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AC Voltage Step-up

Discussion in 'Beginner Electronics' started by Gordon, Nov 1, 2003.

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  1. Gordon

    Gordon Guest

    My outboard boat engine has an AC auxillary output for onboard 12 volt
    use (so the manual states), however I have noticed the voltage varies
    between 8 and 19 volts AC depending on idle to full revs. As most of
    my boating is with low engine revs I am concerned that I'll never
    reach 14.7 volts DC (after AC to DC)for battery charging.
    So I am considering stepping-up the AC using a transformer and then
    using a voltage regulator to limit the DC to 14.7V accepting that the
    available current will be reduced.
    Two questions:
    1) Is there a smarter way of doing this?
    if not, then
    2)How well would a standard 50Hz transformer perform over a frequency
    range of 25 to 250Hz? I'm considering a 115V to 240V converting
    transformer for this.

    Any help would be gratefully received!


    Gordon Jago.
  2. scada

    scada Guest

    The AC output may be adequate after it is converted to DC. The AC you are
    measuring would be "RMS", to calculate the DC equivilant you would use: RMS
    * 1.414 therefore at 10.5 VAC the full wave rectified DC would be 14.87V. If
    you can get your Rev's up to give that voltage you should be OK. If not try

    You could take the AC Voltage and put it through a "DC Voltage doubler
    circuit" then regulate the output to 14.7 VDC. Or rectify the AC to DC and
    use a DC to DC converter. A 50 HZ transformer can not be used for 25HZ, it
    will burn up.
  3. Gordon

    Gordon Guest

    Thank you for the prompt response and also for the reminder on RMS
    from my old school physics theory!. I was wondering if I was trying to
    fix a problem that didn't exist!

  4. Guest

    I don't agree. A transformer will work fine on half the frequency but
    there will be a decrease in performance. The power output will drop.
    If you still need the same power you need a bigger transformer to
    compensate for the losses. At 250hz the performance will increase but
    depending on the core material there will be a limit.

    Regards Simon
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