12vDC to 220vAC converter

Discussion in 'The Projects Forum' started by David Melton, Jan 12, 2015.

  1. David Melton

    Thread Starter New Member

    Jan 12, 2015
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    I need to make a quick, cheap, temporary converter to run a 220v pump from a 12v car battery for about 10 minutes.

    I think it would work to get 2 identical cheap 110v inverters from Harbor Freight and use a 1:1 transformer to shift the phase of one of them 180 degrees.

    Do you think this will work? Is there anything I'm missing?

    Regards,
    David
     
  2. RichardO

    Well-Known Member

    May 4, 2013
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    If you are willing to use a transformer, then just use a single converter putting out 110 volts and a 110 to 220 volt step up transformer. Don't forget to oversize the converter and transformer to supply the starting current of the pump. Others here can give better details on the oversizing required than I can.
     
  3. #12

    Expert

    Nov 30, 2010
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    With no mention of how much current or power the motor uses, there are few guesses coming your way. We've seen people asking us to design 2,000 watt AC inverters to power houses in India. What are you trying to power?
     
  4. David Melton

    Thread Starter New Member

    Jan 12, 2015
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    Sorry, here's the back story. We have a vacation house out in the country. The well is over 1000 feet from the house. If we run the sinks and shower directly from the well, the pressure is weak. Instead, we have a big holding tank in the garage, with its own pump to supply the house with good pressure. When the holding tank gets low, we refill it from the well. Because we only visit the house a few days a month, we only fill the tank about once every 2 months.

    Because the well is so far from the house, it has its own power meter, and its own account with the REMC. They are charging us $37 per month for an electric service that just sits there most of the time. We thought about installing a solar panel and battery bank, but we're afraid it would be stolen. We have had the service wire, pump, and pressure tank stolen several times because it sits unguarded for weeks at a time. (stupid crack-heads) Right now, when we want to use the pump, I have to connect a heavy gauge extension cord from the meter to the pump. When we're done using it, I coil the extension cord and lock it in the house.

    I wanted to explore a way to mount some batteries and an inverter in a kid's toy wagon so we could take the well pump "off grid" and save some money.

    I can't find the spec sheet for our pump right now, but it's a 3/4 horsepower jet pump that runs on 220vAC.
     
  5. David Melton

    Thread Starter New Member

    Jan 12, 2015
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    Duh! I didn't think of that. What an easy solution. I just need to make sure the inverter is big enough to handle the startup current of the motor.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    The starting inrush to a 3/4HP pump is about 25A@240V. It is going to take one hell of a big inverter to do this... The HF inverters you mention don't even come close...

    I play this game while running my deep-submersible well pump during AC power failures here at the ranch. It has a 1.5HP 240V motor. I tried a 2KW Honda gas-engine alternator, and it will not start the pump. A 6.5KW gas alternator will start it, but the starting transient noticeably slows the motor. It is the energy stored in the rotating mass of the alternator rotor that makes it happen.

    I suggest you buy at least a 4.5kW generator. Do not get an "inverter" type of generator. If you get a gas-powered one, do not ever leave auto gas with ethanol in the tank or carburetor. It must be drained after every use... (Voice of Experience).
     
    Last edited: Jan 14, 2015
    #12 likes this.
  7. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    What about using a gas power pump instead of buying a generator?? Also I not sure how mechanical you are but you use try hooking up a gas motor up to the pump...
     
  8. #12

    Expert

    Nov 30, 2010
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    It's hard to get a gasoline motor down a 4 inch well pipe, and even harder to fill its gas tank when it's down there.
     
  9. #12

    Expert

    Nov 30, 2010
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    Thanks for letting me know that generator manufacturers haven't discovered there is alcohol in modern gasoline. How far back does that place their last R&D attempt? About 40 years?
     
  10. Ramussons

    Active Member

    May 3, 2013
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    Never parallel standalone inverters. The inverters will never be at the same frequency or phase. And paralleling them will lead to mutual destruction.

    Inverters designed for Parallel operation have a Common Clock Source (Synchronised Operation) and Load Balancing / Sharing control systems.

    This is besides other issues mentioned by others.
     
    #12 likes this.
  11. David Melton

    Thread Starter New Member

    Jan 12, 2015
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    I was worried about trying to match phase. Thanks for the advice.
     
  12. David Melton

    Thread Starter New Member

    Jan 12, 2015
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    0

    Maybe it's time to think about replacing the pump with a 120v shallow well pump, and run it with our 2kW generator. In the past, we've had trouble with shallow well pumps losing their prime, but I'll bet I could come up with some creative plumbing to fix that problem. Thanks for the suggestions.
     
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