Home made block bells

[RailWest]

42 minutes ago, ikcdab said:

Very nice, I don't need that on my model layout!  But I think we have something similar at watchet and Stogumber on the WSR.  There is a gong at those intermediate stations that is triggered when (I think) a token is released at either end.  I'm not sure exactly how it works, @RailWest will know more.

Ian

Sadly, I don't :-(  In fact, I was not aware that such a facility existed, although I know that at Crowcombe there is an indicator in the waiting room AIUI for when the box is switched out.

 

[5BarVT]

11 hours ago, ikcdab said:

but with 12v i have been getting a bit of sparking and carbon (?) deposits.

5V will give less.  You should be able to reduce it even more by putting a diode across the coils to divert the inductive current when the contact breaks (I think).

Paul.

[LNERGE]

A diode across the coils will delay the release of the armature. 

[Michael Hodgson]

It is standard practice in electronic circuitry to put a diode across the terminals of a relay (or bell) coil to absorb back-EMF when the coil is de-energised.  Failure to do so can generate voltage spikes that are high enough to damage small electronic components; it's also the back EMF that generates the spark. 

 

However for the reason given by LNERGE it isn't normal in block bell circuits, a nineteenth century technology.  The delay in releasing the hammer of the bell limits the speed with which you can send a distinct series of bell pulses.  It's unnecessary as there's no modern electronic components that you could fry. 

 

Even though the supply is only a few volts, if you touch the line wire terminal of a block bell while it's ringing, you will get a kick from that back EMF!

[ikcdab]

Does the material of the tapper contacts make any difference?  I have brass "peg" contacting a brass shim.  You can prob see it in pics.  If I change either to nickel silver, would that change the degree of sparking?

Ian

[LNERGE]

Relay contacts are made from silver and silver impregnated carbon so they are near impossible to weld under fault conditions. 
 

Plunger contacts can be brass to brass as in the commutator in this token machine. The plunger contacts are brass to brass also but in this case a small disc of brass is riveted into a piece of spring steel. 
 

 

[5BarVT]

Thank you to LNERGE and Michael for keeping me right.  
Glad I added “I think” as it gave me a get out for being wrong!

Paul.

[ikcdab]

So i have finished my bells.  Here is a photo and a link to a youtube video. 

 

The lables were ordered on line. Just now need to install them on the layout....

Many thanks for all that offered advice.

 

 

[LNERGE]

Did the yolk across the coils etc make a difference?

[ikcdab]

On 07/11/2022 at 20:56, LNERGE said:

Did the yolk across the coils etc make a difference?

I'm not sure, though it felt good doing it, even though i snapped my last M3 tap at the very last turn.

I'm not seeing the sparking like i did before and it does work on 5v very effectively.

What difference is it supposed to make?

Ian

Edited December 18, 2023 by ikcdab

[LNERGE]

It should be a cleaner more efficient magnetic circuit. They look and sound damn good.

[ikcdab]

Hi all, the bells I made above have been very successful. They work well and are a talking point when visitors come to run the railway.

So much so that I am now making a second pair to work with the other terminal station. 

These are identical to the first set. The only modification might be to put an adjustable stop for the striker return ("at rest") position.

But I do have a question, please. Which of the following layouts for the two coils is correct? Ie should they be wired in series or parallel and should they lie N/N or N/S?

 

On my exisiting bells it looks as if i have wired in series and when i look at pictures of the interiors of prototype bells, they also appear to be wired in series. What I cannot tell is whether i have my coils lying N/N or N/S.

Please can anyone advise on the correct wiring and layout of the two coils?

Thanks again

Ian

 

[bécasse]

Series/parallel will probably depend on the resistance of the coils and the applied voltage but I suspect that series wiring was the norm.

 

The coils will lie N/S-S/N to enable the yoke to complete the magnetic circuit - it is easy to remember, just think of a commonplace horseshoe permanent magnet which necessarily has one pole S and one pole N alongside each other.

[ikcdab]

16 minutes ago, bécasse said:

Series/parallel will probably depend on the resistance of the coils and the applied voltage but I suspect that series wiring was the norm.

 

The coils will lie N/S-S/N to enable the yoke to complete the magnetic circuit - it is easy to remember, just think of a commonplace horseshoe permanent magnet which necessarily has one pole S and one pole N alongside each other.

Thank you.  Amazon have just delivered a coil of enammelled wire, so now I'm good to go.

Ian

[ikcdab]

Here are some pics of work in progress.  As I said, much the same design as before. I have made two of everything.

The base with tapper:

 

Bell and bell pillar:

 

Interior with solenoid cores:

 

Striker plate and new adjusting screw to adjust the striker:

 

The case: