• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

PMDC treadmill motors ---I need speed control

Status
Not open for further replies.

Paul 316

New Member
I have several PMDC motors. I want to control the speed and mount them on my machine tools. (horiz. mill, desk top vert. mill, drill press) I have taken a first step. I have a bridge rectifier. (200v 35 amps) And I have a cap. (1500 mf 20% 200v) I can run the motors directly from these, but I need speed control. So as I understand it, I need some SCR's to switch the current off and on, and some type of feed back loop to control the duration of the pulses. Is there more to this PWM. Can I do it relatively simple, or do I really need lots more components to do it safely for me and my motors?

I am an avid learner, feeling my way through this. The above note may make me sound smarter than I am. My latest score is an old treadmill (working) with an m60 board. I have the motor and necessary related stuff off the TM and it still runs. I also wisely saved the schematic from the soft plastic under belly. And I think I will be fine putting this on a machine. But I still have 2 bigger, better, newer PMDC motors. The digital electronics on them was thick and heavy.
So. What does the big transformer looking thing do on the old one? I know it's called a choke. And my understanding is it somehow protects the delicate circuits from EMF back force from the generator effect of the PMDC motor when it's winding down. How are the curcuits protected in the newer digital TM's?
 

MaxHeadRoom78

Well-Known Member
There are DC motor controllers made by KB, they come up on ebay often, there are two versions, the SCR bridge type which can be a little noisy at low rpm and the better PWM version, if you go to the KB site you can down load the manuals.
Max.
 

MikeMl

Well-Known Member
Most Helpful Member
I bought a defunct treadmill from a junk dealer for $5, and was able to extract a useful SCR bridge speed controller (that responds to a low-level input control voltage that normally comes from the microprocessor in the upper console on the treadmill) as well as the motor.

Max helped me find a schematic of the controller. I am able to control motor speed by wiring a 10K pot to produce the control voltage that would otherwise come from the microprocessor.
 

schmitt trigger

Well-Known Member
So. What does the big transformer looking thing do on the old one? I know it's called a choke. And my understanding is it somehow protects the delicate circuits from EMF back force from the generator effect of the PMDC motor when it's winding down.
The purpose of the choke is to smooth the current pulses that SCR-based phase control produces.

Since the current is pulsed, and at lower speeds where the conduction angle is narrow, the motor may vibrate too much. The choke may reduce the vibration amount, while simultaneously softening the leading edge and therefore reducing EMI.
 

John Weaver

New Member
I know this is dated but I see this question all over the net. The purpose of the choke on a treadmill is to smooth out the treadmill walking platform at low walking speeds like 1 - 5 mph
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top