# Axle magnets and 2k2



## Big Tracks (Jan 3, 2008)

I installed 4 Radio Shack 3/16 round magnets on the axle of my connie. I can only get 2 chuffs per revolution. When that did not work, I installed 
them on the Bachmann sound trigger. So far, the only thing that gives me 4 chuffs in the mechanical trigger that came with the loco.
Anybody have any idea why this is happining. I removed the 2 magnets that would not trip the reed switch and turned them over
thinking that there was an opposing magnetic field. No luck.


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## Bill Swindell (Jan 2, 2008)

In my experience, that type of magnet is not really strong enough for reliable triggering of the reed switch. I would suggest that you either use Phoenix magnets or find some source of very strong magnets. With the correct magnets and reed switch positioning, you will get 4 chuff's per revolution as desired.


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## Greg Elmassian (Jan 3, 2008)

Magnets too close together could also be the problem. If this is the case, smaller, stonger magnets further apart, i.e. build up a "drum" of larger diameter on the axle. 

Just another possibility. 

Regards, Greg 

p.s. you might find that at higher speeds you want fewer chuffs... not 4...


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## Big Tracks (Jan 3, 2008)

Greg, 
Thanks for your response. The magnets are very strong. Will pull the each other across the surface of a 2X4. I did use an old Bachmann sound drum, from my connie, for the larger diameter, to no avail. Maybe the magnets are too strong. I need to find someplace locally, except radio shack, that has smaller magnets. Mail ordering for all my model RR needs is getting to be a real pain. 

Rick


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## Big Tracks (Jan 3, 2008)

Hi Bill, 

I did not know that Phoenix sells small magnets. I was using their brown reed switch but I think the trick is my magnets maybe too strong as they will pull each other across a 2X4 

Rick


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## armorsmith (Jun 1, 2008)

Another suggestion might be to make 2 sets of 2 magnets separated on the axle with 2 reed switches wired in parallel. ie. One pair of magnets 180 degrees opposed on the left side of the axle, the other pair 180 degrees opposed on the right side of the axle and 90 degrees to the first set. A little more complicated, but possibly able to utilize the magnets you have. Using two sets of magnets may also allow placing each set on a different axle. Numerous options. 

Bob C.


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## Semper Vaporo (Jan 2, 2008)

It is possible that your magnets are TOO strong.

Consider how a reed switch works;

It has two metal strips inside it, one from each end. The metal is capable of taking on a magnetic field, but will not keep it. When a magnetic field is nearby the strips become magnetized and attract each other. The inner ends of the two strips extend just past each other (overlap) but one of the metal stripes has an embossed crimp (the embossed crimp is like an oil can bottom or those old "Frog clickers" toys of years ago) such as to try to remain straight and due to the placement of the strips in the switch the ends of the strips do not touch each other. When the magnetic field is strong enough the crimp gives way and the strip bends so the ends will touch. When the ends touch the electric circuit is completed.

If the magnetic field becomes weaker, the embossing will cause the strips to click back to the straight shape and ends no longer touch, thus opening the electrical circuit.

Magnets are not an ON/OFF thing in reality. The field varies in strength by distance. The thing that creates the ON/OFF action is the crimp giving way when the field is just strong enough or just weak enough. There is a Hysterysis associated with this. A certain strength is required to overcome the crimp, but a lessor field will hold the bend such that a much weaker field is required to be reached before the crimp can straighten out the metal strip and break the electrical circuit.

When you mount the magnets on a wheel such as each one approaches the reed switch in turn and then receeds from it. If the magnets are strong enough one magnet may not get far enough away to let the crimp recover and pull the strips apart before the next magnet is supplying enough magnetic field to hold the switch closed and you thus get not chuffing from the circuit because the switch never opens once closed. Or possibly, it may open only between two magnets or remains closed between two magnets. It is a delicate ballance of supplying enough magnetic field to cause the switch to close (and stay closed long enough for the chuff circuit to recognize that it is closed) and not so much as to hold the switch closed during the time between the successive magnets.

Spacing the magnets farther apart (as on a larger diameter wheel) and adjusting the distance from the magnets to the reed switch can be used to get the switch to close when one magnet is approaching the closest distance and still allow the switch to open when the magnet has receeded in distance before the next magnet is so close as to keep the switch closed.

Stronger magnets are nice, but you have to make sure the balance is right for the particular reed switch in use and the distances involved.


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