Help me Comprehend my MC-60 Controller

[SteveHGraham]

I know I'm blowing up the board this week. Sorry about that.

I received the MC-60 controller for my 95V treadmill motor. I figured I would take a look at it and have no problem putting it to work, but my understanding of this thing is pretty superficial, and I don't want to set it on fire.

I have two boards. One says "MC-60" on it. It has two clearly labeled motor outputs. That part, I comprehend.

The other board has what I thought was a transformer on it. I was wrong. It only has two leads, so it's a choke. The number is 2698F. It has two female spade connectors on the ends of its leads. It does have a transformer, which is smaller than the choke. From the Ebay picture, I just guessed the board was a power supply, but it looks like it's not for the treadmill motor.

I found a document which says the SB-12 is a 120V power supply for an incline motor, which must be the motor that tilts the treadmill. I don't see any reference to the motor that moves the belt. Seems like that means I don't need this board, unless I come up with a use for an incline motor. Correct?

As for the MC-60, I found a diagram on the Lumberjocks site which shows AC in, 5K pot, and DC out, all on this one board. No transformer, no big capacitors, no big choke.

I'm sure I have 5K pots lying around, because I use them in guitar amps. I found a schematic which says the pot only has to deal with 12V.

http://forum.allaboutcircuits.com/attac ... png.48870/

If I understand what I'm reading, I can plug an AC cord into this thing, plug the motor in, solder a pot in place, and fire up the motor.

I don't want to blow the motor up. Should I simply check the output voltage against the pot and make a mark at the 95V setting with the notation "Don't turn past this"?

The motor plate says the motor is rated at .75 HP at 95V, but it's a 1 HP motor, so it must be permissible to run it considerably faster as long as I don't leave it on all day. In the process of gathering information, I have read that these things will run for several hours going full tilt, but I can't imagine having any need to run a sander for more than 45 minutes.

[WJH]

Haven't played with the MC60, but all sounds about right. If it wasn't for your posts, i'd be very bored with this forum. At least your doing stuff!

[SteveHGraham]

Trying.

[SteveHGraham]

I am wondering if anyone knows whether I want linear or logarithmic taper on the 5K pot. I would assume linear, since logarithmic is referred to as "audio."

[WJH]

I am wondering if anyone knows whether I want linear or logarithmic taper on the 5K pot. I would assume linear, since logarithmic is referred to as "audio."

Linear, most of the time

[Harold_V]

I am wondering if anyone knows whether I want linear or logarithmic taper on the 5K pot. I would assume linear, since logarithmic is referred to as "audio."

Linear, most of the time

That makes sense, as increasing volume by 3db requires a doubling of power. Or do I have that wrong?

Harold

[WJH]

I am wondering if anyone knows whether I want linear or logarithmic taper on the 5K pot. I would assume linear, since logarithmic is referred to as "audio."

Linear, most of the time

That makes sense, as increasing volume by 3db requires a doubling of power. Or do I have that wrong?

Harold

I'm not an audio person, but I find a linear relationship between input and output to be ideal. Sometimes however, if your motor controller takes a lot of initial movement to get going, an audio taper pot may correct for that somewhat depending on how you hook it up, at least in theory, but if the "exponential" is too great, it'll just make things worse at the other end.
With this all said, I suppose one could hook up a solid state "electronic" pot instead, and use a micro-controller to communicate with a CNC setup, if you wanted a computer to control the spindle speed. But we are talking about a belt sander in this case...

[oldvan]

If you'd like a consistent measure of rotation to produce the same increase of speed regardless of position, linear taper what you need.

linear vs audio taper pot.gif (7.52 KiB) Viewed 5011 times

[chucketn]

Steve, yes you want a linear 5K pot. You only need the board marked MC-60 The incline power supply is not needed.
I will take a picture of my setup for you. I had taken some, but darned if I can find them...
There are 2 spade connections on the board for AC input, 2 for the motor out, and 3 for the wires from the pot. I can't remember how they're labeled, so I'll have to go look.
As I had the whole treadmill, I re-used it's AC cord and 15A circuit breaker for power in and off/on.

Chuck

[chucketn]

I found one picture of my MC-60 setup. The motor leads are at the top, pot leads at the bottom. I will get a better picture in a bit.

Chuck

Edit: I guess the pic was too big, won't appear. I'll get some better ones and post them somewhere.

[chucketn]

Found my pics on photobucket. Pic shows AC, Motor, and pot connections.

http://i571.photobucket.com/albums/ss15 ... /mill1.jpg

Chuck

[tornitore45]

Linear versus Log
All discussion assume that the voltage at the wiper directly controls the motor speed.
In reality the circuit is such that the wiper voltage controls the charge of one capacitor (via a mildly non linear relation); which in turns controls the delay in firing the SCR (in a inverse relationship = Higher voltage lower delay);
The firing angle (delay time) controls the Average Rectified Voltage based on the remaining area of the sine voltage. DC motor RPM is fairly linear to Average Voltage.

While my gut feeling is that we want a linear taper, there is very little linear in the whole affair.
It would be nice if someone took the time to plot RPM = Function of Wiper Voltage and see how all these non linearity fit together.

Log taper produce increment proportional to the current voltage; small change at the bottom, larger at the top matching the ear sensitivity.
I do not think a very fine control at low speed and a courser control at the higher RPM is desirable.