Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Re: Reliable switch for carrying DC

Posted by Steve Eddy on April 16, 2003 at 20:57:52

In Reply to: Reliable switch for carrying DC posted by csown on April 16, 2003 at 06:18:22:

The requirement is for 24V at about 100mA, probably more because the caps are starved to start with. This means we can dissapate up to 2W or so in the worst case. There is an initial spark, some soot deposition, and a bit of welding. Not great for a switch.

The sparking is due to lead inductance. 24 volts isn't enough to break down the air and cause a spark. When you have current flowing through an inductance and the current suddenly stops, you can get a significant flyback voltage which is sufficient to cause sparking and the resultant sooting and welding.

Before you go shopping for a new switch, try placing some small bypass caps (say 0.01uF or so) across the switch terminals and see if your sparking is reduced.

If you can provide a drawing of just what you're switching (I'm assuming it's some sort of power supply) and how it's being switched, I can draw you something up and show you where to place the caps.

se

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