Re: DC Power sources for a 1920's Synchronome master & Current Regulation?

John Hubert

Some years ago I made (and still use) some constant current units.  The design is from the LM317 application notes.  Details attached;

On 3 Mar 2021, at 16:08, Tony Nixon <aknixon@...> wrote:

I would be very surprised if you have to consider the change in circuit resistance due to temperature, I don't think this will vary to any appreciable degree. The inductance will probably vary as the armature moves (how much I have no idea) but there is little you can do about this.  It does not affect the ultimate value of the current, it affects only the profile of the current during the fraction of a second that the coil is energised.

Assuming that the current you have in your setup at present is correct, then if you want to double the voltage you would need to double the resistance of the entire series circuit (i.e. the armature, the slave on the door and and any remote slaves and their connecting wiring) by adding a resistor in series.  A variable resistor is best so that you can adjust it if you change the setup in future.


On 02/03/2021 23:19, James wrote:
Having the system in the house you become very familiar with the sound and now only notice it when it changes - even very slightly.  
I have noted when the sound changes I can see that the speed of the armature has changed too.  Always assumed that this was due to a variation of voltage from the buck converter (which the manufacture says is not meant to happen).  Did not consider changes to the circuit resistance with temperature and moving position of the armature.   
Tony, when you say add a resistor equal to the resistance of the coil, do you mean just the coil or the resistance of the complete circuit?  If I am aiming to double the voltage, would I need to double the entire circuit resistance?
Somewhere in the home office 
Sent from Mail for Windows 10
From: neil
Sent: Wednesday, 3 March 2021 11:35 am
Subject: Re: [synchronomeelectricclock] DC Power sources for a 1920's Synchronome master & Current Regulation?
hi James,
                    Const current is better in this application as it takes care of resistance changes in the circuit due to temperature, and more importantly, contact resistance, points etc.
if a resistor is included in the circuit, and the voltage is increased, the circuit becomes less sensitive to changes in contact resistance, dirty point etc, especially if the included resistor is high compared to the reset of the circuit.

There is also the advantage that a short circuit somewhere won't destroy your power supply, or cause a fire, because the maxim,um current that can flow will be limited to a safe value by the included resistor. 

Also somewhere in New Zealand.

On 3/03/2021 11:07 am, James wrote:
Hi Ian,
In your thoughts below you comment There is something to be said for using a voltage higher than the minimum required and controlling the current with an appropriate series resistor”  For my system (Master with ten slave dials) I have used a buck converter to adjust the voltage and don’t adjust the resistance.  As we all know, using ohms law, we can get 330mA by adjusting either voltage or resistance.  I have gone with voltage adjustment and have no added resistance in the circuit.  
If I was to increase the voltage and then adjust the resistance what differences/benefits would their be?
James G
Somewhere in New Zealand 
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From: Ian Richardson via
Sent: Wednesday, 3 March 2021 7:53 am
Subject: Re: [synchronomeelectricclock] DC Power sources for a 1920's Synchronome master & Current Regulation?
I may be preaching to the converted, but clock systems such as the Synchronome are current controlled, and the recommended current through the system is 330mA.  The voltage applied will be dependent upon the number (and type) of slave dials in the series circuit. There is something to be said for using a voltage higher than the minimum required, and controlling the current with an appropriate series resistor.  In my house circuit, which includes a Synchronome (with 4 slaves) and a Gent (with 4 slaves and a programme unit) everything runs from a 50 v.d.c. supply.  I use physics lab type rheostats to control the current in each circuit to the relevant required values.
The current is not that critical and can be lower than the specified value, but ideally should not be too high otherwise the reset becomes a bit violent (and noisy!).  As Andrew pointed out, the adjustment of the air gaps in the master clock (and the slave dial mechanisms) should all be correct for reliable operation.  Should the current be too low, there is a "warning" given by the master clock in that the gravity arm will not reset promptly, but be helped by being nudged by the returning impulse pallet.  This is clearly audible both at the master clock and at any slaves in the circuit as, instead of a prompt "click" each half minute, there will be a prolonged click as the reset current starts and then ends about 1/2 second later.  Synchronome and Gent both produced a device called a "battery warning indicator" which sounded a bell or gong if the reset duration was too long.

Don't know if any of that helps, but I hope so.
Ian R
Somewhere in France


-----Original Message-----
From: Andrew Nahum <andrew.nahum@...>
Sent: Tue, 2 Mar 2021 18:00
Subject: Re: [synchronomeelectricclock] DC Power sources for a 1920's Synchronome master & Current Regulation?

I use 2 Duracells in series and the clock works well but it has to be in good adjustment on all the contact arm gaps etc. They last about a year. My impression is that more volts give more noise. 
On Tue, Mar 2, 2021 at 3:54 PM John Hubert <jfphubert@...> wrote:
The master draws 300 - 350 mA …….. but the duty cycle is low; approximately 100 - 150 mS every 30 seconds, so the average is low. 

On 2 Mar 2021, at 15:31, Thomas D. Erb <tde@...> wrote:
I'm not familiar with this type of master - but if it is really voltage-sensitive you can also use a diode - each diode will subtract .7 volts from the power supply.

alkaline batteries nominal voltage is 1.5VDC so 3 in series would give you 4.5VDC. 

If the master really draws 350ma - you would'nt get a lot of life - 
A D cell battery will give you 12000-18000 mAh
12000/350=34.2857 to 18000/350=51.4286

so between 34 and 50 hours of run time.  

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