Help buying a DC speed controller please

Discussion in 'General Electronics Chat' started by T Werner, Feb 16, 2012.

  1. T Werner

    Thread Starter New Member

    Feb 16, 2012
    7
    0
    Hi
    I didn't want to start a new thread when there was an old one on a similar topic, but it was too old for me to post to. I also want to apologize in advance if my question is silly or demonstrates too much ignorance.

    I won a new Dayton 2h588 motor on eBay, and will be using it to turn Stave Drums on a Router Jig. The motor is probably overkill for my purposes, but it was a good deal. http://www.grainger.com/Grainger/DAYTON-DC-Gearmotor-2H588

    I'm on a budget and I don't want to order the wrong controller for it and ruin the motor. I was hoping someone could explain why some of the controllers are so expensive, and others are quite cheap.

    This: http://www.ebay.com/itm/130475158159?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 seems like the cheapest and easiest option. Seems like you just plug it in and wire it to the motor. But the ones from Granger or other suppliers are a lot more money, so is this one unsafe for me or the motor?

    I also saw on ebay that people are selling the chassis versions of several of the more expensive options, for low prices.

    Is something from KB or Minarik, like this:
    http://www.ebay.com/itm/310377714850?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
    or this:
    http://www.ebay.com/itm/Minarik-MM2...081?pt=LH_DefaultDomain_0&hash=item3cc1efa239
    a much better choice?

    And if they are, is it a big job to buy the case and build/wire the board and chassis into it? It looks like a case, some wires, and a 10K pot are all that I'd need, but I'm on a budget, and if the KB or Minarik will require another $50 in parts, then the speed control will be more money than the motor, and I should probably keep watching ebay for a less expensive option.

    Thank you,
    Todd
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    the difference in controllers can range from one being a simple voltage dropping pot, to one that has current/speed limiting, dynamic braking, reversing, etc. It's up to what suits your needs.
     
  3. T Werner

    Thread Starter New Member

    Feb 16, 2012
    7
    0
    Hi GDI,

    Thanks for replying. I don't want anything fancy. The motor is a permanent magnet motor, so my understanding is I don't need a field tap on the controller.

    My concern is really that I don't want to harm the motor. I've been reading a lot and searching, and I found this, but don't know if it is safe to use with a 1/6 HP motor, when it says 1/2 HP. http://www.ebay.com/itm/310379258071?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649


    I almost ordered a KBWD-13 board/chassis, that also seems perfect. It's a PWM speed controller like the one above, but I got a little concerned about having to buy a case and a pot and a "HP resistor".

    I worry about the one on ebay, because if I need to buy the correct "HP resistor" for the KBWD-13, to use it with a 1/6 HP motor, then does that mean the one I linked to above has a resistor that is set for a 1/2 HP motor, and would fry a smaller 1/6HP motor? If these devices limit/regulate voltage, then that doesn't seem possible. Wouldn't you just apply the correct voltage. As long as the controller can provide sufficient current without overheating, it seems like it would be safe. Or is the issue that the 1/2 HP speed control will provide too high a voltage if the resistance of the motor is too small?

    Thanks,
    Todd
     
  4. T Werner

    Thread Starter New Member

    Feb 16, 2012
    7
    0
    Sorry, that should be if the resistance is too HIGH. Since less current flows. Will the controller supply a higher voltage due to less current flow through a resistor inside it. And then would that exceed the 90V that the motor is rated for?
     
  5. hspalm

    Active Member

    Feb 17, 2010
    201
    8
    I guess the HP resistor is a high power resistor for current sensing. You can't really do any serious damage to your motor as long as it can handle free running with no load. Motor controllers mostly limit current, they don't source it like a constant current source.

    edit: of course, a motor COULD be damaged if the controller is defect in some way that it delivering more voltage than the 90 v rating. Just to clarify that a motor is not indestructible in any application.
     
  6. T Werner

    Thread Starter New Member

    Feb 16, 2012
    7
    0
    I thought the motor controller was like a variable transformer, and let me adjust the voltage. I also assumed the current would be proportional to the voltage. I'll have to do some reading since I'm not sure what a constant current source is.

    If the controller's internal resistor is too small compared to my 1/6hp motor, then the motor will "drop" more of the voltage at a given current. So it will see more than 90V across its terminals?
     
Loading...