Failed microswitch

[hamster_nz]

I've repaired a Voice recorder switch (something like https://www.fishpond.co.nz/Health/AbleNet-10002100-Bigmack-Communicator/0736846869142

The fault was a standard microswtich - rated 1/2A 125VDC, 1/4A 250V.

The fault was that the device would play back, but it wouldn't record. The cause was that the NO contact would not stay closed while the switch was depressed. The switch is grounding a pull-up resistor on the microcontroller, so only a few mA is being switched.

Another complicating issue as that the return spring on the switch was being used as the 'lifter' for the external switch plate - when I replaced the switch I had to include some open-cell foam to give my weaker microswitch some added oomph.

My questions:

- Does using a mains-rated switch to switch minuscule currents and voltages case it to fail early (ie. do they need the higher voltages to keep the contacts clean?)
- If a microswitch is not the correct thing to use, what is the correct thing to use?
- Should there be mechanical isolation from the switch pad to the switch - so if somebody bashes the switch the full force is not directly transferred to the switch?
- is using the switch as a spring 'bad form'?
- Where can I get some microswitches with greater lifting power?

edit: fix typos

[hamster_nz]

So I had a look to see what was wrong...

It looks like there is something like an oxide or something building up on not the switch contacts but the pivot point (on the left in pictures). It also built up the unused NC contact. Doesn't seem to be moisture or contamination.

Maybe it is some sort of corrosion from the DC potential over it? - I can't help feeling that if the wires were swapped over if would only upset the NO contact, where it would be harmless...

[Gyro]

Mains rated microswitches will use a contact material suited to mains switching without excessive arcing, probably one of the silver alloys, eg. Silver Cadmium oxide, which is not good for signal switching.

If you're lucky, you may be able to find an alternative switch with gold flashed contacts. Check for minimum current/voltage spec.

You could try adding a capacitor directly across the switch contacts. That would give a current pulse through the contacts as they close which might be sufficient to allow them to self-clean.

[SeanB]

Replacement should be a V3 style microswitch with gold plated contacts, not a 10A one. This is designed for low level switching reliably.