[ZipSnipe]

I have this speed controller New PWM DC Converter 12V 36V 10A DC Motor Speed Adjuster Controller Driver | eBay

I am trying to locate the ground on the speed pot. I tried finding cont. between the pots leads and the power in ground but no luck.

Is it possible that one of the chips keeps the pots ground open until power is supplied?

[Al_The_Man]

By ground I assume you mean common for the analogue in?
If you apply power and measure the voltage across the pot, it should typically be 0-5v/10v.
The '0v' end is the common.
Shouldn't take much to reverse engineer the whole board, the IC, according to the print pattern is most likely a 555?
The POT does not appear to be at P.S. common, but the 0v end will still be the common for signal purposes.

Al.

[ZipSnipe]

Thanx Al, that was next attempt at finding ground was to measure voltage. I was told the pot has a common, wiper and 5 volt load, would the wiper(whatever that is) have a reading?

[Al_The_Man]

Wiper is the centre terminal and will read WRT to the common, from 0v to whatever the reference voltage is as the pot is rotated.
Al.

[ZipSnipe]

Here are the results of testing the pot. Powered on and pot running motor at about half speed.

I set my meter to dc 20 v, I had the com lead from the meter to the power in ground, the red meter lead went to the right side of the 3 terminal pot and I got a 10.2 reading, then I touched to the far left lead and got a 5 reading, heres where it went weird, I touched the center pot and the motor speeds up and I got a reading of about 2

The good thing is I know I can now run my momentary switch to this center wire so that I can have rapid traverse on the powerfeed. But I still don't know which is ground.

[Al_The_Man]

As I mentioned, go from the outer ends of the POT, it should not change appreciably with RPM, also as mentioned, according to the circuit trace, the POT is above common, if so you would not use this for any external control.
However it looks like you may not be able to replace the pot with an external signal with this circuit, as this circuit is rather different from the typical 0-10v analogue control as seen on VFD etc, which are normally a reference input to a OpAmp.
I believe this pot is part of a R/C network that varies the charge time of the cap.
If so, speed variation will be purely manual!
Al.

[ZipSnipe]

Thanx again Al, I guess I should have pointed out the main reason for finding the ground on the pot.

On another forum a guy uses almost the same controller except his was 15 amp 12 volt. Mine is 5 amp 12 volt ( was supposed to be 10 amp shady Ebay seller) anyway the guy mention trying out different resistors on the speed pots ground to get it to slow the motor down even slower. However the guy did it 2 years ago and doesn't recall exactly what and how he did it.

So I figured I would give it a try and see what happens. Right now when I slow the motor down to its slowest, it gets a lil jumpy(speed jumps a lil)

I might still buy another speed controller as this one might not have the juice I need to run the table on my mill. I am still testing it, I am hoping by adding the resistors that I can get rid of the jumpyness and get it to a pretty slow crawl.

[Al_The_Man]

If you Google 555 PWM controller you will get many examples of the circuit you have, and how the pot is wired.
e.g. https://www.google.ca/search?q=555+p...w=1920&bih=954
I imagine if you add resistors to common you may affect the linearity of the control?
Al.

[ZipSnipe]

Thanx again Al. SO I tried the momentary button it didn't work, I need to replace the button as I broke it installing it and now it wants to get stuck when you push it in. So now I have to wonder why it sped up like it did when I touched it with the tester lead. I thought maybe it was connecting to ground through the tester leads.

[ZipSnipe]

Ok, the motor has the power it needs, but at its slowest setting its very jumpy. I tried resistors on the pots common lead with no effect. So maybe a new controller is in order?

[Al_The_Man]

Those are very simple basic controllers, you may need to look at some of the KB/Baldor SCR drives, or for a bit more they have PWM also .
Al.