Fixing over-swing in Quartz movements w/ fake pendulum

Discussion in 'Electric Horology' started by timeandagain, Dec 20, 2017.

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  1. timeandagain

    timeandagain Registered User

    Dec 28, 2007
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    This is the simplest way to reduce the amplitude of swing for those quartz movements with electromagnetic pendulum swingers. Carefully bend the plastic suspension above the permanent magnet away from the drive coil, applying just enough force to permanently slightly distort the suspension hanger to increase the air gap. Try as little distortion as possible and re-bend if needed. Forgive me if is common knowledge or obvious (although I've never seen it mentioned anywhere) and forgive me for talking quartz. I've sometimes struggled with replacement customer quartz/pendulum movements. In some narrower clock cases (e.g., schoolhouse), the pendulum bob annoying swings out enough to contact the case on each swing. I've tried all kinds of workarounds, some reported on this and other clock sites, including adding weight to the bob (does not work), placing tape across the coil and/or magnet (does not work). Adjusting the pendulum length is unacceptable as most of these clocks have a window to view the bob.
     
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  2. JTD

    JTD Registered User

    Sep 27, 2005
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    It is good to know this information - but perhaps it would reach a wider (electronic expert) audience if you posted it in the Electric Horology section.

    JTD
     
  3. Steven Thornberry

    Steven Thornberry User Administrator
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    As JTD suggested, I have moved this thread to the Electric Horology forum, which encompasses battery-driven movements (including quartz).

    There is actually a permanent thread on quartz movement issues, and I can merge with that thread if desired.
     
  4. MartinM

    MartinM Registered User

    Jun 24, 2011
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    I'd have opted for the torsion clocks area.
     
  5. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    Thanks very much for this tip. I had a miserable time with one of these. I tried gluing an air dam to the back of the pendulum (it worked before it fell off) and finally wound up pouring lead shot into the hollow pendulum. That fixed the problem reasonably well, but considering that I've taught several courses in electric motor theory I'm feeling dumb. It's a good solution, because the pull of the electromagnet on the permanent magnet in the pendulum goes down as the square of the distance between them. Thus a small increase in the air gap will have a reasonably significant effect.

    It might be interesting to see if the motion could be decreased by placing a piece of sheet brass or copper (maybe a US 25 cent piece) between the two magnets. While there's no good way to shield a permant magnetic field, the rapid changes in the electromagnet's field will induce current flow in a conductive shield. The current will (1) heat up the copper or brass shield, thus diverting mechanical energy into heat, and (2) produce a magnetic field that opposes the field of the electromagnet.

    Mark Kinsler
     
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  6. bruce linde

    bruce linde Technical Admin
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    i tried the suggestion but was unable to bend the suspension rod away from the magnet...

    BUT...

    after removing the cover over the magnet i did notice that there was some flex in the circuit board that holds the magnet and was able to press the magnet down slightly, moving it away from the suspension rod and increasing the distance. while holding it down i hot-glued around it to hold it in place... it seems to have reduced the pendulum swing just enough to no longer gently tap against the sides of the throat of my knock-off banjo clock.

    just an fyi...

    btw... they ought to put trim pots in those movements to let you dial in the amount of pendulum swing!!!!!
     
  7. bruce linde

    bruce linde Technical Admin
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    ok, so i decided the ever-so-slightly reduced pendulum swing was not enough and increased the distance between the magnet in the bottom of the crutch and its power by sliding it out (there's a little plastic overhang spring clip) and grinding it down to about half its original height and then just sitting it back in its spot... even thought it no longer clips into place it's not going anywhere.

    not the prettiest thing to look at, as the magnet didn't really grind down evenly... small chunks would come off... but much better results.
     
  8. bruce linde

    bruce linde Technical Admin
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  9. leeinv66

    leeinv66 Moderator
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    Great thread! I have a replacement movement that has the bob bashing into the side of the clock case. I'll give this a try.
     
  10. bruce linde

    bruce linde Technical Admin
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    note that the magnet did not grind easy into the night... i probably should have taken it down by hand grinding it against the side of a grinding wheel (for example), but it was past midnight and i just went out to my shop and used the powered grinding wheel... some of it came off in chunks, leaving a ragged surface... but i didn't care about aesthetics and i figured it was a $10 experiment... very happy with the results. let us know how yours turns out.
     
  11. bruce linde

    bruce linde Technical Admin
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    peter - did you even try this? b.
     
  12. leeinv66

    leeinv66 Moderator
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    Not as yet Bruce. I'll move the job up the que.
     
  13. leeinv66

    leeinv66 Moderator
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    Tried it Bruce, but without much success. The coil in my movement is just far too strong. Even when I replaced the original magnet with a chip the size of a grain of rice, the pendulum would still swing widely. Not to worry though as I managed to get the original unit to work. It must have had a dry solder joint as all I did was reheat all the solder joints on the circuit board.
     
  14. bruce linde

    bruce linde Technical Admin
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    dang... i wonder if there's a bit of shielding that could be put between coil and magnet and allow more precise tweaking?

    glad you got the original working
     
  15. leeinv66

    leeinv66 Moderator
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    I think your idea of fitting a potentiometer would be worth looking at. But then, you would expect a new movement to work properly in the first place :(
     
  16. bangster

    bangster Moderator
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    I just put a link to this thread in the "Hints & How-Tos" forum
    bangster
    moderator
     
  17. bruce linde

    bruce linde Technical Admin
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  18. Berry Greene

    Berry Greene Registered User

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    #18 Berry Greene, Sep 10, 2019
    Last edited by a moderator: Sep 11, 2019
    Oh Kinsler do I know that dumb feeling. Yeah and me a retired electronics engineer and this circuit so simple. Foolish - what, - I should say so! I have one of these fey pendulum quartz Carriage style by Metamec UK. The movement is by them - it says. It was brought to me because of my background and because I am a clock collector. Which fact does not make me a clock-maker I hasten to say! Well the transistor was blown. I replaced it like for like but it was so reluctant to run. Persistence with swinging it taught me that it would eventually maintain if you mimicked its throw and speed for a while. It ran for 18 hrs, Then 8, Then 48, then 12 and eventually for 2 weeks. I had to move it and off we went again. Same reluctance. {Note that word - it could be relevant!}.

    Its in the bedroom now - so I check it every morning. One day recently I laid it down on its back on the bed for a while as I needed to clean & dust the area. Now the pendulum seems reluctant to swing as if permanently magnetised. All this while the time part is keeping up and accurate. Its just the false pendulum that plays up.

    Could it be leakage in a capacitor? Changes made not a jot of difference. I cleaned the PCB with spirit. No change. And there you have it. I just checked the maker name & movement for this thread. It had stopped. I swung it for about 30 secs - slowly and in time with its usual rate and slowly it starts to show energy and is swinging again. It's been here for weeks now. Pretty little thing. Rubbish of course but ...... a timepiece ...... yes s'pose so.

    Don't you know I have an alternative life to live?! I deliberately choose things that will justify my madness! Don't beat yourself up. Know me; the idiot. Maxwell's right hand rule....... Don't know: Won't go! :<))
    Best regards, BerryG
     

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