Reed Switch Question

masada · Aug 14, 2012

Is it possible that a reed switch could go bad if it was stuck to a magnet for a considerable amount of time, say a year or so? I had a couple of them sitting in a drawer and they were stuck to a pack of earth magnets. Now it looks like the contact inside the glass tube is fused together.
I guess I can't tell if the two reeds are stuck together because of the magnets somehow, or if the distance between them is just really short.

I'm a novice to electronics, but I anticipate one answer to this would be to test them. If that's the case, what's the best way to test them / with what equipment?

shrtrnd · Aug 14, 2012

If you have a multimeter, you can run a continuity check through the reed switch
using the ohm function.
Close to zero ohms for closed contact, Infinite ohm value for an open.

john monks · Aug 14, 2012

Yes. I ruined a number of relays by sticking them onto neodymium magnets.
If you did this you might try a tape demagnetizer.
In my case I gave up on them and threw them away.

CocaCola · Aug 14, 2012

john monks said:

If you did this you might try a tape demagnetizer.
Click to expand...

A wonderful tool, especially if you work with speakers that have a tendency to magnetize every thing and tool on the bench as you move stuff around...

masada · Aug 14, 2012

Thanks for the quick responses! I think I'll just get some new ones instead. Save myself the hassle. I'll have to check if Radio Shack has these. Seems like they would...

Raven Luni · Aug 14, 2012

If you fancy building your own demagnetiser, the principle is pretty simple - just an electromagnet driven by AC to give you an alternating field. Other examples include the degauss function on old CRT monitors and a larger version used on ships to stop them attracting mines.

CocaCola · Aug 14, 2012

Raven Luni said:

If you fancy building your own demagnetiser, the principle is pretty simple - just an electromagnet driven by AC to give you an alternating field. Other examples include the degauss function on old CRT monitors and a larger version used on ships to stop them attracting mines.
Click to expand...

I looked into that when I was in need of one, but since magnetic media has been on the phase out for years now you can get demagnetisers cheap now on the second hand market... I picked up an older bulk tape eraser on Ebay for $8 delivered, with $7 of that being the shipping Just had to be patient for a few weeks watching for one that wasn't involved in a stupid bid war... I use it at least once a week on my tools, that always seem to find their way to being magnetized...

masada · Aug 15, 2012

Thanks for that advice. I figure in the time it takes to order a demagnetizer, I could just get a new pack of reed switches. I suppose I'll get one soon enough as I get more into electronics.

Does anyone have a reliable place in the U.S. for me to order reed switches that you'd recommend? The size I'm looking for is about 13mm in length by 3mm wide (not including the leads).

CocaCola · Aug 15, 2012

www.jameco.com
www.mouser.com
www.digikey.com
www.alliedelec.com

masada · Aug 15, 2012

Thanks CocaCola. I tried Radio Shack and the clerk looked at me as if I had seven heads.

CocaCola · Aug 15, 2012

You can get them at Radio Shack if you gut them out of the reed relays they carry in stock...

But, yes Radio Shack has become a joke overall unless you need batteries or a cell phone...

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