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Hartley118 17th May 2021 2:14 pm

Re: Metamec A909 clock- broken coil

Originally Posted by Jamey80 (Post 1375070)
If I unwind it gently on to a suitable bobbin as far as the break, would I damage the insulation on the wire or would it be ok? Not sure how much you can flex enamelled wire, but reusing it would avoid problems sourcing a replacement.
Looks like I'm going to need to find some meccano.
I will protect it with a 20mA fuse if I rewind it like this- don't want it catching fire if I screw something up!

If you were to find the break early on in your unwinding process, I guess it would be worth checking the resistance of the remaining coil and comparing it with the resistance of the removed wire. That would give you an idea of the appropriate transformer ratio required to run the clock, or even a series lamp or capacitor.

I guess though that Murphy's Law would ensure that the break turns out to be near the centre of the coil. In that case, as already suggested, a rewind with a manageable thicker wire gauge and running from a lower voltage transformer would work, Maybe 110V?

I guess that none of this is economically sensible, but we all know what it's like to get one's teeth into a technical challenge!

Best of luck.


Jamey80 20th May 2021 8:13 am

Re: Metamec A909 clock- broken coil
I note that there seems to be some disagreement here about how old something has to be to be valuable or worth looking after. For my part, I don't care what it's worth as I'm not going to sell it, I want to enjoy it, and anything worth keeping is worth looking after.

Time doesn't stop, despite what this clock may currently be claiming, and everything will become old eventually.

Station X 20th May 2021 9:00 am

Re: Metamec A909 clock- broken coil
I've successfully rewound simple coils using a hand drill held in the bench vice with the coil former mounted on a piece of rod held in the chuck. I've also heard of something similar being done with an electric screwdriver.

The trouble with any form of powered coil winder, when winding thin wire, is that the wire tends to snap due to the sudden jerk when the motor is started.

If the wire is wound off a rotating spool this can also put strain on the wire. For this reason spools of wire generally have curved end cheeks so that the wire can be pulled off the end of the spool without having to rotate it.

paulsherwin 20th May 2021 10:00 am

Re: Metamec A909 clock- broken coil
You may be able to rewind the coil using a sewing machine bobbin winder.

Perhaps the best compromise is to rewind the coil with thicker wire for 6V or 12V operation, and power the clock using a transformer in a wall wart. Some people like to convert synchronous clocks to LV operation simply for safety reasons, and there is plenty of info around if you google.

Originally Posted by Jamey80 (Post 1376123)
I note that there seems to be some disagreement here about how old something has to be to be valuable or worth looking after.

I don't think there are any real disagreements, just several alternative solutions depending on your priorities and expertise.

Jamey80 24th May 2021 10:40 am

Re: Metamec A909 clock- broken coil
1 Attachment(s)
I found a break!
This is the unspooler I made out of a coat hanger and a lint roller... It's a bit ugly but it works, the handle is a friction fit so plenty of slip if the wire gets stuck.
I'm getting 4.3kΩ resistance through the wire on the cardboard tube (that's 513m of wire, counting the turns (3950) and circumference of the tube (0.13m), or 12800ish turns of the coil) but unfortunately still open circuit on the remaining coil, so I guess I need to keep going.

Nickthedentist 24th May 2021 12:50 pm

Re: Metamec A909 clock- broken coil
I would definitely try re-winding it with thicker wire for low-voltage operation.

It's not difficult to do, using the original bobbin on some kind of mandrel, and spun slowly using a cordless drill.

Rewinding with original wire would challenge even very experienced winding experts.

I love your way of unwinding the coil, by the way, well done!

Jamey80 24th May 2021 3:26 pm

Re: Metamec A909 clock- broken coil
Thanks! Low voltage operation with thicker wire is definitely an option on the table, along with rewinding with new wire of the same spec or rewinding the original wire. I think I could do with a resistance reading on the remaining wire to work out how much of any replacement I need.

ex 2 Base 24th May 2021 5:23 pm

Re: Metamec A909 clock- broken coil
I made a coil winder using a lathe on very slow speed, I fitted an inverter several years ago. I made a ring using Tufnell which fits around the partially open chuck jaws, in the Tufnell I inserted/fitted a small magnet. In between the ways of the lathe bed sits a small block of wood, which has a reed relay attached to it. I did a surgery job on a 1 calculator so that as the lathe rotates, the turns are shown on the calculator display. It works both ways, I've wound coils for motor starters using used wire and removed windings so that 415 volt starters will operate on 240. Ted

Jamey80 6th Jun 2021 4:16 pm

Re: Metamec A909 clock- broken coil
I finished unspooling it... I calculate that the wire was about 900m long and has a resistance of 8.4Ω/m making it SWG47/AWG44 according to google.
It did break several times in the process so the original wire's not going back on, so I guess it's a choice between rewinding with the same gauge wire or less of something more manageable. I've not decided, but SWG47 wire may drive me insane...

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