On 03/01/2018 19:42, wrote:
On Wednesday, 3 January 2018 12:30:33 UTC, wrote:
On 03/01/2018 08:35, John Rumm wrote:
On 02/01/2018 23:10, wrote:

I need to replace an ancient bell/call box power supply with a modern
wallwart. The original transformer (from the 1930s, with internal fuses
in both L and N) was wired into the lighting circuit. It would be very
difficult to get non-lighting power to this location (near the ceiling,
in the kitchen), I don't have space for a fused spur and I can't find a
13A socket with a built-in fuse. I'm planning on using a standard 13A
socket, fitting an internal 500mA in-line fuse and adding a suitable
label to the socket.
What does the jury think?

Nothing wrong with it in principle. A 3A fuse would probably be more
useful.

You could also look at 2A plugs/sockets if you can't find a
PSU/transformer that can be wired directly. e.g:

https://www.tlc-direct.co.uk/Products/CB7046.html

Having said that, you can get neat bell transformers that can be wired
directly. What is it to power? Do you need DC or is AC ok?


It's for a servant call board, almost identical to this:
https://www.youtube.com/watch?v=VNZxBMfUmZ8. There's also a repeater
bell at the far end of the house.

It was running, very feebly, on AC. I experimented with a bench supply
and found that it's much happier with about 5V DC so found a 5V wart in
a box and added a 470uF cap inside the indicator box. The socket needs
to be 13A because of the wart plug.

I got better results with several thousand uF at the PSU end of the wire before the switch. Electromagnetic movements benefit from a good kick. That was running an old mercury switch dingdong.


NT

I didn't explain that well. The cap is inside the box but across the
output of the wart, if it was across the bell it would make things worse.