Mixing Synchronome & Gents slave dials

H Daniels

Registered User
Hi
I have Synchronome and Gent slaves running in the same circuit. Circuit current is 0.3A which is too much for the Gent which clunks noisily. How do you limit the current to the Gent which has a 4 ohm coil?
Thanks Dan

Toughtool

Newbie
Synchronome and Gent slaves running in the same circuit. Circuit current is 0.3A...
This can be a little complicated to fix. First, in a series circuit, the current is the same through each voltage drop. Also in a series circuit the sum of the individual voltage drops must equal the source voltage. (See Kirchhoff's Law) I believe in your Synchronome master clock system (if that is what you are using), the source voltage to the series slave units is adjustable so that the current to the slave clocks is maintained, if units are added or removed from the circuit. Generally all the slave units are the same. In your system the units are different, meaning the requirements have different currents for different brands of slaves.

To fix your problem you will need to treat each slave unit in the overall system series circuit as an individual voltage drop that will have the highest current needed (0.3A mentioned). Therefore a unit that requires less current than the units requiring 0.3Amps (300mA) must have resistors placed so the overall current [of that unit's voltage drop network] will be 300 mA. A resistor added in series with the unit, and a resistor in parallel with the “resistor and unit” should work.

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H Daniels

Registered User
Before posting this I tried working out the value of a parallel resistor and got really confused. Hadn’t thought to put a another resistor in series with the slave. If any one has any ideas of resistors R1 and R2 values that would be a good start and I could avoid the calculator and go straight to the ammeter.
Dan

Toughtool

Newbie
It would be good to find the voltage drop of the slave unit requiring the highest current first. You can measure it. Then using R=E/I, E =the voltage drop, I=current requirments of that unit, R will be the total resistance for that unit (resistor + unit's resistance) at it's required current, say 0.200A. Then configure the parallel resistance needed of the two resistances, to acheive the 0.3A through the total circuit path. One path at 0.200A, the other path at 0.100A. I'll have to think about how to figure that out.

Toughtool

Newbie
I still think I'm right. I found this PDF on the Synchronome clocks that may be helpful. According to the paragraph on page 3, the “dials” require one volt each. For ballpark calculations of your resistors I suggest you measure the voltage of a movement (dial) with the correct current flowing through it to determine the voltage drop value. Then using this value to assume the voltage across the Gents movement in the same series circuit, compute the additional resistance needed to obtain the lower current for this movement with the voltage drop value measured earlier. R=E/I (or R+2.45 ohms=E/I) Here I am assuming a Synchronome slave unit resistance of 2.45 ohms mentioned in the paragraph quoted. We are measuring DC voltage and currents here so the value measured across the coil will be the coil's DC copper wire resistance, in ohms, and you should be able to use that value.

Then subtract this current from the 0.30A (300mA) and compute the value of a resistor needed to produce the [excess] current of this value (the remainder) using the same voltage drop. R=E/I R= parallel resistor, E is the voltage drop, I is the current remainder. Also remember to compute the wattage using P=E*I. P=1*0.3= .3 watts so a standard 1/2 watt resistor will be required for this circuit.
Joe

“... Electrical Circuit Questions are often asked about the battery voltage required. The following rule of thumb may be used to determine the voltage for a particular installation. The master clock requires about 3 volts to operate the armature and reset the gravity arm and an additional 1 volt to operate its slave dial. A 4i volt dry battery is therefore suitable for operating a complete master clock. Where additional slave dials are included, for each dial add 1 volt. The current flowing in the circuit is however more important than battery voltage and for correct operation of any installation it should be adjusted to 0.33 amps. (say * amp for easy calculation). The resistance of the master clock solenoid is 8.7 ohms and that for its slave is 2.45 ohms. The resistance of any other slave clock varies with its size. In general the standard movement used for dials up to 10" dia. has a resistance of 2.45 ohms. Larger clocks have higher resistancesand if any of these are included special account must be taken in the calculations. The total resistance of the circuit will be 8.7 2.45 no. of slaves x 2.45 ...”

H Daniels

Registered User
Really informative, I’ll feel guilty if I don’t now fix it! Thanks again.
Dan

John UK

Registered User
I run several circuits round the house, all 30 second impulses, single polarity. There are 33 dials in total including that in the master and those in the distribution board.

The pulse 'source' is a Synchronome master clock. The circuits are in fact driven from a Synchronome distribution board and that enables the current to be set in each circuit independently. The system has been running fairly unchanged and reliably for best part of 20 years.

I have found that mixing slave dial 'makes' is simply a case of not worrying too much about it! I use/have used slave movements from Gents (both standard, parapole and 'silent triangle' types), Gillett & Johnson (both standard and earlier quiet types), Princeps, Synchronome (both standard and 'quiet' types) and TMC/TR. The current used is 300 - 325 mA. The Gents are admittedly running a little 'over driven' and the G&J a little 'under driven', but they do run reliably.

It would have been possible to separate the circuits 'by maker', but it would have needed extra wiring and didn't seem necessary.

rogerj

Registered User
In a series circuit with mixed slaves, specified for a certain working current, it is not necessary to have the same voltage across each device. The Synchronome statement referred to by Toughtool above is not an exact requirement, but an approximate one and so relatively unimportant.
Therefore, if you need to be exact with your current distribution, only a parallel resistor is needed across the slave with the lower current drive requirement.
If the resetting lever is included in the loop, that's the one that needs the most careful setting (for a snappy action but with the minimum noise) and a Synchronome slave will always work with that.. In my experience so will a Gents.
When considering the noise from a slave dial bear in mind that the armature closure does not advance the hands directly and there is some leeway in the closing speed.

Toughtool

Newbie
In a series circuit with mixed slaves, specified for a certain working current, it is not necessary to have the same voltage across each device
rogerj's statement is correct. The voltage drops would only be the same if all series loads were the same. i.e. same model secondary or equal resistors, etc. Since the OP stated a mix of secondaries, not only different model of the same brand but of different brands and almost certainly different current requirements, I would expect different voltages, totaling the source voltage (Kirchhoff's law). I am not familiar with Synchronome or Gents secondaries or their systems so I have no idea of their individual voltage drops. Even though there are some unknowns [to me], this is a simple series circuit that even I can understand. So maybe I need to explain the circuit of post #2.

The Synchronome statement referred to by Toughtool above is not an exact requirement, but an approximate one and so relatively unimportant.
Therefore, if you need to be exact with your current distribution, only a parallel resistor is needed across the slave with the lower current drive requirement.
I have found that mixing slave dial 'makes' is simply a case of not worrying too much about it!
Really! For one thing, "Good enough is not (good enough). It yells of incompetence, laziness, and in most cases both. I believe people visit the NAWCC forum to get correct and accurate information about the clocks and watches they adore. It is a disservice for someone to spout "relatively unimportant" information and I for one, do not want to recommend anyone to do something to their beloved time piece that is potentially damaging.
I tried to answer the OP's question with an accurate solution, based on tried and true practices.

The circuit:
1. The series circuit shown is setup to provide a 300 milliampere (mA) current, as specified by the manufacturer. In a mixed secondary circuit the current here must be the greatest current used by any of the mix of secondaries in the circuit. In other words, if one secondary is specified as 300 mA and a different brand is specified to use 250 ma, then the current must be setup for 300 mA. The lower current device is then adjusted to consume 250 mA, but must also consume the 300mA overall current; because this is a series circuit and the same current (300 mA) flows throughout the series circuit.
2. R1 is the voltage adjustment of the source voltage. It is used to adjust the voltage up or down when a unit is added or removed from the series circuit to maintain the designed current. Nothing different here, except if the source voltage is a battery then a different battery voltage will be needed.
3. R3 is placed in series to limit the current through the device's coil to the 250 mA, as specified. R3 will have a voltage drop and the device will have a voltage drop at this rated current. This resistor, R3, and the secondary's coil resistance will consume 75 percent of the 300 mA current available and the parallel resistor R4 will provide a path and consume 50mA of current for a total current of this series/parallel part of the circuit to 300 mA. So just adding a parallel resistor to the secondary requiring the lower current is not enough.

Toughtool

Newbie
only a parallel resistor is needed across the slave with the lower current drive
After rethinking this problem, rogerj is right. Only a parallel resistor is needed. The starting point to solving this problem for H Danials is to find the voltage developed across he coil. Therefore the DC resistance of the coil needs to be measured, with a good quality Ohm meter.

Then we can compute the voltage drop using the current specification and the resistance of the coil with the formula E=I*R.
Then we can compute the resistance needed for the parallel resistor to consume the difference current (300 mA minus the coil's current). From the previous computation we should now know the voltage across the coil and the difference current. Again using Ohm's law, R=E/I, we have the parallel resistance needed, and giving us a total combined currents equaling 300 mA. Don't forget to check the power requirement. P=E*I, to determine the wattage of the resistor needed.

rogerj

Registered User
Hi
I have Synchronome and Gent slaves running in the same circuit. Circuit current is 0.3A which is too much for the Gent which clunks noisily. How do you limit the current to the Gent which has a 4 ohm coil?
Thanks Dan
You could connect a resistor across the coil. The value would depend on how well adjusted the dial mech is. Gents claim (in the online instructions I've read) that they should work reliably down to 0.13 amps. It also says the standard operating current in a Gents loop is 0.22 amps. So if the dial is set up well enough to operate at 0.13 amps you could place 3.9 ohms across it - the nearest preferred value available. If it doesn't work with 3.9 ohms, try 4.7 or 5.6
This all assumes your loop current can't be reduced below 0.3 amps
But to quieten it down the max possible check the mech. adjustments, particularly the gap between the armature and the E magnet.
I've quietened a 12" Synchronome dial a bit by sticking self adhesive sound dampening sheet material (as sold for vehicles) to the rear of the dial plate.

John UK

Registered User
It yells of incompetence, laziness, and in most cases both.
You may well consider me incompetent, lazy - even both. I don't come to these forums though laziness - and if you think me incompetant and lazy - frankly it isn't a very helpful reply to anyone.
The approach I have used is both practical and pragmatic.

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rogerj

H Daniels

Registered User
All useful information and good to know that mixing things up hasn’t been a problem. With limited space my Synchronome with slaves has been replaced by stand alone G&J which after refurb is now on test. Will return to original set-up again soon and experiment with low value resistors as suggested. Such fun!
Dan

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