C3 Clock Question

[Mike Baker]

Re: Anyone interested?

Terry,

I'm not smart enough to have thought of this on my own. This was mentioned in a similar thread a couple years ago, and seemed like a prudent thing to do.

I believe I picked up a mini fuse holder and some slow burn 1 amp fuses at radio shack. The wire lead extends far enough from the clock so that the fuse holder can be accessed easily by removing the trim panel in front of the shifter console.

[Terry F.]

Re: Anyone interested?

Thanks! It sort of makes sence to have a fuse in there considering. I am not sure what years had a seperate fuse for the clock. It would be nothing for me to make about 50-100 and see what happens. I bet the vendors would sell them. Not very expensive and a safty devise. Terry

[Terry F.]

Thanks, one amp it will be! Terry : ) *NM*

[Jeffrey S.]

Re: Thanks, one amp it will be! Terry : )

I have 2 comments for what they are worth. first, never use WD40 to clean/lubricate the clock mechanism. It will work for a while but will soon gum up and the clock will again need cleaning. The way to properly clean the mechanism is to bring it to a jeweler and have it soaked in an ultrasonic cleaner for about 2 minutes. Be careful to keep the face out of the solution. Dry it well with a hair drier. Oil only the shafts with clock oil using a pointed dispenser. I have done many clocks this way and unless there is something broken they run for years. Second, I installed a battery cut off switch with a 3 amp fuse that jumps across the cut off so that the clock runs when battery is disconnected (and the interior lights come on when the door opens)but if there is a short or someone tries to start the engine (which I have done by mistake)the fuse blows immediately. Hope this helps.
Jeff

[Jeffrey S.]

Re: Thanks, one amp it will be! Terry : )

Sorry, I forgot to mention my car is a '69.
Jeff

[Gary S.]

Re: C3 Clock is on and off

As Jack and others have noted, you may simply need a good cleaning. When I took the non-functioning clock out of my 72 it would do the same thing. A good cleaning with an electrical contact cleaner and some VERY small drops of oil and it started ticking when I applied power to it. Again as Jack suggested, the biggest issue with C3 clocks is the removal and re-installation. To ensure that this was a fix and not a bandaid, I took an ac/dc converter, the kind that most of us acquire with kids toys, games etc and cut the pin off and soldered on alligator clips. I let the clock run on my work bench for several days to ensure it was working properly. Still ticking two years later. I do use a battery disconnect each and every time I shut the car off.
Gary

[Jack H.]

Re: Anyone interested?

Well, a 1-amp fuse might get the job done A-OK, but we're going by 'gut feel' instead of science. What we're dealing with here is a pretty dynamic little item...

When the point contacts close, you get a pretty healthy surge current through the solenoid followed by inductive kickback when the points open and current tries to stop flowing. This only lasts a few milliseconds, but the current waveform will look something like a typical spark pulse.

The area under the pulse curve represents the absolute energy required to 'cock' the clock's winding spring. Electrical safety designers DELIGHT in studying/solving these kinds of problems!

You want a fuse who's 'blow point' is safely ABOVE the winding current's peak AND it's cumulative blow energy threshold is safely above the surge current waveform's time integral. That way you're guaranteed the fuse won't false trigger from repeated use.

That's why fuse mfgr's offer a line of 'slow blow' components. They're ideal for pulsed circuit applications like this one. BUT, without putting a few tick tocks on the bench and using a storage scope to derive a current profile model, I'd just be guessing like the rest of us...

If a 1-amp, standard fuse, seems to work OK from gut feel/limited experience, cool--go for it! But, if the objective is to get into business offering a safety 'product' to the market, I'd suggest doing the study/model due diligence that OUGHT to be done! Remember, engineers, like doctors & lawyers, are open to malpractice threats. I know I don't know what the 'correct' numbers are in the case of ye olde tick tock!

[Terry F.]

Re: Anyone interested?

I think a 1 amp slow blow would be a good place to start. I wonder how far above the peak current the fuse should be? Also, I suspect slow blow fuses have characteristics that are charted that tell how long they will last under various conditions? It should be left to an engineer to figure out.... Terry

[Dixon Green]

Re: Anyone interested?

A Time Current Curve graph for Buss AGC fuses is located at http://www.cooperet.com/pdfs_html/AGC_Specs.PDF

[Terry F.]

Re: Anyone interested?

Great info!

I was thinking about it some more. If the clock starts to go bad it will probably get sluggish and possibly spend more time on the contacts (milliseconds). This may increase the current. But I suspect there is a relative leveling off before it goes open. Not that that matters much because you want to have the fuse configured to a healthy clock that doesn't spend much time on the contacts. The goal is to prevent a fire and not necessarily save the windings of the clock. So, if you picked a fuse that was rated at a low current but could handle the short current surge associated with the point contact just before the points seperate, you would have it set up correctly. The current map that you described is nice because I think it would allow you to overlay it on the fuse map and get an idea if you are exceeding the characteristics of the fuse. Vibration while in use could possibly increase the time on the contacts. It is nice to know that the fuse will blow in short order (ms). I don't think much heat or fire potential exists in such a situation. Just my opinion. I could be all wet. I will look into making a bunch. I recall, it will just require a male and female spade terminal that locks together. Any idea what gage wire is used to feed the clock or what color. The color should be uniform throughout the years because GM tended to do that (power sources had one color I think throughout the car). I can look it up. Thanks, Terry