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New lamp dimmer application?

Discussion in 'Electronic Repair' started by default, Feb 4, 2008.

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  1. default

    default Guest

    I was at the hardware store shelling out $20 for an "infinite range
    control." It is a proportioning control for an electric range burner.
    It is primitive. A small 3 W heating element warms a bimetallic
    leaf which moves a set of contacts, which opens the connection to the
    range element and modulates the power.

    I'm thinking it is stupid to keep replacing these things . . . I go
    through one a year and its a hassle to change out or repair a broken
    one.

    What's the consensus on getting an ordinary $3 lamp dimmer and putting
    a 40 amp triac on it and using that for element control? Anyone see
    why it shouldn't work or what to look, look out for?

    I've got a half dozen 40A 600 V triacs already mounted to heat sinks
    that I got for free. Plan A: would be to just open the lamp dimmer
    and wire the Triac in place of the one inside, and mount it outboard
    on its heatsink. Perhaps changing the size of the phase shift
    resistor to accommodate 240 instead of 120.

    Plan B: But how about using the 120V lamp dimmer as-is? I would just
    use it to trigger the heatsink mounted triac. Any idea if that
    could/should work?

    Any downside to using a phase control element instead of
    proportioning? Would it cause my power bill to go up?

    I figure I could do it safely.
    --
     
  2. default

    default Guest

    The range is old and I use it a lot - cooking and beer making are
    hobbies. That last can be hard on ranges.

    AND I want an excuse to tinker with it.


    --
     
  3. Ecnerwal

    Ecnerwal Guest

    If you go through one a year, then something is wrong with your range,
    or the power supply in your house. Our range must be 30+ years old, and
    I know for a fact that it has not needed any of these in the past 13
    years, if ever.
     
  4. James Sweet

    James Sweet Guest


    Try it, see what happens, most range burners are 240V which may or may not
    be ok for the dimmer, but so long as you keep an eye on it I don't think
    anything too bad will happen.
     
  5. Ecnerwal

    Ecnerwal Guest

    As it happens, I make beer on mine. Invested in a "canning element" 13
    years ago, put a 10 gallon pot on there and boil 8 gallons or so of wort
    down to 5, no problems with the range at all in 13 years. Catching the
    drips the exhaust fan can't keep up with and cleaning everything to suit
    me before I get started is more of a problem. The range, and the range
    controls, have had no trouble at all with this...
     
  6. N Cook

    N Cook Guest


    Add a snubber over the triac ?
     
  7. default

    default Guest

    Well, I'm not looking for reasons why I shouldn't do it, but how to do
    it.
    --
     
  8. James Sweet

    James Sweet Guest


    Sounded like you already had it figured out. Replace the triac with the
    bigger one, upgrade the wiring between the load and MT1 and MT2 accordingly
    and give it a go. You'll want a mechanical on/off switch as well, the one
    attached to the dimmer pot will be too small.
     
  9. And, when you test/use it -- keep one hand in your pocket.
     
  10. whit3rd

    whit3rd Guest

    Not going to work, I suspect. The 'triac' in a light dimmer is
    actually a 'quadrac', which has a builtin trigger device, and isn't
    readily available in larger sizes. Phase control like
    in a light dimmer makes for non-flickering illumination.

    But, you don't need any of that; the problem is just that
    long duty wears out the switch contacts, not that the
    few-seconds-on/few-seconds-off is a bad match for the
    heater interface. Your options are many: wire the
    replacement to a solid-state relay instead of directly to
    the load, or use an industrial-grade furnace controller
    (put a thermocouple sensor in your cauldron).

    I have some mercury relays in my junk box that would
    give decades of service without a problem. Even simple
    contactor relays, if you use appropriate snubbers (I like
    surge-protector varistors for this duty) will last a long time
    compared to a consumer stove control.
     
  11. James Sweet

    James Sweet Guest

    Not going to work, I suspect. The 'triac' in a light dimmer is
    There may be some like that, but all the light dimmers I've opened have a
    diac triggering a standard triac. A lot of times a lamp will fail and short
    the triac, so I've replaced them from time to time with whatever I had on
    hand.
     
  12. Ross Herbert

    Ross Herbert Guest

    ::>
    :> :> >I was at the hardware store shelling out $20 for an "infinite range
    :> > control." It is a proportioning control for an electric range burner.
    :> > It is primitive. A small 3 W heating element warms a bimetallic
    :> > leaf which moves a set of contacts, which opens the connection to the
    :> > range element and modulates the power.
    :> >
    :> > I'm thinking it is stupid to keep replacing these things . . . I go
    :> > through one a year and its a hassle to change out or repair a broken
    :> > one.
    :> >
    :> > What's the consensus on getting an ordinary $3 lamp dimmer and putting
    :> > a 40 amp triac on it and using that for element control? Anyone see
    :> > why it shouldn't work or what to look, look out for?
    :> >
    :> > I've got a half dozen 40A 600 V triacs already mounted to heat sinks
    :> > that I got for free. Plan A: would be to just open the lamp dimmer
    :> > and wire the Triac in place of the one inside, and mount it outboard
    :> > on its heatsink. Perhaps changing the size of the phase shift
    :> > resistor to accommodate 240 instead of 120.
    :> >
    :> > Plan B: But how about using the 120V lamp dimmer as-is? I would just
    :> > use it to trigger the heatsink mounted triac. Any idea if that
    :> > could/should work?
    :> >
    :> > Any downside to using a phase control element instead of
    :> > proportioning? Would it cause my power bill to go up?
    :> >
    :> > I figure I could do it safely.
    :> > --
    :>
    :>
    :> Try it, see what happens, most range burners are 240V which may or may not
    :> be ok for the dimmer, but so long as you keep an eye on it I don't think
    :> anything too bad will happen.
    :>
    :>
    :
    :
    :Add a snubber over the triac ?

    Probably not required since the load is purely resistive.
     
  13. Ross Herbert

    Ross Herbert Guest

    :I was at the hardware store shelling out $20 for an "infinite range
    :control." It is a proportioning control for an electric range burner.
    :It is primitive. A small 3 W heating element warms a bimetallic
    :leaf which moves a set of contacts, which opens the connection to the
    :range element and modulates the power.
    :
    :I'm thinking it is stupid to keep replacing these things . . . I go
    :through one a year and its a hassle to change out or repair a broken
    :eek:ne.
    :
    :What's the consensus on getting an ordinary $3 lamp dimmer and putting
    :a 40 amp triac on it and using that for element control? Anyone see
    :why it shouldn't work or what to look, look out for?
    :
    :I've got a half dozen 40A 600 V triacs already mounted to heat sinks
    :that I got for free. Plan A: would be to just open the lamp dimmer
    :and wire the Triac in place of the one inside, and mount it outboard
    :eek:n its heatsink. Perhaps changing the size of the phase shift
    :resistor to accommodate 240 instead of 120.
    :
    :plan B: But how about using the 120V lamp dimmer as-is? I would just
    :use it to trigger the heatsink mounted triac. Any idea if that
    :could/should work?
    :
    :Any downside to using a phase control element instead of
    :proportioning? Would it cause my power bill to go up?
    :
    :I figure I could do it safely.

    Ideally, heater elements with triac switching should employ zero-crossing power
    control.

    This Philips (now NXP) application note shows in 6.2.3 the use of a dedicated
    time proportional triac controller ic (TDA1023) for heater element control. In
    your case the circuit of Fig.14 would be required.
    http://www.nxp.com/acrobat_download/applicationnotes/APPCHP6.pdf
     
  14. Bob Monsen

    Bob Monsen Guest

    Triacs have different requirements for current at the gate. It's possible
    that your 40A triacs may need more current to trigger them than a dimmer
    will supply. However, why not give it a try?

    Regards
     
  15. default

    default Guest

    The lash up works. I can control a 120 VAC lamp with the dimmer
    triggering the external triac. So at least it triggers on 120.

    Before it goes into the range, I need some mounting washers for the
    triac. These are bolted to a bare heatsink and I'd rather insulate
    the triac than insulate the heatsink.

    Still want to tinker a bit to see if the bare, out of the box, dimmer
    can be made to work the triac with only the two wires they supply.
    --
     
  16. James Sweet

    James Sweet Guest

    Wire it up on 240 powering a couple of 200-300W incandescent bulbs in
    series, if that works then it should work fine with the burner.
     
  17. default

    default Guest

    I'll give that a try.

    My current interest is to see how to get a lamp dimmer (pure out of
    the box, so to speak) to trigger a triac. It may be unnecessary, but
    there's some crud on the inside of the stove chassis; mostly rust and
    condensed oil - not too bad but what one might expect from a 30 year
    old, well used, kitchen range.

    Anyhow, my reasoning goes like this - I see the stuff behind the panel
    and figure that the potentiometer in the dimmer might just die from
    crude ingestion (or significantly shorten its life).

    I don't know about you, but I hate having to EVER repair something I
    designed and built . . . If the $3 lamp dimmer can be considered a
    component only, and work the secondary triac that seems better to me.

    I'm still not ready to do any hardcore installation - no triac
    insulators and (one of the things I overlooked) no suitable "hard"
    means of breaking power to the element . I think it was you who said
    that - thanks. So I need a DPST switch capable of 10 amps ( and
    another hole through the porcelain finish to mount it)

    This is way more fun than just going to the hardware store and
    shucking out money for another ancient design range control.

    I have one burner that doesn't work now, so I can apply it as soon as
    I trust it. It hasn't worked for years but that's immaterial.
    --
     
  18. default

    default Guest

    The idea of getting a hardware store lamp dimmer and mating it to a
    higher voltage higher power triac could have some commercial
    implications. Especially if it can be done without additional
    circuitry.

    Most of the old stage lighting and centrifuge (industrial) stuff I've
    seen. A: they want you to buy the carbon pile/rheostat or variac to
    "fix it" and that costs hundreds or thousands of dollars. Or their
    "updated" controller that only cost hundreds++.

    I'm guessing but the one or two theater's left with rheostat controls
    belong to Catholic schools or very old theaters.

    Oh. Forget that stuff, I just want an option for my range.


    --
     
  19. whit3rd

    whit3rd Guest

    Two things might be worth worrying about: first, the trigger
    of the new triac might be incomplete or unreliable (might
    miss some cycles); if you have an oscilloscope, it would
    be worth checking this. The current that triggered the old
    triac could trigger the new one only 90% of the time, or could
    miss negative half-cycles, or misbehave in lots of ways
    that wouldn't fail the lightbulb test.

    Second, triacs have a dI/dt limit, so a heavy load should
    always be turned on/off at zero crossings (also for RF noise,
    but that's not tihe big issue). The failure mode if your
    phase-control trigger does too much switching at full
    current from a dead stop, is short circuit of the triac.
    Beware scorched wort! Solid state relays aren't terribly
    expensive, and include the desirable zero-voltage-switching.
     
  20. Mark

    Mark Guest

    I'd worry about 2 things..

    1)lots of EMI generated from 50 Amp pulses floating around

    2) if the triac shorts your burnner will be on full tilt and may be
    dangerous if you are not there, may want to include a mechanical
    overtemp saftey device. The triac could decide to short even when
    the burner is not in use when you are not home etc......

    Maybe triac + mechanical overtemp saftey + mechanical on/off


    The other failure mode I have seen is that the burner shorts to its
    outer shell and this is very bad becasue you can't turn it off
    because the burner stays activated by one side of the 240 line unless
    you have both sides of the line switched...

    take care

    Mark
     
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