Author Topic: Reed Switches  (Read 409 times)

Offline Kiwi_Roy

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Reed Switches
« on: December 03, 2022, 01:00:48 AM »
Handy little devices.
Reed switches are a contact hermetically sealed in a glass envelope, they are usually normally open and can be closed by a magnetic field
They have a very long life expressed in billions of operations
they tend to be rated in milliamps but 2 Amps ones are quite common
if you exceed their current capacity they can seal shut and its possible to weld weld the contacts together from which there is no recovery.
I use several on my old Eldorado in the direction/Dimmer switch.
A direction/Dimmer switch on my Eldorado, the blinkers are self cancelling when you pull the clutch in
the RH switch drives a relay in the bucket to select High or Low headlight filament
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front brake switch and rear brake switch.
The front brake switch is protected inside a brass tube and triggered by small magnets glued to the brake lever.
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The contact closing field is expressed in Amp Turns AT 15 - 20 is common
So suppose you want to trigger the switch based on a current all you need to do is wind a coil around it e.g. 15 turns of wire for 1 Amp of current or 30 turns for 1/2 Amp etc.
A sensor like that could be used to verify a lamp is working
A switch and magnet could be used as an everlasting hermetically sealed stand switch
On my V7III I use a pair of switches inside the headlight bucket triggered thru the buckets plastic case by a small magnet on the outside to switch my 10 Watt spot lights.If I dont want the lights I just move the magnet to an adjacent piece of steel.
I used one on my VII Sport to trigger the Speedhut speedometer, a magnet spinning in the cable drive at the gearbox delivered speed pulses directly to the speedo
These little devices have a million uses.
« Last Edit: December 03, 2022, 02:42:46 AM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert
Half a V9 Roamer

Moto Guzzi - making electricians out of riders since March 15 1921

Offline Petrus Rocks

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Re: Reed Switches
« Reply #1 on: December 04, 2022, 11:53:54 AM »
Thanks for the post!  So, the magnet is on, say the brake lever and the switch is positioned next to it.  Move the lever, switch comes in contact with the magnet and switch closes/ brake light come on?  I have a lot of old bikes would love to have a front brake switch.  I've seen the mechanical ones on old Japanese bikes

Offline Wayne Orwig

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Re: Reed Switches
« Reply #2 on: December 04, 2022, 01:16:41 PM »
I worked with a product at one time that was filled with reed switches on a PC board. There were also magnets attached to the PC board. So the switch was 'always' on so to speak. Then there was a plunger with a metal plate that move in between the reed switch, and magnet, to shiel the field from the switch and turn it off.
Not sure that info helps anyone, but you may run into a case were moving a thin metal plate works better.
Scientist have discovered that people will believe anything, if you first say "Scientists have discovered...."

Offline Kiwi_Roy

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Re: Reed Switches
« Reply #3 on: December 05, 2022, 02:41:36 PM »
Thanks for the post!  So, the magnet is on, say the brake lever and the switch is positioned next to it.  Move the lever, switch comes in contact with the magnet and switch closes/ brake light come on?  I have a lot of old bikes would love to have a front brake switch.  I've seen the mechanical ones on old Japanese bikes
The magnet doesn't touch the switch, it just comes close, the switch can be installed in any non-ferrous material e.g. Plastic, Aluminium, Brass or Stainless Steel
72 Eldorado
17 V7iii Special
76 Convert
Half a V9 Roamer

Moto Guzzi - making electricians out of riders since March 15 1921

Wildgoose Chase Moto Guzzi

Re: Reed Switches
« Reply #3 on: December 05, 2022, 02:41:36 PM »

Offline jcctx

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Re: Reed Switches
« Reply #4 on: December 06, 2022, 01:12:05 PM »
Many years ago in the early part of my career in Telecommunications I worked on switching systems that employed the little  devices. They often failed by "sticking" closed. The first few we replaced the elements (bitch to do); later we found by just tapping the module it was mounted on they would return to functioning. They worked as well as the repaired ones and were no more likely to fail. These early common control systems only were built for a few years as the solid state time division creatures came on line!!

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Crusty Cycle, Vintage Moto Guzzi Parts
Ambassador, Eldorado, 850T, T3, 1000SP, G5, Convert, etc. Good Prices - Fast Shipping
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