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12v dc to 12v ac inverter

Discussion in 'Hobby Electronics' started by lentildude, Aug 1, 2006.

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  1. lentildude

    lentildude Guest

    Is there a simple way to make a 12v dc to 12vac inverter so I can run
    an ac pump from a car battery. ac pumps have coils in epoxy with a
    magnetic impeller so can run long periods continually. dc pumps break
    down after continous use?

    Also anyone know where u can get cheap ex telecom deep cycle batteries
    near Penrith/lower bluemountains? They cost a fortune new. I am
    trying to pump water out of
    the dam and am killing car batteries with extended discharging.

  2. quietguy

    quietguy Guest

    Are you using a bilge pump? I think these would be designed for long
    term running.

    David - who uses a bilge pump for a similar purpsose
  3. quietguy

    quietguy Guest

    Another thought would be one of the big garden fountain pumps - these are
    designed for continuous running

  4. lentildude

    lentildude Guest


    No I found some 12vac pumps not a bildge pump.
    The ac pumps dont have much flow but dont use much current.
    dick smith sells 24v fountain pumps - even they would do. (some
    submersible pumps are 240v.) I am thinking of running them off solar
    and have it pumping whenever there is sun. Might avoid batteries

    I do have a 12vdc bildge pump that chews 10 amps and gives 6m head but
    kills the car batteries if I leave it on more than `15mins or so. I
    want to find
    deep cycle batteries to run this dc pump.
  5. Poxy

    Poxy Guest

    I'd kind of wonder about the overall efficiency of a DC-powered AC pump -
    depending upon what head you're pumping to and what rate you need, I suspect
    a DC pump is going to be cheaper and make better use of available energy.
    Also, depending on the water, bilge pumps are often better able to pass
    solid objects than pond pumps.

    Have you considered trying a PWM speed controller on your existing bilge
    pump to wind back the power consumption?
  6. Geoff C

    Geoff C Guest

    Most cockys use a windmill.
  7. lentildude

    lentildude Guest

    PWM - I might look at an oately kit for a high current pwm but I really
    need the full head 6m to get water from dam to vege patch. PWM might
    reduce current but also reduce head??? even if it drops a few amps
    withPWM still cant use car batteries. Maybe have to go super low tech
    and build a wind powered pump??

    The dcpump has 19mm hose - I was wondering does reducing apeture to
    say 13mm hosing increase head?
    , might buy this

    also this chopped dc circuit might reduce current
    might be able to run an ac pump off chopped dc too!
  8. APR

    APR Guest

    Reducing the cross sectional area of the hose will not increase the head,
    but it may reduce the flow rate because of increased friction through the
    hose. What you need to look at is if the pump is exceeding it's designed
    flow rate, as the power requirement can go up significantly if the designed
    capacity is being exceeded.

    When trying to pump the most water at a specific head with the least power
    consumption pay attention to keeping all hose directional changes on a
    larger radius rather then a small tight radius. If the pump is not a
    submerged type, but has a pickup or suction hose, place the pump as close to
    the surface of the water as possible and keep the suction hose as short as
    possible as pumping efficiency will be increased.

    Here is a link to an article that you may find of interest..
  9. lentildude

    lentildude Guest

    thanks for the comments - yeah I was going to experiement with a 100w
    12/240v inverter but figure I wouldnt be able to run it directly off a
    solar panel. Im thinking the ac fountain pump idea will be useless for
    anything practical at all after researching more.

    \\therfore will stick to dc bildge pump and batteries, solar trickle

    I will try to pump water 6m "above" the dam, to either a water tank
    which will then gravity feed drip irrigation lines or may try to feed
    drip lines directly via a bildge pump but figure there wouldnt be much
    pressure to directly feed dripper after the 6m head.

    and will look at PWM the bildge pump to reduce current (now 12v 10
    amps!) . Perhaps run the pump 30mins day to top up tank that feeds
    drippers. I will be able to move more water in that 30min in a tank
    rather than feeding drippers directly. then let sun recharge
    batteries rest of time. Am looking for good batteries but am on a

    thanks for all the comments!
  10. David

    David Guest

    Why don't you just buy a decent pump. Bilge pumps really don't like
    pumping too much head. I have used a Shurflo pumps, and some of the
    lower power 12V ones draw only 4 amps or so.

    This will pump 8.3L/min, at 7m head, and draw only 4 amps.

  11. Poxy

    Poxy Guest

    As APR said, reducing pipe diameter will just increase friction and reduce
    the head it will pump to, or decrease the flow rate at a given head. If you
    use a PWM speed control, the reduced current will also reduce the height it
    will pump to, but you may find it will still pump to 6m, but with reduced
    flow rate.

    There are things called "solar pumps" designed for pumping to high tanks at
    very low flow rates - I get the impression they are positive-displacement
    pumps and they tend to cost a bomb. One option might be a diaphragm pump,
    like the Shurflo pumps used in sprayers and marine plumbing. Even at reduced
    current, these pumps should still be able to pump to high heads.
  12. lentildude

    lentildude Guest

    Thanks for that last note;
    Diaphragm Pumps seam brilliant - high head, low power, long life.
    that sureflow had 28m head!!! Holy cow!

    Seems perfect candidate to run off a big panel and a maximiser
    and perhaps avoid batteries.
    Pump while sun shines!

    will now look at filters for the inlet as the dam full of tadpoles!

    Thanks for that, will definately invest in a diaphram pump !
  13. Poxy

    Poxy Guest

    That is one catch with those Shurflo diaphragm pumps - they can't tolerate
    any solids being passed (I think it catches in the valves and stops it from
    working) so they need a pretty fine filter on the inlet - you might need to
    use two filters, a coarse block type one over the actual inlet like they use
    for pond pumps, and then a fine mesh filter closer to the pump.

    The other thing to keep in mind is what their duty cycle is - they might not
    like running for a couple of hours straight, although this may be helped by
    running at a lower speed. There's heaps of info around on the Shurflo pumps
    so you should be able to find out something via Google.
  14. lentildude

    lentildude Guest

    Hi, I emailed the pump wharehouse and they dont recommend to use their
    shureflo pumps with a maximiser and solar panel, strange...

    heres their reply


    I do not recommend that you use any 12v DC above ground diaphragm
    pump without a battery - it will fail. "

    I checked a solar retailer and there is a pump 5x the price that is
    used with a maximiser.

    I think Ill try the cheaper $200 pump and risk it..

    Thanks for all the info and advice. Hopefully can make use of this dam
    water as its just evaperating in the hot Ozzie sun.
  15. Why does an AC pump draw "less" current than a DC pump in your
    application? I think it is very obvious that the DC pump is overloaded
    and since it is unable to generate full back EMF it will draw more
    current than it would if it could run full speed.

    By adding PWM to the circuit you can expect to draw more current the
    slower it runs, and though the average power might be less, it won't be
    linear. The thing to avoid with DC motors is stalling them or running at
    near stall speeds as they look almost like dead shorts to the drive circuit.

    If you want maximum efficiency you will need a motor that is rated for
    the job - simple. DC motors work best when they can run at optimum speed.

    To convert 12VDC to 12VAC why don't you use a H-bridge circuit driven
    from a simple micro? Since a transformer is not involved you can do
    simple PWM to simulate a sine wave.

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