treadmill motor questions for belt grinder

[Scratch]

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. 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.

1.jpg

Sounds like a great idea I thought, so I bought one off Amazon and gave it a whirl.

It came in yesterday. 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.
Then I hook the SCR up to the BR, then to my motor. The motor spins, and the SCR controls the speed, but I'm getting major sparking from the back of the motor.

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 this video:
https://www.youtube.com/watch?v=_NmAFZMAfH8&app=desktop

When I switch back to controlling it with the factory treadmill speed controller, I don't get any sparking out of the back. Any ideas as to why I'm getting the sparking?

Hey Acourtjester,

I know you have a 2x72 belt grinder with a treadmill motor, what did you use to control the speed?

[weldguy]

Wish I could help Scratch but you've got me stumped. Can't use the treadmill speed controller instead?

[TrinityFabworks]

Did you switch out the trim pot? I had to put a different potentiometer in mine when I built one a few years ago. I built mine out of tubing back then because I didn't have my plasma table. I'll be building a new one this winter with an actual motor and all plate design using the plasma table. My motor finally burned out about a month ago, and I've been lost without having my belt grinder. One of the most frequently used tools in the shop

[acourtjester]

I did use the setup the guy did in the video with the changes he did, Now on thing you need to consider is the voltage that your motor is designed to run on. The one I use was max at 130 Volts DC some of the treadmill motors are rated at 90 Volts DC so you could be putting in to much and that is causing the sparks. Another problem I ran into is the controller did not put out enough voltage to obtain the full RPM of the motor I used therefore not enough power for heavy grinding. I bought another controller for the input but still could not reach higher RPMs. I did reduce the diameter of the motor wheel but was not happy with the overall performance so I went with a 3 PH 1.5 HP and a VFD 110 Volts AC, much better but I think a 2 HP running off 220 volts AC and VFD input would be better.

tread mill motor.jpg

tread mill motor2.jpg

DSCN3291.JPG

DSCN3298.JPG

[Scratch]

My motor does say 100 VDC so maybe that's my problem...?

[Scratch]

Wish I could help Scratch but you've got me stumped. Can't use the treadmill speed controller instead?

I could, but it's two large circuit boards with a large LCD display. I was wanting something more compact than that.

[weldguy]

I could, but it's two large circuit boards with a large LCD display. I was wanting something more compact than that.

Ah ya, I see. Big circuit boards, LCD display, that would be one high tech lookin belt sander!

[Scratch]

I could, but it's two large circuit boards with a large LCD display. I was wanting something more compact than that.

Ah ya, I see. Big circuit boards, LCD display, that would be one high tech lookin belt sander!

Actually.... I'm going for a "low tech" look for this sander... I'll post pics when it's done.

If I ever get this motor thing figured out. I'm tempted just to go AC.

[acourtjester]

her is what I ended up with, with this VFD I can get about 1.5X the AC freq to get extra speed about 2100 RPM with a 4" wheel. Last image is full speed, it do eat metal

DSCN3906.JPG

DSCN3907.JPG

DSCN3910.JPG

DSCN3909.JPG

DSCN3908.JPG