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lowering voltage in extension lead - potential hazards?

Discussion in 'Electrics UK' started by mrmisior, 18 Jul 2019.

  1. mrmisior

    mrmisior

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    Hi
    I am wondering if lowering voltage in an extension lead can cause potential hazards?

    I want to control the speed of an AC 240V motor. Actually an array of 4 of them.
    Each is fitted with standard UK 3 pin plug. They are earthed to their metal casing.

    Found this voltage regulator on ebay:

    https://www.ebay.co.uk/itm/AC-220V-...474438&hash=item261f0c372e:g:kC8AAOSwxGBc~12R

    I would have to replace the plug with UK one.
    It comes with single socket for a single plug. What if I plug in a 4 way extension lead into it and populate it with my 4 fans?

    And dangers?
    Thanks in advance.
     
  2. bernardgreen

    bernardgreen

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    That voltage regulator. It looks very dubious quality. The potential hazards are in that voltage regulator.
     
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  3. JohnW2

    JohnW2

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    As I imagine BAS would probably have pointed out ....

    upload_2019-7-18_19-5-0.png

    ... not to mention (as the OP points out) ...

    upload_2019-7-18_19-6-41.png

    Kind Regards, John
     
  4. Nozzle

    Nozzle

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    Not only that, depending on the type of motor you want to control, it might not even respond to voltage control. They're not all wound for it.

    Nozzle
     
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  5. echoes

    echoes

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    What sort of a.c. motor?

    That piece of kit may be suitable for certain applications, but speed control of a.c. motors is not straightforward.
     
  6. Notch7

    Notch7

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    What sort of 3 pin plug is that? -not come across that before (n)
     
  7. SFK

    SFK

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  8. conny

    conny

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    And you would need to change the socket on the controller to accept your standard 13A motor plug.

    As said above, not all single phase motors are wound for voltage control. You could very easily burn out the start winding, destroy a start capacitor and cause a few other problems.

    If you posted what type, size, application etc the motors are, there may be someone on here who could point you in the right direction for the right, (safest), equipment.
     
  9. mrmisior

    mrmisior

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    it is a pc fan
    COMAIR ROTRON AC CLE3T2 020191 254x254x89 mm 25.4cm fan AC 220V
    very little info in the datasheet.
    Electrical Specifications Rated Voltage: 230 VAC AC Frequency: 60 Hz Power Supply: 60.0 Watts Line Current: 0.25 Amps Locked Rotor Current 0.70 Amps Nominal Speed: 1650 RPM

    Anyway, my concern is the lowered voltage in the extension lead. Would this not affect the RCBO operation in a fault condition? its a TT system.
     
  10. JohnW2

    JohnW2

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    Unfortunately, I suspect that may well not be the case (that looks rather like a 'one size fits all' socket)!

    Kind Regards, John
     
  11. winston1

    winston1

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    Your motor is not even suitable for UK 50Hz supplies!

    Interesting to know what that voltage regulator is. Initially looks like a variac, but no way could a 4kW variac be that small in size or price. So must be some form of triac control with almost certainly a horrendous waveform. Forget about it.
     
  12. conny

    conny

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    Actually a 60Hz device running on 50Hz will perform at approximately 20% less than the rated figure. So it would work but not be as efficient.
    As for controlling the speed when it is running at 20% less then that throws another problem into the equation.
     
  13. Nozzle

    Nozzle

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    I wouldn't go as far to say it's unsuitable for UK supplies, just that it will run more slowly. (You can even see the 50Hz line on the chart at http://www.comairrotron.com/content/caravel-ac-cle3t2-19020191a)

    Given the specs provided (60Hz rating and the nominal speed of 1,650 rpm) you can assume it's a squirrel cage induction motor, broadly synchronous. You cannot alter the speed of it by voltage, it would need an inverter.

    I write "broadly synchronous" as its speed WILL vary with load, as it's the difference between line speed and field speed that produces the torque.

    That type of controller is for a "universal" motor.

    Nozzle
     
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  14. mrmisior

    mrmisior

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  15. Nozzle

    Nozzle

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    Very cheap, surprisingly cheap, might-set-your-house-on-fire kinda cheap.

    Plus check out the comments section - there's a claim it's not actually an inverter.

    Nozzle
     
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