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fan speed controller

Discussion in 'Electronic Design' started by [email protected], Jan 9, 2004.

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  1. Guest

    Hi and help

    My problem is I have a strong inline extraction fan pulling air through my
    cooker hood through a filter to remove smells which runs loud and is more
    than adequate for the job. So I want to be able to lower its operational
    speed. My first thought was to wire in a lighting dimmer switch, but was
    told that this would blow the dimmer as the current drawn by the fan would
    be greater than the max current load on the dimmer switch.

    Now I am cheep and when I was told to spend £70.00 on a dedicated fan
    controller I balked, the hood, fan and filter have all been 'recycled' from
    other uses,

    Well can I modify the dimmer switch in some way to enable it to cope with
    the higher power device ( the fan) (450watt motor). or can a simple circuit
    be built to do the job, I would prefer to use a pot to vary the fan speed,
    but would be happy to settle for a 5-6 setting device at say 15% 30% 50% 65%
    85% and 100%.

    When I say simple circuit, I mean simple, I have not picked up a soldering
    iron for a long time, and while I can still remember (I / V =R I have not
    applied this since school.

    Looking about I have seen 500w pots advertised at a huge price, this I
    believe I could just wire into the mains supply, but at probably a higher
    cost than the dedicated device. What I am struggling with conceptually is
    what would such a control circuit actually do? if I used a resistor to drop
    the voltage by half 240 to 120 say, wouldn't the fan then just try to draw
    double the amps through the circuit and run at close to normal speed ?

    Look I understand if you guys think this posting is below you to respond,
    and I fully acknowledge my idiot status in this field, but I have a have a
    go mentality, and if I didn't the lovely shiny purring 27yr old Honda 750
    F1 in my garage would still be a rusty heap.

    Have I bitten off more than I can chew here? I don't think so, I may not be
    able to identify components in a catalogue so quickly, and may well have to
    rely on a few reference texts and when wiring in diodes I will have 2 check
    which is the cathode and which is the anode more than once, hehe, but that's
    half the fun isnt it guys..

    any help and advice appreciated

    Thanks in advance
  2. Luhan Monat

    Luhan Monat Guest

    For this type of problem, I have used light bulbs. A 200 watt lamp in
    series with the motor will cut its speed about in half. You can just
    put in different bulbs to get the speed you want. I used this with
    window 'box fan' motors to make them run super queit.

    This is about a 'low tech' as it gets.
  3. Michael

    Michael Guest


    And it shows: R = E/I
    At least, it did where I studied.
  4. Ross Mac

    Ross Mac Guest

    How about a higher wattage dimmer. That is assuming the motor will run
    reliably at a lower voltage....Ross
  5. Guest

    Thanks 4 pointing out the error,

    Yep ur right , n im wrong, well im not gonna loose any sleep about
    misrecallin an equation after 30 yrs of not even thinkin about it. The fact
    Im in here looking 2 find that someone who has allready done the hard work,
    and is willing to share thier experience should hint that Im a long way off
    actually applying (V/I=R), other than checking, This is a play project,
    after all I can allways go n buy an off the shelf solution which costs less
    than an hour of my time.
  6. Guest

    That's a nice solution, and the cost of a few lamp holders will be pennies,
    and whats more the lights will act as illumination for the cooking area.
    but a 200watt bulb?? a rare animal indeed, but surely of I hook up 4 60watt
    bulbs in series that will do the same thing there about.

    Thanks for your elegantly simple solution
  7. Guest

    Hi Ross

    Thanks for taking an interest, but checking in RS and maplin, high watt
    rated potentiometers are Very expensive, I am treading new ground for myself
    in here, my expertise in a different field completely, The friendly chap in
    our local hardware shop, (Yes we still have one), advised against using a
    dimmer switch, and he had a range, and his reason was that the fan would
    draw to high a current through the switch and burn it out, Now that makes a
    kind of sence to me with my schoolboy recolections, but I could easily be
    confused and be miss-quoting. Its just sparked my interest thats all, I
    would like to have a conseptual undrstanding of what actually is involved in
    doing this, as well as a real world solution in my hands at the end of the
    day. And it would be even better to have a solution that.... OK I could not
    design, but I am confident I could fabricate it.

  8. Tweetldee

    Tweetldee Guest

    Electronic Goldmine has a fan speed controller that may be exactly what you
    are asking for, and is extremely affordable. Surf over to to see the listing
    at Goldmine ($3.95 USD). It is a current production model from the
    manufacturer (Control Resources Inc); see the spec sheet at At that price, you probably
    should buy several, for spares.
    It can be controlled in any of several ways, in your case, a simple 0-5 volt
    signal from a potentiometer across a 5V supply. a caveat, however... you
    didn't say what kind of motor is in the fan you want to control. It may or
    may not be controllable with this type of controller. A little research on
    your part is in order to determine the applicability.
    Hope this helps you.
    Tweetldee at att dot net (Just subsitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  9. Better hook 'em up in parallel with each other for 240watt :) Why not wire
    'em up to a switch so you can select 240watt 180watt etc. ?
    Could you try an old ceiling fan controller of the choke type ?
  10. Guest

    Thanks Tweedldee ur a star. A handfull of simple components (ones i
    understand), an off the shelf product at a bargain price, (with very clear
    documentation) and away we go. I have just orderd a couple of those
    controlers, and I can even play with the temp control option, how about an
    automatic cooker hood extractor eh? cooking raises the temperature and the
    extractor fan turns on, now that would be flash. Though Im probably racing
    ahead a bit there...

    and yes the fan is suitable for this type of control, a valid question

    Thanks again

  11. Tweetldee

    Tweetldee Guest

    Glad to have helped.. In fact, I had seen those controllers in Goldmine's
    catalog a few weeks ago, and meant to return to order a couple, but had
    forgotten about it. Your question helped refresh my memory. I have now
    placed an order for a couple of them too.
    Tweetldee at att dot net (Just subsitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  12. Quack

    Quack Guest

    fan speed related to temperature ... I'd rather it run according to
    smoke density, maybe open up a smoke alarm and see how they work.. :)
  13. Tweetldee

    Tweetldee Guest

    I question the usefulness of a smoke alarm type circuit for controlling fan
    speed, as the OP wanted. A smoke alarm is a bang-bang device,,, either
    full on or full off. The OP wanted a variable speed fan controller. Smoke
    density would probably prove to be unreliable as a controlling phenomena
    also, since, as can be attested by many barbequers, a relatively low heat,
    along with the right quantity and type of drippings can produce huge
    quantities of smoke.
    Tweetldee at att dot net (Just subsitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  14. Ben Bradley

    Ben Bradley Guest

    Also, a boiling pot of water will produce no smoke, but will make a
    lot of steam. A burner running with nothing on it will make a lot of
    heat, but no steam or smoke. A "good" controller would measure
    temperature and humidity as well as smoke. It should also be
    adjustable for sensitivity to each of these.
    I think a manual control right next to the on-off switch on the
    exhaust hood (or most convenient location for the chef) would be best.
    Mostly it would be turned to the lowest effective speed. And if you
    overcook some fish you can crank up the fan to high to keep the smell
    from going elsewhere.
  15. I read in that Ben Bradley <[email protected]> wrote (in <[email protected]
    com>) about 'fan speed controller', on Sat, 10 Jan 2004:
    Au contraire; the object is to make the smell go elsewhere as soon as
    possible. Unless the fan revolves the wrong way, of course.
  16. N. Thornton

    N. Thornton Guest


    My favourite simple motor speed control is a capacitor, use same way
    as a bulb. Its small, doesnt need replacing and uses no energy. The
    only thing is you have to calculate the value: if you just pick and
    play you'll soon hit the value that makes the motor go bang (LC

    Regards, NT
  17. Tweetldee

    Tweetldee Guest

    AMEN, Brother!!!!!

    Tweetldee at att dot net (Just subsitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  18. Reg Edwards

    Reg Edwards Guest

    How about a series resistor or choke?

  19. Guest

    Hi NT,

    Ok I have to ask, just how do you go about calculating the capacitor values
    that will not blow up the motor then?

    This is my first foray into the field of electronics beyond changing a fuse
    or when I substituted the blown rectifier on my bike with an RS component
    and a heat sink costing penies when the official component was costed at

    I'l not be offended by a pointer to a basic text, in fact would welcome one,

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