square wave. Take a look at this website, and mine is somewhat close to the second from the top photo. I defiantly wouldn't run a motor long term on this. Works well with the sawzall or skill saw in the lumber yard parking lot, however.

More info when I get back from the property this weekend.

Mufflers: the listeroids are shipped with "pepper pot" mufflers. Somewhat loud. Many people replace them with automotive mufflers, and almost eliminate the noise. Probably not going to as effective with a higher speed Briggs engine, but it will definitely help.

Michael


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## Jim-mi (May 15, 2002)

Yes those "truck stop" inverters would/will be a crap shoot.
All to many of those units are nothing more than a can of contained smoke . . . waiting for someone unlease the smoke.

I remember 'Tripp-lite' as being square wave units great for lights Bad for motors--heat.

For a while I watched fleabay for a Trace\Xantrax DR series mod sine to have as a back up. Yes they are quite a few bucks more but if someone has to go the mod sine route I would recommend the DR series because they have been tried and proven to work over a bunch of years. Plus the battery chargers in them are good.


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## HermitJohn (May 10, 2002)

Well just to get my feet wet, bought a used 750 watt cheapie ($23 plus few bucks shipping) off ebay. I was totally surprised I won the bid as I'd been getting outbid right and left with people waiting until last minute. 

Got it today and just as experiment hooked it to battery that was inside on charger (unhooked charger first). No problem running fan on high and I plugged my bedside lamp with the CFL into it and it started right up and just as bright as when plugged into wall and no odd noise or flickering or anything. That was encouraging as I had read horror stories of CFL on inverter.

I get things set up little better in way of engine/alternator, will have it running and see what happens when I plug in freezer. But if this thing can only handle couple fans and decent light, I wouldnt be unhappy. Those are the most important basic needs. As to slightly shorter lifespan from square wave versus perfect sine, shrug, why would I buy a several hundred dollar inverter to get an extra year or two from a $150 freezer???? Plus doubt it would make much difference when just used for occasional emergencies. Probably invest in better inverter if I were going full time off grid and couldnt afford something better like Danzer that doesnt need an inverter.


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