Inverters

[tanner0441]

Hi

Reading through some of the postings on fridges and freezers tripping inverters into overload, and having a few hours to kill, I decided to have a look at the output waveforms and voltages on the two inverters I have. One is a 1000W Nikkai, the other one is an IBM badged UPS.

The Nikkai produces 255V at 50 Hz with no load, connect it to a 1000W ceramic fan heater it drops to 250 V at 50 Hz. I wondered if the high readings were due to transients, or harmonics. I then put the scope on the waveform, Tektronix 465 with a X10 probe.  The output was a very good square wave, rise time 2uS no overshoot, no apparent harmonics, zero volt dwell 1 mS between positive and negative half cycles.  I then connected a 370 W induction motor, the inverter tripped. Next my Pillar Drill 500 W induction motor, that ran perfectly, but all the time the output remained a square wave, and the motor was noisy AC/DC motors ran perfectly including several that pull more than 1KW on load..

The IBM UPS, the output looked as if it was from an ADSR filter, rapid rise time, a long reducing voltage and a rapid drop off. Add an inductive load and the waveform becomes almost a sine wave, but with transients and overshoot to over 300 V. They both run a standard flourecent lamp with no problems, albeit with a lot of noise from the choke.

Its been a long time since I did the maths on induction motors and I am not going to attempt to remember the electronics or look for my books, but I am sure there are others on here that can.

If anyone can use this infomation I would be interested in reading their reply.

Brian.

[cdog]

My inverters won't start my fridges that I have tried either!!!

I put an aftermarket ,external cap and relay on one fridge and it didn't help.

Last week I purchased a 1600 watt redi-line inverter from flea bay, if this doesn't make the fridge start I am going to be very annoyed!!!!

On  of my inverters has a watt load display, it goes to 1700 watts fairly quickly, but the entire time the fridge just sits there and clicks until the inverter kicks out.

There has to be a reasonable way to keep my beer cold during hunting season, and I plan on finding it!!!

Cdog.

[scottsAI]

Check out:

http://www.fieldlines.com/comments/2008/9/20/145014/548/11#11

48 cans enough?

Have fun,

Scott.

[cdog]

What if I have company?

Cdog.

[cdog]

Are there full size fridges using this method??

Cdog.

[wooferhound]

Here are a couple of stories about running a refrigerator from an inverter...

 http://www.fieldlines.com/story/2008/5/23/115041/076

 http://www.fieldlines.com/story/2008/2/18/7248/96617

[chubbytrucker01]

 I use a counter height mini fridge from sears in my truck running it off of a coleman msw 2500 watt inverter with no problems. It takes alot of abuse as well. The inverter has a bar graph that goes to about 900 watts on startup and settles to about 250 watts running. It ran about 7 days in the heat in July in my truck before I realized I forgot to turn it off. It still had ice buildup on the freezer compartment when I opened it. I have 400 ah of battery and they were probably close to 50 percent. It was about 125 degrees in the truck and must have cycled like mad. My father in law had an apartment fridge in his that was about four feet tall and had a separate door for the freezer and he ran it for two years on a 2000 watt Roadpro inverter. He kept popcicles in his. Roadpro stuff has never been know for high quality. His ran like a clock until it fell on its face while it was running. Thats what happens when you don't check for screws coming loose and drive too fast. Stuff flys apart at the worst possible time.I new a guy who had a mini fridge from Walmart that he ran 24 hrs at a time in his car from a 750 watt inverter on a marine trolling motor combo starter battery. He would keep his insulin in it traveling back and forth from Florida hiding from hurricanes  

[wiredwrong]

I decided I needed to see if my fridge would run from my inverter, I have tried the freezer before and always assumed the fridge would be fine, but after your post it was time to make sure.

So i grabbed this battery off the shelf,

hooked up this Inverter

I ran a 50ft drop cord from the garage to the kitchen, Then I dumped the ice trays, filled them back up and waited for the compressor to kick on, in less than a minute after closing the door it was on. I stepped back into the garage to see what the inverter was doing, the hum was slightly louder than unloaded, but not as loud as when I run electric weed eater from it. I let it run a full cycle, then took this picture from inside the fridge to show the specs of the fridge

As soon as I closed the door the fridge cycled back on, so I let it run another cycle, It sounded completely normal and as you can see the cables are not optimal, very small for this Inverter, but barely got warm. Tomorrow I may plug in the chest freezer and the Fridge to see if I can manage to run them both at once. When I have time I will post the results.

And since I'm sure everyone is wondering about the Bike/Truck, I'm having axle issues, so no new progress yet.

[tanner0441]

Hi

I had an old inverter in a box like the one in your picture, it had a transformer in it, it hummed and buzzed beautifuly, and ran anything I plugged into it.  The output waveform was a sine wave, it had a bit of distortion and plenty of harmonics but it was more or less a sine wave.

The thing I was checking yesterday produces a square wave output, induction motors are not going to like them, the words ringing and back emf spring to mind.  I am going to have to sort out my old books out and do some reading.

I would have thought with modern power FETs it would be possible to produce a cheap sine wave inverter.

Brian

[Basil]

I run my 4ft frig on a cheep 1000 watt inverter. ( Won it with 11 dollars on EBay )Frig rated at 3.67 amp on the tag. It has no problem starting. All I need is more batteries to run it. Now I miss those batteries I gave a way.

[Opera House]

I run my fridge off a 2000/4000 watt inverter.  I buy these defective on ebay.  Usually a pair of the 50A parallel FETs in the output H bridge are shorted and I just wiggle them out.  In theory this should make it a 1000/2000 inverter. The freezer is only 100W uinning but draws over 17A at start up.   After running the fridge for a couple months, I hooked it up to a 850W microwave.  That shorted out the inverter in about 4 seconds.  Good thing I have a stack of inverters.

[dnix71]

The Engel 45 will hold 60 cans of beer. It runs from 12v directly, so it may be cheaper in the long run. I have the Engel 40. It will freeze or cool, but not both at the same time. There are lid extensions that allow more storage, or set to freeze at the bottom but not freeze at the top.

http://www.bigfrogmountain.com/searchresults.cfm?Type=Efficient%20Appliances&SubType=Engel%20Por
table%20Refrigerators%20%26%20Freezers

[scottsAI]

Cdog,

It helps if you reply to my post.

Here you replied to main story, not mine almost missed you were talking to me. (I think:)

Going back I see in 5jun08 you replied to a post of mine, except you replied to the main.

I normally do not reread stories. Thus will miss a post unless replied to mine.

I check for replies for a few weeks.

Are there full size fridges using this method??

Not that I can find. Over the years I have seen many announcements, nothing in long term production except the Colman cooler.

Consider using the guts of the cooler and build a full sized fridge around it?

Would be a COOL project!-)

Need thick insulation 4 inch fridge and 6 for freezer, uses very little power.

For fun designed a 8x8 ft room freezer using chest freezer parts.

Required 6-8 inch insulation on all surfaces. Depends on assumptions.

Like some help with designing this project!?

Have fun,

Scott.

[cdog]

Sorry I'm not so bright!!

Could a person simply put the guts of the cooler into an old fridge that has given up?

4" of insulation seems like a bunch.

I may try something like this if my new inverter doesn't do the trick, I'ts a good idea I think.

Sorry for mixing up postings,

Cdog.

[scottsAI]

Cdog,

You have to know about it before you can learn!

Now you know!

Could a person simply put the guts of the cooler into an old fridge that has given up?

Yes, Good starting point. Make sure you understand which part goes inside and out.

4" of insulation seems like a bunch.

Yep, then again, comes down to this choice:

One time spend money on insulation or forever spend more to run it?

Make sure the extra insulation will have a payback in a reasonable time.

Check out the couple existing off grid Fridges, similar thickness to get their low numbers.

As you have seen many ideas to reduce the cost, energy, equipment etc.

Let us know what your issues are, always good to show what you have found and why you need something else. The more you share the better we can help without telling your life story!-)

Have fun,

Scott.

[wdyasq]

4" of urethane foam was minimum for refrigerators in boats. This would be closer to 7 inches styrofam. Freezers got more.

Ron