I just bought a DC gear motor- I'm trying to spin a 20 pound disk. I realize I need to hook it up to a power source, but I'm having trouble figuring out the proper source. PS I also got a DC speed controller and I'd like to use the two in conjunction. How do I do that?

Here are the specs on the motor I've got

PM DC Gear 90 vdc input hp 1/30 full load amps 0.35 47 rpm 26 lb full load torque

Here are the speed controller specs

DC Speed Control

HP 1/50 to 1/6 Voltage Output 90 Input Voltage 115


  • \$\begingroup\$ The power levels involved don't look too terribly large, but the 115V input is kind of heavy-duty for battery based applications. You might want to check out golf cart or wheel chair systems for examples, though I suspect these are probably more in the neighborhood of 24V \$\endgroup\$
    – JustJeff
    May 15, 2010 at 20:14
  • \$\begingroup\$ or i should have asked, does this have to be a battery based system, or would you consider using 'the grid'? \$\endgroup\$
    – JustJeff
    May 15, 2010 at 20:15

2 Answers 2


Using it is as easy as it sounds. You will connect it to power, hopefully through a switch. You need something like nickel metal hydride batteries(forgive my spelling). You need high current at a relatively low voltage, and the first time you do it, do it in pulses of increasing length, checking for heat in each component of the system.

Next, the motor controller should have a pair of pins for power(one from battery, other from ground of battery), pair for the motor, pair for control. control is done by a 50Hz square wave(20ms period) that has a duty cycle between 1.1 and 1.9 mS. The minimum being full reverse, maximum is full forward, 1.5mS will be idle. There are also controllers that use on and off, but you probably have one of the nicer ones.

To control it electrically I suggest a power MOSFET or BJT. MOSFET is probably more what you will want.

PLEASE NOTE: when you use any sort of electrical control(a MOSFET you pick or such) you need to have a diode, reverse biased in normal opperation, pointing from ground pin of the motor to the high side. This needs to be a relatively large diode in operating current. The motor will act as a voltage source and can generate very high voltages, as it is pretty much a large inductor. This diode will allow the current a path that does not involve over-voltage'ing your motor.

  • \$\begingroup\$ Sorry, I answered the question before it was edited. \$\endgroup\$
    – Kortuk
    May 16, 2010 at 5:48

Greg, this is an answer to your later question, "Determining Power Source for DC Gear Motor?"

I'm hoping you'll merge that question into this question.


Let's start with the battery. 90 V is high enough to be dangerous. You can run the motor with a lower voltage, but with two side effects-- the top speed will decrease, and the torque will drop. I'd start with a few lantern batteries connected in a series string (+-+-+-) and turning it on and off by hand with a wire.

If you can tell us a little more about your DC speed controller, we might be able to help with that too. (For example: What does it look like? Where did you get it? Are there any words written on it?)


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