PWM - Potentiometer ohm importance...

Like any component in an electronic circuit, the value is dependent on the function it does in that particular design.
In this case a typical value could be 100k linear pot.
What is the reason for the question?
M.

 

In a SMPS, anything that adjusts the output is adjusting the duty cycle. If you want a better answer, you need to get the controller chip part # and look at the datasheet to see if it is on a control line or the feedback loop.

Are you just trying to learn how these work in general or do you need to modify it for a particular reason (which would be helpful to mention) ?

 

It could be that you have been supplied with a logarithmic track potentiometer instead of a linear track version.

Can you see any identification marks, numbers, codes on the pot you are using?

 

It is difficult to tell fro the pictures in your link, but it is probably based on a 555 timer and if so the value of the pot is quite important. Using a smaller value would increase an already high switching speed.
There also seems to be a lot of bits, which probably includes a voltage regulator, on the board for what is a fairly simple circuit.

 

That marking could indicate either a linear or logarithmic taper pot, depending on manufacturer and country of origin. You probably need a linear taper pot.

 

^ concur.... annoyingly the North American marking differ from the European marking in that they are 'reversed' i.e. European has A for logarithmic and B for linear whilst N.A is the opposite!!!

It 'sounds' like you're using a log pot - simple matter to get a replacement (linear) which should fix your problem.

 

The one I picked up is very similar and mine has a 100k linear pot.
Place the pot slider in the centre and measure to each end, that would tell you.
Also are you using a power supply at the voltage rating of the motor? With a PWM drive you normally would be at least 10% higher voltage than the motor rating.
M.

 

Did you try an automotive lamp? See if the same results?
M.

 

Had a quick look at the one you bought, and its switching speed is 25KHz which is a bit fast.
I run mine at between 50 and 300Hz. You might expect the motor to make a bit of a racket at that frequency but mine is OK but, having said that, mine are fairly low power 50 to100W or so. But I do get good control.

 

In the first link to Ebay, the photo of the pot on it's own shows B10K written on front of the bakolite insulator opposite the 3 terminals.

 

Currently using it for my hand held 12V mini drill which is often to fast for some of the jobs I do. It runs at about 250Hz if I remember correctly.

 

New Bee, a quick 'n dirty way of checking your pot value, and if its Linear or Logarithmic can be done thus:
Value of pot:
With ohms on highest scale, measure end to end tag (outer two solder tags).
Lower ohms scale on meter until you get a reading.
The nearest standard value will be the pots rated resistance value.
LOG vs LIN:
From the wiper to each of the end tags, check ohms while turning the pot fully CW and ACW.
A LIN taper will gradually cruise from minimum to maximum resistance.
A LOG taper will leap after turning a few degrees (on a standard 300^o travel).