Period doorbells - AC & DC?

[Feltwell]

Hello,

I've picked up a probably 1920's electric doorbell which works on the usual "make & break" principle - the current excites a coil which pulls a sprung lever over, but this then breaks the circuit so it springs back again and so it bounces back and forth causing the bell to ring, the usual stuff:-

Doorbell.JPG (97.91 KiB) Viewed 614 times

It works fine on DC current on batteries, I've had it running at 7.5v no problem. Wired-in to mains doorbell transformer outputs are AC however? I would have thought that it would still work OK, can anyone see why not? You can get ones that output at 8 volts that should be OK.

[Feltwell]

Just answered my own question, based on the "put your finger in and see if it hurts" school of experimentation!

I stuck a multimeter across the present, ancient bell transformer - it outputs AC, though at 6.5v rather than the claimed 5v, with no load at least. Stuck a couple of temporary wires in to my "new" doorbell and it rings, a bit weakly but it rings - so 8 volts AC should be about right.

I still have eyebrows and all my fingers, the house has not caught fire, all is good! I didn't think a low voltage, fuse protected transformer could do me much harm

Once cleaned up, and the wooden cover put on straight (!), this should look more appropriate than a modern doorbell. There are some excellent reproductions out there but they all just look too shiny and perfect for the "faded grandeur"(*) of Feltwell Towers!

* Faded Victorian middle class pretensions more like - it's not that posh here!

Doorbell2.jpg (95.51 KiB) Viewed 606 times

[Gothichome]

Great, now all you need to do is make it look pretty and put it back to work.

[paulc]

A transformer will, by design, give a higher voltage reading when not under load, so 6.5V is not unexpected.
I would suggest wiring up a bridge rectifier and small capacitor which would give you a nominal 7V DC rising to 9V with no load - The bell will be more than capable of handling the extra voltage.
A small capacitor (0.1uF) across the contacts would reduce any tendency of arcing..

[Feltwell]

Thanks Paul. I had a feeling that not being under load would affect the voltage reading.

There is a little bit of arcing at the points, not much but some.

What's the point of the bridge rectifier then, why is it advantageous to convert the AC to DC? As you can no doubt tell, I'm not into electronics! I'm guessing you have to convert to DC in order to have the capacitor?

[paulc]

What's the point of the bridge rectifier then, why is it advantageous to convert the AC to DC? As you can no doubt tell, I'm not into electronics! I'm guessing you have to convert to DC in order to have the capacitor?

Electromagnets generally work better with a DC voltage. With AC, the attractive force will rise and fall with the voltage - You may even find that the thing will just sit there and buzz if the AC voltage is low enough. The capacitor is just there to smooth out the troughs and peaks after converting the AC to DC.

[LadyArowana]

What a lovely find, congratulations. I’ve had to go for the repro version ( and I did want a chrome bell because all our fittings are silvery ). We are keeping our original 🛎 on the outside though and I can recommend Peek polish for revitalising tired brass, got such good results it almost looks like new.... so that might be counterproductive for you.

[Feltwell]

Electromagnets generally work better with a DC voltage. With AC, the attractive force will rise and fall with the voltage - You may even find that the thing will just sit there and buzz if the AC voltage is low enough. The capacitor is just there to smooth out the troughs and peaks after converting the AC to DC.

Thanks Paul. So a couple of very naïve questions then - on the return from the bell push, so not under constant power, I presume I could put something like this:-

https://www.ebay.co.uk/itm/KBPC3504-Sil ... SwPK1ZVivi

I could hide that in a small enclosure under the floorboards above the bell, not sure there enough room in the bell casing - I could put the capacitor across the output there as well.

[Feltwell]

What a lovely find, congratulations. I’ve had to go for the repro version ( and I did want a chrome bell because all our fittings are silvery ). We are keeping our original 🛎 on the outside though and I can recommend Peek polish for revitalising tired brass, got such good results it almost looks like new.... so that might be counterproductive for you.

Ahh, I'm no fan of shiny brass LadyA - tarnished and a bit faded is fine for me, matches my personal appearance . I think the bell on this is actually painted brass. The wood will come up with a bit of a clean off with some meths and a careful polish.

I've been looking for an outside bell - can't find one for the life of me. This "new" internal one ( and our current one in fact) is nice and loud in our hallway, you can hear it clearly outside the front door (doesn't stop certain delivery drivers from hammering on the leaded light window in our front door as well though ), but if I'm working in the garage with the radio on it's a bit marginal if I hear it or not.

[Flyfisher]

Electromagnets generally work better with a DC voltage. With AC, the attractive force will rise and fall with the voltage - You may even find that the thing will just sit there and buzz if the AC voltage is low enough. The capacitor is just there to smooth out the troughs and peaks after converting the AC to DC.

Thanks Paul. So a couple of very naïve questions then - on the return from the bell push, so not under constant power, I presume I could put something like this:-

https://www.ebay.co.uk/itm/KBPC3504-Sil ... SwPK1ZVivi

I could hide that in a small enclosure under the floorboards above the bell, not sure there enough room in the bell casing - I could put the capacitor across the output there as well.

Somewhat over-specified but that bridge rectifier would certainly work. However, if you used the diodes in Paulc’s schematic they could probably be fitted within the bell casing. Cheaper as well, though we’re not exactly talking big money either way.

Good job keeping the bell in proper service though.

[paulc]

Somewhat over-specified but that bridge rectifier would certainly work.

Agreed. Way over the top and I could probably do something to do the job in a similar sized package including a capacitor.

If you are in no hurry, I can knock something up and pop it in the post to you FOC - Just pm me an address...

[RBailey]

if I'm working in the garage with the radio on it's a bit marginal if I hear it or not.

This is what you need for the workshop the Furze doorbell

https://www.youtube.com/watch?v=rrLtoC8nNeA


And a very nice find with the 1920's one.

[Flyfisher]

I've been looking for an outside bell - can't find one for the life of me. This "new" internal one ( and our current one in fact) is nice and loud in our hallway, you can hear it clearly outside the front door (doesn't stop certain delivery drivers from hammering on the leaded light window in our front door as well though ), but if I'm working in the garage with the radio on it's a bit marginal if I hear it or not.

I had exactly the same problem. However, I solved it with a 'smart' IP camera. I used a Hikvision 2CD2142FWD-IS dome camera (I'm sure other makes have similar functions) , which apart from the usual recording functions has various analytics built in to allow movement within a specific area or crossing a user-defined 'virtual line' to trigger a software alarm. That alarm can then be used to trigger other actions such as send an email, take a sequence of photos plus operate a physical relay, the contacts of which can be connected to a suitable bell, lamp or whatever you like.

In my case, the camera is set up to trigger when anything crosses a virtual line across our driveway entrance. This is ideal for when couriers arrive and I'm in the workshop and would miss them. The camera also supports an app on my smartphone (and any PC or tablet of course) so that when alerted I can immediately see the cause of the trigger and respond accordingly, which is handy if was the cat or very often a Muntjac deer.

Just a thought.

[Feltwell]

Somewhat over-specified but that bridge rectifier would certainly work.

Agreed. Way over the top and I could probably do something to do the job in a similar sized package including a capacitor.

If you are in no hurry, I can knock something up and pop it in the post to you FOC - Just pm me an address...

That's really kind of you Paul, and much appreciated - I'd feel guilty at taking up your time though for something so trivial!

Yes, I thought the bridge rectifier I linked to was well & truly over-specified, what attracted me though was the ability to use auto-type spade terminals to connect to it, I've got loads of those and the proper crimp tool - rather than it being PCB mount like the others. I could soon solder a small capacitor across the outputs. I reckon I can just get it in the case - I shall splash out a whole £2.79 and experiment! If it won't go then I may come back to your generous offer.

I have got a 2nd option though, not sure it'll fit in the case either mind...

https://www.ebay.co.uk/itm/Powercon-Bri ... Sw5K5ffYE8

[Feltwell]

This is what you need for the workshop the Furze doorbell

Why do I suspect that Colin is single? Or if not then he will be one day? His partner, if there is one, must be a very tolerant person....