Mini trim pot to big potentiometer

[Mobilesport]

I tried to wire in a big potentiometer in place of
the mini trim pot that came with my heater , the trim pot looked
to me like it only used 2 out of the three legs , so I wired in the big potentiometer using just the left and center pins , didn't work , heater is always on high.
Does the mini trim pot use all three legs or is one just to help mount it?
Which pins do I wire to what?
Thanks

[Mobilesport]

Final with mounting bracket attached

[Mobilesport]

Pictures of it finished
Its just a piece of 1 inch PVC conduit pipe with a metal washer glued to the end with The Amazing goop, the potentiometer is mounted in the metal washer.
The PVC pipe was painted navy blue and then glued to the original case that held the little circuit board.
Going to try to find a knob with numbers.

I highly recommend this heater

[Dave5143]

Glad you got it to work. I was going to mention that there are basically two different types of pots. Linear taper and audio taper. Linear is probably what you want for this application. Audio goes up in a logarithmic manner as you adjust it.

[Mobilesport]

Got it to work using TomM picture , I had to wire center pin of the mini pot to the center pin of the new bigger pot ,
Then the pin in Toms picture that is labeled left I had to wire to the right pin of the big pot.
The pin in Tom M picture that is labeled right i had to wire to the left pin of the big pot.

[Mobilesport]

Sorry ,not 10 ohms ,,, I meant 10k ohms

[wa8yxm]

Mobilesport wrote:
@landyacht318

Bought it from EBay, the seller told me that it is a 8kohm even though it reads 10ohm on the side of the pot.
I bought it and confirmed it with my ohmeter 7.9kohm
Here's were I bought it from.

There you have it marked 10 ohms.

Put a VOM (Multi-Meeter) in resistance on it and MEASURE It. Do not take the seller's word for it.

[Mobilesport]

Deleted

[landyacht318]

8k ohm is a strange value.

I've never been able to measure resistance of a pot with it still soldered in place.

I've only run one 3 wire pot in the dozens of voltage buckers that i have run remote pots on, and it turns out 2 wires would have been enough as two legs always seem to have continuity between them when I test before removal.

Is your solder perhaps bridging the contacts? I've done that before for zero voltage control effect nut was able to remove the bridge to return full function, but none were on dual sided circuit boards.

[Mobilesport]

wnjj wrote:

Tom_M wrote:

Connect all three pins. Circuit board is double sided so traces can be on both sides.

So you didn’t remove the small pot? You can’t just put two equal sized pots in parallel since the resistance will be reduced significantly, especially if you leave the on-board one turned anywhere but to 8k ohms. Best case you get 4kohms max.

You can get close if you use a much larger value for the added one. For example if you parallel a 100kohm pot, twist the small one to 8k and the large one to 100k you will end up with 1/(1/8 + 1/100) = 7.4k max down to 0 when you turn the big pot all the way down (leaving the small one alone).

However it would probably be simpler to just remove the small one.

Also since there are traces on top, did you confirm there isn’t one to the 3rd pin there?

The small one was removed

[DrewE]

Did you measure the old pot while still in the circuit? There's a very good chance it's not an accurate measurement if that was done; the surrounding circuitry will affect the resistance reading. It does depend on how the circuit is arranged.

I would be mildly surprised if it's indeed an 8k pot; that's not a particularly common value. I'd expect a larger value most of the time. However, it's certainly not beyond the realm of possibility.

(It is also possible, though not at all likely for a simple thing like this, that there are more than just the top and bottom layers of a circuit board, and some traces on the inside where they are hard or nearly impossible to see. This is almost certainly a two-sided board, though, and not a four or more layer board; no need for the extra cost of inner layers for a heater controller gizmo.)

[wnjj]

Tom_M wrote:

Connect all three pins. Circuit board is double sided so traces can be on both sides.

So you didn’t remove the small pot? You can’t just put two equal sized pots in parallel since the resistance will be reduced significantly, especially if you leave the on-board one turned anywhere but to 8k ohms. Best case you get 4kohms max.

You can get close if you use a much larger value for the added one. For example if you parallel a 100kohm pot, twist the small one to 8k and the large one to 100k you will end up with 1/(1/8 + 1/100) = 7.4k max down to 0 when you turn the big pot all the way down (leaving the small one alone).

However it would probably be simpler to just remove the small one.

Also since there are traces on top, did you confirm there isn’t one to the 3rd pin there?

[Mobilesport]

Tom_M wrote:

Connect all three pins. Circuit board is double sided so traces can be on both sides.

Thanks for taking the time to label the pins , helps a bunch!

[Mobilesport]

wa8yxm wrote:
Are you sure you got the right value Pot to replace the mini? I mean if you use a 1K pot to replace a 10K odds are .. exactly what you expierence.

Yes , I measured it at 7.9 kohm

[Sam_Spade]

Gotta ask:
WHY are you doing this ?

Most of the time, a pot mounted like that is indeed used as "trim" pot that is intended to be set once and then never touched again......unless some service is done on the board.