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Resister in series to decrease wattage

Discussion in 'General Electronics Discussion' started by abk111, Dec 13, 2010.

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  1. abk111


    Dec 13, 2010
    Hopefully this is a simple question for all you seasoned electronics buffs.
    Using a 220 V 2500 W water heater element in a 110 V line.
    As is, it heats much faster than needed and uses about 1250 W.
    Wanting to decrease the current through this line to be able to use a lighter duty thermostat,
    reduce surges, reduce element temperature, reduce total line current, and save electricity (to about 600 W usage).
    Could one add a resistor in series with this element to decrease the current and watts used?
    Or not that simple?
    Thanks for your expertise.
  2. LTX71CM


    May 23, 2010
    You could but a resistor would dissipate that energy... as heat. While it is that simple to add a resistor, it is not the solution you want.
  3. abk111


    Dec 13, 2010
    >>not the solution you want
    So, can't use the above water heater element?
    Or some other solution with it?
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Do you have 2 of these elements?

    Placing 2 in series will halve the total dissipation and all the energy will go into the the load (the water)

    Alternatively, if you place a diode in series with it, it will only conduct for one half cycle of the mains and that will halve the total dissipation (but will do nothing for the maximum current)

    Also beware using the diode idea because the DC potential that will exist across the heater winding may well accelerate any corrosion the element might suffer.

    This was a quick and dirty way of making soldering irons operate at half power.

    The major issue is finding a 200V diode that can carry over 10A and heatsinking it in a way that you won't get electrocuted by it.
  5. abk111


    Dec 13, 2010
    Thanks (*steve*),
    Could get a second element, but that solution wouldn't work here.
    And sounds like the diode solution wouldn't work either.

    Maybe a transformer?
    Would a transformer also give the energy savings?
    Any ideas for locating a 110 V to say 60 V transformer?

    Also trying to locate a smaller water heating element.
    Any other ideas?
  6. Resqueline


    Jul 31, 2009
    A diode would be perfect here, but depending you might experience a slight flicker in your house lighting when the element is on. I wouldn't worry about corrosion issues.
    Cooling/mounting issues on the other hand must of course be addressed, but standalone air-cooled 10A diodes exists.

    An 82V transformer could be used but would be big, heavy, & very expensive. A 690uF (motor) capacitor could be connected in series but would also be big & expensive.

    But I'd rather go for a (triac) lighting dimmer rated at (at least) 10A / 1.1kW. The only side effect here could be interference on AM radios in the vicinity.
  7. abk111


    Dec 13, 2010
    More great ideas!
    Reading up on triac lighting dimmers and that does sound perfect.
    Thanks Resqueline.
  8. David Sparks

    David Sparks

    Jul 12, 2012
    There are solutions for your delema abk111, but as mentioned above, none of them are cheap or easy. You could buy a buck transformer as mentioned above, but for the same price a SCR controller (with ac output) would run much cooler and give you the option to adjust the power levels, hence the temperature. A resistor or variac is out of the question, as they would create the same heat your are trying to avoid!
  9. davenn

    davenn Moderator

    Sep 5, 2009
    Hi david

    you do realise how old this thread is ? ;)
    it hasnt been active for some 2 years :)

  10. David Sparks

    David Sparks

    Jul 12, 2012
    Oop's. Will check date's from now on.
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    The guy probably replaced it with a solar heater by now. :D
  12. David Sparks

    David Sparks

    Jul 12, 2012
    Not unless his luck changes - lol. It seemed like such an absurd problem anyway.:rolleyes:
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