Date   

Re: Master Clock contact spark quenching

markotime
 

Another thing about contacts: Some level of current must be carried through mechanical contacts
to prevent buildup of oxide or other contaminants which will eventually inhibit conductivity.  If
memory serves me correctly, "sealing" current is the proper term.  For Hipp, there is probably
enough wiping action to prevent buildup if the "needle" is part of the circuit.  I'm inclined to use
optical devices rather than mechanical contacts.
Haven't yet worked my way thru Arduino logic for a Hipp solution.

On 1/8/2021 6:12 AM, Simon Taylor wrote:

The GPO used a 200 ohm resistor in series with a 1 micro farad capacitor across the contacts on later type 36 clocks with simple make contacts. The earlier types with make before break contacts had a 2000 ohm resistor. and worked with the earlier relay 90A which had 2 x 500 ohm coils in parallel.

All of the contacts are made of 10% iridium and 90% platinum. The hipp toggle contacts pass between 400-500mA for the pendulum drive coil. Although running a GPO slave cct direct it is quite possible, I would still recommend using either traditional relay (coil 2000-5000 ohms) or a solid state device or arduino system.
--
Simon GPO Clocks

http://www.lightstraw.uk/gpo/clocksystems/index.html



Re: Master Clock contact spark quenching

Simon Taylor
 

The GPO used a 200 ohm resistor in series with a 1 micro farad capacitor across the contacts on later type 36 clocks with simple make contacts. The earlier types with make before break contacts had a 2000 ohm resistor. and worked with the earlier relay 90A which had 2 x 500 ohm coils in parallel.

All of the contacts are made of 10% iridium and 90% platinum. The hipp toggle contacts pass between 400-500mA for the pendulum drive coil. Although running a GPO slave cct direct it is quite possible, I would still recommend using either traditional relay (coil 2000-5000 ohms) or a solid state device or arduino system.
--
Simon GPO Clocks

http://www.lightstraw.uk/gpo/clocksystems/index.html


Re: Master Clock contact spark quenching

markotime
 

They didn't have Silicon diodes in Strowger days, only Selenium, which devices were
leaky and bulky.  R/C was the appropriate tech.  Now, Si.

On 1/7/2021 3:03 PM, Ian Richardson via groups.io wrote:
Hi Darren,

You are quite correct, but there are also other ways to minimise the voltage across the contacts as they open.  One is to put a capacitor in series with the power supply such that it is the capacitor charging current which drives the solenoid, then blocks any further current flow.  This approach works well with clocks whose impulse is prolonged, eg Brillié, but may not work for the very short impulse of a Synchronome.  Another is to use make-before-break contacts arranged such that the coil is shunted before the supply contacts open.  This is used on GPO Type 36 clocks. A less familiar approach was used by Matheus Hipp whereby the make-before-break switch actually short circuits both the coils and the supply!  In that case, a resistor was put in series with the power supply to avoid the direct short.

I made full use of the capacitor blocking approach in my electrically reset gravity escapement clock (of which I have written before) wherein the gravity arms form the poles of a reversing switch, but the driving current comes from charging and discharging capacitors so arranged that the operating current is applied via the capacitors on making contact, but when the contact is broken there is no current flowing.

While on this subject, it is worth remembering that Strowger type telephone exchanges used hundreds if not thousands of relays and other electromagnetic switching devices and they nearly always used the R/C type of snubber across the contacts - so they must have reckoned it to be a good solution to the sparking issue!

Best regards,
Ian R
Auvergne,
France



-----Original Message-----
From: Darren Conway <darren.conway@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 20:52
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

Hi
There are two parts to this problem.
One is to reduce the back emf from the coil that generates the voltage to arc across the opening contacts.  A diode across the coil will achieve this.
Two is to maintain a near zero voltage across the contacts as they open, for long enough to open far enough to prevent an arc forming.  This is solved with an RC snubber across the contacts. 

Regards

Darren Conway
36 Orr Crescent
Lower Hutt
New Zealand
ph +64  (0)4 569 1963

On 7.01.21 11:33 pm, Ian Richardson via groups.io wrote:
In the pipe organ world, the use of diodes in direct electric actions is standard practice.  I have just fitted up a direct action unit extension organ with about 200 electromagnetic valves, each runs on 15 vdc. and carries a current of about 250mA.  Each coil is shunted with 1N400X diodes or equivalent. There is no sparking - imagine if there was, the organ woiuld break down every day as the coils are activated hundreds of times with each performance!  The diodes cost about €1 per 100.

The point about polarity is, of course, valid but simply solved by using a high current silicon diode in series with the power supply.  If connected the correct way round, all works well; if the wrong way round, it doesn't work at all, so it "fails safe".

Ian R
Auvergne,
France



-----Original Message-----
From: John Hubert <jfphubert@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 11:17
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

I do just as you suggest on all my dials and masters.  1N400X series diodes.  The maintaining of current is minimal (looked some years ago with an oscilloscope and it was insignificant).  There is typically some variation of impulse length dependant on the master anyway (Gents tend to be longer and early Synchronome clocks rather short - lighter parts?).  Typically, the coil carries about 300 mA and has a resistance of about 5 Ohms, with a parallel resistor of about 50 Ohms.

Diodes work well - but of course you have to have the right polarity.

John

On 7 Jan 2021, at 10:06, John Haine <john.haine@...> wrote:

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


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Re: Master Clock contact spark quenching

Ian Richardson
 

Hi Darren,

You are quite correct, but there are also other ways to minimise the voltage across the contacts as they open.  One is to put a capacitor in series with the power supply such that it is the capacitor charging current which drives the solenoid, then blocks any further current flow.  This approach works well with clocks whose impulse is prolonged, eg Brillié, but may not work for the very short impulse of a Synchronome.  Another is to use make-before-break contacts arranged such that the coil is shunted before the supply contacts open.  This is used on GPO Type 36 clocks. A less familiar approach was used by Matheus Hipp whereby the make-before-break switch actually short circuits both the coils and the supply!  In that case, a resistor was put in series with the power supply to avoid the direct short.

I made full use of the capacitor blocking approach in my electrically reset gravity escapement clock (of which I have written before) wherein the gravity arms form the poles of a reversing switch, but the driving current comes from charging and discharging capacitors so arranged that the operating current is applied via the capacitors on making contact, but when the contact is broken there is no current flowing.

While on this subject, it is worth remembering that Strowger type telephone exchanges used hundreds if not thousands of relays and other electromagnetic switching devices and they nearly always used the R/C type of snubber across the contacts - so they must have reckoned it to be a good solution to the sparking issue!

Best regards,
Ian R
Auvergne,
France



-----Original Message-----
From: Darren Conway <darren.conway@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 20:52
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

Hi
There are two parts to this problem.
One is to reduce the back emf from the coil that generates the voltage to arc across the opening contacts.  A diode across the coil will achieve this.
Two is to maintain a near zero voltage across the contacts as they open, for long enough to open far enough to prevent an arc forming.  This is solved with an RC snubber across the contacts. 

Regards

Darren Conway
36 Orr Crescent
Lower Hutt
New Zealand
ph +64  (0)4 569 1963

On 7.01.21 11:33 pm, Ian Richardson via groups.io wrote:
In the pipe organ world, the use of diodes in direct electric actions is standard practice.  I have just fitted up a direct action unit extension organ with about 200 electromagnetic valves, each runs on 15 vdc. and carries a current of about 250mA.  Each coil is shunted with 1N400X diodes or equivalent. There is no sparking - imagine if there was, the organ woiuld break down every day as the coils are activated hundreds of times with each performance!  The diodes cost about €1 per 100.

The point about polarity is, of course, valid but simply solved by using a high current silicon diode in series with the power supply.  If connected the correct way round, all works well; if the wrong way round, it doesn't work at all, so it "fails safe".

Ian R
Auvergne,
France



-----Original Message-----
From: John Hubert <jfphubert@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 11:17
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

I do just as you suggest on all my dials and masters.  1N400X series diodes.  The maintaining of current is minimal (looked some years ago with an oscilloscope and it was insignificant).  There is typically some variation of impulse length dependant on the master anyway (Gents tend to be longer and early Synchronome clocks rather short - lighter parts?).  Typically, the coil carries about 300 mA and has a resistance of about 5 Ohms, with a parallel resistor of about 50 Ohms.

Diodes work well - but of course you have to have the right polarity.

John

On 7 Jan 2021, at 10:06, John Haine <john.haine@...> wrote:

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


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Re: T&N switching, was Solari Flip Clock Driver

Ian Richardson
 

Ernie,

In order to photograph the commutator switch, I will have to stop the clock and lift out the movement.  The commutator is mounted on the back board, but the spindle which drives it is part of the clock movement, so I'll endeavor to show both parts although I would assume that the part which is on the clock movement is still existing (or is it?).

I will do all this this weekend, assuming that you can wait a bit!

I have to confess that I have little or no understanding of all the microelectronic stuff - all my clocks run "as built".

Best regards,
Ian R



-----Original Message-----
From: Ernie Jenson via groups.io <erniejenson@...>
To: synchronome1@groups.io <synchronome1@groups.io>
Sent: Thu, 7 Jan 2021 21:09
Subject: Re: [synchronomeelectricclock] Solari Flip Clock Driver

Thanks Ian for the offer of pictures.  Thanks Thomas for the suggestion of the h-bridge circuit.  Since I have modefied the T&N to deliver a contact closure for 10 seconds every minute, I couldn't figure out how to make that work with out a micro controller to complete the operation.  I programed a micro controller but encountered problems with interference from the many master clocks in the room on the same circuit.  I programed and reprogramed and then decided that this was not the right way to go.  Whoever gets the clock after me will most likely not be able to maintain the circuit.  My choise was to buy another T&N to get the part and keep the clock original or build a replacement part that does the job in the manor that would have been used at the time the clock was new.  My first attemp at a mechanical device was also a failure.  I now need to look at the way that T&N solved the problem.  I have an ENEM master clock and their solution to the problem is far too complex.  I can't find another T&N to purchase.
Thanks for all the help, I really appreciate the effort.
Ernie



Re: Solari Flip Clock Driver

Ernie Jenson
 

Thanks Ian for the offer of pictures.  Thanks Thomas for the suggestion of the h-bridge circuit.  Since I have modefied the T&N to deliver a contact closure for 10 seconds every minute, I couldn't figure out how to make that work with out a micro controller to complete the operation.  I programed a micro controller but encountered problems with interference from the many master clocks in the room on the same circuit.  I programed and reprogramed and then decided that this was not the right way to go.  Whoever gets the clock after me will most likely not be able to maintain the circuit.  My choise was to buy another T&N to get the part and keep the clock original or build a replacement part that does the job in the manor that would have been used at the time the clock was new.  My first attemp at a mechanical device was also a failure.  I now need to look at the way that T&N solved the problem.  I have an ENEM master clock and their solution to the problem is far too complex.  I can't find another T&N to purchase.
Thanks for all the help, I really appreciate the effort.
Ernie



Re: Master Clock contact spark quenching

Darren Conway
 

Hi

There are two parts to this problem.

One is to reduce the back emf from the coil that generates the voltage to arc across the opening contacts.  A diode across the coil will achieve this.

Two is to maintain a near zero voltage across the contacts as they open, for long enough to open far enough to prevent an arc forming.  This is solved with an RC snubber across the contacts. 


Regards

Darren Conway
36 Orr Crescent
Lower Hutt
New Zealand
ph +64  (0)4 569 1963

On 7.01.21 11:33 pm, Ian Richardson via groups.io wrote:
In the pipe organ world, the use of diodes in direct electric actions is standard practice.  I have just fitted up a direct action unit extension organ with about 200 electromagnetic valves, each runs on 15 vdc. and carries a current of about 250mA.  Each coil is shunted with 1N400X diodes or equivalent. There is no sparking - imagine if there was, the organ woiuld break down every day as the coils are activated hundreds of times with each performance!  The diodes cost about €1 per 100.

The point about polarity is, of course, valid but simply solved by using a high current silicon diode in series with the power supply.  If connected the correct way round, all works well; if the wrong way round, it doesn't work at all, so it "fails safe".

Ian R
Auvergne,
France



-----Original Message-----
From: John Hubert <jfphubert@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 11:17
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

I do just as you suggest on all my dials and masters.  1N400X series diodes.  The maintaining of current is minimal (looked some years ago with an oscilloscope and it was insignificant).  There is typically some variation of impulse length dependant on the master anyway (Gents tend to be longer and early Synchronome clocks rather short - lighter parts?).  Typically, the coil carries about 300 mA and has a resistance of about 5 Ohms, with a parallel resistor of about 50 Ohms.

Diodes work well - but of course you have to have the right polarity.

John

On 7 Jan 2021, at 10:06, John Haine <john.haine@...> wrote:

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


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Re: Master Clock contact spark quenching

John Haine
 
Edited

Well, I said "may cause a problem".  This is based on one case of which I can't recall the details but I think there was a transistor driving a relay which stayed "on" longer than desired when the transistor switched off because of the diode.  Easily solved by a series resistor if needed but as people point out it probably won't be.


Re: Master Clock contact spark quenching

John Hubert
 

If this is done in the musical world - then I think the assumption that any effect on the timing (i.e. lengthening of coil current duration) is insignificant.  

In a clock circuit, if you do get the polarity wrong, the diode (assume 1N400X type) can cope with the forward current (about 300 mA and it is OK to an Amp) and the dial concerned dial simply doesn’t advance - so easily spotted and corrected.  I have never in 10 years with maybe 50 dials running knowingly had a diode fail.

John

On 7 Jan 2021, at 10:33, Ian Richardson via groups.io <irichar361@...> wrote:

In the pipe organ world, the use of diodes in direct electric actions is standard practice.  I have just fitted up a direct action unit extension organ with about 200 electromagnetic valves, each runs on 15 vdc. and carries a current of about 250mA.  Each coil is shunted with 1N400X diodes or equivalent. There is no sparking - imagine if there was, the organ woiuld break down every day as the coils are activated hundreds of times with each performance!  The diodes cost about €1 per 100.

The point about polarity is, of course, valid but simply solved by using a high current silicon diode in series with the power supply.  If connected the correct way round, all works well; if the wrong way round, it doesn't work at all, so it "fails safe".

Ian R
Auvergne,
France





Re: Master Clock contact spark quenching

Ian Richardson
 

In the pipe organ world, the use of diodes in direct electric actions is standard practice.  I have just fitted up a direct action unit extension organ with about 200 electromagnetic valves, each runs on 15 vdc. and carries a current of about 250mA.  Each coil is shunted with 1N400X diodes or equivalent. There is no sparking - imagine if there was, the organ woiuld break down every day as the coils are activated hundreds of times with each performance!  The diodes cost about €1 per 100.

The point about polarity is, of course, valid but simply solved by using a high current silicon diode in series with the power supply.  If connected the correct way round, all works well; if the wrong way round, it doesn't work at all, so it "fails safe".

Ian R
Auvergne,
France



-----Original Message-----
From: John Hubert <jfphubert@...>
To: synchronome1@groups.io
Sent: Thu, 7 Jan 2021 11:17
Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching

I do just as you suggest on all my dials and masters.  1N400X series diodes.  The maintaining of current is minimal (looked some years ago with an oscilloscope and it was insignificant).  There is typically some variation of impulse length dependant on the master anyway (Gents tend to be longer and early Synchronome clocks rather short - lighter parts?).  Typically, the coil carries about 300 mA and has a resistance of about 5 Ohms, with a parallel resistor of about 50 Ohms.

Diodes work well - but of course you have to have the right polarity.

John

On 7 Jan 2021, at 10:06, John Haine <john.haine@...> wrote:

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


Re: Master Clock contact spark quenching

John Hubert
 

I do just as you suggest on all my dials and masters.  1N400X series diodes.  The maintaining of current is minimal (looked some years ago with an oscilloscope and it was insignificant).  There is typically some variation of impulse length dependant on the master anyway (Gents tend to be longer and early Synchronome clocks rather short - lighter parts?).  Typically, the coil carries about 300 mA and has a resistance of about 5 Ohms, with a parallel resistor of about 50 Ohms.

Diodes work well - but of course you have to have the right polarity.

John

On 7 Jan 2021, at 10:06, John Haine <john.haine@...> wrote:

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


Re: Master Clock contact spark quenching

John Haine
 

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.


Re: Solari Flip Clock Driver

John Haine
 

It's interesting looking at the photo that the coil appears to be part of a Lavet-style stepper motor!  I have seen patents that show that pattern of a 2-pin "lantern" pinion, and the core shape looks right too.  I wouldn't be surprised if it was perfectly happy on a lower voltage than 48 if the quartz clock variety is any guide.  Assuming it is the Arduino needs to give it alternate pulses, each quite short.

To be pedantic, the driver shield you show is just an ST Micro L298 dual H-bridge with supporting components, exactly what you need, but not what nowadays would be classed as a stepper motor driver.


Re: Solari Flip Clock Driver

Darren Conway
 

Hi

I am aiming to use a stepper motor driver with an Arduino like this one.  Only $USD10 for the driver including shipping.


Regards

Darren Conway
New Zealand


On 7.01.21 3:20 am, Thomas D. Erb wrote:
Any of our tower clock controls have a reverse polarity output.


If you want to make your own driver - you need a h-bridge circuit 

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Re: Master Clock contact spark quenching

Darren Conway
 

Hi

The problem with a capacitor across the contacts is that when the contacts first touch, the capacitor charging current is very high. This damages the contacts.

The problem with a resistor is that when the contacts open, full current is flowing through all the coils.  The coils try to maintain this flow by raising the voltage (back EMF).  This can easily reach 100's of volts.   This voltage will arc across the open contacts.  The resistor will only reduce the current.

The solution is to use an RC snubber circuit as described here

These reduce the initial capacitor charge current and hold the voltage across the contacts low enough  for long enough to allow the contacts separate far enough to prevent an arc forming.    When applied to a Synchronome with a 12V supply, these formula limit the initial charge current to "only" 24 Amps with a 1ohm resistor.  I would increase the resistor 10x.  This initial charge current is overstated because with a 12V supply, I have 54 ohms in circuit to limit the current to 220mA required by the slaves.   

The other part of the approach is to reduce the back emf from each coil.  This can be effectively done with diodes but that requires making sure each slave coil has the right polarity connected.    Not difficult to do.

An alternative is to connect two zener diodes, back to back, in series across each coil.  Each zener should be rated to at least twice the supply voltage.   These devices were not available when Synchronomes were made.  


Another alternative is to use a driver circuit to separate the contacts from the coil/slave circuit.  This works except for the coil in the master clock and the coil for the in-case slave.


Regards

Darren Conway
Lower Hutt
New Zealand


On 7.01.21 5:12 am, John Hubert wrote:
Can anyone explain why we stick with the Synchronome resistor?

I can make a few guesses;
  1. In a Synchronome, the ‘ON period’ is very short - a few hundred milliseconds per minute, so the losses in a resistor (which only occur in the ON period) are similarly low.  In a car it is MUCH higher.
  2. In the pre WW1 days, resistors were easy.  Larger value capacitors were not.
  3. Many higher value capacitors were then both bulky and relatively expensive - and many (all electrolytic types) were polarity sensitive.
  4. The inductance across a car system is near enough fixed - whereas a clock system will vary from system to system (number of dials) - and so ‘one size fits all’ may not be optimised.
  5. The increase in power consumption for a Synchronome was approx 10%, which is not very significant.

Synchronome and G&J used a resistor across each coil (both master movement and slave dials) whereas Gents only fitted a (capacitor based) system in the master - not the slave dials.  Gents do however have very heavy duty contacts.

One manufacturer whom used an interesting ‘different’ approach was the original Princeps system.  A very light contact based on the pendulum rod ‘made’ the contact (there is no spark on the ‘make’) - but the current break was done by a much heavier duty ‘break’ contact - driven by an electromagnet giving a fast break.  The light contact set only opened after the current had already stopped - so never arcs.

John

On 6 Jan 2021, at 15:22, Andrew Nahum <andrew.nahum@...> wrote:

Can anyone explain why we stick with the Synchronome resistor?


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sparks

markotime
 

Use diodes!  Unless I've missed something earlier in the thread, quenching diodes will
solve any sparking problems.  In early days, rectifiers were either in vac. tubes or
made up of stacked plates of Selenium, far from practicality or perfection.  Cathode to positive
shunting the coil.  Back emf on open circuit is entirely carried through the coil.  Schottky
diodes have lower voltage drop than Silicon, and fast-recovery diodes have speed advantages.
/mark


Re: Master Clock contact spark quenching

John Hubert
 

Can anyone explain why we stick with the Synchronome resistor?

I can make a few guesses;
  1. In a Synchronome, the ‘ON period’ is very short - a few hundred milliseconds per minute, so the losses in a resistor (which only occur in the ON period) are similarly low.  In a car it is MUCH higher.
  2. In the pre WW1 days, resistors were easy.  Larger value capacitors were not.
  3. Many higher value capacitors were then both bulky and relatively expensive - and many (all electrolytic types) were polarity sensitive.
  4. The inductance across a car system is near enough fixed - whereas a clock system will vary from system to system (number of dials) - and so ‘one size fits all’ may not be optimised.
  5. The increase in power consumption for a Synchronome was approx 10%, which is not very significant.

Synchronome and G&J used a resistor across each coil (both master movement and slave dials) whereas Gents only fitted a (capacitor based) system in the master - not the slave dials.  Gents do however have very heavy duty contacts.

One manufacturer whom used an interesting ‘different’ approach was the original Princeps system.  A very light contact based on the pendulum rod ‘made’ the contact (there is no spark on the ‘make’) - but the current break was done by a much heavier duty ‘break’ contact - driven by an electromagnet giving a fast break.  The light contact set only opened after the current had already stopped - so never arcs.

John

On 6 Jan 2021, at 15:22, Andrew Nahum <andrew.nahum@...> wrote:

Can anyone explain why we stick with the Synchronome resistor?


Re: Master Clock contact spark quenching

Andrew Nahum
 

I have often wondered why spark quenching can’t be done better with a capacitor as used across the breaker points in all older style automotive ignitions.  Can anyone explain why we stick with the Synchronome resistor?


On 5 Jan 2021, at 09:40, John Haine <john.haine@...> wrote:

As it's now 2021 you could consider using a solid state relay - silent, should last for ever, no inductive kick to make any arcs across the clock contacts.

https://uk.rs-online.com/web/p/solid-state-relays/9061079/

RS sell 'em in 5s which is inconvenient unless you have a use for the other 4, or could share a pack.  There are probably other suppliers - in fact eBay:
have them at double the price in ones though.


Re: Master Clock contact spark quenching

Thomas D. Erb
 


Re: Solari Flip Clock Driver

Thomas D. Erb
 

Any of our tower clock controls have a reverse polarity output.


If you want to make your own driver - you need a h-bridge circuit 

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