Modified sine wave for a fridge?

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Modified sine wave for a fridge?

Postby Diesel Dan » Mon Jun 11, 2012 9:46 pm

Okay, I apologize in advance for stirring up trouble. :lol: This topic often gets people riled up - but I gotta ask: How many people have successfully run a refrigerator off a modified sine wave inverter for a reasonably long period of time (years). What I've gathered from previous discussions is that electronics are okay to run on MSW, but anything with a motor is better off with pure sine wave. Am I remembering that right? Anyways, I don't want to spend all that money on one of those pure sine wave inverters if I don't have to. I'm currently running lights, fans, and electronics on my 1500 watt modified sine wave inverter with no problems, but I'm getting ready to put in a fridge so wanted to see if anyone has any real-world experience with this to share.

Thanks!
Dan
Last edited by Diesel Dan on Tue Jun 12, 2012 12:16 pm, edited 1 time in total.
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Re: Modified sine wave for a fridge?

Postby usmcbay » Mon Jun 11, 2012 11:40 pm

I'm interested to see the replies....

No answers here tough...
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Re: Modified sine wave for a fridge?

Postby chev49 » Tue Jun 12, 2012 3:44 am

there was a pure sine wave on eBay a week or so ago that was used, but i had already spent more than i should have this month so i didnt bid on it... :(

all i have is a modified sign wave one, and have only run the micro and tv system on it, and that works fine, runs the smaller ac ok also.. but not at the same time.

i think eventually i will get a real spendy pure sine wave inverter, as well as something like a 8-12k diesel gen set, since that is the right way to have things in a conversion.
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Re: Modified sine wave for a fridge?

Postby bansil » Tue Jun 12, 2012 4:01 am

I am looking to do similar,except use a 5cu ft freezer converted to fridge.
I have read yes and no about invertors.
The fridge will use about 3 amps running(I am going withway highside and using 5amps fkor the math) so some say 8 to 10 times that to start the motor so 50 amp startup max.that would be a 6000watt surge needed.(problem is it works fine on a 15 amp 120 circuit so those number must be wrong)
Ithink that is way off tho' based on a 3000watt generator will easily power a fridge and small ac(unless they both kickon at the same time.
I am going to try it with a 1500 watt(3000) surge invertor,I have a couple laying around,it may work,may not
Last edited by bansil on Tue Jun 12, 2012 8:23 am, edited 1 time in total.
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Re: Modified sine wave for a fridge?

Postby somewhereinusa » Tue Jun 12, 2012 7:19 am

I ran a refrigerator on modified sine wave in my semi for years. Never had a problem. I'm also running the same setup in my camper. I can't tell any difference
running shore power or inverter. My latest inverters have a readout showing amps. I've never seen either one go above 80. Usually they do about 70 on start then drop off to
about 30. Your mileage may vary. :D
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Re: Modified sine wave for a fridge?

Postby bansil » Tue Jun 12, 2012 8:22 am

Good to hear that,lot's of people have said that they run small dorm and single door fridges off of 1500w inverters...but way to many cyber-neer's

What size fridge dorm type with what inverter size?just curious :?
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Re: Modified sine wave for a fridge?

Postby lornaschinske » Tue Jun 12, 2012 10:01 am

Diesel Dan wrote:... What I've gathered from previous discussions is that electronics are okay to run on MSW, but anything with a motor is better off with pure sine wave...

It's the other way around... MSW for everything but electronics. SOME microwaves have problems with MSW. My theory is this... Plug it in and see. I know a lazer printer is Pure sine only but an ink jet is just fine on MSW. It's mostly "some" that don't like MSW on electronics.

MSW will power most anything. Start with MSW and if something objects, buy a little PSW unit. But I am a firm believer in using multiple inverters (that must be kept within 10 ft of battery bank) rather than one large one. I like to know that if one unit poops out, I can pull another unit into service temporarily. But mostly it's because I have one 750Watt(?) inverter now and may add another one later. One for lights and front TV. One in the rear for desktop computer, printer and rear TV. I don't really NEED the 2nd (rear) inverter but I would like one.

Figure to DOUBLE running watts for startup motor surge (minimum estimate... to be safe 2.5X and figure the fridge runs 24 hrs for load)
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Re: Modified sine wave for a fridge?

Postby bansil » Tue Jun 12, 2012 10:24 am

lornaschinske wrote:
Figure to DOUBLE running watts for startup motor surge (minimum estimate... to be safe 2.5X and figure the fridge runs 24 hrs for load)

I figured in 30 AH for the fridge should be less in reality(if we don't consitently open and close it...also reason for using a freezer,cold air wont "roll" out)
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Re: Modified sine wave for a fridge?

Postby Diesel Dan » Tue Jun 12, 2012 12:27 pm

I will be getting a dorm fridge/freezer like this one: http://www.bestbuy.com/site/Haier+-+2.7 ... Id=1931487

There are no technical specs for Amp draw on this website, but I'm guessing it will only be like 1 or 2 running Amps. I have a 1200 watt MSW inverter, or maybe it's 1500 watts, I'll have to look. But either way, I think it will be fine even with the surge when the compressor kicks in. At most I'll be drawing 4 or 5 amps for a couple seconds.
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Re: Modified sine wave for a fridge?

Postby bansil » Tue Jun 12, 2012 12:54 pm

those are the type of numbers I am expecting also
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Re: Modified sine wave for a fridge?

Postby somewhereinusa » Tue Jun 12, 2012 1:25 pm

This is similar to both that I have, If you have the height I would recommend one with a separate freezer. In my opinion the freezer works much
better if it's a separate unit.Amps is what I said in previous post.

http://www.bestbuy.com/site/Frigidaire+-+3.1+Cu.+Ft.+Compact+Refrigerator+-+Silver/9723536.p?id=1218159864574&skuId=9723536
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Re: Modified sine wave for a fridge?

Postby Diesel Dan » Tue Jun 12, 2012 2:02 pm

somewhereinusa wrote: If you have the height I would recommend one with a separate freezer. In my opinion the freezer works much
better if it's a separate unit.


I've been agonizing over that decision for some time now. The ones you describe are all about 3ft tall, and I need to squeeze whatever fridge I get into a 31" high space under my counter or face the prospect of tearing apart all my cabinetry in that part of the bus and rebuilding for the larger fridge. This was one area I did not plan out very well. I guess I was planning on using coolers but then changed my mind. :? Anyways, I think I'm going to just settle for the smaller fridge with built in freezer compartment for now and see how that goes.
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Re: Modified sine wave for a fridge?

Postby bansil » Tue Jun 12, 2012 2:20 pm

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Re: Modified sine wave for a fridge?

Postby Serenity » Tue Jun 12, 2012 9:53 pm

We had no luck burned up our 1st 18 cf "soft star" fridge so our current build we are going to use one of these as the fridge is the only AC device other than the 12v converter... New fridge is 16cf soft start....

It's a gamble but still cheaper then a Xantrex

http://www.ebay.com/itm/Ramsond-SunRay- ... 9772wt_722

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Re: Modified sine wave for a fridge?

Postby Diesel Dan » Tue Jun 12, 2012 10:19 pm

Yeah the chest freezer hack is a great idea if your space allows and you don't need a freezer. I definitely need a freezer (I use ice packs for my sore old back!), and I need the door to open in the front since it will be under a cabinet.
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