Plastic body/shaft potentiometer - where to buy?

[Agent24]

The air speed control potentiometer in my hot air station failed.
It went open circuit on one end.

I swapped the wires around and it works now, but backwards.
That's fine, but I want to replace it in case it fails completely.

They used a standard 16mm potentiometer, but the front and shaft are plastic.
It's plastic because the control is directly connected to mains circuitry.
(It's basically a triac lamp dimmer circuit!)

Does anyone know where to find a replacement?

[harp]

You can always perform a transplant operation of shaft/body on regular B500K pot... just look that dimension shape are the same.

[mon2]

Which brand of air station? Contact the mfr for assistance. Many are very good on spare parts. We chose the BEST brand for this reason after meeting with them in Hong Kong at an electronic fair.

[stj]

i use plastic pots.
find yourself an OMEG dealer
https://www.rapidonline.com/omeg-eco...ontrol-65-1400

[Agent24]

You can always perform a transplant operation of shaft/body on regular B500K pot... just look that dimension shape are the same.

I was thinking about that, but the question is, can I transplant the wiper? I wouldn't want to use the old one as it's probably worn, but if I can, that's probably a good idea.

Which brand of air station? Contact the mfr for assistance. Many are very good on spare parts. We chose the BEST brand for this reason after meeting with them in Hong Kong at an electronic fair.

It's custom branded for a local electronics chain, but the OEM is ZhongDi. I guess I could ask, but I get a feeling they won't care. I couldn't find spares of the control PCBs for it either. They work, but the LCD driver perhaps seems messed up. But they work enough to know what temperature I'm at, so it's not too bad.

i use plastic pots.
find yourself an OMEG dealer
https://www.rapidonline.com/omeg-eco...ontrol-65-1400

I guess something like that is the fallback option, the issue with the station is the cutout for the potentiometer is not just a round hole. They have two overlapping holes kind of like a Venn diagram, and the original pot goes in the smaller one. If I tried to enlarge the small hole with a drill, it's just going to go sideways (literally and figuratively). Mounting a new potentiometer in the larger hole would make the control off-center. So I'm hoping to find something with the same bushing size.

I guess I could file the smaller hole larger with a rat-tail file, but was hoping to avoid too much messing about.... hmm

[stj]

you said the original was 16mm - so are those plastic ones.

[harp]

Not sure about plastic ones, but I think it is posible to transplant... https://m.youtube.com/watch?v=rUkrpqEmXb8 ... shaft is fixed to wiper only to ensure to not came out if pulled, otherwise, it can operate just inserting shaft into wiper. Anyway, shaft is not the same part as viper, so can be posible to change it if no other option. If you buy and replace with new, please disasemble plastic one and post photo of wiper/shaft fixture, probably only melted plastic, or metal clamp and it that case is fixable.

[harp]

Also, the wiper may not to be damaged at all (maybe need just cleaning) so in that case replacement not be needed, then it is easy fix...

[Agent24]

you said the original was 16mm - so are those plastic ones.

Yes, but the original one has a narrow bushing, M7 size. The ones you linked are M10, it would need a larger mounting hole.
The space behind the panel could fit a 24mm body potentiometer or even larger, but all of those have large bushings.

Not sure about plastic ones, but I think it is posible to transplant... https://m.youtube.com/watch?v=rUkrpqEmXb8 ... shaft is fixed to wiper only to ensure to not came out if pulled, otherwise, it can operate just inserting shaft into wiper. Anyway, shaft is not the same part as viper, so can be posible to change it if no other option. If you buy and replace with new, please disasemble plastic one and post photo of wiper/shaft fixture, probably only melted plastic, or metal clamp and it that case is fixable.

Also, the wiper may not to be damaged at all (maybe need just cleaning) so in that case replacement not be needed, then it is easy fix...

No it's definitely the track which is bad - I measure around 7 meg ohm from end-to-end, not 500K.
If I connect to the good end, the resistance increases normally as I turn the shaft, and right near the end I can read 500K between the track and wiper, but at the very end it goes open.

As I said, the potentiometer works fine when I swapped the track connection to the other end, it just works backwards.

But I have found what might be a suitable replacement...
A plastic-fronted potentiometer with switch designed for light dimmers,
It has an inbuilt switch, but I imagine I can just leave that disconnected.
https://www.aliexpress.com/item/1005005388305194.html

They sell them in lots of 5 for only a few dollars, so I might get some and see...

I haven't opened the original one yet as I didn't want my hot air station to be unusable while looking for a replacement potentiometer.

[harp]

In post #8 I mean a wiper (the metal moving part crimped to shaft), so, if is not worn or damaged, it may be using that original part, only replace carbon track from new one... Be aware, if you choosing that pot with switch, you can not expect that you can do a transplantation at all if neccesary, for me, it is unclear how is mount on knob and dimension of shaft... also, you have only one side of pot...

[Agent24]

In post #8 I mean a wiper (the metal moving part crimped to shaft), so, if is not worn or damaged, it may be using that original part, only replace carbon track from new one... Be aware, if you choosing that pot with switch, you can not expect that you can do a transplantation at all if neccesary, for me, it is unclear how is mount on knob and dimension of shaft... also, you have only one side of pot...

Yes but I don't know the condition of the original wiper or the design of the potentiometer internals, transplanting the parts may not be possible, I don't know. I don't want to break the original trying to find out, since it still does work (just in reverse).

The air control circuit only uses 2 connections, so the ones from AliExpress would work, I was thinking of replacing the whole potentiometer with one of those, as I wouldn't have to modify the front panel.

[stj]

if it still works in reverse then the track is cracked at the rivet.
strange that they chose logarithmic (B variant) over Linear,
unless they got them for cheap.

[harp]

B = linear, A = logaritmic

[stj]

from an OMEG datasheet:

Resistance Laws (Taper):
•
Linear: A
•
Nonlinear: B - Log (Audio) or C - Antilog (Reverse Audio)
•
Other laws: Please refer to Sales office

PIHER / MEGGITT show the same coding

[harp]

LOL, so yet another marking mess... "Important regional note: European potentiometers sometimes reverse these codes, with “A” meaning linear and “B” meaning logarithmic. Always verify the taper from the datasheet rather than assuming from the marking." https://pcbsync.com/potentiometer-guide/ ... to highlight in citation quote "SOMETIMES" ... in past I was confused about that, and learned in some video acronimes: A is for audio (log) and B is balanced (lin), and I think that I learn something valuable. Now I know that is bs... where is go good past time where every pot has label LIN or LOG...

[stj]

there is a 4th type, pretty rare - split-log.
used for the balance control in high-end audio.

[Agent24]

Mine is linear, I tested it. The midway point measures 250K.

I don't think the track is cracked at the terminal, since the resistance will go almost all the way to 500K when measured from the good end, then, when I turn the shaft right to the end, it goes open.