Small, Slider Type SPST "Slider" Switches: Reliability Of ?

[Robert11]

Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss, to operate as a gravity system between the high and low temp. limits of the furnace. Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use. Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

Bob

[trader_4]

Probably depends greatly on whether it's a quality switch from a major supplier or a 10 cent one from Ebay. I would suspect oxidation would be the problem. Using a cheap alloy would make it more problematic. They use dip switches of various kinds on circuit boards in furnaces and similar and I guess they mostly work. Though those switches probably rarely are moved, to it's a bit different.

[Clare Snyder]

The contacts oxidize a WEE little bit and the milivolts cannot get through.

[Dean Hoffman]

Is there any reason he couldn't replace it with a regular three way mercury switch?

[Jim E]

[snip]

Mercury is considered a hazardous material?

[rbowman]

It's a common problem for dry circuits (very little current or voltage across the contacts). Relays and switches meant for those sort of applications often have gold plated contacts or are designed with a wiping action across the contacts.

Are the contacts exposed or is the switch sealed? Back in the day of backplanes with edge connectors, the Pink Pearl fix was the first thing to try. Pink Pearl is a name for a Papermate eraser which worked very well for removing oxidation from the fingers on the circuit board.

[Clare Snyder]

The old-tyme TV tuner cleaner works well - or De-Ox_it. Squirt, operate the switch 50 times or so and try it.

[makolber]

+1 the problem is due to a combination of the material the contacts are made of and the low voltage and current.

I would replace the switch and just slide the switch once a month to keep it clean as a maintenance item.

mark