help with PWM and volt/amp meter

[KMoffett]

Placing a pot in series with the buck converter's output is not the way, as you have found, to control the voltage to the motor. You need to replace the pot in the buck converter with an equivalent external pot,

Ken

[Macman]

Ok Ken I ordered a new buck converter because the one I had even the mounted POT was not changing the volt output so I figured I start with a new one. the problem is going to be getting an external POT for it. only electric store here is Fry's not sure they have many to choose from

[KMoffett]

Can you you post a link to your new buck regulator?

Ken

[Macman]

http://www.ebay.com/itm/301484905256?_t ... EBIDX%3AIT

I got this one because these motors can pull some amps and I wanted to be safe

[KMoffett]

It looks like that also has an on-board trim pot to adjust the voltage. So you would have to remove it and run wires to an external pot.

Ken

[Macman]

right but do you think this 2000 ohm POT I have p/n RV4NAYSD202A will work?

[KMoffett]

I can't read the values of the trim pots in the photos, so I can't say.

Ken

[pebe]

With an on-screen magnifier I can just make out '103' on the LH pot and '?03' on the RH one. That accords with the buck converters I have used.

Check that yours are, if fact, marked 103. If so they are 10k linear pots

[Macman]

ok I got the buck converter now which POT is the volt output and what external POT should I get to replace it

[KMoffett]

On your web link, they indicated the there was adjustments for voltage and current limit. Is there an instruction sheet that indicates which of the trim pot is used for voltage adjustment? Is there any printing on the PCB that indicates voltage adjustment?

Ken

[Macman]

yea on bottom of circuit board under each pot. one says V-adj and one is I-adj. so guess V-adj is volts

[KMoffett]

Do you have the equipment and skill to carefully un-solder and remove the V-adj trimmer pot? You would then solder in three wires into the empty holes, to connect to your external 10K pot. Wire in center hole goes to the pot's center (wiper) lug. The other two wires go to the pot's outer lugs. The convention is that clockwise rotation increases the voltage. If you find that counterclockwise increases voltage, swap the wires to the outed lugs.

Ken

[Macman]

I can solder and I have a solder remover (wouldn't let me use the word that I really call it.. sounds like pucker but with an S..LOL) I guess I can use to help remove the pot but reality is I have never removed an item from a circuit board before. what would happen if I just soldered the external pot to the solder spots on bottom of board and left the original pot on the board?

[KMoffett]

That wouldn't work. You can't parallel the pots in this case. I might suggest you find some old PCB's from consumer electronics devices (TVs, stereos, radios) and practice on those. Your regulator is probably not a high quality PCB, so it might be easy to overheat a trace during desoldering and lift it off the board.

Ken

[Macman]

OK now im worried because these buck converters take so long to get I don't want to mess it up. my solder iron is set at 800 should I lower it so I don't over heat the board. on my way right now to get a 10k pot then we will see what happens