Comments on: PWM Control of a Larger DC Motor

By: Jon Lambert

Jon Lambert — Sat, 25 Feb 2017 18:45:48 +0000

Keith – I enjoyed your research, nice work. I’m preparing to build a similar motor drive system for use with a DeWalt 18-V drill motor and am wondering if the .54 Ohms of “On” resistance of the FET significantly reduced the power delivered to the motor. Did you notice any difference between the max speed/torque using the original factory circuitry and the max speed/torque using your assembled drive? Obviously, I’m trying to squeeze all available power from the battery. Thanks,
JL

By: Brian Gladden

Brian Gladden — Fri, 09 Mar 2012 03:51:01 +0000

Hi Keith, saw this write-up and thought I’d ask a question. I’m looking for an all in one ready to go (maybe solid state) small device that will turn a 1.5-3v motor on and off every 2-3 seconds (doesn’t need to be exact). I’ve had my techie buddies say get a 555 timer, a microcontroller, anything that would handle the 2 second on / 2 second off cycle and something else. I’m not technical that way. I have a 300rpm motor that’s connected to either 3xAAA batteries or 2xC batteries. I’d like to put this on/of switch in between so the motor goes on/off automatically. If I can put it in a box with an on/off button on the outside, bonus. Know anyone in the US I could outsource this to? Or find that damn timer thing?

By: DT

DT — Tue, 13 Dec 2011 18:37:08 +0000

I’m using this idea in a project of mine.My main aim is to control the DC motor speed using a 555 timer circuit which generates a square wave.Any idea how i can implement that?

By: Matt

Matt — Tue, 20 Sep 2011 01:07:09 +0000

Hi Keith

If the FET was replaced with an IRF510L, could it be driven directly from the IC output and the transistor omitted? I understand the ‘L’ means the FET will fully switch on with 5V at the gate. Thanks!

By: Keith Neufeld

Keith Neufeld — Fri, 01 Jul 2011 17:22:47 +0000

Todd, if you add series resistance to the load, the added resistor will get hot too. I think the original PWM variable-speed control is really what you want to use here — what you’re doing, although with heat rather than with motion, places much the same constraints on the current-control system that the original motor did.

One thing you may want to do is limit the range of the PWM so it can’t go far enough to overheat. I would pull the trigger until the shape memory wire was as hot as I ever wanted it to get, then mark that trigger position and power down and take things apart. Get the trigger back to that position and measure where it is on the potentiometer, then connect a series resistor at the “top” of the potentiometer to change the voltage divider so that the full range of the pot : the pot plus resistor :: the usable range of the pot : the whole pot.

If this makes sense, I think you’re good to go. If I’m diving too far into terminology, I can give you more detail about the process.

By: Todd M

Todd M — Fri, 01 Jul 2011 16:32:21 +0000

I am using a .75mm diameter, 60mm long piece of nickel titanium wire as the resistive load. This material is commonly known as shape memory alloy. (The wire ruturns to a programmed shape when heated)
I am using current in the wire to create the heat required to make the shape change. If the temperature in the wire gets too high, it will lose the ability to return to the original shape, therefore, I need to limit the current.

By: Keith Neufeld

Keith Neufeld — Wed, 29 Jun 2011 11:53:26 +0000

Todd, I’d need to know more about the nature of the resistive load to be able to make a suggestion.

By: Todd M

Todd M — Wed, 22 Jun 2011 20:38:10 +0000

By the way, the control is presumably PWM.

By: Todd M

Todd M — Wed, 22 Jun 2011 20:23:37 +0000

I have a brand new Dewalt DCD710 cordless drill/driver. 12volt.
I am making a specialty tool in which I remove all mechanical components including the motor,gearbox, clutch and chuck. None of the electrics have changed. Now the two wires that went to the motor hang loose. I need to connect a resistive load to the wires that went to the motor but there is too much current. What would be the best thing to add to limit the current?

By: Keith Neufeld

Keith Neufeld — Mon, 31 May 2010 02:37:54 +0000

Gouthami, you can use the circuit exactly as it is to control a DC fan motor.