Using an AC rated switch with a DC Voltage?

Morrolan

Hi basic newbie question here concerning switches and voltages.

I have one of these pushbuttons www.maplin.co.uk/module.aspx?ModuleNo=2332&doy=13m6#overview rated at 10A/250Vac, and measuring the continuity it closes the circuit when pressed and opens it when released.

Yet, when I apply a DC voltage it doesn't register that the circuit is closed when pressed?

Is there a valid reason why this would be so?

Many thanks in advance,
Morrolan

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Flying is simple. You just throw yourself at the ground and miss.

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
Stephen Hawking

Leon

It should work with DC. What voltage are you using and what are you switching with it?

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Mike Green

It should work. You have to derate it when you use it with DC. A 10A AC rated switch might be good for 2-3A of DC. If you're switching very low currents (like logic levels), the switch might not conduct well enough at these low currents. Sometimes the high current / high voltage switches count on the 100 or 200V to burn off an oxide layer on the contacts. Low voltage / current switches often are gold or silver plated to provide a low resistance contact at low voltages and low currents.

LoopyByteloose

There are some differences is what happens to an AC switch versus a DC switch as it ages. And AC switches are most usually for power while DC switches are either for power or for logic.

Anyone that has tuned up an old motorcycle or car with traditional ignition points will know that DC causes metal to migrate in only one direction. The contacts become worn out much faster at compariable current flows.

With AC, the metal goes back and forth between the contacts. With AC, this results in less overall wear and tear. And in some cases, special alloys or mercury wetting have been able to make AC switches very durable at high amperage.

So with DC, one has to de-rate. You often see relays with the contacts clearly de-rated for DC - usually lower voltages and lower amps. But it is often harder to find switches clearly labled for both DC and AC as almost nothing is high amperage DC any more. Automotive switches are about the only remaining devices.

If you are using logic-level DC it might be easier to go to something that includes innate debouncing of the switch, like a Hall-effect push button. Debouncing is another bugaboo that plagues logic level push buttons. The only drawback is that such switches are likely to NOT be packaged as an easy panel mounting.

As Mike Green points out, while an AC switch may work; it is just as possible for it to be insensitive to small voltages and small currents.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

PJAllen

What's all this stuff?·

I have yet to see a switch that cannot be sorted with an ohmmeter (which, by the way, is a DC test.)·

So, if you've verified "continuity" with an ohmmeter, then it's your application.· Let's have more about that.