Lotus Elan

Keinzle clock protection circuit & PCB

PostPost by: JonB » Fri Oct 11, 2019 8:34 am

Hi

As you might have read, I am trying to repair my Plus 2 Kienzle clock. I found the attached document which contains some modifications to help preserve the clock winding mechanism in the event of the normal problems - internal short circuits and low battery voltage, both of which lead to the winding coil overheating.

Question is, has anyone actually tried these circuits? In particular the protection circuit. Reason I ask is that 16uF (microfarads or as shown in the document, mF) seems a very low value for a capacitor that is going to provide a big enough kick to fire the solenoid off. The document refers to it as a "large capacitor"... well, it's not...

Fingers crossed someone's done it..
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Kienzle Clock Repair2.doc
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Last edited by JonB on Tue Oct 15, 2019 1:20 pm, edited 1 time in total.
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PostPost by: bob_rich » Fri Oct 11, 2019 10:19 am

Hi Jon

yes I am the Bob who wrote the article and my clock has been running for over 5 years now
and seems fine. seen your PM so added my comment to your thread

firstly the capacitor is 16mF which is 16,000uF so it a moderate size.
My clock took a current pulse of around 1.0A for around 15mS
so with a 16mF capacitor and 1A the droop of capacitor voltage is around 1V

so as the capacitor alone can provide enough pulse energy to rewind the clock all
that is required now is to top up the capacitor by the 1V depletion between pulses, which with my clock took around 2 minutes between pulses and the 470ohm series resistor does this

When things go wrong with electric then the 12V could be removed but the capacitor would (maybe) still charged so the series Red Led could be reverse biased and would probably fail. The 68ohm and the IN4001 diode protect the red LED against this effect. the green LED shows the capacitor is charged up so closing S1 give the clock the kick to start it. This network also means when starting the car the drop in volts does not deplete the capacitor too much

Finally if the clock fails the stored energy in the capacitor plus the current through the 470 ohm will not overheat the
coil and burn it out.

AS you have a scope Jon I have attached my scope tests. At the bottom their is a mention of the clock stopping
a ultra sock clean and then oiling (DO NOT OVER OIL) with watch oil clock has been running for over 5 years

Hope this helps

Best of luck Bob
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Kienzle Clock Waveforms.doc
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PostPost by: ericbushby » Fri Oct 11, 2019 11:14 am

Hi bob,
Thankyou for the explanation.
Having been involved with small and large electronics from being a schoolboy to retirement, I have never come across a 16 millifarad capacitor, nor can I find one in the CPC catalogue.
Because we have no `micro` character on our keyboards, microfarad is often written as mf and advertised as such also.
Please will you confirm this and perhaps show an example or part no. as I am curious.
Thanks
Eric in Burnley
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PostPost by: JonB » Fri Oct 11, 2019 12:35 pm

Ah millifarad... ok, that’s a whopper. But could be made up by connecting other, smaller caps in parallel, if the part itself can’t be found.

The waveforms are interesting. I put my probes across the solenoid and got this:

ca08c803-2042-4d6d-a6ac-175dfd7669bd.png and


No back EMF visible but I am running it off a switched mode PSU with limited current capabilities.
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PostPost by: JonB » Fri Oct 11, 2019 1:14 pm

Oh one more thing.

I thought it might be useful to have the enclosure mounted in the glove box so that the switch and LEDs can be accessed. I've ordered one of these:


enclosure.jpg and
Flanged enclosure



..with a view to having it stick out of the side of the glove box with the LEDs and switch mounted on the lid. Very discreet as only the lid will protrude into the box, but accessible. I found 16mF capacitors on a certain online auction site but they are very large and quite expensive (£20-£40), so I'll bank up 4 x 16v 4700uF (£2.50) for a total capacitance of 18.8mf and try it. Might be able to get away with three, and if I'm really lucky, I may be able to shoehorn them into the enclosure (otherwise I'll drill holes and they can stick out the back). I'll use strip board to make up the circuit. Would like to have a proper PCB fabricated but I'd end up with hundreds of them!
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PostPost by: JonB » Fri Oct 11, 2019 2:57 pm

OK, just for fun, then...

kcprotector.jpg and


J1 is the power input and J2 is the clock power output. The LEDs and switch are per the original design.
Last edited by JonB on Fri Oct 11, 2019 3:14 pm, edited 1 time in total.
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PostPost by: bob_rich » Fri Oct 11, 2019 3:02 pm

Hi Jon

and also to other posters

Dont use the high ripple current parts they are larger more expensive and have screw terminals .CPC don't seem to have the part I used now . I have checked Farnell UK ( Not CPC even though it is a Farnell company) site and found a couple of parts either of which should suffice both are 22mF 16V. They are electrolytic and should adequate for this application. A high ripple current and high temperature rating are not necessary for this application Farnell number 2476257 is £2-25p while part number 1839274 is a similar price. Note I had 16mF in the article and have now suggested 22mF but anything more than around 10mF should be fine.

The box suggested should be fine I fitted mine just behind the glove box. I have a safety switch that disconnects the battery from the car but for the clock I fitted a 1A fuse in a line direct to the battery so it is on all the time even when I switch off the battery safety switch. Vero or strip board assembly is ideal for this.

Very nice render of the idea Jon as I said the capacitor does not need to be precise suspect you could get away with just 2

hope this helps best of luck

Bob
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PostPost by: JonB » Fri Oct 11, 2019 3:18 pm

I think I got a bit carried away, there! I doubt I'll get it fabricated as there will be many left over boards. But if there are other people who would like to chip in then I could do it.

The caps are vanilla electrolytic 4700uF 16v types. Quite cheap, about the same as the Farnell part you quoted but as a bank I think they will be smaller or a better form factor to fit in the enclosure. I will build a prototype and experiment with different values. If I could use two that would reduce the size of the board but we'd be at 9200uF. Maybe that is a little marginal?
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PostPost by: bob_rich » Fri Oct 11, 2019 3:33 pm

hi Jon

Suggest that the 10mF should fine. I have only every repaired a single clock and so suspect that the biggest variation could be the time the contact take to clear. If bearings are gummed up , spring is stronger than mine, or WHY, it might be more that 15mS that I saw.

It is a simple idea and I think it will be tolerant of wide variation of parts values

Hope this helps

Best of luck

Bob
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PostPost by: ericbushby » Fri Oct 11, 2019 5:34 pm

Bob, thank you, I understand now. Fascinating, I did not know there was any such animal.
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PostPost by: awatkins » Sat Oct 12, 2019 4:12 am

“Because we have no `micro` character on our keyboards, microfarad is often written as mf and advertised as such also.”

Really? I always use uf for microfarad. Using “m” just seems like asking for trouble. And in this case getting it.

I also see these:

https://www.amazon.co.uk/s?k=10000uf+ca ... ss_sc_1_18

This range of sizes is utterly routine in building linear power supplies.
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PostPost by: JonB » Sat Oct 12, 2019 8:19 am

Big caps are nice, but expensive, as your link demonstrates.

With a capacitor bank on my board I have a greater choice over enclosure form factor. I’m really tempted to get the board fabricated. I mean, strip board is OK but it’s hardly elegant. Wouldn’t it be so much nicer to have a proper PCB?

:wink: .
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PostPost by: ericbushby » Sat Oct 12, 2019 8:43 am

Hi awatkins,
I agree `u` is better than `m` and causes less confusion, but the missing character is like a u but with an extra longer tail at the front.
it is the greek letter mu and is used to represent ` micro` in science and electronics.
Cheers
Eric
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PostPost by: JohnP » Sat Oct 12, 2019 1:40 pm

Like this
µ

:D
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PostPost by: JonB » Tue Oct 15, 2019 11:07 am

The enclosure arrived yesterday and it looks to be a bit on the small side. However, I thought I'd go ahead anyway.

img_6098.jpg and
50p coin gives an idea of the size of the thing.


img_6099.jpg and
Spade connectors are soldered directly to the board.


img_6100.jpg and
Underneath, the tracks are made by soldering short lengths of wire point to point.


img_6102.jpg and
It just about fits!


img_6101.jpg and
This is the result - a tiny module not much bigger than the Smiths voltage regulator. The capacitor is mounted outside of the case. The connections are +12v, GND, Clock power, Capacitor +ve, Capacitor -ve.


From underneath it looks like a Smiths control module of some sort.

So, the idea is to mount it on the side of the glovebox with most of the enclosure sticking out. There will be a small panel visible inside the 'box with the switch and two LEDs accessible.

Regarding the circuit itself:

  • I found a single 4700uF capacitor was enough to throw the clock winder round. We do not want to go large on this component, because it would deliver a bigger whack to the contacts causing unnecessary wear.
  • The LEDs work as described but are very dim, especially the red LED. Another good reason to hide it in the glove box; you can see it glowing only when it is surrounded by darkness.

img_6104_li.jpg and
The spark arrester components only just fit across the solenoid without fouling the minute wheel.


I still have the face plate of the enclosure to do, and I am thinking about whether to glue the board and spade terminals into place in the enclosure. On the one hand, better reliability; on the other, no maintenance if it stops working...
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