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Master Clock contact spark quenching
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Darren Conway
Hi I now have 1 Master and 2 Slaves running from a 12V supply. There is enough resistance to limit the current to within spec (~240mA). I am seeing arcing across the Master clock contacts. This can't be good. Is there a standard solution to this problem? If not, I would
add an RC snubber between the top terminal and the cast iron frame
from the back. Regards Darren Conway
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Tracy and Raymond van Orsoy de Flines
Best is to use a relay. I got a Gents masterclock (Hipp Toggle) and run the 30 second slave clocks through a relay.
On Tue, 5 Jan 2021, 12:50 Darren Conway <darren.conway@...> wrote:
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neil
Hi Darren, Raymond is correct ...the clock contacts are only rated to drive the old post office 2000 series relays, which pull little current, and the slaves are driven by the relay. I also have a gents po36 hipp toggle clock and I operate the slaves via a small Philips relay inside the clock, so the clock contacts only see the relay current. If you like I can post you a suitable relay if you tell me what voltage you are running. Neil
On Tue, 5 Jan 2021, 12:55 pm Tracy and Raymond van Orsoy de Flines, <raytray.van@...> wrote:
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John Haine
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.
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Ian Richardson
Pardon me being thick, but the RS relay you quote doesn't seem to specify a driver voltage?
Ian R
-----Original Message-----
From: John Haine <john.haine@...> To: synchronome1@groups.io Sent: Tue, 5 Jan 2021 10:40 Subject: Re: [synchronomeelectricclock] Master Clock contact spark quenching 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.
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John Haine
That's because it's opto isolated, it needs a current of ~3 mA into the input pin to light up the internal LED, so you drive it through a suitable resistor to get that current from whatever voltage is across the contacts. In this case with 12 V that would be 12/3 = 4 K ohms, or 3.9 K NPV.
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Darren Conway
Hi If I only had to
drive slaves from the Synchronome, an opto isolator would be the
obvious choice. I already have one.
I am thinking
of using a cheap Chinese motor/power switch shield with an
Aduino to generate the bipolar drive for the flip clock.
Generating a bipolar signal requires and H driver circuit,
as used to drive stepper motors or DC motors. If I get a
Auduino wifi version, there is the potential to use an
on-line NTP server as the master clock, complete with
automatic daylight time corrections. The only problem
is that shipping times from China are currently about 3 to
6 months.
The master
still needs to drive its own solenoid coil and case fitted
slave, so a snubber circuit would still serve a purpose.
Regards
Darren Conway New Zealand On 5.01.21 10:54 pm, John Haine wrote:
That's because it's opto isolated, it needs a current of ~3 mA into the input pin to light up the internal LED, so you drive it through a suitable resistor to get that current from whatever voltage is across the contacts. In this case with 12 V that would be 12/3 = 4 K ohms, or 3.9 K NPV.
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Darren Conway
Hi Here is a Aduino
Motor shield that would be ideal for driving the Gents and
Solari slave clocks. Regards Darren Conway 36 Orr Crescent Lower Hutt New Zealand ph +64 (0)4 569 1963
On 6.01.21 7:12 am, Darren Conway
wrote:
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Tony Nixon
Darren,
I am really surprised that the delivery time from China to NZ is so long. I have been buying Arduino and other small electronic parts from China using ebay for the last 5 years, generally keeping orders below GBP10 to avoid attracting duty. Delivery has usually been 2-3 weeks (and free too!) Most of the same parts can also be purchased from UK suppliers on a weeks turn round but at about double the price. Are there no similar suppliers in NZ?
I have noticed in the last two months though that free delivery seems to be disappearing, I read somewhere that some concessionary deals offerd to the Chinese for cheap shipment have now ended. A more worrying development that I have just started to hear about is that post Brenxit the UK is apparently going to require all suppliers selling into the UK to register to pay VAT with the UK authorities. One European supplier (of bike parts) has apparently already decided no longer to deal with customers in the UK.
I am just beginning to experiment with an ESP8266 Node MCU to get a time stamp from NTP to log temperature, pressure and error on my Pulsynetic.
Regards
Tony
On 5 Jan 2021, at 19:48, Darren Conway <darren.conway@...> wrote:
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neil
Darren - i am still buying electronic supplies from China, and
turnaround is a few weeks. If the value is low, then GST is not an
issue - so far anyway.
toggle quoted messageShow quoted text
Neil Jepsen. B.Sc. M.Sc(Hons).CPL.MASNZ. Jepsen Acoustics & Electronics Ltd 22 Domain Street Palmerston North. New Zealand. Ph +64 6 3577539 Mob 0274428094 Web site: www.noiseandweather.co.nz www.noiseandweather.com E.& O.E. On 6/01/2021 11:55 am, Tony Nixon
wrote:
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Darren Conway
Hi Prior to Covid, delivery from China was usually 4-8 weeks. I
currently have 13 items on order that I am waiting for. The
oldest order is 22 Oct 2020. The problem here is that most of those small packages were
carried by passenger aircraft. Those services aren't running and
there is big demand the slower and now more expensive channels. Regards
Darren Conway New Zealand
On 6.01.21 11:55 am, Tony Nixon wrote:
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Thomas D. Erb
you probably need a snubber circuit, and some but NOT all solid state relays have them built in.
some examples https://forum.digikey.com/t/power-switches-what-is-a-snubber-circuit/7776?utm_adgroup=Switches&utm_source=google&utm_medium=cpc&utm_campaign=Dynamic%20Search_RLSA_Buyers&utm_term=&utm_content=Switches&gclid=Cj0KCQiA3NX_BRDQARIsALA3fIKGV1-pot0DdJbtbitHTH462ngURDnm1S81t1UfYOY3oC8TnF4uT8AaAobrEALw_wcB BTW relays have different ratings for both inductive and resistive loads.
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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?
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On 5 Jan 2021, at 09:40, John Haine <john.haine@...> wrote:
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John Hubert
Can anyone explain why we stick with the Synchronome resistor?
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
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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:
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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.
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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.
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Diodes work well - but of course you have to have the right polarity. John
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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
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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.
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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
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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.
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