[WalterBright]

My old Dodge instruments need 5 volts, so there's a mechanical device to convert 12V to 5V. It involves heating a bimetalic strip that opens and closes a circuit quickly, i.e. buzzing, which produces 5V.

Some people have decided to fix this by using an electronic voltage circuit to get a clean 5V from the noisy 12V supply. But the instruments just wouldn't work right.

It seems the instruments relied on the 5V supply being jittery. With a smooth voltage, the mechanical instruments would get stuck.

Watch a pilot in an older airplane. He'll tap the gauges, too, to get an accurate reading.

[Johnythree]

Actually the reason is that the instrument itself also uses a bi-metal strip and it relies on the ratio between the two strips to cancel out voltage fluctuations.

It's very elegant, but if you take out one, it goes haywire.

[zkms]

> My old Dodge instruments need 5 volts, so there's a mechanical device to convert 12V to 5V. It involves heating a bimetalic strip that opens and closes a circuit quickly, i.e. buzzing, which produces 5V.

Are you sure that this is not a https://en.wikipedia.org/wiki/Vibrator_(electronic) that would be powered by a solenoid and not just a bimetallic strip?

[WalterBright]

I think you're right.

[zkms]

No.

You were actually initially right, I searched for that actual part and it is indeed a bimetallic strip along with a heater (that turns off when the strip moves away from a contact) and not a device with a solenoid/relay.

Apparently whatever it supplies is tolerant of that sort of interruptions in its power source -- I imagine that it would operate on a quite lower frequency than a "vibrator"-type power supply where magnetic force moves the contacts (and elasticity returns them).

[WalterBright]

I read about this probably 10 years ago, my memory was clearly a bit faulty on it. I didn't want to take the device on my Dodge apart just to verify it :-).

The thing is, the instruments require the noisy 5V.

You can buy kits with an electronic 5V source, and also to replace the old guts of the instruments with modern ones. That retains the original look, with modern accuracy and performance.