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Discussion Starter · #1 ·
I've successfully rewound a couple 214 cell coils now, using 0.015 polyurethane-coated copper at about 0.6 cN tension, and am finding that the conventional wisdom of 90 meters and 8000 turns per coil (2000 for feedback, 6000 for drive) is too much wire. I get resistances much higher than what I measure on originals, although the originals do vary a fair amount. I have excellent results with less wire, more like 2000 and 4900 turns, giving amplitude and current draw that pretty much match the originals. So I wonder if anyone knows where this spec comes from that seems echoed all over the web? The only contrary thing I've found is an ad that says "More than 500 feet". If the original spec was 250 feet per coil, not 90m, that would help explain my results.

The other thing I'd like to do is modify the coil (number of turns, specifically) to give lower amplitude (and I suppose lower current draw) than the originals. Does anybody know whether an increase or decrease of turns, and of which of the two coils, is likely to give that result? I guess I am prepared to experiment to find this. The circuit seems self-balancing and really pretty unpicky about the coils. I think the drive pulse needs to be shorter (less feedback coil maybe?) or the drive current needs to be lower (but as you add turns, current goes down proportional to length, and turns inducing force increase proportional to length too. Is this why amplitude doesn't seem to care about number of turns? Or is there a square in here I'm missing? Is there an EE Accutronner?)

One last question, I hope it's not a mistake to put them all together: Does anyone have resistance measurements from a larger number of coils? I have:

3 wire feedback: 2.38 2.37 2.31 2.26 2.21 1.81k (variation of 30%!)

3 wire cell side drive: 5.55 5.61 5.61 5.62 5.76 6.02 6.29 6.73k (variation of 20%!)

3 wire circuit side: 7.70 7.77 7.79 7.86 7.94 8.54k

I haven't started on 2-wire coils yet, since most of the ones in my bad pile are 3 wire.

Here's my second successful coil running:
coil-try2.jpg

Feedback coil:


Completed rewind:


Thanks to any collaborators!
Chris
 

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Discussion Starter · #4 · (Edited)
Yes please don't! I have always saved the duds. I serviced a lot of Accutrons 15 years ago, and I could still usually get complete coils - ebay, dashto, elsewhere - most people didn't even separate the halves back then. Now that I'm getting back into service work, coil availability is much worse BUT the wire has become available! I started looking for the wire in 2007 and it was simply not available. Fortunately that has changed. This has been a long-term project and I'm really excited I no longer have to tell people I can't get a coil for their watch anymore.

I put the first rewound coil in an Accutron desk clock my mentor gave me back in 98 when I was just starting. He ran a jewelry store and loved Accutrons (he had sold them when new and they were always special to him) but he couldn't see well enough to service them anymore. He was so good to me, he gave me his parts stash and so much wisdom, and lots of reliable work through his store. I've had that clock for 20 years and never wanted to use a good coil set on it, but it is running now with my rewind, since I serviced it last night. I miss him and wish he was still around to see it.
 

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Please try attaching photo again using "Go Advanced". What you have done is fantastic. I have been hoping some one would start rewinding 218 coils, particularly cell coils. If any one wants them I have about 70 duds. Rewinding coils is an opportunity to overcome triple indexing problems by tailoring them for running at 1.55volts.
 

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I have tried to rewind these and failed.
Still have a selection of Robs bad coils here at wiork.
Happy to pass them on if Rob is ok with that.
 

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Yes please don't! I have always saved the duds. I serviced a lot of Accutrons 15 years ago, and I could still usually get complete coils - ebay, dashto, elsewhere - most people didn't even separate the halves back then. Now that I'm getting back into service work, coil availability is much worse BUT the wire has become available! I started looking for the wire in 2007 and it was simply not available. Fortunately that has changed. This has been a long-term project and I'm really excited I no longer have to tell people I can't get a coil for their watch anymore.

I put the first rewound coil in an Accutron desk clock my mentor gave me back in 98 when I was just starting. He ran a jewelry store and loved Accutrons (he had sold them when new and they were always special to him) but he couldn't see well enough to service them anymore. He was so good to me, he gave me his parts stash and so much wisdom, and lots of reliable work through his store. I've had that clock for 20 years and never wanted to use a good coil set on it, but it is running now with my rewind, since I serviced it last night. I miss him and wish he was still around to see it.
Good friends like that are few Chris, I'm sure he would be proud of your work.
 

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I always wondered about those soldered connections, they look cold from the factory and I'm sure you can't use much heat anyway. Almost looks like cold solder paste type compound. Do you actually solder the coil wires to those terminals? And it's a polyurethane insulation? How do you remove the insulation to get bare wire? Use light guage rosin core leaded solder?
Any questions? :biggrin:
 

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When measuring current like in your pic, does the current from the unloaded fork differ much from a fork connected to the index wheel and gear train?
 

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Discussion Starter · #12 ·
I always wondered about those soldered connections, they look cold from the factory and I'm sure you can't use much heat anyway. Almost looks like cold solder paste type compound. Do you actually solder the coil wires to those terminals? And it's a polyurethane insulation? How do you remove the insulation to get bare wire? Use light guage rosin core leaded solder?
Any questions? :biggrin:
Some are a pain because they're covered with the original varnish/potting compound, but they are definitely solder. Once the coating is scraped off or carried away by flux, I don't have any trouble soldering. I'm using old fashioned leaded solder because I find it more reliable and I'm sure it's what's on there already. I've been soldering at 375 degrees with a good quality temperature controlled soldering station with a very fine tip, and the plastic form does not melt at that temperature.

I dunk the wire into the pool of solder and just keep it hot until I see the coating on the wire disappear. You can see when it changes and quits repelling the solder. It takes several seconds. I'm thrilled that the plastic doesn't melt. It would be much harder if I had to do it quickly.
 

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Discussion Starter · #13 · (Edited)
When measuring current like in your pic, does the current from the unloaded fork differ much from a fork connected to the index wheel and gear train?
Yes, I don't have an exact number for you, but running a clean train adds maybe 1 or 1.5 uA. For a dirty watch it can be a lot more.

On the 218 where the center wheel tends to gum up and stick to its post, current draw can be pretty high and the watch will still seem to work ok, and the only sign it needs service is a shorter battery life. It makes me cringe to think about them running that way. I've seen some very bad center wheels.
 

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Discussion Starter · #14 ·
Rewinding for lower current from silver oxide cell

Awesome news! I've been experimenting with varying the number of turns, to tailor operation to new silver oxide cells.

The 3-wire cell coil I rewound with 1800 and 6895 turns (giving 1.80k, 9.22k) runs 3uA unloaded and takes 4.3uA running a freshly-serviced movement. (So watchabit, there's your answer: 1.3uA)

As best I can tell, the amplitude is exactly 2 index wheel teeth, right in the middle of the amplitude range that gives correct indexing (just over one tooth to just under three teeth). This is with a new silver oxide cell.

The Energizer 387s data sheet says the cell has a capacity of 63mAh. Calculating from that: a typical stock Accutron 214 will draw 6uA, giving about 14.3 months of life from a cell. This is a pretty familiar cell life.

But in addition to indexing properly, an Accutron 214 with this low-current coil I've wound should last 20 months!

I am absolutely tickled.
 

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Discussion Starter · #17 ·
I'm excited too! But to follow the rules I think we need to keep this thread about sharing technical knowledge/accomplishments and not about buying and selling. I certainly do want to use this new ability to keep as many Accutrons running into the future as possible. I think it's an important part of them not getting retired or junked. For more details than that, I welcome emails.

I started winding the first 2-wire cell coil last night. I thought it might be harder to solder, since there's no screw plate for the tap, but it went fine. I think these had fewer turns, so adding turns to reduce current will not fill up the form quite so much. I expect to take a few tries to get the current and amplitude where I want it, just like it took some experimentation on the 3-wire.

Weirdly it seems like everyone but me has mostly 2-wire duds. Mine are almost all 3-wire.

I also stripped a 218 cell coil, will try winding that. Does anyone know whether they use the same wire, and how many turns I should try, to start?

I've also got some oddballs in my rapidly-diminishing dud pile, 219 and 230. Didn't see any 221. That 230 is a whole other ball game.

My latest finished coil is in here. Isn't this dial amazing?

twotone.jpg
 

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That's considerate of you,Chris. Thank you.
The Mods and Admin. have nothing against ANYONE buying and selling, just as long as you follow the rules- have *the required # of posts to your credit, keep the merchandise legal, and buy or sell ONLY in the Sales or Want to Buy Forums. Posting anywhere else will be considered off-topic, and subject to deletion without prior warning.

*You need at least 10 posts to use the Wanted to By Forum; 25 posts to sell in the Sales Forum.

(As always, the Moderators will be happy to explain anything you don't understand)
 
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I'm excited too! But to follow the rules I think we need to keep this thread about sharing technical knowledge/accomplishments and not about buying and selling. I certainly do want to use this new ability to keep as many Accutrons running into the future as possible. I think it's an important part of them not getting retired or junked. For more details than that, I welcome emails.

I started winding the first 2-wire cell coil last night. I thought it might be harder to solder, since there's no screw plate for the tap, but it went fine. I think these had fewer turns, so adding turns to reduce current will not fill up the form quite so much. I expect to take a few tries to get the current and amplitude where I want it, just like it took some experimentation on the 3-wire.

Weirdly it seems like everyone but me has mostly 2-wire duds. Mine are almost all 3-wire.

I also stripped a 218 cell coil, will try winding that. Does anyone know whether they use the same wire, and how many turns I should try, to start?

I've also got some oddballs in my rapidly-diminishing dud pile, 219 and 230. Didn't see any 221. That 230 is a whole other ball game.

My latest finished coil is in here. Isn't this dial amazing?

View attachment 177266
Did you get that off ebay recently? I let one exactly like that go. Very cool. I'm stoked about these coils. Your time in this endeavor is much appreciated.
And I wasn't asking make to purchase but to know if you were going to make your service available, so I didn't think the mods would mind. I will be emailing you soon though.
:thumbup:
 
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