Brake van rear red light

footplate1947
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Re: Brake van rear red light

#11

Post by footplate1947 »

Brian wrote: Mon Jan 07, 2019 7:31 pm That's a Latching reed switch. Normal ones will revert immediately the magnet in moved away. Latching reed switches are becoming harder to find foir some reason?
Thanks Brian I would not have known that.................John
If only there was enough hours in the day..................John
shroomy
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Re: Brake van rear red light

#12

Post by shroomy »

John look for
magnetic reed switch normally open
On eBay loads on there
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Brian
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Re: Brake van rear red light

#13

Post by Brian »

shroomy wrote: Mon Jan 07, 2019 6:57 pm Use a reed switch instead of a single pole then wave a neo magnet wand over it to switch it on and of
shroomy wrote: Tue Jan 08, 2019 5:07 am John look for
magnetic reed switch normally open
On eBay loads on there
Hi Shroomy
How does the contact remain closed when the magnet is moved away? The reed will revert back to its normal open contact state when no magnet is near it. A magnet would have to be left next to the reed switch to enable the reed to close and be maintained closed.
Only a mechanical latching reed will lock into each position and then the magnet can be removed and the reed remains latched (or unlatched).

Basically there are four types of reed switch. Normally Open (NO) contact. Normally Closed (NC) contact. Change over contact (SPDT) and Latching.
All need a magnet to be placed close by to their glass or plastic encapsulation to effect a change of contact state.
So....
When a magnet is placed near to a Normally Open reed its contacts close all the while the magnet is close by. Move the magnet away and the contact opens.

When a magnet is placed near to a Normally Closed reed its contacts Open all the while the magnet is close by. Move the magnet away and the contact closes again.

SPDT Change-over. Is basically a combination of the above two and has three wiring connections. No magnet near by and the moving armature contact makes to the NC contact. Place an magnet near to the reed and the armature contact moves and makes connection to the NO contact. Remove the magnet and the switch reverts to its NC position. i.e. the magnet near by causes the reed to change over its contact position.

Latching this mechanically locks into the last used position and remains there until a magnet is again placed near by and it then moves to the other state and remains there. These are now quite hard to find but can be located with a search of the internet.

The only way for a standard reed switch to remain either On or Off depending on type is to have the magnet placed next to or close to the reed all the time its required to be in that state. An example could be a NC reed switch glued into the roof of a van and then when the light is not required a magnet is laid permanently on the roof until sometime later and the magnet is then removed and the light comes back on with the reed contact closing without a magnetic field near by.

Edit to add as Steve has correctly said often they are know as Bistable reed switches
Last edited by Brian on Tue Jan 08, 2019 9:10 am, edited 1 time in total.
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Steve M
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Re: Brake van rear red light

#14

Post by Steve M »

Aren’t the latching ones normally called ‘bistable’?
Couldn’t see any of them online.

I bought one of the kits for this some time ago but never got round to fitting it - can’t shift the idea that battery power is not the way to go. As I am DCC I may try adding pickups to the wagon and feeding the LED that way (fiddly but not difficult). A bit more of an issue with DC as the light would switch off when the power is turned down and without including diodes in the circuit it wouldn’t work if the wagon is turned.
"Not very stable, but incredibly versatile." ;)
shroomy
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Re: Brake van rear red light

#15

Post by shroomy »

Brian wrote: Tue Jan 08, 2019 8:45 am
shroomy wrote: Mon Jan 07, 2019 6:57 pm Use a reed switch instead of a single pole then wave a neo magnet wand over it to switch it on and of
shroomy wrote: Tue Jan 08, 2019 5:07 am John look for
magnetic reed switch normally open
On eBay loads on there
Hi Shroomy
How does the contact remain closed when the magnet is moved away? The reed will revert back to its normal open contact state when no magnet is near it. A magnet would have to be left next to the reed switch to enable the reed to close and be maintained closed.
Only a mechanical latching reed will lock into each position and then the magnet can be removed and the reed remains latched (or unlatched).

Basically there are four types of reed switch. Normally Open (NO) contact. Normally Closed (NC) contact. Change over contact (SPDT) and Latching.
All need a magnet to be placed close by to their glass or plastic encapsulation to effect a change of contact state.
So....
When a magnet is placed near to a Normally Open reed its contacts close all the while the magnet is close by. Move the magnet away and the contact opens.

When a magnet is placed near to a Normally Closed reed its contacts Open all the while the magnet is close by. Move the magnet away and the contact closes again.

SPDT Change-over. Is basically a combination of the above two and has three wiring connections. No magnet near by and the moving armature contact makes to the NC contact. Place an magnet near to the reed and the armature contact moves and makes connection to the NO contact. Remove the magnet and the switch reverts to its NC position. i.e. the magnet near by causes the reed to change over its contact position.

Latching this mechanically locks into the last used position and remains there until a magnet is again placed near by and it then moves to the other state and remains there. These are now quite hard to find but can be located with a search of the internet

The only way for a standard reed switch to remain either On or Off depending on type is to have the magnet placed next to or close to the reed all the time its required to be in that state. An example could be a NC reed switch glued into the roof of a van and then when the light is not required a magnet is laid permanently on the roof until sometime later and the magnet is then removed and the light comes back on with the reed contact closing without a magnetic field near by.

Edit to add as Steve has correctly said often they are know as Bistable reed switches
Remove my comments then
Wouldn’t like to point someone in the wrong direction
Just trying to help
We can all be wrong sometimes
Or maybe you want to take me out and flog me as well
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Brian
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Re: Brake van rear red light

#16

Post by Brian »

I'm not criticising, just ensuring correctness is maintained. Making comments on a public forum that are not quite correct would lead a reader to believe they are correct and possibly proceed along that course.

How do your lights work?
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footplate1947
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Re: Brake van rear red light

#17

Post by footplate1947 »

Morning Steve..........I don't think the battery is much of an issue as you can buy packets of 10 or more very cheaply. I thought about changing wheels and fitting pick-ups but I don't like the light only coming on when the train is moving because I am DC. And I don't like the idea of converting over 200 locos to DCC :lol: I am going to do an LMS 20 ton van to see how it turns out and if it works well will do the others.
Happy new year Steve..............John
If only there was enough hours in the day..................John
shroomy
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Re: Brake van rear red light

#18

Post by shroomy »

Brian wrote: Tue Jan 08, 2019 9:29 am I'm not criticising, just ensuring correctness is maintained. Making comments on a public forum that are not quite correct would lead a reader to believe they are correct and possibly proceed along that course.

How do your lights work?
God forbid we give people incorrect information
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Steve M
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Re: Brake van rear red light

#20

Post by Steve M »

footplate1947 wrote: Tue Jan 08, 2019 9:30 am Morning Steve..........I don't think the battery is much of an issue as you can buy packets of 10 or more very cheaply. I thought about changing wheels and fitting pick-ups but I don't like the light only coming on when the train is moving because I am DC. And I don't like the idea of converting over 200 locos to DCC :lol: I am going to do an LMS 20 ton van to see how it turns out and if it works well will do the others.
Happy new year Steve..............John
Agreed, issues with either method if wired to track pickups. For me, batteries are an issue as I wouldn’t bother to change them (I know, lazy bu##er). That’s why I may try the TrainTech kit as it is motion sensitive.
I’ve not done any investigation of motion sensitive switches so I don’t know if there is anything available that may avoid the problems Brian has highlighted with reed switches.
"Not very stable, but incredibly versatile." ;)
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