Electrical: How do I install 6V positive ground clock after 12V conversion?

[Tipjar]

The previous owner of my '50 Commander did a 12V conversion. I had the original clock repaired without thinking things through properly beforehand. Now the 6V positive ground clock functions correctly on bench test. The clock will not run by reversing polarity (it makes a rather angry electrical growl if attempted). I got a 12V-6V step down converter for reinstall, but since the clock's housing is positive ground not only can it no longer ground to the dash the 12V instrument light support flanges can no longer ground to the clock's housing either. While trying to think of solutions I thought maybe I could place insulators in the right spots and route the ground back to a positive line but the idea is so fraught with complications (dash aesthetics, potential shorts, voltage difference) I'm thinking nope.

Is there someone who converts these clocks? Can I rob the guts and and/or housing out of a 12V negative ground unit and swap my clock face? (I'm thinking not likely).

Any solutions?

Thanks.

[RadioRoy]

The clock winding mechanism is just a solenoid. It does not care about polarity. The angry growl must be about something else.

Look in Hemmings Motor News for people who convert clocks to quartz movements if you want it converted.

[StudeRich]

I HAVE heard of Negative Ground 12 Volt to Positive Ground 6 Volt Converters, if those are still available that would be be how I would go, but it STILL needs insulation.

You would have to do without Clock lighting though (no big deal), because you can't connect the light socket to the + grounded Clock Case and you want always Hot power on the Clock and Instrument Lighting Circuit on the Clock Light, NOT possible.

Your Clock may not have been properly repaired if it IS quite loud, but there will be a motor winding the Spring sound that is Normal, but Not usually Loud and grinding, it's more of a "Buzz".

[RadioRoy]

The unhappy growl is probably the undersized power converter straining to put out.

A 1 ohm, 100 watt resistor might do the job instead.

[RadioRoy]

I HAVE heard of Negative Ground 12 Volt to Positive Ground 6 Volt Converters, if those are still available that would be be how I would go, but it STILL needs insulation.

You would have to do without Clock lighting though (no big deal), because you can't connect the light socket to the + grounded Clock Case and you want always Hot power on the Clock and Instrument Lighting Circuit on the Clock Light, NOT possible.

Your Clock may not have been properly repaired if it IS quite loud, but there will be a motor winding the Spring sound that is Normal, but Not usually Loud and grinding, it's more of a "Buzz".

Nope. The clock solenoid does not care about polarity. The solenoid inrush current is rather high, but only for a short time.

[StudeRich]

So you know it is Not a winding Motor going backwards Roy?

[Tipjar]

Well, after a few phone calls it looks like some of the quartz conversion places can do it, which would address both polarity and voltage. They say mine can be tricky so they'd do it in house rather than sell me a kit.

Otherwise, this guy dealing with another vintage positive ground car clock suggests that reversing the polarity between the rectifier and coil leads changes the clock to negative ground (if you feel lucky or know a shop that will do it): https://www.sa.hillman.org.au/TT_SmithsClockPC.html

[Tipjar]

Your Clock may not have been properly repaired if it IS quite loud, but there will be a motor winding the Spring sound that is Normal, but Not usually Loud and grinding, it's more of a "Buzz".

Yeah, it's a buzz, but it only makes that sound when trying to run it with the polarities reversed.

[RadioRoy]

So you know it is Not a winding Motor going backwards Roy?

Typically, energizing the solenoid winds a clock spring, the clock ticks for however many minutes until the spring winds down and then the solenoid energizes again and winds the clock spring.

The solenoid is the only part that sees battery voltage and the solenoid is not polarity sensitive.

Converting the clock to a 12 volt quartz movement with yield a clock that actually keeps time.

[Tipjar]

[QUOTE=Look in Hemmings Motor News for people who convert clocks to quartz movements if you want it converted.[/QUOTE]

Thanks for pointing me towards Hemmings. They only listed three shops under Services > Instruments. And only one of the three deals with clocks, which did have the shortest turnaround time (2-3 weeks compared to 12 or more) but also charged an extra $50-$75 at $275.

[RadioRoy]

So you know it is Not a winding Motor going backwards Roy?

In 1950, there were no motors small/powerful enough to fit in a clock case and wind the clock spring.

It's typical of clocks in 1950 to have a solenoid pull a set of gears to wind the clock spring a couple of rotations. The solenoid is not sensitive to polarity. No matter what polarity of DC you feed it, it will energize. It's a high current for a short time. That high current demand is probably overloading that little power supply.

The modern motors that can be reversed rotation-wise by reversing the polarity have a permanent magnet field.

Most motors used in 1950 cars are series wound, where the current goes into the armature, through the field and back out again. Think of a starter motor or a heater fan motor. Reversing the polarity does not reverse the direction of rotation. The way to change direction of rotation is to change the RELATIONSHIP of the the magnetic flux of the armature and the field.

If the clock has really been rebuilt, it's possible that feeding 12 volts through a one ohm, one hundred watt resistor will make the clock work. If not, then converting it to a quartz movement will make a much better clock and it might even actually keep time.

[altair]

Why not install a 6 volt dry cell battery and connect it to that, it will last at least 7 - 8 years.

[Tipjar]

Why not install a 6 volt dry cell battery and connect it to that, it will last at least 7 - 8 years.

I've already got a 12V-to-6V step down converter on hand to power it, the positive ground would remain an issue.

[gordr]

Radio Roy knows his stuff. I agree that there is about zero chance of the mechanism of a 1950 clock being polarity-sensitive. The buzzing is typical of a clock that does not get enough power to fully stroke the winder. You get the same sort of buzzing from a starter solenoid when the battery is dead, or nearly dead.

[RadioRoy]

Why not install a 6 volt dry cell battery and connect it to that, it will last at least 7 - 8 years.

Nope. The significant inrush of current attempting to energize the solenoid would drain the dry cell battery in minutes.