# motor speed controler



## hobby (Feb 9, 2011)

Hi guys,

I am in the process of changing my benchtop mill machine over to belt and pulley drive.

While I have the motor and its speed controle board apart from the machine, 

I decided to do some reading up and getting a good grasp of how 'pulse width modulation works' for a speed control, because I have replaced these boards several times now, and it gets expensive after awhile.

So since electronics has been my hobby for the last 30 years, I decided this would be a nice oppurtunity to combine the two together and try to design and make my own speed control for my milling machine.

This way if it needs fixed, I know exactly what to do to get it back up and running.

My hobby in electronics is designing circuits from scratch using all discrete components, transistors, resistors, caps, ect...

In any design work in electronics, I always build a scaled down version, as a prototype, just for a proof of concept, to see how the circuit performs, according to design parameters.

Here is a test prototype of a circuit I designed, and built, on a breadboard, to check for proof of concept.
This is designed for a small 5v. DC geared motor, so the components are small wattage.

If I was to use this design for my mill motor, the components would need to be more massive in power handling capability.

But for now this is just a scaled down version to check performance, of the design itself.

Here is a video, of it running a toy motor.

http://www.youtube.com/embed/wSi5pON7LFQ?

The next part is I need to design some feedback control circuitry, that as the motor shouild stall at low speeds the speed will automatically increase, which is also known as torque controle.

Even if it doesn't work for my mill machine, it is a great learning experiance in this circuit design work.
I still have a comercial speed control board on hand if I need to put it back on the mill.

Have a great day...


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## imagineering (Feb 10, 2011)

I'm looking for a simple PWM Controller for a 24Volt 8Amp Wheelchair Motor.
This will be eventually be used in a Model Locomotive. 
Doesn't need to be H-Bridge as a DPDT Switch will control reversal. 

Murray.


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## Ken I (Feb 10, 2011)

I've built a number of power supplies using the LM338 3 pin power regulator IC - it doesn't get any simpler.

Ken



View attachment Lm338.pdf


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## picclock (Feb 10, 2011)

Hi hobby

Are you in the UK ? I assume you will be using a treadmill motor.

My mill motor, and AFAIK all treadmill motors work on mains rectified phase angle control (someone will correct me if I am incorrect here - I can only speak from experience). Pulse width modulation relies on a DC source which from smoothed mains in the UK is around 375V. This is way above the 180 average volts used for these motors. You may be better off using the speed controller for the treadmill motor.

Either way take care, as working with powerful mains equipment can cause serious injury.

Knew a chap who was replacing a lamp up about 15 feet. Got a shock, jumped off the ladder and broke his leg. So its not always the shock that does the damage but the consequences.

Good luck with your project

picclock


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## hobby (Feb 10, 2011)

Hi picclock,

No, I am from the states,
The motor I have is the motor that came with the micro -mill drill, harbor freight,
Iv'e gone through about 3 control boards already, after so long of running the control boards begin to work erratic, with the speed, that's why I am looking at building my own simple version, so that I don't have to rely on comercial products to keep this machine running.

I will be using a 1:1 isolation transformer, for the input voltage, to keep away from the mains.
Then from there probably a low regulated voltage circuit, for the electronics, and a seperate higher voltage regulated circuit for the motor itself.

The reason for the "PWM" circuit is to be able to have some torque control, at very low speeds.


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## Stan (Feb 11, 2011)

KB Electronics make DC drive controls that are surprisingly good and seem to last forever. They are reasonably priced and there always seem to be some on ebay. My mill has a GE 1/2 HP PM industrial motor with a KBIC-120 control that has been foolproof with good speed and torque control. I also use a KB unit on my small drill press that never gets bits larger than 1/4" with a 1/3 HP PM motor.

Like you I spent many years designing and building electronic equipment but discovered I couldn't build a control as good or cheap as KB does.

BTW: I also have DC controls that cost several times the price of the KB units and may be better for things like interfacing to a computer and having multiple inputs for external controls but they don't really surpass in performance in my home shop.


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## Paulsv (Feb 11, 2011)

The KBIC120 is a really nice controller. It also has outputs for a digital tach, and inputs for Potentiometer and an Emergency off switch. Here's a link to the manual.

http://www.kbelectronics.com/manuals/kbic_manual.pdf


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## John Rudd (Feb 11, 2011)

I have the KBIC 240 on my mill here in the UK...

The guys at KB were very helpful when it came to providing me with techie info...

Would I buy another?...You bet..

Thing is they are not pwm controllers...they use thyristors for speed control..Doesnt make them a bad controller tho'


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## hobby (Feb 11, 2011)

Thankyou guys, 
for the information and the testimonies about the KB controllers.

I still have a brand new board from LMS. I have yet to put back in the machine, however I've been getting so caught up in the design and experimenting with the circuitry, that it's becoming more of a design challenge, now, that I want to see if I can design and build my own motor controller, so as to make some good use out of this electronics hobby.

But I'll keep those KB controllers in mind, should I not decide to build my own.

Thanks everyone for your help...


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