Thread: Potentiometer taper

I would think linear, but again that may depend on the circuit you already have.
Log pots are usually used in Volume controls etc for amplifiers.
If your circuit contains Logic Intergrated Circuits......I would bet that the pot is a linear.

That was my guess(although a somewhat uneducated guess). They dont "cost" a lot so I'll order one.
Thanks
Stuart

Hi Stuart,
Watson is correct, 10K linear is what you want, usually has a "B" suffix, if you want to go upmarket a bit, you could get cermet (conductive plastic) which are much harder wearing than carbon elements.

Jaycar have these... 10K 9mm Square Potentiometer Linear Single Gang (B) - Jaycar Electronics

RS have these, (for a bit more money)
Bourns | Passives | Resistors | Trimmers, Potentiometer and Rheostat | Conductive Plastic |91A1A-B28-E15L

Regards
Ray

Thanks RayG, I have some cheap ons on the way, I doubt I will be using it much. Still undicided about how far to push the over/under limits and if you don't push them a bit it hardly seems worth it.
Stuart

Log taper pots are often approximated by having the track made three different sections of carbon resistance. If you use a log taper on a speed controller you'll notice at least one setting with a jump in speed that you can't adjust around, as the wiper goes from one track transition to the next. Conductive plastic pots are fairly reliable but you may want to find out what happens to the motor speed if it goes open circuit for one reason or another.

Originally Posted by Graziano

Conductive plastic pots are fairly reliable but you may want to find out what happens to the motor speed if it goes open circuit for one reason or another.

There is always a catch. I have no idea. All I can add is that it uses all three legs.
What if I put two 10k pots piggybacked in parallel, it would be unlikely they would both go open circuit at the same point?
Stuart

Originally Posted by Stustoys

There is always a catch. I have no idea. All I can add is that it uses all three legs.
What if I put two 10k pots piggybacked in parallel, it would be unlikely they would both go open circuit at the same point?
Stuart

That's pretty much the solution: buy a 20K pot and parallel a fixed 20K resistor across it. The pot resistance though is no longer linear but curved, though not as bad as logarithmic. The link below has some good info

Potentiometers (Beginners' Guide to Pots)

I was thinking something more like this
25K 24mm Potentiometer Linear Double Gang (B) - Jaycar Electronics
But rethinking that, it would still jump if one pot went open circuit.

Originally Posted by Stustoys

I was thinking something more like this
25K 24mm Potentiometer Linear Double Gang (B) - Jaycar Electronics
But rethinking that, it would still jump if one pot went open circuit.

Hi Stuart,

Umm... you don't need it. If the pot wiper goes open CCT at some stage in the future when it wears out.. The input volts will drop to zero, stopping the drive. The drop won't be instantaneous either, it will decellerate at whatever rate the decell is programmed.

On the drive itself there is an input CCT that will go to zero volts if nothing is connected.
Just the pot you have already ordered is all you need.

Edit: You could always put a capacitor to ground from the pot wiper, maybe 10uF and that would hold the control voltage for a short period if the pot is getting scratchy or you had some really bad vibration or something.... but as I said earlier it's not really needed.

Regards
Ray
PS 30 degress and humid in Linz...

Originally Posted by Stustoys

I was thinking something more like this
25K 24mm Potentiometer Linear Double Gang (B) - Jaycar Electronics
But rethinking that, it would still jump if one pot went open circuit.

It all depends on your speed controller, I use some small 180 V dc units that go flat out if you lose any of the three pot wires. Those Jaycar pots are about as cheap as you can get in the pot world: the terminals on these pots are riveted to the carbon track on the bakelite surface and can work loose with a bit of mechanical loading and also can go open if you get any rosin solder flux between the terminal and the carbon. After a bit of use the metal wiper wears through the carbon and the wiper goes open circuit. A good quality hermetic sealed pot with a thick conductive plastic track from somebody like Bourns will go a long way to preventing failures.

Having a guard resistor back at the speed controller just means the jump in speed won't be so bad if the pot or the wires fail or get bashed off accidentally.

Good luck with it all.