Replacing a Potentiometer on a DC Motor Speed Controller

[francoCNC]

Many of the small machines made in Asia have DC motor controllers with a Potentiometer labeled P1, P2 and P3. See image.

Since the Acorn has a 0-10V analog output, I'm thinking it should be easy to "override" the potentiometer and have the Acorn control spindle speed. Would I simply connect the Acorn AN GND terminal to the P1 (GND) and the Acorn AN OUT to the P2 (Wiper)? Is it that simple? Are there any ground loop issues to be concerned with?

I know the Acorn has spindle control relays, but I'd like to get this potentiometer thing figured out first.

Thanks,
-Franco

[DICKEYBIRD]

Elmer fudd once said: "Be vewy, vewy careful."

You must be sure that the speed control pot circuit is isolated. One method is to use a KB signal isolator. Here's the one I use: https://www.kbelectronics.com/manuals/k ... manual.pdf

I think this is the one Marty has used: https://www.kbelectronics.com/data_shee ... si5si6.pdf

If you don't isolate that speed control properly it will instantly vaporize the circuit on your CNC control. I don't know for sure what would happen to an Acorn but my prevous system's CNC4PC C-11 went ka-POW & lit up like a flashbulb.

[ScotY]

I'd like to know how to do this as well, wiring up the pot as well as the relays...hopefully with forward/reverse. Oh, Marty...video???

A while back, I bought a board from CNC4PC to do this but I opened up the motor control box, looked at it, and decided I wasn't sure how to wire it up. That's about as far as I got with it.

[Stuartcol]

Going to see what I can work out using a motorized potentiometer. That way you maintain manual control of speed when not using CNC

You see them on many modern stereo systems where if you turn the volume up or down by remote the knob on the stereo system actually moves

https://au.mouser.com/Passive-Component ... otentiomet

[Stuartcol]

Another aleternative ... change the potentiometer to a digital potentiometer, with 2 buttons on control pad for up and down so you maintain manual control on the mill or lathe. Momentary press of button to increment speed by one step or hold button in for rapid incrementing of speed. From reading the datasheet, with this chip you could design a circuit to remember last setting used, or set it up to power on with a preset speed. Who knows ... once I have an acorn to play with you may also be able to output to a digital display on the mill the spindle speed if you don't already have that.

https://au.mouser.com/Search/Refine.aspx?Keyword=X9C102

This one only supports 5v, but higher voltages are available such as AD5290

This may well be a better solution. See PDF document for info. Just a matter of finding out what size potentiometer I need for the BF46

[frijoli]

Many of the small machines made in Asia have DC motor controllers with a Potentiometer labeled P1, P2 and P3. See image.
P1P2P3.PNG
Since the Acorn has a 0-10V analog output, I'm thinking it should be easy to "override" the potentiometer and have the Acorn control spindle speed. Would I simply connect the Acorn AN GND terminal to the P1 (GND) and the Acorn AN OUT to the P2 (Wiper)? Is it that simple? Are there any ground loop issues to be concerned with?

I know the Acorn has spindle control relays, but I'd like to get this potentiometer thing figured out first.

Thanks,
-Franco

It's very important to make sure you're voltages are on the same potential. The 0-10 analog is NOT going to be the same as the power on the potentiometer.
Smoke escaping will happen if your not careful. Some form of isolation is necessary.

[DICKEYBIRD]

That way you maintain manual control of speed when not using CNC

An easier way (using the KBSI-240D I linked to) is to follow the schematic on the bottom of page 11 in the manual. Manual/CNC control with the original pot retained. Easy-peasy to wire up, I have it on my ORAC & works perfectly!

HTH

[martyscncgarage]

Don't do it....
KB Electronics drive and signal Isolator.
I won't do a video on letting smoke out....
Do you need to reverse the motor?
I am going to to a video on connecting a KBIC120 with SI-5 signal isolator on a D&M4 bench top Sherline based CNC mill. I'll see what the next few days brings.....

As for manual spindle control, just use the manual override section of the virtual control panel, press the auto/man button to take it out of manual, press the green start button to start the spindle and the arrow buttons to change speed. Red button to stop the spindle.
Marty

[francoCNC]

In a perfect world, I'd like to be able to use the Acorn relays to turn the spindle off/on and control the direction. I would be extremely appreciative if you could make a video explaining what to buy and how to hook it up. That would be awesome!

[martyscncgarage]

In a perfect world, I'd like to be able to use the Acorn relays to turn the spindle off/on and control the direction. I would be extremely appreciative if you could make a video explaining what to buy and how to hook it up. That would be awesome!

Is this going on a lathe? Already has a DC motor? What HP is the motor? What is the armature voltage? Needs to reverse?

The drawback here is that Acorn doesn't do +/- 0-10VDC, there is a work around. Simple circuit. So in its normal state, it drives the drive forward, then with a +5VDC input (SPIN REV) output, it drives the spindle in reverse. Seems like several need such a board.

The drive we used was a KBMG-212D with an SIMG signal Isolator. The KBMG-212D is good for 1HP@115VAC and 2HP@230VAC WITH the auxillary heatsink.

If you can go with a VFD and an inverter duty 3 phase motor, that's the easier way to go. The DM3000 lathe we have has a servo motor, with a Tach (Which the KBMG can use to help maintain speed) and a spindle brake. The motor is relatively small in diameter and long. So I think fitting a 3 phase motor might be a challenge.