National electric clock restoration or modernisation project

don't you dare put a modern quartz unit in it! Sure fire way to ruin a clock!

I'm no expert but I have a collection of old clocks I've found places. There are basically two types. Those that run independently off mains power and those than run of a signal from a central 'master clock'. The former are generally as simple as connecting them to mains power. The 'slave clocks' require a pulse from a pulse generator and that needs to be at the right voltage etc. (They do very)

I'm afraid I cant tell you what type you have but I'm leaning towards slave clock from the look of it. don't put any voltage through it until you've had an expert look at it if I were you! I'm pretty sure theres clock forums and what not out there that could help

thanks for the input Gents,the idea of it being a 'slave' clock rings a bell now it's been said.that give me something to look for,so fingers crossed.

regards Bryan

In the spirit of sharing... Here is our big slave clock. (By 'ours' I mean it belongs to work and was rescued when we moved building.)




It's a second loop version (ticks every second) and, unusually, it seems to be a series one. Which is really annoying.
Chloride bought Gent in about 1981 and then sold them again the following year so that nicely dates it.
It got to the new building safely and then somebody put it on a high shelf with the face up and some other idiot dropped a box on top smashing the glass and bending the hands. Hopeless people!

Here's the mech.





I'd never seen it working (it was in a previous control room at the old place and had already been put aside when I joined). The new building doesn't have pulse loops, we went onto timecode data instead.
So to see if it worked, and possibly to get it working and back on a wall, I built this.





It's an Arduino single chip computer (to do the ticking) with a driver circuit I made to drive the actual clock. As a test thing it proves the clock works and allowed me to dial in the voltages and currents I needed to get it running. But it's not locked to anything so it's uselessly inaccurate. It's much worse than my 150 year old long case clock at home. But it proved it works. I wish I had the time to restore it and get the driver working and locked to something. I have a bad feeling it's just going to kick around at work getting increasingly damaged. (Which I'll be really upset about.)

James

Here's some more!

From what I remember you normally drive a slave clock from a 50V square wave. Like this...





The frequency depends on the clock you are trying to drive. So 'my' clock is on a second loop. Yours doesn't have a second hand and probably will be a half minute loop (ticks every 30 secs) or possibly a 1 minute loop.
This 50V thing... Sounds like a lot of volts but I'm pretty sure our system was really 50V. Now yours might be different. Who knows. It'll probably run quite happily on a lot less volts and if I was making something I'd try and run it on less. I'd try and run it on just enough to keep time properly to be honest.

It's important to note that it is not a 50 volts on for a period and then off for a period. It actually reverses direction. So for the first period current is running, say, forwards. For the next period current will be running backwards. If you stick a multimeter across the pair of wires you'd see +50V, then -50V, then +50V and so on as it switches.

Now... Series and parallel systems.

This is series.



Each clock has a fairly low resistance coil but the 50V is shared across several clocks. I'm not sure how many clocks or how many volts each coil would see to be honest.
The big disadvantage of series systems is that if any clock fails, or you need to remove one, the whole loop breaks. For that reason they weren't very popular. As it happens 'my' clock is a series one. It's a pain in the bum to drive. You'd think I could just run it on say 10V instead of 50V and it'd work. But it didn't seem very happy like that so I'm actually running it on 24V and I have a big dropper resistor that pretends to be another clock.

Parallel was more common.



Here if you have to take a clock out you only affect that one clock. Each clock should have a much higher resistance coil so it can run on a higher voltage without drawing to much current and burning it out. Again, I couldn't tell you what resistance to expect though. I could measure mine though and compare numbers.

Interestingly the wiring on your clock appears to tun through a round thing which looks like a high wattage variable resistor. I've never seen that before but I'd guess it's a way to tweak the current.


If yours is a parallel clock I think you may be able to buy a driver off the internet. I think they exist out there. God only knows if they are any good. As mine was a series clock (and therefore a bit odd) I didn't really bother looking and just built something. We had an apprentice at the time so I got them to do a bit of the development before we tied the design down.

Ask if you want to know more!
Or tell me to shut up - that's fine too!

James

Bryan,

Probably, yes!

First of all, having looked through his site, it looks like there is another way of driving slave clocks that I wasn't aware of. And it's probably more common that the way I was familiar with.

I said that it was a square wave and it reversed polarity (current went forwards and then backwards.). Well it looks like this new way is a string of short pulses. Like this...



So every 30 secs or a minute you get a short pulse. He also seems to be using a lower voltage than I managed with our big clock. I did say our clock was odd.

Here's what I'd recommend you do.

Do you have a multimeter? If so you need to measure the resistance of the coil - and of that strange round thing that I think is a variable resistor.
You also need to find if the thing works and if it's a 30 second or 1 minute mech. To do that, the coil will move a lever near by. If you can find that lever and move it the clock should advance by either half a minute or one minute.

Then... I'd take some close up photos of the mech and contact the chap. Send him the photos and the coil resistance and see what he says.
He's evidently played with a lot more clocks than me!

Again, if I can be of more help please let me know.

Good luck, I hope you get it working 'cos there is something magical about seeing an old slave clock ticking again. I'd love to see a video of it running if you get it going.

James



PS, Cost wise, who knows. In reality it's s lot of money for a few bits. But what you are really paying for is his expertise and development time. And that's fair enough. At the end of the day it doesn't matter what it cost so much as what you are prepared to pay to see it going again. And like I say, there is something magical about seeing an old clock running again. Certainly when I got ours going I just stood and grinned at it for about 5 mins.

I reserve the right to be a bit strange...