Variable speed pump for shower

Discussion in 'Electronic Projects' started by eem2am, Oct 18, 2010.

  1. eem2am

    eem2am VIP Member

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    Hi,

    Do you have any suggestions for a motor and a variable speed drive combination for a pump for a domestic shower?

    We already have a fixed speed AC motor as a pump, but now we want to do variable speed drive.
    (so people can have variable pressure shower water, as they choose)
    Our fixed speed motor has a fan, so we cannot use this motor with a variable speed set-up, as the fan would spin too slowly at the lower pumping settings.

    We also want to do it cheaply, so am i right in saying that we are looking at a thyristor drive?

    We are thinking of say a 3-speed drive, or in fact we may consider a more widely variable speed drive, if its not too expensive.

    I believe Triac drives are out becuase of the non-symetric nature of triacs.(?)
    eem2am, Oct 18, 2010
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  2. eem2am

    KMoffett VIP Member

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    Wouldn't a simple valve on the water line to control flow be much cheaper and easier than trying to add a variable speed pump/controller?

    Ken
    KMoffett, Oct 18, 2010
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  3. eem2am

    shrtrnd VIP Member

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    I'm figuring your pump IS your water flow for the shower, otherwise KMoffett's idea is best.
    Motor control is usually accomplished with SCRs (Silicon controlled Rectifer). But it controls speed by driving the motor during part of the sine-wave of an AC voltage. So
    changing the length of the SCR 'on' time, causes the speed of the motor to increase or decrease. Also But;
    One SCR only works on the positive OR negative slope of the waveform. So you need
    two SCR's, one to conduct during the positive going slope, and the other to make use of
    the negative going slope of an AC waveform.
    shrtrnd, Oct 18, 2010
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  4. eem2am

    eem2am VIP Member

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    hi
    i like your thyristor idea.....

    would you agree that Triac's are of limited use here because of their non-symetriacl nature...also, you can't be sure they'll commutate off at the zero crossing....and you can't be sure how long after triggering that they'll switch on....

    eg the following triac circuit for motor control
    http://i52.tinypic.com/23u2xxu.jpg


    by the way, the motor to be controlled is this:
    Detailed datasheet of pump = Part No 46407
    http://www.stuart-turner.co.uk/media/13214-Showermate-Standard-Twin-Datasheet.pdf
    eem2am, Oct 21, 2010
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  5. eem2am

    shrtrnd VIP Member

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    Looks like your in the UK.
    I would not use a Triac in your application.
    SCR's are commonly used for motor control applications.
    Thyristors running at 50hz would not cause you to be concerned about their on and off times, ... but Triacs are not commonly used for motor control.
    shrtrnd, Oct 21, 2010
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  6. eem2am

    KMoffett VIP Member

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    I'm a little confused by your answer. SCRs and TRIACs are both thyristors. SCRs can conduct only on one half of the AC voltage cycle. TRIACs can conduct on both haves. Either can be used for controlling the right kind of motor. Series wound or universal motors (brush-type) work well with SCR or TRIAC controllers. This does not include induction motors...like the OP linked. Induction motor's speed is determined by the line frequency. They do not work well with voltage phase control. Induction motor speed controllers are VFD, variable frequency drives. And, these are usually only used on 3-phase motors.

    Still looks like a simple valve would solve the problem. That's what all plumbing hooked to mains water supplies use.

    Ken

    Ken
    KMoffett, Oct 21, 2010
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  7. eem2am

    rob_croxford VIP Member

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    What you are talking about is phase control. I would not suggest phase control as you will get all sorts of nasty harmonics. Another method that can be done using relativly the same technique (however removes the problem of harmonics) is burst fireing. Burst fireing is where you control the power by fireing a certain number of full wave cycles at a time. For instance you could run your control over 100Cycles with full power being 100 cycles on and 50% power being 50cycles on/50 cycles off.

    It is basically the same idea as phase control where you use the zero crossing points for timing and fireing however rather than chopping up the wave form (this is what causes the harmonics) you leave the waveform fully intact and only have it on for full cycles.

    If using this method you should use a traic as you will want the AC to remain "on" even if it crosses through a zero crossing point.
    rob_croxford, Oct 22, 2010
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  8. eem2am

    eem2am VIP Member

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    -sorry about this.

    That motor above is one of ours but its not the one for which we will be having the VSD.

    The one that needs the VSD does not have any ID on it, other than on the enclosure which says "220-230V ,250W, 50Hz IPX4".

    It has brushes.

    on the laminations is marked

    "645064
    230/50
    01405"

    sorry about this,

    my initial job here was just to make the SMPS....but the VSD has just been thrown in aswell, and the people who chose this motor etc have now left the company.
    eem2am, Oct 22, 2010
    #8
  9. eem2am

    KMoffett VIP Member

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    KMoffett, Oct 22, 2010
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