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Thread: Will this controller work?

  1. Will this controller work?

    I am trying to build a ride-on train for my son.

    I need to get a controller for the motor and I wanted to know if the SYREN 25 would work for this motor.

    Here are the motor specs: 36 Volt, 750 Watt, 2800 RPM, 27.4 Amp, permanent-magnet motor. It's original purpose was for a chinese scooter.

    I am only running the motor at 24V.

    What I cannot figure out is if a motor called a "permanent-magnet motor" is considered a BRUSHED motor.

    PLEASE HELP! :-)

  2. #2
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    Re: Will this controller work?

    If it has two wires, it's brushed. If it has more, it prolly won't be
    Since it's from a chinese scooter I'm thinking it is. Attach a car battery and see if it spins. If it does you're all set, though the controller you're linking to isn't going to be able to cope with the motor for very long, it might even kick into protection immediately preventing the motor to turn alltogether.
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  3. Re: Will this controller work?

    Even if I am running at 24v, won't that reduce the amperage?

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    Re: Will this controller work?

    I replied to this via PM, but once i hit the send button I started wondering..

    I told you the amperage would increase since the power rating of the motor remains the same, yet the voltage is decreased, i.e. it would demand more current to overcome static and dynamic friction.

    But as i said, ohm's law says otherwise, so I'm guessing there's something to do with inductance here.

    I'm going to scratch my head a bit over this one and get back to you, but something tells me there's been posts about this on this very forum before
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    Re: Will this controller work?

    If you lower the voltage to 24v the amps will go higher than 27.4Amps. Basiclly the motor compensates for the loss in power by pulling more amps. Even thou it sounds crazy your actually putting more strain on the motor running it at a lower voltage. You can run it at a lower voltage but the motor has a max amp rating once you go past this things start to wear out. And going higher than 36v is just a waste of power since the magnets in the motor will hit saturation. Basicllly its try to magnatize the iron beyond a reasonable amount.

    You need a larger controller or a smaller motor. Since you have the motor already you need a beefier controller.

    Paul

  6. Re: Will this controller work?

    Any suggestions on what controller to get? I need one that will work off a basic Potentiometer if possible.

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    Re: Will this controller work?

    This IFI speedcontroller should do the thing... a tad over the top with 120A continuously, but it seems there's not a lot of 36v speed controllers out there.
    If you're willing to undervolt (but live with the higher current draw) there's more options, yet they all come at a price.
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  8. #8

    Re: Will this controller work?

    If you reduce the voltage supplied to the motor the current will also be reduced. The resistance of the motor is the constant factor. The 750 Watt rating is with the 36 volt supply, where it operates at peak efficiency. If compared to the 36 volts times the 27.4 Amp calculates out to 986 watt total of rated voltage and stall current, showing max values. There will be a linear reduction of of max current when reducing the voltage, so with 24 volts being 2/3 of 36, the stall current will also be 2/3 going down to 18.7 Amps. The Syren 25 is adequate to run the motor at the 24 volt level. Note the motor output would now be about 500 watts at peak efficiency.
    Last edited by robologist; 05-11-2009 at 02:58 PM. Reason: added qualifiier

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    Re: Will this controller work?

    I'm actually not too sure about that. A motor is definetely not a resistive load, and as such its resistance is not a constant.
    So too does the back-emf change as the load increases, and will also be different with another current and/or voltage.

    It's been too long since I've had to do with the physics behind motors though, but there's something in the back of my head saying the current will increase with a lower voltage at the same mechanical load.

    I wish I could explain why I think this way though... Where's Lynn when you need her?
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  10. #10
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    Re: Will this controller work?

    Right here... :P

    The startup current will go up, otherwise I agree with Robologist. I have some 750wt @ 36v motors here, I run 'em on a dual 80A controller which is perfectly happy with 'em. That said - stall current IS a resistive load. Once it stops spinning, it's a giant power resistor.

    For my money, the IFI Thor is on sale right now here: http://www.robotmarketplace.com/products/IFI-T883.html

    Of course, that's only useful if you never plan to go to 36v.

    The 4QD is a good pricepoint: http://www.robotmarketplace.com/prod...VTX-40-36.html

    Honestly, I've found the Dimension Engineering products to be over-rated. My 10A dual won't handle more than 7.5A reliably/continuously without shutting itself down repeatedly even with an enlarged cooler, fan, and heatsink. I was a fan until I started pushing them a bit harder... I wouldn't get behind them without reservation.
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