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Electrical switch question

S

SamQ aka Ah! Q!

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Sam
This is for any electrical gurus out there. Bob9f springs to mind, but he's a busy fellow, so other contributors please feel free to chip in.

The problem is from a 'Pacer' type train and the faulty item is the bimetallic(?) strip shown at the top of the unit. It's corroded and not conducting/buzzing properly. Rather like faulty points on an older car. Does anybody know of a possible replacement item?

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The lads running this for Aln Valley Railway will be gratified if we can, between us, fix this signal buzzer.

Thank you in anticipation, Sam
 
Looks to me like the principle of an old battery electric bell.

The coils get energised with DC and become electromagnets. The lump carrying the strip gets pulled down and the copper/brass strip breaks the contact and the electromagnets let go...it springs back up and makes contact... then gets pulled back down - the buzz.

So... are the coils OK? Is there a spring lifting the bar? does it move OK? Is the strip sound - no cracks or weak points?

You adjust the height of the contact screw at the top to get it to work properly.

hard to tell from just pictures so could work differently but that was my guess :)

Follow the wires and draw a circuit diagram for us if it seems different to my guess.
 
It could be the contacts are so corroded they are not connecting, I used to have a fine diamond file I used to dress the mag points on my BSA A10.
 
In the dim and distant past I have cleaned many a set of connections like that using emery cloth, diamond files did not exist in my world at the time. They can get pitted by sparks over time. It is not a bimetallic strip just a springy thing
Start by cleaning the points and then adjust them using the adjustable thingy at the top to get the right buzz tone.
 
Blimey, I've just recognised what it is.

Back in the 50s, my dad was a GPO telephone engineer (with a green van) and used to bring home buzzers and bells and bits of wire and bell batteries the size of a milk bottle.

I used to do all that you suggest above to get them buzzing.
 
Two coils is unusual maybe one holds it in to stop the buzzing.

But clean the contacts tighten the screws that hold the contacts, I have had them need tighten up to work properly.


Pete
 
There are a couple of weird things about this, and I'd trace the thing out as a starting point:

1. If the coils are in series with each other it would work at 48-50V. I know nothing about railway leccy, but this makes sense, as most phone systems work at that voltage. Do you know what voltage the unit gets when it is supposed to buzz? If they're in parallel, I'm with Pete! I can't think of any reason why one coil might operate differently to the other, however - it's possible that parallel is a safety/redundancy thing (since these are presumably driver-guard comms).

2. I note there's a terminal not connected now, but with a cut-off wire tag still attached: do you have an understanding or wiring diagram showing what each terminal is for? Could it simply be wrongly wired?

If there's a fault there and they are in series, neither coil will function... Test their resistance with a low resistance meter (traditional AVO 8, for example), to see what the windings are like.

Otherwise it doesn't look particularly poor condition. If the paxolin insulators are failing, you might fix it with a couple of layers of Kaptan tape either side (then gently reassemble), but I'd want to know how it was supposed to function before any remedial action...
 
Thank you all Gentlemen; those replies considerably help; especially the series/parallel issues and the combined voltage comment. Train carriage lighting is 24/48V; something I have yet to dabble in. .

As Neil H. presented the issue to me, he reckoned everything in the 'buzzer box' was working, but the spring steel strip - as HappyHacker identified it - was "faulty". I will go back to him and see if I/he can work through the circuit, 'school' me through incoming power and what the cut off terminal is all about, etc.

We do have a resident sparky, but he's not in until Thursday...A big problem with us all is that some folks travel quite a distance, so they limit travel to a domestically convenient day/time. Getting planets to align is sometimes easier than getting two 'needed' individuals in the same space, at the same time.

Sam
 
Flying Haggis, you're a whole good'un! Neil is under the impression the manufacturer is defunct; we'll go via that link and see what can be achieved. Thank you.

Working with 'old' trains, you end up at a brick wall so often, we have developed an unfortunate 'revert-to' attitude of: "Oh sh1t, won't get one of thoe again; another doofinkle to fabricate ...somehow".

Sam, off to do some tapping and shunting. (Yes, tapping - as a working method - really does exist).
 
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