AC to DC conversion

Discussion in 'General Electronics Chat' started by bladerunner, Nov 15, 2012.

  1. bladerunner

    Thread Starter Member

    Apr 15, 2012
    83
    4
    I have reviewed the AC /DC motor guides found in the archives and still need a little help.

    I have a pump that has a 1/2 HP motor , rpm 1725 , 115 VAC, amps 7.8
    I would like to replace this motor with a DC motor for portability.
    With the pump loaded, the AC motor only draws 5.8 to 7.0 A. at any time.
    The time factor is critical, since portable batteries run down quickly. A 30 minute window would be enough to complete the job.
    By my calculations, I would need a 24 volt DC motor and accompanying batteries to have any chance of working.
    Am I full of it or will something like this work?

    Thanks for any advise given!
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,013
    3,233
    Assuming each motor has about the same efficiency, the 24VDC motor will draw 115/25 * (5.8 to 7) = 26.7 to 32.2A from the 24V battery. Thus you would need a minimum battery capacity of 16.1AH for a half hour of operation. You should approximately double that for margin. I would think two deep-discharge type marine batteries in series, which typically have a capacity greater than 30AH, should work.

    Don't use standard auto batteries as they won't last long under heavy discharge type use such as this is.
     
  3. bladerunner

    Thread Starter Member

    Apr 15, 2012
    83
    4
    Unfortunately, I am trying to make it more portable by downsizing the batteries to those similar to a 18-24V drill battery. Will have to re-think the motor needs and possibly the pump itself. Thanks for the info.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Have you tried running a battery powered electric drill at full load for 1/2 hour? Mine won't do it. Batteries go dead first.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,013
    3,233
    You either going to need larger batteries or a much smaller pump if you want to use drill type batteries.

    How much liquid do you need to pump and at what pressure?
     
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