Interior: Clock data

[Desert53Stude]

I’m asking about the runtime on the clock in my 1953 Commander K body. My clock seems to run about 2.5 minutes per winding. If I have no power it seems to run about 5 minutes before it stops. Does this sound about right?
My clock has been serviced and it seems to draw about .7 - .8 amps per winding does that seem typical? The wind time is quick, maybe 1 second.
Thanks, John

[Fred Winterburn]

My Stude clock is stationary (63 Hawk). One day I will take it apart and make it tick again. However, based on two other clocks, one from a 36 Chev and the other a German Kienzle that I owned, what you describe is about right. If there is room, you can put a 0.1µF film capacitor across the points to limit arcing there which will prolong the operating lifetime of the points. Fred

[Desert53Stude]

I will have to look to see if there is room, that cap might be a good idea. I had my point clean when it was serviced. Not sure how long they will last pulling full power through them.
I found if the clock stops the unit draws about 1.2 - 1.5 amps to restart. It's still quick but the peak is higher.

[Andy R.]

OP that sounds about right.
The clock in my ‘62 Hawk does this just a little under 3 minutes/cycle.

[gordr]

I will have to look to see if there is room, that cap might be a good idea. I had my point clean when it was serviced. Not sure how long they will last pulling full power through them.
I found if the clock stops the unit draws about 1.2 - 1.5 amps to restart. It's still quick but the peak is higher.

Sounds perfectly normal to me. If there is no power to the stud, the clockwork will continue to run for a few seconds after the moving contact first makes contact with the fixed one, thus prolonging the duration of contact once it is powered up, A small capacitor across the points sounds like a good idea. What about putting a large capacitor, say 1000uF, shunting the power stud to ground, and feeding the power through a resistor? Select a resistor such that the RC time constant is much smaller than the run time of the clockwork. If the discharging capacitor has enough energy stored to fully wind the clockwork, it should run tickety-boo. And if the mechanism stalls, the series resistor ought to prevent burning the points, and running the battery completely flat if the clockwork stalls due to low voltage.

As it happens, I have an Avanti clock apart on the bench right now, so I will try this, and report back if I can make a "CD" clock circuit work.

[Desert53Stude]

Well, this sounds interesting. Take some pictures and draw the circuit and post it, if it works.
I'm doing a 12v to 6v and polarity swap on this car. At this time, I have a 12v to 6v converter (10 amps) in stalled for gauges and this clock. Keeping the clock points healthy would be a good idea.

[gordr]

Ok, an update. Hooked up a 3300 uF capacitor, rated at 50 volts, and a 2200 ohm resistor. RC time constant should be 7.6 seconds. The capacitor discharging into the coil gives a full wind, for about 40 seconds worth of ticking. The flaw? It won't start a stopped clock. The stopped clock puts an effective short across the capacitor, and the 2200 ohm resistor cannot pass enough current to wind the clock (or burn out the points). I have it running on the bench right now. I have a work-around in mind for the "start a stopped clock" situation. Another 3300 uF capacitor, charged through another 2200 ohm resistor. This cap gets momentarily connected to the main capacitor by a relay driven by timer circuit using a 555 timer chip. Set the time constants for the 555 so that every ten minutes, it throws a contact closure for one second, then opens the relay until another ten minutes have lapsed. If the clock has stopped, that jolt of juice should start it, if it is capable of running. If it is already running, then a charged capacitor is briefly connected to another charged capacitor, and nothing much happens, other than the charges equalize. The whole shooting match could be built with a few dollars worth of parts, and put in a small box called "clock driver module".

[gordr]

Further update: this clock keeps quitting on me. It winds just fine using the R-C network to power it, but it runs for a while, and stops before the contacts close to wind it again. So a clockwork issue, not a winder issue.

[Fred Winterburn]

Gord, Rather than put the resistor in series with the 3300µF cap, why not do away with the series resistor and instead put a 1 MΩ resistor in parallel with the drive capacitor? When the point contacts close, the drive capacitor will charge through the winding coil. When the points open, the parallel resistor will discharge the drive capacitor slowly so it is ready for the next winding cycle approximately 3 minutes later. You could even go up to 10MΩ for the bleeder resistor. You don't need to worry about a time constant as the winding coil will take what current it needs and slow the charging of the drive capacitor naturally. Also, this way you could possibly even use a smaller drive capacitor but your choice of 3300µF seems like a good one to me. Fred

[gordr]

Ok, Fred. I think I understand. Disconnect the ground leg of the coil from the contact point, and put the shunted capacitor between it and the contact points. Inrush current for the charging capacitor makes the coil armature wind the spring. In the event the clock stop with the points closed, battery drain is limited to capacitor leakage current plus whatever passes through the shunt. Requires a mod to the clock's internals. But the shunt resistor would have to be small enough to fully discharge the cap before the spring winds down in about 40 seconds, otherwise no inrush current. I would probably go with 2.2k anyway; only draws about 5.5 mA from 12 volts. Clock is still on the bench, I could try this.

[gordr]

Next update: Building on Fred's idea, I shunted the 3300 uF capacitor with the 2.2k resistor, and put that network in series with the clock. Clunk! It winds the clock for about 25 second's worth of runtime, and did it several times in succession. Seems like the inrush current to the cap commences the wind before the cap reaches full charge? I had a 21000 uF cap in the junkbox; tried that. It wound the clock right up, ran for about a hundred seconds on the wind. Found two 3300 uF caps, rated at 16 WV, paralleled them, with the 2.2k shunt, and it winds the clock for about 90 seconds. I left it running on the bench that way, we'll see what happens. You need the shunt resistor to discharge the cap before the wind cycle completes, otherwise you are trying to charge an already-charged cap, and nothing much will happen. I think a 6800 uF cap, rated at 25 working volts DC, shunted by the 2.2k resistor is about the sweet spot, and would probably cost you a buck or two from an electronics supply house. One advantage of this series arrangement: if the clockwork should stall with the points closed, the points won't burn out, since the cap won't continuously pass DC at all, and the 2.2 k resistor will flow a little over 5 mA. And you could re-start the clock simply by disconnecting the battery for half a minute, and reconnecting it.