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Thread: Variac

  1. #1
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    Default Variac

    Looing at two variacs for sale. One is 500 watt and the other is 2000 watts. What does the 2000 watt do that the 500 watt doesn't? Thanks guys.

  2. #2
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    Quote Originally Posted by Proudpappy View Post
    ... What does the 2000 watt do that the 500 watt doesn't? ...
    It can handle 1500 watts more power (i.e. supply more current).

  3. #3
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    Quote Originally Posted by Proudpappy View Post
    Looing at two variacs for sale. One is 500 watt and the other is 2000 watts. What does the 2000 watt do that the 500 watt doesn't? Thanks guys.
    +1 with RichR and it will also lighten your wallet more.
    Work hard play hard

  4. #4
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    Plus, the surge when turning on the bigger one will be bigger, and household breakers may not like it.

    That all said, the bigger one is just as good at low power. And it has lower impedance, it introduces less voltage drop, allowing the output to act more like the real power line. So it has advantages aside from pure handling of more current.
    1601

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    Hashim Khan

  5. #5
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    Quote Originally Posted by Proudpappy View Post
    Looing at two variacs for sale. One is 500 watt and the other is 2000 watts. What does the 2000 watt do that the 500 watt doesn't? Thanks guys.
    What is the intended purpose, a dedicated use or general purpose?
    If the latter, go with the larger one.
    Max.

  6. #6
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    Default variac

    was thinking about using one to control treadmill motor

  7. #7
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    Quote Originally Posted by Proudpappy View Post
    was thinking about using one to control treadmill motor
    How much do you weigh? If you haven't seen your feet in awhile then you'll definitely want the 2000W transformer
    Work hard play hard

  8. #8
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    Quote Originally Posted by Proudpappy View Post
    was thinking about using one to control treadmill motor
    I'm guessing the purpose is not for a actual T.M.?
    All you would need is a 50amp Bridge rectifier assuming the normal DC brushed motor..
    An actual surplus drive might be a better option.
    Max.
    Last edited by MaxHeadRoom; 08-09-2018 at 01:45 PM.

  9. #9
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    With the bridge rectifier it will run the motor, but with less speed regulation under load than you would get with a controller like KBIC or the like.

  10. #10
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    A Variac is a variable auto transformer. That means it has only one winding which serves as both the primary and the secondary windings. The primary is usually fed in on two fixed terminals, a neutral and a hot. The output is taken from the neutral and from a rotating brush that travels across the windings. That brush can usually travel from the zero Voltage point (at the neutral connection) to some distance past the hot input. So it can deliver any Voltage from zero to 125 to 150 percent of the input Voltage or even more.

    A 2000 Watt unit can handle more power than a 500 Watt unit. But there will also be a current rating for that winding and power equals Voltage X current. So at low Voltages you may reach the current limit before you reach the power limit, perhaps a lot sooner and your 2000 Watt unit may only be able to deliver 100 Watts or less. At higher Voltages the power rating will take over as the limiting factor. You need to read the spec sheet carefully, but in general it should be able to handle the rated power at the one to one point where the output Voltage equals the line Voltage.

    What will the 2000 Watt one do that the 500 Watt one will not. Well, it will allow you to control larger motors. Both of them will handle a motor that consumes 500 Watts, at least up to the one to one point that I mentioned above. With a 1000 Watt motor you will not be able to run at full speed with the 500 Watt unit without overheating the Variac and possibly damaging it. The only warning you would get before failure would be the amount of heat it gives off. In general, when going past the ratings, the larger the motor, the more limited you will be with a Variac.

    You will probably be on the safe side if the power rating of the Variac is 1.5 to 2 times that of the motor. Otherwise, you can do a careful calculation of the Voltage, power, and current at various settings. That would allow you to minimize the size of the Variac for a given motor and load.
    Paul A.

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