I'm a bit over my head on this one!

Discussion in 'Clock Repair' started by shutterbug, Aug 28, 2017.

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  1. shutterbug

    shutterbug Moderator
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    This cool old movement comes from an old schoolhouse master clock. It apparently counts the seconds on one lead, and the minutes on another. It doesn't have a power source except for a self winding mechanism which you can see at the bottom of one of the sides. The 50 AC power source, along with the coils at the bottom are supposed to push that silver thing upward, winding the clock with enough power to keep it going. When fully wound, the "push" won't stop the clock, it just waits for the next try when it can move it by one tooth. My issue is that the coils seem to activate and try to push the lever, but there's not enough power to get it to wind. I thought I'd try the collective brain power here before jumping over to the electric forum. Any experience with these? Anything you can spot? 314608.jpg 314609.jpg 314610.jpg 314611.jpg
     
  2. Vernon

    Vernon Registered User
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    Looks like a Standard Electric Clock Co. I have worked on one before but no expert. These work on DC current somewhere between 6-12 volts. I used an adjustable power pack on the one that I worked on to find out the clocks needs which was 9 volts DC. Yours acts like that it's not getting enough voltage. Start low and work your way up to prevent damaging the coils.
     
  3. Jerry Kieffer

    Jerry Kieffer Registered User
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    Shutterbug

    It is very difficult to diagnose this type of movement without in hand inspection. However a few observations base on your photo`s.

    (1) The mechanism appears to be in the typical fully wound position.

    (2) The coils appear to be misaligned with the winding mechanism probably decreasing winding strength.

    (3) Given the "gummed up" appearance of the movement, its unlikely the coils could overcome the winding mechanism resistance until cleaned and freed up.

    (4) Assuming the movement is actually in need of cleaning per my comments, it is likely that the coil contacts are also in need of cleaning and service. If so, this will greatly decrease current flow and coil strength.

    Jerry Kieffer
     
  4. bangster

    bangster Moderator
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    Good luck, Mate!
     
  5. shutterbug

    shutterbug Moderator
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    I did put an Ohm Meter on the transformer, and it reads 50 volts AC. I thought that was a bit high to, but the clock had been running fine for many years.
    Thanks, Jerry. Yeah, it needs a good cleaning, but I wanted an idea of how it's supposed to work before tearing it down :)
     
  6. David S

    David S Registered User
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    Sbug can you show more information on the electrical part. I can;t tell if that is meant to be an a/c engergized coil, or if rather there is a rectifier in the circuit.

    David
     
  7. harold bain

    harold bain Registered User
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    An Ohm meter would only tell you the resistance of the coil. Is there a rectifier somewhere to convert it to DC volts?
     
  8. Ralph

    Ralph Registered User
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    They run on 24VDC. As Jerry pointed out, the coil is misaligned and out of adjustment. There is a small mainspring, that you should be able to wind manually, and test the mechanical part of the movement.

    I believe these maintain the wind once every minute. If I remember right, it is not a vibrating type wind, and only picks up a ratchet tooth or maybe two... it's been a while.

    The moderator might move this to the electric clock category for better response.

    Ralph

    Ralph
     
  9. bangster

    bangster Moderator
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    Should this be over in Electric Horology?

    Just askin'
     
  10. roughbarked

    roughbarked Registered User

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    Oh so many times I've had this dilemma. For all the world it looks like a clean should fix it when the weakest link is the last thing you can actually test this way. It is why the most profitable method seems to be; replace the movement rather than repair it.

    - - - Updated - - -


    six of one....
     
  11. shutterbug

    shutterbug Moderator
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    finding a replacement would likely be harder, rough :)

    OK, I'm not an electrical guru like some of you guys are. What would a rectifier look like?
    For testing, would four 6 volt lantern batteries work?
     
  12. David S

    David S Registered User
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    Can you show some pics of the transformer and any wiring from the secondary side to where ever it goes.

    David
     
  13. shutterbug

    shutterbug Moderator
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    Sorry, the transformer is in the case at my customer's home. It's way huge....too big to move. The transformer attaches to those springy looking wires you see in the photos. I'll try to get some more focused ones today.
     
  14. harold bain

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    Without the power supply you won't be able to run the clock for any length of time. You could try using 4 six volt lantern batteries to test it, but you need to know what you are doing.
     
  15. john e

    john e Registered User

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    As pointed out, the coil is misaligned. the pole tip of the coil should be parallel to the object it is attracting. If the mechanism's pivot is close to the coil end anyway, you may have to experiment a bit.

    The intent is for the current in the coil to attract the magnetic part of the wind mechanism. With DC, the current and therefore the magnetic field strength will rely on the dc resistance of the coil. If you energize it with AC, then the inductance of the coil will be the limiting factor. If the inductance is very high, that would explain why 50 volts AC is being used. If the part being attracted were a magnet with either north or south pole, that would not work well with AC. But I suspect it is simply a piece of magnetic iron.

    You need to first align the parts to allow the pole tip to attract the iron. Then, once you have it aligned, see if you have to dither it a bit. I mention this because if the rotation of the arm causes a large angular misalignment with the pole tip, the force may not be enough..so it will be a guess as to whether you have to align parallel at closest approach or furthest.

    John (I am an EE and actually work with electromagnets, and I would not have seen this post in the electric horology section.)
     
  16. shutterbug

    shutterbug Moderator
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    Thank you all for your insights! I should have mentioned that the clock functions fine, but won't wind without help. I'll take a bunch of pictures and disassemble it for cleaning and repair. Then I'll keep you posted. I'll be on vacation for a couple of weeks, so I'll have to set it aside for a bit.
     
  17. roughbarked

    roughbarked Registered User

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    Also clean out all or any of the usual black powder that accumulates where the electro magnet attracts it. This mechanism requires to work like a pundulum similar to the Kundo. In that it needs to be aligned correctly and be interference free. You will note that at one end of the coil there is a spring mounted. Check that this spring is properly adjusted.
     
  18. Tinker Dwight

    Tinker Dwight Registered User

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    I'm with John in that I find it unusual that it used an AC source to power the coil.
    I suppose it would work but more likely to burn the contacts faster.
    The alignment is off. It may be the the coils mount is upside down.
    With the A shaped frame and the screw holes aligned to the frame,
    the end mount for the coils would compensate for the angle.
    And John, why don't you look at electric clocks as well? I aways
    select "clocks" and get all.
    Tinker Dwight
     
  19. kinsler33

    kinsler33 Registered User

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    One thing that might help here is a look at any labels on the transformer. If the clock coils are indeed meant to run on DC, then the 'transformer' would have to do two things: reduce the 120 volt alternating-current from the home's outlet down to, say, 24 volts alternating current, and then make the 24 v AC into 24 v DC. This last task is done with one of several kinds of 'rectifiers,' which are electrical one-way valves.

    Now, the usual rectifier used these days is made of silicon: a little plastic cylinder or something with two wires emerging from it. But these were developed long after your clock was made. An earlier version was the selenium rectifier, which generally took the form of a finned assembly bolted somewhere onto the frame of the machinery to keep it cool. I tend to doubt that this sort was used on your clock, because the currents involved would be rather high.

    Then there are the stranger kinds of rectifiers: vacuum tube (you don't have one) or electrolytic (ditto) or mechanical, which is a possibility if the clock really required DC from an AC source. You'd know you if have one of these because they emit a healthy buzz if they're working.

    What I don't understand is, if you have the clock at your shop and it's separated from its power supply, what you were powering it with when you read that 50 volts, if that's what it was. If you were measuring the coil's electrical resistance, for which you wouldn't need any power, then what you read was a coil resistance of 50 ohms, which is actually about right for a 24v DC coil (an AC coil would have a much lower resistance.)

    Yes, four 6v lantern batteries should indeed power the winding mechanism for a while. My guess is that the original arrangement had the clock running off of four small six-volt lead-acid batteries (like small car batteries) and that these were kept charged by your house-current-operated 'transformer.' This would maintain the clock through power outages.

    When you apply power to the coil to wind the clock, remember that the electromagnet coil is meant to carry its full current for a few fractions of a second, after which it overheats and burns out. The coil won't burn out partially: if it works at all it's very likely okay.

    M Kinsler
     
  20. Ralph

    Ralph Registered User
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    This really belongs in the electric category. The SET movement is very common and the folks there are very familiar with them.

    All the SET clocks I have seen are 24V clocks.

    If the customer is using an unfiltered power supply, and measured 50 volts DC, the voltage is probably more like 80V pulsating DC, assuming a bridge rectifier. The peak voltage will even be higher if it is a half wave rectifier... You are seeing average voltage.

    If it is 50 DC and is filtered, the transformer is probably around 36VAC or so. The filter capacitors will charge to peak voltage.... around 50 V in that case.

    Ralph
     
  21. shutterbug

    shutterbug Moderator
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    I believe the transformer was labeled 120 in and 50 AC out. What happens after that is unknown. I may move this to the electrical forum when I get back, but lots of you guys knowledgeable about these types of clocks, and I'm familiar with you all.
     
  22. Tinker Dwight

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    I expect someone might have used 50VAC to drive the coil without a rectifier.
    The only issue I see with this is that without a peak switching circuit, the first
    cycles current can be quite high. If it saturates the cores of the magnets,
    it will cause a very high current to flow, doing significant damage to the points.
    If using a transformer, I'd think it best to use a full wave rectifier and a lower
    voltage.
    As for selenium rectifiers, they made ones that could handle 5 to 10 amperes.
    It would have been a big finned thing.
    These do suffer from age. Moisture gets in them and they short out.
    Tinker Dwight
     
  23. Ralph

    Ralph Registered User
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    The coil operates in the millamp range, not amps. A general purpose diode, 600 or 1000 PIV, 1 amp should work fine. PIV is peak inverse voltage.

    Ralph
     
  24. john e

    john e Registered User

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    My day job involves pretty much every type of electrical/mechanical device ever made. So I guess looking at more motors and coils just didn't seem interesting at all after 8 hours of it.

    At the museum, I'll fix up the electrics when the guys aren't sure what to do, but other than that, just wasn't that interested in perusing the electric forum..

    John
     
  25. kinsler33

    kinsler33 Registered User

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    True. The other great virtue of selenium rectifiers was that when they failed they'd emit a cloud of poisonous selenium gas. But I have an ancient variable DC power supply, supposedly rated @ 30 amperes that uses a pair of huge selenium rectifiers bolted to the case. Hasn't killed me yet, I don't think.

    My major question about Mr Shutterbug's clock and its power supply is its age. If it dates to, say, the 1920s or '30's, I'm fairly sure that it could only have supplied DC to the clock with a vacuum-tube or, more likely, a gas-filled rectifier tube. These last looked like light bulbs and were used in auto-shop battery chargers as well as 'battery eliminators' to power your home radio set. Possibly there were filter capacitors, too.

    In any event, if the transformer's output is indeed 50 volts (presumably RMS) then its peak voltage would have been around 70 volts, which seems awfully high for this application, and thus I wonder if that's the correct transformer.

    I clearly know nothing about this particular clock, but I do recall that there were plenty of devices back in the day that ran exclusively on batteries. There were burglar alarms and telephone systems powered by bundles of huge old #6 dry cells, each one 1.5v, connected in series. These weren't re-chargeable at all: just a zinc case the size of a can of tennis balls with a big carbon rod (suitable for other boys' science projects) down the middle and a pair of brass screw terminals on top.

    So I'm curious to find out more about this project.

    M Kinsler

    awarded the Electricity merit badge circa 1959
     
  26. kinsler33

    kinsler33 Registered User

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    For some reason I've always felt that electric clocks, even the ones with lots of gears and Westminster chimes and all, somehow exist in an entirely different universe from mechanical clocks. I like both kinds, but they're just not the same.

    M Kinsler

    and then there's quartz
     
  27. shutterbug

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    #27 shutterbug, Oct 28, 2017
    Last edited: Oct 28, 2017
    I wanted to give you guys an update on this one. I got it repaired and back together OK, aligned the coils and tested it with four 6 volt batteries wired in series. All seemed OK. I delivered it yesterday, and set it up to test it in the case. It was trying to wind every second (activated by the EW on an electrical contact at every tooth), and the owner said that's not right. He was a bit chagrined about it. I pondered it a bit, and thought about the power source having + and - requirements. So in desperation, I reversed the polarity and EUREKA, it works like it should. The customer was so happy that he gave me a $40.00 tip! Nice! Here's some pics I took before I took the movement out of the case, and a couple of the case after the re-install. LOVE that clock! Sorry about the pics. All I had was my cell phone. My original pics seem to have disappeared!

    Self winding master clock.JPG Self Winding School Master (1).JPG Self Winding School Master (2).JPG Self Winding School Master (3).JPG Self Winding School Master (4).JPG
     
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  28. R. Croswell

    R. Croswell Registered User

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    I missed this thread when it started but in retrospect, the transformer and the bridge rectifier attached to it appear to be a newer than what would have been available when the clock was made. My guess is that it may have originally ran on a bank of batteries or had a transformer power supply that burned out and was replaced. Glad to see you have it working now. Nice looking clock!

    RC
     
  29. john e

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    Ah, ok. You didn't mention the transformer feeds a full wave bridge rectifier (the small four terminal device). The two white wires from the transformer are connected to the AC input terminals of the bridge, and the black and white wires that go into the hole of the wood are the full wave rectified voltage.
    That bridge rectifier is simply four small silicon diodes encapsulated into a plastic case. My guess would be one ampere devices. The transformer looks to be maybe half ampere capability at 50 volts, and recent vintage (last 30 years or so as a guess).

    John
     
  30. shutterbug

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    I wish I knew as much about electrical circuitry as some of you guys do! Most of it is mysterious to me, and scary :) Getting to 24 volts DC for the testing part of this one was not too hard, but looking back, I wouldn't have needed the large batteries :) Two 12 volt batteries (like they use in garage door openers) would have done it.
     
  31. kinsler33

    kinsler33 Registered User

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    Really old electrical stuff requires quite a bit of archeology. It would seem that the original clock ran on 24 volts DC, and you could indeed obtain that from two 12V batteries or your four 6V batteries. But I'm still puzzled as to why the clock's behavior changed when the polarity of the DC source was reversed, for an electromagnet like the one that winds this clock shouldn't care which way the current flows through it: it will attract a piece of 'soft' iron either way. About all I can think of is that there's a permanent magnet or some other polarity-sensitive item in that movement, which doesn't seem likely given the age of the clock.

    Yes, that's a modern transformer and bridge rectifier standing in for the batteries. It should last pretty much forever.

    M Kinsler
     
  32. shutterbug

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    One part connected to the seconds feeler, and the other connected to the minutes. When I reversed the polarity, it switched the winding cycle to the minute instead of every second. That's the way it's supposed to work :)
     

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