Reed Switch sticking

I’m using a reed switch in a circuit with a 12V 500mA power supply.
Rees switch data states 1A and 200V
When I check the resistance across the reed switch with a multi-meter I can see
the resistance change when close to a magnet. As expected, but the multi-meter is
a bit slow to respond so I replied it with a 12V light bulb connected to the power supply.
The light comes on when a magnet is near the reed switch, as expected, but it stays on!
I have tried a couple of reed switches with the same result.
Can you help please?


Hi Dick
What size (Watts) light bulb.
Cheers Bob
Another thing. Exactly what are the reed switches. I think some of them latch and the magnet polarity has to be reversed to unlatch.

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Hi Dick,

Looks like you’re not the first to wonder, and there are a few mechanism that can contribute:

Good catch by Robert, if you can link to your reed switch’s product page, that’ll be super helpful

Maybe measuring the current through the switch will reveal something?


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Hi Robert, I can’t tell, its and old bulb from my HR holden head light!


That might be as high as 55W. 4.6A. If your power source has supplied this it could well be the end of your reed switches. 12V + 1kΩ + LED would be a better option (and safer).
Cheers Bob


Ahhh thanks Bob, yep the reed switch is car-put!