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Old 12th Oct 2019, 4:27 pm   #1
Welshey
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Default Vintage IBM clock.

I've bought a 1950's IBM Clock, Model 95925.
I used to work for IBM so I bought it when I left - the plan is to hang in my kitchen.

My issue is with how best to power it, so I'm looking for some advice. Mine is wired to a standard US plug but simply using a standard adapter would cause it to be slow due to UK 50Hz.

I want to keep it as original as possible. The clock motor is a Syncron 610 - 110V, 60Hz, 1 RPM.
My first thought was to find another Syncron/equivalent motor designed for 240v 50Hz....but I'm yet to find one that could be a direct replacement. A few 1RPM synchronous motors about but they are usually for heating system valves.

I could use a transformer of some sorts, but ones I've found seem to be for industrial high wattage applications. Any UK to US adapter only changes the voltage, and the frequency stays the same.

If I used a standard UK > US adapter, what would then be the best way to step 50Hz up to 60Hz?

Bizarrely there seems to be a few 240v 50Hz to 110V 60Hz transformers about that are specifically for hair clippers? But they are about £70!

Any advice welcome

Last edited by AC/HL; 12th Oct 2019 at 7:34 pm. Reason: Thread split
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Old 12th Oct 2019, 9:05 pm   #2
TrevorG3VLF
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Default Re: Vintage IBM clock.

One solution which I have seen, is to make a 300Hz oscillator and phase lock it to 50Hz and then divide it to 60Hz, I am sure that someone more clever than me could do this with a micro.
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Old 12th Oct 2019, 9:15 pm   #3
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Default Re: Vintage IBM clock.

You don't need a lot of power.... 60Hz divided down from a suitable crystal oscillator like this:


http://www.electronicecircuits.com/e...tal-oscillator


Can be fed to a small audio amplifier and drive a step up transformer to give you the 120V needed by the clock motor.


The crystals cost little ~£1 and are stocked by the usual sheds.
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Old 12th Oct 2019, 9:58 pm   #4
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Default Re: Vintage IBM clock.

http://www.electric-clocks.co.uk/Fre...cyconvert.html
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Old 13th Oct 2019, 12:39 pm   #5
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Default Re: Vintage IBM clock.

Quote:
Originally Posted by Welshey View Post
I've bought a 1950's IBM Clock, Model 95925.
I used to work for IBM so I bought it when I left - the plan is to hang in my kitchen.

My issue is with how best to power it
Ken Reindel makes some very good frequency converters, look at his site, here is one.

https://www.kccscientific.com/product/1930/

I run three 1930's vintage GE-Minutemaster cyclometer clocks here in AU on 50Hz. The rotors were designed for 60Hz use 110V (we are 230V 50Hz). For one I was able to find a 50Hz rotor, it was rare (this is the name of the assembly/housing that has all the gears in it and has an output shaft that rotates at 1 rev/minute).

For the other two:

I disassembled the rotor and found by calculation I could change one cog on the output shaft to get one RPM at 50Hz operation. Ken kindly machined the cogs for me.

To get 115 V operation on 230V I simply added the correct value series capacitor so the voltage vector across the motor was 115V, not a common way to do it. It works fine with a 1000V rated poly cap, however I learnt the hard way that an X2 capacitor in this application degrades with time and loses capacity. A small transformer is probably a better option, but if you got one of Ken's converters you will be right as rain.
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Old 13th Oct 2019, 3:27 pm   #6
jimmc101
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Default Re: Vintage IBM clock.

If you want a DIY solution Roman Black's website may give you some ideas. https://www.romanblack.com/one_sec.htm
About halfway down the page are various inverters using a PIC giving 60Hz from 50 Hz or a 12MHz crystal.

Jim
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Old 13th Oct 2019, 5:22 pm   #7
Neutrino
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Default Re: Vintage IBM clock.

A search on ebay for "clock motor 1rpm" produced some results, including a Synchron 650 from US, although I have no idea whether they will fit or work in your clock. For example:
https://www.ebay.co.uk/itm/Synchron-...IAAOSwQA1de8lS

https://www.ebay.co.uk/itm/synchrono...QAAOSwKEhcuxM7

David
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Old 13th Oct 2019, 11:49 pm   #8
Welshey
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Default Re: Vintage IBM clock.

Thank you all for the advice!

I like the idea proposed by @herald1360 - likely work out quite cheap and reliable and I may be able to add circuitry that allows for some adjustment, in case the clock is slightly fast or slow, even with the correct frequency.

The other off the shelf options are very tempting, but I've decided I would probably learn a lot more by having a go.

Solving this by modifying the gears manually had crossed my mind, however I had concerns about the longevity/potential malfunction of running the clock at the wrong electrical frequency. But having examined the inner workings it's pretty basic, so it boils down to the motor which shouldn't really care what the frequency is, it will just turn slower/faster. So I may look at that option too.

With regards to a complete new motor, I had not seen those specific ones on eBay so that could be an option. They look similar, appart for the additional gearing, so I could look at a direct swap. Might be my backup.

I'm going to ponder and play about with the options and will feed back the result.

Cheers, Gwyn
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Old 15th Oct 2019, 12:16 am   #9
Herald1360
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Default Re: Vintage IBM clock.

Be a bit leery about running a 60Hz motor on 50Hz- it may overheat if it takes a noticeably higher current. Reducing the voltage to keep the current down to the same as on 60Hz might be needed.


(Same problem can occur with mains transformers)
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Old 16th Oct 2019, 9:01 pm   #10
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Default Re: Vintage IBM clock.

Quote:
Originally Posted by Welshey View Post
I like the idea proposed by @herald1360 - likely work out quite cheap and reliable and I may be able to add circuitry that allows for some adjustment, in case the clock is slightly fast or slow, even with the correct frequency.
You won't need any adjustment. With this type of clock, the motor is moving exactly in sympathy with the crests and troughs of the supply waveform, and the gearing ratio is fixed. The only thing that can affect the speed is the frequency of the supply. As long as the frequency is correct, the clock will always run at the right speed. A synchronous motor moves on exactly two poles for each full cycle (= 2 reversals) of the mains. So a 24-pole motor running from a 60Hz supply, which is 3600 cycles per minute, will turn at 3600 cycles per minute / 12 pairs of poles per cycle = 300 rpm. Of course if the voltage is too low, then there may not be enough power to move the hands; and if it's too high, the windings will run hotter. But it won't run any faster or slower (except perhaps not at all, if there is insufficient energy or the windings have already burned out from over-voltage .....)

If you use an oscillator based on even a cheap quartz crystal, it will be accurate to a few parts per million. Which, to a first approximation, is a matter of a few seconds per fortnight .....
Quote:
Originally Posted by Welshey View Post
The other off the shelf options are very tempting, but I've decided I would probably learn a lot more by having a go.
That's the spirit! Have some hands-on fun and learn while you're doing it -- it's always the best way.

You just need to find a quartz crystal whose frequency is an integer multiple of 60Hz. 3MHz (which is about the upper limit for copper strip breadboard) would need dividing by 50 000; so you just need to build a counter that counts up to 50 000. The crystal needs connected between the output and input of a NOT gate (or a NAND or NOR gate; the other input can be used as a stop/start input, if you want to be able to halt your clock precisely. If you just removed power from the circuit, the clock probably would run on a little while the power supply smoothing capacitors still had enough energy to move the hands) with a 22pF capacitor as close as possible between each lead and 0V. (Remove one capacitor, or replace with 33pF, if the oscillator does not want to start up every time. If you build a trial version on solderless breadboard, don't expect the same capacitor values to work when you transfer the circuit to something more permanent.) The output from the NOT gate then needs to be fed into a chain of five decade counters, one of which must be configured to divide by 5 as opposed to 10. (Or whatever figure is appropriate for your crystal.) If the final stage has no !Q output, you will need another NOT gate (but you'll have spares anyway). Use Q and !Q to drive, via resistors of a few kΩ, the gates of a pair of chunky MOSFETs (I have some IRF540s in my parts drawer, but it's not hugely critical so just use whatever is to hand) with the drains connected to each of the outer ends of the secondary of a suitable centre-tapped mains transformer, centre tap to +V (unregulated). The clock motor goes to the primary. (As a refinement, you could use a smaller count, and select between that and 60Hz to run the clock at a faster speed; this might be useful for setting purposes. I have heard from "the horse's mouth" at a manufacturer of architectural feature clocks -- which still use synchronous motors -- that modern clocks will run at up to double speed. An older one probably will need handling a little more gently. but you can experiment while you have the bits ..... or just use a much cruder oscillator, possibly adjustable, since it doesn't have to be so accurate.)

Unfortunately, the transformer probably will have to be chosen by experiment, because small transformers tend to be quite lossy. It needs to be able to handle enough VA for the clock motor. You could get away with a slightly lower rating, because the frequency is 1.2 times higher, but you really want the thickest possible wire on the secondary to minimise voltage drop. If the motor is not marked with a power rating, just apply an old dodge: weigh it! (After all, it's mostly made of copper and steel .....) Then pick a transformer a bit heavier than the motor (because it will contain twice as much copper). You might expect a 15-0-15 transformer to give 120V out when the drive circuit is using a 12V DC supply (=24V peak-to-peak) but it will sag under load, and the effect of voltage drop in what is now the primary will be made worse by the step-up ratio.

As an even further refinement, if your chosen transformer has a voltage a bit higher than you are comfortable with, you could use a PTC thermistor to drop the excess voltage.
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Old 16th Oct 2019, 10:41 pm   #11
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Default Re: Vintage IBM clock.

This looks an interesting approach: https://mitxela.com/projects/phase-locked_inverter.

There appears to be lots of support for the ATtiny and very cheap development boards.
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Old 17th Oct 2019, 8:24 am   #12
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Default Re: Vintage IBM clock.

It might be worth checking how many poles the clock motor has. If it has a 12 pole synchronous motor its speed will be 600 rpm at 60 Hz and 500 rpm at 50 Hz. In this case, if you can find a 10 pole synchronous motor that can be fitted, it will run at 600 rpm at 50 Hz.

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