Electrical question

[nothanks]

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?

[Robin]

Can you not use a bell transformer? Eg

[tabbypurr]

won't be a problem. But any mains fuse below 3A does fail in time.

NT

[Bill Wright]

Not when the load is constant and small. I fitted 2A or 3A fuses at every one of the thousands of TV distribution head-ends and repeaters I built between 1975 and 2015 and there was no problem with spurious fuse breaks.

Bill

[nothanks]

I could, but I've already got a suitable wallwart

[Johnny B Good]

Our 34 year old central heating system is still on its original 3A fuse and I have a reasonable expectation that the fuse will outlive the boiler even if it lasts another 16 years or more (assuming the system doesn't suffer an electrical fault in the meantime).

[tabbypurr]

I fitted many 2A fuse years ago with tiny loads and many eventually failed. But not thousands. Perhaps they weren't as good quality as they appeared.

NT

[harry]

Your door bell system with transformer uses a lot of energy. Low power but on all the time. Consider getting a (wireless) battery replacement.

[tabbypurr]

nonsense

unwise

[John Rumm]

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:

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?

[Brian Gaff]

Have you tested said wart does the job adequately? I've no idea of the load but if its got any inductance in it then they don't like that very much. Brian

[Brian Gaff]

I'm always finding fuses of many sizes in plugs stopping working recently after about 10 years. the all just fell to bits in that the wire inside came off the end.

Brian

[Harry Bloomfield]

Fuses range in value from ratings of 1,000's of amps, down to just a few milliamps in equipment fuses. They only tend to blow when subjected to either a fault load or a regular surge load.

[Dave Plowman (News)]

Are you sure it is up to the job? Most bell transformers are bigger than wall warts. Since you already have the wiring in place for a proper bell transformer, why not just replace it?

[Dave Plowman (News)]

And you think battery costs will be less?

Which ain't going to last 80 years. ;-)

[nothanks]

It's fine with a big capacitor across the output.

[tabbypurr]

by definition they don't 'blow' when they break, they just break.

[tabbypurr]

yes, done that before. A switched mode wart would get rid of the wasted 2 watts.

NT

[nothanks]

It's for a servant call board, almost identical to this:

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.

[harry]

The battery is only in use for a few seconds each week. The transformer is continually drawing current