5 ms·

Bimetallic strips are pretty slow, I can't imagine them being audible. I'd guess what you're hearing is almost certainly a relay, very likely driven by the bime

Bimetallic strips are pretty slow, I can't imagine them being audible. I'd guess what you're hearing is almost certainly a relay, very likely driven by the bimetallic strip edit: Replies have pointed out that they sometimes do "snap", so i guess i'm wrong there. I'm still pretty sure anything in a kettle/coffee pot/toaster etc would be a relay to avoid arcing edit 2: i'm just going to shut up now

frabert 3y ago
It's totally possible to shape a bimetallic strip in a way that makes it bistable, thus clicking between the two states, just like an electrical switch which uses springs inside which are normally not noisy either.
- HeyLaughingBoy 3y ago
  This is actually the only type that I've ever seen.
  - bagels 3y ago
    They used to use a coiled strip with a mercury switch on the end of it.
    - HeyLaughingBoy 3y ago
      Right!!! In the old thermostats. I forgot about those.
- aidenn0 3y ago
  One construction I've seen is with a permanent magnet for hysteresis; the strip jumps to the magnet when it gets close, and then requires extra tension to release. The thermostat in my first apartment worked this way (and it looked to me like the strip was actually carrying the current to operate the gas heater; presumably a NC valve).
- quickthrowman 3y ago
  Indeed, this is how (non semi-conductor) motor overload relays (aka ‘heaters’) work, a simple bimetallic strip with two states. https://www.c3controls.com/white-paper/what-is-overload-protection/ https://www.c3controls.com/white-paper/what-is-overload-prot...
tgv 3y ago
Also not great for higher voltages and power.
- idiotsecant 3y ago
  You can in fact purchase right this very moment bimetallic temperature switches for nearly arbitrary voltage / current combinations.
  - Turing_Machine 3y ago
    Right. Mouser (a general electric/electronic component distributor in the USA) has 'em on the shelf rated for 600 V, 50 A. I'm sure that specialty distributors offer a much wider range.
- Pathogen-David 3y ago
  I've opened up my water kettle before and it uses a little bimetalic strip to shut itself off once the water is boiling. According to the label it sucks 1500 watts and it's just shoving mains voltage through the heating coil.
- deleted 3y ago
  [deleted]
rcxdude 3y ago
It depends on the kind: a lot of bimetallic strips are designed to have hysteresis, so they snap to a different shape at one temperature and then stay like that until the cool down further (at which point they snap back), and this can produce a click.
sarchertech 3y ago
A bimetallic strip making a noise when it flexes is the origin of the original blinker noise. Cars these days just emulate the sound, but that’s where it came from.
- rjmunro 3y ago
  Technology connections covered them as part of this video: https://youtu.be/2z5A-COlDPk?t=330 https://youtu.be/2z5A-COlDPk?t=330
jacquesm 3y ago
> I'm still pretty sure anything in a kettle/coffee pot/toaster etc would be a relay to avoid arcing You'd be wrong again. The Bi-Metal strip switches the current directly.
- byhemechi 3y ago
  ahh well, guess i should probably just stop saying anything at this point

frabert 3y ago

It's totally possible to shape a bimetallic strip in a way that makes it bistable, thus clicking between the two states, just like an electrical switch which uses springs inside which are normally not noisy either.

HeyLaughingBoy 3y ago
This is actually the only type that I've ever seen.
- bagels 3y ago
  They used to use a coiled strip with a mercury switch on the end of it.
  - HeyLaughingBoy 3y ago
    Right!!! In the old thermostats. I forgot about those.
aidenn0 3y ago
One construction I've seen is with a permanent magnet for hysteresis; the strip jumps to the magnet when it gets close, and then requires extra tension to release. The thermostat in my first apartment worked this way (and it looked to me like the strip was actually carrying the current to operate the gas heater; presumably a NC valve).
quickthrowman 3y ago
Indeed, this is how (non semi-conductor) motor overload relays (aka ‘heaters’) work, a simple bimetallic strip with two states. https://www.c3controls.com/white-paper/what-is-overload-protection/ https://www.c3controls.com/white-paper/what-is-overload-prot...

tgv 3y ago

Also not great for higher voltages and power.

idiotsecant 3y ago
You can in fact purchase right this very moment bimetallic temperature switches for nearly arbitrary voltage / current combinations.
- Turing_Machine 3y ago
  Right. Mouser (a general electric/electronic component distributor in the USA) has 'em on the shelf rated for 600 V, 50 A. I'm sure that specialty distributors offer a much wider range.
Pathogen-David 3y ago
I've opened up my water kettle before and it uses a little bimetalic strip to shut itself off once the water is boiling. According to the label it sucks 1500 watts and it's just shoving mains voltage through the heating coil.
deleted 3y ago
[deleted]

rcxdude 3y ago

It depends on the kind: a lot of bimetallic strips are designed to have hysteresis, so they snap to a different shape at one temperature and then stay like that until the cool down further (at which point they snap back), and this can produce a click.

sarchertech 3y ago

A bimetallic strip making a noise when it flexes is the origin of the original blinker noise. Cars these days just emulate the sound, but that’s where it came from.

rjmunro 3y ago
Technology connections covered them as part of this video: https://youtu.be/2z5A-COlDPk?t=330 https://youtu.be/2z5A-COlDPk?t=330

jacquesm 3y ago

> I'm still pretty sure anything in a kettle/coffee pot/toaster etc would be a relay to avoid arcing You'd be wrong again. The Bi-Metal strip switches the current directly.

byhemechi 3y ago
ahh well, guess i should probably just stop saying anything at this point