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Old 10-28-2019, 04:51 PM
Scratch Scratch is offline
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Default Treadmill motor speed controller

So I've been working on a 2x72 belt grinder for a couple weeks. Its pretty much done minus paint, but I've been waiting to do that until after I get the electronics enclosure done. I'm using a 2.9 HP DC treadmill motor that I got for free, and I see tons of people using them with great success, and they're using one of these SCR's with a bridge rectifier to control the speed. Sounds like a great idea I thought, so I bought one off Amazon and gave it a whirl.

It came in, I hooked it up on the bench to test it. I put 110 VAC in and I get 110 VAC out... but no change in voltage when I adjust the pot.
Good thing I used Amazon Prime.

They sent me another one and exact same thing.
No voltage change.

I thought maybe I'm hooking it up wrong so I watched a bunch of videos using the same SCR, and I have it wired correct.

Oh well, maybe this seller has crappy stuff. So I went on Ebay and found a different design that's actually more common to all the other videos I see on line.
It came in yesterday and again... no voltage change!

The Ebay seller has already refunded me the money, and told me to keep this unit, but come on... Three different units, all bad out of the box!
What do I do?

I was thinking maybe I could figure out whats wrong with this one and replace the bad parts...? It's a super simple circuit, and I do know my way around a soldering iron. I do have a digital specialist degree from a 2 year tech college. (of coure that was almost 30 years ago...) I did inspect the circuit looking for burnt components or cold solder joints, but it looks fine to me.

I'm at the point where I'm almost thinking about going with an AC motor instead!

What should I do? Any input?
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Last edited by Scratch; 10-28-2019 at 05:04 PM.
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  #2  
Old 10-28-2019, 06:32 PM
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Are using the ground screw for ground when testing and not the common?
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Last edited by digr; 10-28-2019 at 06:40 PM.
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  #3  
Old 10-28-2019, 06:50 PM
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Quote:
Originally Posted by Scratch View Post
It came in, I hooked it up on the bench to test it. I put 110 VAC in and I get 110 VAC out... but no change in voltage when I adjust the pot.
Good thing I used Amazon Prime.

They sent me another one and exact same thing.
No voltage change.


What should I do? Any input?
It is likely a Triac control ..... (see if there is a part number on that 3 pin part that is on the heat-sink).

its not going to output DC for your DC motor without a rectifier.

they should work fine on an incandescent light bulb.

they work as a variable on/off switch so it is unlikely to see much of a voltage change.
if you were to flick a wall switch on/off at a slow rate the light will be dim but still seeing 120 volts

also needs a load, connect it to a light.
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Last edited by GWIZ; 10-29-2019 at 01:50 AM.
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  #4  
Old 10-28-2019, 09:13 PM
Scratch Scratch is offline
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Quote:
Originally Posted by digr View Post
Are using the ground screw for ground when testing and not the common?
No, I'm not using the ground screw.

I'm wiring it up just like this feller:
https://m.youtube.com/watch?v=_NmAFZMAfH8
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  #5  
Old 10-28-2019, 09:41 PM
Scratch Scratch is offline
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Quote:
Originally Posted by GWIZ View Post
It is likely a Trac control ..... (see if there is a part number on that 3 pin part that is on the heat-sink).

its not going to output DC for your DC motor without a rectifier.

they should work fine on an incandescent light bulb.

they work as a variable on/off switch so it is unlikely to see much of a voltage change.
if you were to flick a wall switch on/off at a slow rate the light will be dim but still seeing 120 volts

also needs a load connect it to a light.
Ok...

Dumb me.

I was testing it with a multimeter checking for a drop in AC voltage which I never got. When I hook up a light bulb to it, I DO get a dimming result of the bulb... So I know the SCR is working.

When I hook the SCR up to the BR I don't get a change in DC voltage from my meter. When I hook it up to my motor, I get nothing.
My motor has 4 wires coming out of it. 2 blues, 1 red and 1 black. I'm hooking the red and black to the BR just like in the video. Motor doesn't spin at all.
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Old 10-28-2019, 11:02 PM
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Scratch, I don't know anything useful about those larger treadmill motors than what I was told by a representative/salesman from one of the companies that make dc motor controllers. I was about to buy a 2 hp unit from them & this fellow asked my intended use of it. He said it might save us both some time and shipping cost. When I specified the treadmill motor I had (and still have) he told me that treadmill manufacturers tend to use motors listed as "Form Factor 1" on the more powerful units because they run quieter & ladies don't like to hear their treadmills roar at them. And he said that Form Factor 1 motors require pulse width modulated (PWM) controllers so you can't just buy the cheaper triac-based controllers & get good results.

Again, I am not any kind of reference for treadmill motors or for PWM controllers. I'm just passing on a snippet of a conversation with someone who claimed some knowledge.
But you might check the data plate on your motor.
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Old 10-29-2019, 01:21 AM
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You're approaching this wrong. Buy a $25 treadmill that works and you'll have everything you need.
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Old 10-29-2019, 02:08 AM
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Quote:
Originally Posted by Scratch View Post
Ok...

Dumb me.

I was testing it with a multimeter checking for a drop in AC voltage which I never got. When I hook up a light bulb to it, I DO get a dimming result of the bulb... So I know the SCR is working.

< TRIAC


When I hook the SCR up to the BR I don't get a change in DC voltage from my meter.
< Its not going to change much more than it did on AC.


When I hook it up to my motor, I get nothing.
< connect the light and see if the light dims.


My motor has 4 wires coming out of it. 2 blues, 1 red and 1 black. I'm hooking the red and black to the BR just like in the video. Motor doesn't spin at all.
Hard to say without any information on the motor.
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  #9  
Old 10-29-2019, 06:44 AM
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Quote:
Originally Posted by gimpyrobb View Post
You're approaching this wrong. Buy a $25 treadmill that works and you'll have everything you need.
I had a treadmill that works. I could use the control boards that came with the treadmill, and have used them for testing the motor on the belt sander to make sure the tracking works and see how it runs... but then I have to make an enclosure for two big circuit boards and the cable that connects them.

These little SCR's are nice and compact and I'd rather keep the electronics as small as possible.
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  #10  
Old 10-29-2019, 06:54 AM
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Quote:
Originally Posted by GWIZ View Post
Hard to say without any information on the motor.
Here is the label in the motor
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