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How to go from 1200w to 600w???

Discussion in 'Hobby Electronics' started by K Dog, Aug 30, 2003.

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  1. K Dog

    K Dog Guest


    I have a small fan heater which I am going to use to design my own fruit
    dehydrator (on of those food dehydrators that people use dry fruit and beef
    jerky etc). I have the fan and heating mechanism (the fan heater has
    everything I need for that) and a 0 to 70.C thermostat which I will use the
    control the temperature.

    I have only one small problem. The wattage is just too high, at 1200w, I'd
    cook the fruit instead of drying it. I only need 600w. How would I adjust it
    to reduce it to 600w? I will note that there are three settings on this fan
    heater, one is 2400w, one is 1200w and the other setting just uses the fan.

    Thank you,

  2. K Dog

    K Dog Guest

    1. A triac dimmer set to 50% duty cycle - pretty cheap.

    I didn't think dimmers could take a load of 1200 watts and that they'd just
    burn out and melt if they took too big a I wrong?
    Sounds interesting.

  3. Phil Allison

    Phil Allison Guest

    ** Huh ? I did not say or mean a $10 wall plate job from K-mart.

    Something just a bit bigger will do you - I built a heat / fan control
    for a fan heater for myself with a simple 15 amp triac / diac dimmer cct -
    no problems.

    ............. Phil
  4. Simple option. Put a diode in series with the heating element. It'd only
    conduct on half the cycle so would halve the power output giving 600 on low
    / 1200w on high. You'd need a diode with at least a 400V 5A rating.

    Leave the fan wired up to the full 240v (i.e. before the diode).
  5. Phil Allison

    Phil Allison Guest

    ** But a **very nasty** one.

    Put a diode in series with the heating element. It'd only

    ** Doing that draws DC current from the AC supply and is *not legal* for an
    appliance that is used continuously.

    One side effect is creating a DC offset on the supply of several volts
    forcing larger power transformers on the same cct into core saturation -
    particularly any toroidal ones - with consequent high losses and loud
    humming noise.

    Another side effect is anodic ( or cathodic ? ) corrosion to AC system
    ground stakes and earthed conductors that connect to the neutral.

    This crude idea was in fact the first I thought of but **deliberately**
    did not include in my list of 5.

    ............ Phil
  6. Spajky

    Spajky Guest

    rewire those 2x1200W heaters to serial connected inside: even cheaper!
    -- Regards, SPAJKY
    & visit -
    Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
    E-mail AntiSpam: remove ##
  7. Rod Speed

    Rod Speed Guest

    Complete and utter drivel.
    Very bloody unlikely indeed.
    Your problem. And I bet you're lying.
  8. Rod Speed

    Rod Speed Guest

    It aint.
    Its not that uncommon if the power required isnt that high.
  9. Phil Allison

    Phil Allison Guest

    ** Robot nonsense.

    ** Robot nonsense.

    ** Robot nonsense.

    ............ Phil
  10. Phil Allison

    Phil Allison Guest

    ** AS3100: 3.12 DC Component from AC normal use.

    " Equipment shall be designed so that in normal use the value of any direct
    current in the equipment neutral will not contribute uduly to the failure of
    the installation earth electrode by corrosion. "

    "The permissable direct current in the equipment neutral shall not
    xceed -

    (i) for equipment considered as operating continuously 5mA or

    (ii) for other than continuously operated equipment ( 5 x 24 ) / t
    mA where t = daily average time in hours."

    " The maximum value of direct current permited in the neutral is 1.4 amps
    which could be applicable to equipment with assesed daily average operating
    time of 5 minutes or less. "

    reduction but we were only talking

    ** I have a 1600 watt hot air gun ( Black and Decker made in UK) which
    uses a diode for half power - when in use the AC supply develops a 1.5 volt
    DC offset. Toroidals of 225 VA or greater go into near full saturation and
    other transformers on the same AC circuit growl audibly.

    If an appliance has a mains tranny then no DC current in the AC
    supply is possible.

    ................ Phil
  11. Rod Speed

    Rod Speed Guest

    Some completely unemployable pathetic
    excuse for a bullshit artist claiming to be
    Phil Allison <> desperately attempted
    to bullshit its way out of its predicament in message
    and fooled absolutely no one at all. As always.

    No wonder its completely unemployable.
  12. Phil Allison

    Phil Allison Guest

    ** Yes, but robots are such narcissists they only read science fiction.

    ........... Phil
  13. Rod Speed

    Rod Speed Guest

    And its an approach thats been used for many years too.
  14. Phil Allison

    Phil Allison Guest

    ** Ahhhh, so the Robot charges his battery banks directly with half
    wave AC mains.

    Typical of the rusty cheapskate

    .......... Phil
  15. Rob Judd

    Rob Judd Guest

    You could use an autotransformer to supply the fan heater. But a better
    solution is to use refrigerated drying, which is a lot cheaper to run.

    I'll leave the research to you.

  16. Bristan

    Bristan Guest

    Put a diode in series with the heating element. It'd only
    ........Interestingly, two commercial appliances I recently pulled apart both
    used this method of power reduction.
    A small hair dryer for the low heat setting and one of those room
    deoderisers which contain a small heating element to evaporate the
  17. Phil Allison

    Phil Allison Guest

    ** Did you see the word "continuously" in my post above ????

    Did you read the sections I quoted verbatim from AS3100 in this
    thread ?????

    and one of those room

    ** See above info - learn something.

    .............. Phil
  18. Bristan

    Bristan Guest

    well I don't think the original posters requirement was for "continuous"
    operation either which makes your rule quoting not applicable.

    Yes ,see above

    Sounding defensive there....
    What am I supposed to learn ???,

    I merely made the observation that these commercially available items, which
    one would assume had approval , used a method which you claim to be illegal
    for an application similar to that required by the original poster.
    Either they are wrong or you are.
  19. Phil Allison

    Phil Allison Guest

    ** Bullshit - the app was a continuous one.

    ** See above.

    ** What a goose you are.

    ** Wrong.

    See the 1.4 amp DC 5 minute limit ?

    The OPs app would exceed it if done by a diode.

    ** A third possibility exists - that you are a fool.

    ........... Phil
  20. Bristan

    Bristan Guest

    so your one of those............
    Bullshit and abuse when defeated.

    Ta Ta !!!
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