Mixing Synchronome & Gents slave dials

H Daniels

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Aug 14, 2020
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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

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Aug 12, 2016
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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.

Synchronome_Series Circuit.jpg
 
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H Daniels

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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.
Thanks Toughtool for your help.
Dan
 

Toughtool

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Aug 12, 2016
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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

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Aug 12, 2016
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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

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

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