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Minky

Using Neo Magnets with Reed switches

Finally gotten magnets that are sufficiently powerful enough to activate my Reed switches and have tested the two different types on a simple LED circuit. Work fine.  

Sooo..
What's the best way to to fix them into shells?
I think this is a daft question but, will heat shrink over the Reed switch (or magnet) cause any 'interference' between them?
Will the magnets fade over time?
Boff mentioned that EMF is a factor when using these so in regard placement.. Not near motors, are they okay next to other circuits?

Thanks for any advice
OldNoob

Keep them away from any EMF sensitive stuff. I never put any heatshrink over the glass tube of the reed switch.
To fix them in you need to heavily scuff the nickel plating on the side you intend to glue to, then use a high strength epoxy like araldite slow to hold them in place. I have had limited success with Devcon on them, it doesn't like the nickel plating much. You need to get a really good amount of adhesive around the magnet or it just pulls out of the glue.
SSGT

Heatshrink should be fine. You can't "block" a magnetic field per-se you can only divert it (e.g. through a material that channels magnetic flux such as iron). The only thing it will do is increase the distance between the magnet and the reed switch, which will reduce the strength of the magnetic field at the reed switch, but unless it's very thick heatshrink that shouldn't be an issue.

EMF generation shouldn't be too much of an issue either as long as the magnet isn't moving fairly closely along a wire (think back to motors - the magnitude of the EMF generated depends on the rate of change of magnetic flux "cutting" through a wire which in turn depends on the relative speed, and distance, between the magnet and the wire). The field of the magnet could interact with the field generated by a motor's magnets (which may alter the motor's performance) but again you'd need to get the magnet pretty close to have the fields interact in any significant way.
Minky

Thanks both. I've got two places to mount them on, a couple on plunger rods of the roughcut (so presumably high Gs) and a few on the rack in the same blaster (so low Gs). I was thinking about seating the ones on the rack inside heat shrink and attaching the lot. The ones on the plunger rods are going to experience pretty massive acceleration and deceleration so I'm thinking maybe a plasticard mount devconed on.

Worth noting that I think reed switches 'sense' through the ferrous metals in them, which includes the pins/terminals. From my very limited testing of the switches I have the glass part actually appears to be the least sensitive part.

SSGT - so another circuit being made near to the reed switch won't affect it? There's not chance of some kind of electromagnetism?
OldNoob

I would be very surprised if any on the plunger rods stay there.
Minky

I'm struggling for space for switches...



..not impossible but hard. Whereas I think I can either fit the magnets...



...inside the the plunger rods themselves or onto them in a couple of bits of 1.5mm plasticard with a hole through them just big enough to force the magnet in.
SSGT

Minky wrote:
so another circuit being made near to the reed switch won't affect it? There's not chance of some kind of electromagnetism?

If you mean will a current passing through a nearby wire affect the reed switch then no, it shouldn't. The field strength around a single piece of wire when passing an electric current through it should be pretty minimal even at largish currents - you'd need to make a coil (ideally with an iron core) and position it very close the the switch.

Also, a reed switch doesn't work simply by using the magnet to attract the switch contacts towards the magnet, it works due to the switch contacts channelling the magnetic field through them which induces magnetic poles on each of the contacts which acts to pull them towards each other. Since field orientation matters so does magnet (pole) orientation and position. This video is quite good at showing the different positions/orientations that can activate a reed switch.

If you physically mount the magnet by surrounding it in plastic/epoxy it should stay in place.
Minky

Yes, you got the meaning of my question dead on. Thank you.

I knew that only certain Reed switches were bothered by specific polarity and I'd realised that the area that was affected by the magnetic field was larger than the reeds themselves (see my little test circuit below) but I didn't know how different areas of the switch would be affected differently so thank you for the link!
I'm enjoying thinking of potential uses for these and it makes me glad I bought two types. The one I'm testing below is much more sensitive across a much greater area than the other that has to have the magnet in a much more closer and specific location/orientation.


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