Waterproof potentiometer?

August 19, 2009 2:42 PM

Attention electronics tinkerers: I need to find a waterproof potentiometer without breaking my budget, and I'm not having much luck. Long-winded explanation inside.

I'm looking for a waterproof potentiometer, though water resistant would also work. This is for a one-off project for a boat (a remote hand controller for a trolling motor), so it could get wet. Spec-wise, I am looking for one like this one, offered by PrecisionSales.com:

p/n 87M43-102
1k Ohm
1 watt (or thereabouts is fine)
1 turn (prefer non-continuous, so something like 180° - 330° rotation would be ideal)
panel/bushing mount
waterproof/water resistant

Unfortunately, the above website is more or less a dead end; it seems to lead to a single individual, who is on vacation until the end of the month. And I'd like to get this before then if at all possible.

Digging a little deeper, I found what I believe to be the manufacturer of the above component, maureyinstrument.com. We exchanged email, and they stated that the above item isn't really water resistant, never mind water proof. They have suggested a slightly different potentiometer, their p/n 87-P82, which meets many of my requirements, but which also costs $189 each...which may be a very fair price, but it's more than I want to spend on this component for this project. For comparison's sake, I can find a basic, non-water resistant 1k Ohm potentiometer for $1.49, and I'm sure I could one cheaper than that if I looked harder.

I've perused the Digikey and Mouser sites, but they are a) overwhelming, and b) don't seem to carry waterproof potentiometers.

So...I'm looking for suggestions on where I might find a cheaper water resistant bushing-style potentiometer. Due to form factors in the controller I'm building, it needs to be bushing-style, and not a linear-style. I'd ask for suggestions about waterproofing a cheaper potentiometer, but I'd really rather find one that was designed for a harsh environment.

Any ideas?

posted by plowhand to Technology (9 answers total)

Could you get a normal pot and enclose it in a waterproof box, with some kind of extended axle and a knob on the outside of the box?
posted by DMan at 3:17 PM on August 19, 2009

Best answer: If you search for "potentiometer IP66" (IP66 being a dust- and water-resistant enclosure) you will get a lot of results; first one here.

The throttle position sensor on many cars is a 3/4 turn potentiometer, though I'm not so sure 1 k ohm is standard. Quite a few of these are suitable for harsh usage.
posted by jet_silver at 3:24 PM on August 19, 2009 [2 favorites]

Second the make-your-own enclosure for a low-cost pot. Mount the pot in a small watertight container with a seal around the shaft.

mcmaster.com sells rotary switch shaft seals for under $4 for 1/4"-32 and 3/8"-32 bushings. e.g. part number 70205K92, catalog page 869. Other seals available as well under $10, for example see pg 3439.
posted by buzzv at 3:28 PM on August 19, 2009

I think sealing it within an enclosure with a shaft seal is the best way to go. If that's not possible, consider redesigning the circuit to use a rotary encoder (e.g. optical [IP68 rated] or magnetic [IP67 rated]) instead of a pot. You have the added benefit that an encoder is much more precise, durable, and rugged than a pot.
posted by Rhomboid at 4:10 PM on August 19, 2009

And if you're on the cheap, you could even take the rotary encoder from an old ball mouse and use that. The LED/photodiode assembly shouldn't care about moisture as long as the electrical leads are sealed (e.g. hot melt glue, silicon, etc.)
posted by Rhomboid at 4:16 PM on August 19, 2009

on the make-your-own tip, you can improve the waterproofness of a given setup by sealing the container and filling it with mineral oil. Mineral oil is not electrically conductive, but it does repel water.
posted by idiopath at 4:29 PM on August 19, 2009

Response by poster: Thanks so much jet_silver -- the IP66 (and IP67/IP68) designations are really helpful! I'm making a lot more progress with that as an additional qualifier in the search terms.

Rhomboid, I think a rotary encoder will be overkill for this application, and unfortunately, designing a circuit to use a rotary encoder as a variable resistor is beyond my skill set.

More background: I have a small 12' fishing boat with a bow-mounted trolling motor. The only controller for the trolling motor is a foot switch, but I find it very annoying to use, especially since I usually run the boat from a sitting position in the rear, near the gas motor. I want to transfer the controls to a hand controller of my own design. The switches in the foot controller are simple, analog switches, with one linear "membrane"-type potentiometer for trolling motor speed. The wiring is all 18 ga., so neither the switches nor potentiometer are carrying any real power. I think I can easily copy transfer these controls to a hand-held unit.

While I could make my own seal, my preference is to start with a sealed potentiometer.

Since you mention McMaster-Carr, I should say I'm using one of these hand-held polyamide enclosures (9215K12) for my new enclosure. The finished unit will hold three switches and the potentiometer.
posted by plowhand at 4:47 PM on August 19, 2009

Best answer: C3 Controls has NEMA rated Pots.
posted by Confess, Fletch at 10:21 PM on August 19, 2009

Response by poster: Thanks, everyone. The C3 Controls pot was perfect -- right features, right price. Thanks, Confess, Fletch. And thanks jet_blue, Rhomboid, and everyone else for the info and suggestions -- I know a lot more than I did when I started.
posted by plowhand at 11:41 PM on August 19, 2009