Multi turn Pot failures

[floobydust]

Do an autopsy on one of the failed pots, take it apart.

[xavier60]

Do an autopsy on one of the failed pots, take it apart.

I did. The helical wound wire that is the resistance element, gets broken.
https://epci.eu/wp-content/uploads/2019/10/Figure-R4-31-Cutaway-view-of-a-multi-turn-bushing-mount-potentiometer.jpg
The Pot then functions as a switch, outputting either 0V of full reference source, 5V.

[maxwell3e10]

  Either design the circuit to be tolerant of that failure or buy better parts like from Bourns.

Yea, that's why I was surprised a bunch of (what I believe were genuine) Bourns turned bad. Luckily the supply was designed properly, so no damage done.

[xavier60]

As well as the WXD3 series which have proven reliable so far, Bochen also make the a 3590, http://www.bochen-cn.com/3590.html
Maybe they are good quality?

[floobydust]

What is breaking the wire? Just weird. Is it just trashy quality or corrosion or maybe you have an overload damaging it (but rated 2W). The wire is NiCr I thought.
Most wire metallurgy from china is pretty bad, lots of impurities and lumpy diameter.
This might be the reason the Bourns are $20. Those fail from old age oxidation so I have taken them apart and cleaned them.

A shorted LM317 will smoke the potentiometer so I add a fuse/PTC after realizing how expensive a quality multi-turn pot is, much more than the IC.

[Pawelr98]

For one, doing a slight redesign of a control loop to stop the voltage from shooting up is a good start.
With simple feedback I just connect a pullup resistor, if the potentiometer breaks, then the voltage at the feedback input goes high (higher than usual feedback voltage) and the output goes to 0V.
And for my designs that is a basic thing, because I often use two pots in series to get that rough/precise adjustment.

Those 20$ multiturn pots are more expensive than the devices that I build, so I just buy old military stock stuff, that I know is fairly high quality.
Mainly older US-made, USSR-made and other non-chinese things.
In fact often the prices are lower than the chinese things.

[Vovk_Z]

It were times when milty-turn 'Bourns' (?) cost 2 eur and worked fine. Now we have the same 2 eur pots which fail after a short time, and there are $10-$15 ones which I don't know how reliable are (because it seems too costly for me).