Hi Guys,

I want to find out if I could run a fridge and a well pump from a modified sine wave inverter?

Thank you much,



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     Mr. John  

    Bill from the woods.

   You are correct, another answer would be any absorbsion system. Now we can use any sourse of heat, 12 volt, 120 volt or gas. Without a compressor the powers wave forms or, or, become irrelevent. It also does away with starting surges needed by compressors.

Mr. John and W.R. lost me with the last two comments.

The reason I asked for single phase 220 to 3 phase 220 hook-up is that I already checked that there are inverters/transformers which "change" 220V to 220V 3 phase for about $250.  I just don't know how they work and if it is possible to use only two of the three phases.  It appears to be a "no problems" thing, but unless someone has a better understanding of these things I probably will not be the first to try it.

Since everything (all the inverters, chargers, etc.) is being powered by the solar panels, running a motor to provide two phase 220V to run the pump does not feel right to me.

I remembered that I have 110V AC conditioner in the attick.  I got it from a garage sale several years ago.  I think it is supposed to keep the votage in good range and condition!?  Maybe it will fix the modified sine wave.

Thank you, guys, for the nice answers.



First, forget 3 phase. Unless your running high demand loads, in the shop it has no place in this discussion.

Near every home uses single phase power.  The power company sends high voltage down the line to a transformer near you, usually the pole in the country! The secondary winding or output side is wound to deliver 220 volts, single phase! The 220 volt winding is next center taped, leaving 110 from center to right or left end legs and 220 across the outside legs. 3 phase is another set of windings and a 3rd leg all the way from the generator.

If we looked at the wave form from this transformer, across the out side or 220 volt legs it would go up to a peak then down to the center. The start and the center are both zero volts, the peak is 110 volts. As the wave now goes below the center we start working to a valley or reversed peak! again to 110 volts. From the center tap to either the right or left leg we will get 110 volts in opposite phase. Across the outer legs we combine the 110 from each side making 220 volts.

In the generator the magnet is at 90 degrees to the coil at zero volts. As rotation starts the magnetic power gets closer to center and the most powerful point, the peak of the wave. The magnet still rotating now leaves the peak and returns  to 90 degrees or zero volts point. you now have seen half a cycle! The magnet continues to rotate but what was north on top is now becoming south for a pole, the cycle is now reversing to the bottom, 360 turn is one full cycle, half turn 180 degrees is a half cycle of power.

A modified sine wave is not generated with a coil and a rotating field. It is D.C. power applied and let raise to the about 80 volts, then given some time and 110 volts.  It makes near a sign wave with square corners. It works well for some applications, synchronize motors isn't one.


Luby, I'd be surprised if you have 3 phase on the place. Could be wrong. I do have it in my shop for some special tools, I generate it on site. It isn't on all the power poles.


Hi Bill,

First of all - a big thank you.  You explained things so well.  You are right - I do not have 3 phase at home.  I have 220V, as we all do.

We kind of deviated from my initial question.  I just want to be able to run my well pump(spring box, not real well) with a solar system (plus a fridge and a freezer, at least).  I know the pump is 220V, because there are two hot wires to the relay and everything else and they go to a double 20A breaker.  I measured 7.8A on one of the legs.

So far I understand that it is not too good to run the fridges on mod. sine wave.  OK, I will buy a pure sine wave inverter.  I also understood that it is very hard to run the 220V well pump with solar, unless someone comes up with a great solution.

Thanks again,


      Mr. Luby

    Bill here, First, your very welcome for any help, few old fellers helped me alone the way and we just pass it on!

  Second, I have a son that chatted with me last night, you were discussed! We are checking on an idea for you. So, if you can hold a day or so I will be back to you with  a good answer that will do what were after, give us a few we won't forget and you will get an answer good or bad.


       Mr. Luby

   Bill again, What I was looking for was a transformer, just the componet in hand. The kid says thats not as easy today as when I was working everyday. He however did get us some good answers!

  W.W. Grainger Co. has what I was going to have you do already built, they can be found on the internet. I have 2 part numbers for you. These plug in to your 110 volt inverter and 220 comes out the other side. Cost isn't terrible and Grainger is a good company to deal with.

   16V988 is a 3000 watt unit for $167

   18C925 is a 2000 watt unit for $220

   I beleive you had said you needed about 8 amps at 220 volt, thats working real hard on 1800 watts!. I'd advise thinking larger so it runs cooler, electric heat is spendy to make!

   This should set you up with a just plug it in and go answer. Grainger also has extended warenties if your concerned.   

    The boy came thru far faster then I figured he would on this one!



OK, it appears Mr. Bill & Son have found you an answer,,,

Now, let's look at the other side of the project...how many and at what size batteries are you gonna need to drive the pump...I see figures like 8 amps @ 220 volts (a.c. I assume), and 1800 watts (I don't know if that's a.c. or d.c.),,,,,

I am imagining how my six battery bank (125 Ah each) reacts to the 1500 watt a.c. surge when my refrigerator compressor comes on, the inverter will beep 3 times, I am assuming for that very brief moment, the entire battery bank drops below the warning voltage, but then recovers and the frig runs between 150 and 175 watts smoothly...

So, lets say you have a large enough inverter (which will cost you a chunk of change even before we continue) to run the pump, and the pump will not switch on, then off briefly, once it's on, it will stay on until you have pump switch off pressure...will you need to double what I have, triple it? Will you need 12 batteries, 18?

My friend has a 2300 watt PowerBrite inverter, I think he paid around 500 bucks for it, I pay $100 a battery for the 125 Ah bats, and at the least, $167 for the transformer above..doing the math quickly in my head, this would be pretty pricey, just to run the pump...I came up with a similar price scenario when I thought I could run my window air conditioner on batteries, as you might imagine, that idea went out the window in a flash...and after all that, the price of the solar panels to keep all those batteries charged, I won't even go there...

So, think about the entire picture before you drop any cash on this project, financially, it may not be wise, there may be a large span between can I do it and can I afford it, but good luck anyways!!!

Bill here. I would guess your correct that when the compressor starts your short on battery and the inverter warns of low supply voltage.
The starting point as always is do some tracking and find out exactly what the appliance is using. Realize the same fridge may us more power in a different home, I DON'T LIKE WARM BEER!
On sizing the battery bank realise that if what I'm running runs more in day light hours one can down size the battery bank as we can power directly from panels, in the dark that changes.
In this case keeping up with an 1800 watt load, and presuming were running more on top,,,,, That's a challange!
I use the grid as my back up, it runs large draw loads. I run lights and entertainment on solar. My well can be run on either as it has a 110 volt pump. It has high start demands but truely running isn't a hudge user, also short run duration.
I would agree that it seems every body wants to power everything with solar, it can be done, but not cost effectively.

Hello, Guys,

I will combine my reply to both W.R. and Bill K. and his son.  Thank you for putting your heads and hearts in finding answers to my questions!  It feels really great to be connected in the spirit of helping.  I really appreciate that!

I am surprised that the 3000W unit is cheaper than the other.  This step-up transformer may do the job.  I'll talk to someone from the company for specifics.  I am hoping that I will be getting a 4 battery bank which will be about 800 Ah.  Since the pump and the fridges run only part of the time, I am not too concerned about running down the bank (the battery bank, that is;-).  I will further have timers on the fridges, so they do not run at the same time, to avoid the surge hit - I have to experiment with that.  The fridge consumption is constant after it has started.  If one wants it to be colder inside, then it runs longer, but the load is constant.  Mine runs from 175W in the beginnig, gradually down to 140 before stopping.

I understand that we cannot beat the power company for price of electricity.  In my case, and I am sure in many of yours, the goal is different and we are all working on that.  The hobby or the outcome we want to achieve could be pricey, but some time we have to pay to have fun.

You, guys, gave me quite much of infromation and input and I have to figure out which of the suggestions to follow and experiment.  Thank you, one more time!


Ok, Luby, I guess you're determined to make a go of the pump project, the frig is the easiest of the 2 to run on batteries, but be forewarned, the frig temp is linear, meaning, if you turn it off now, you will still use the power (longer) to cool it later, and again, I've tried all these tricks, the bottom line was, just let the frig run when it wants, you balance out in the end...

Also, Bill (w.r.) has a good point about night running...none of my appliances and devices run on batteries after 4:30 p.m (at that point, I am re-charging the battery bank for the next day)., I use the sun mostly to run these things, but at night, I am at the mercy of the power company, and this is why I will never be completely off the grid, I need them at night...however, in an emergency, yes, I can run day and night, just about indefinately, but that involves a special plan, a plan too long to describe right now, here....

I still think you may have bit off a little more then you can chew with the pump project, but I will sit patiently and watch as you progress, I hope it does work without putting you in the poor house, but I guess we'll see, again, I wish you all the luck in the world...

Hi Bill,

I use this post, because your last one did not have a "Reply" button.

Thank you very much for your best wishes and thoughts!!!  I am still thinking, gathering prices and ideas and I will come to a point when I will know how deep in the poor house I will be.  I have not gotten the batteries yet and I am hoping that they will be at the price I was quoted initially.

I also hope that I will get the following: "4- SHARP 230W SOLAR PANEL MADE WITH 60 SOLAR CELLS NEW B GRADE"  You could type this in and find what they are.  And so on, with the other equipment.  As you said - we will see.

Thanks again,


why not hook up a bunch of GTI`s and feed the power back into the meter?


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