Barr & Poole Barr Electric Question.

Discussion in 'Electric Horology' started by H.Weiland, Dec 23, 2007.

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  1. H.Weiland

    H.Weiland Deceased
    Deceased

    Some time back I brought up a question regarding a later Barr Electric that operates on 120 volt line current. I was surprised that the magnetic circuit was not laminated.

    This clock has run for some months, but suddenly stopped. It appears that the magnet was no longer being supplied with enough current. After doing a number of tests, nothing seemed to be at fault except the electro-magnet not being strong enough.

    Removing the dial, I found that a small resistor was mounted behind the dial, to the contact connection. This had deteriorated and cracked. Unfortunately the resistor was of the very inexpensive carbon molded type used long ago in vacuum tube radios.

    I will have to replace this with a new resistor, but here is my problem. The colors of the rings on the body are no longer vivid enough for identification. And to be honest, I am partly color blind which makes this all the more difficult. My plan is, when I know the correct resistance originally used, to parallel two resistors of double the value of the original, thus retaining the same resistance, but doubling the wattage for a longer life.

    Does anyone know what the value in Ohms these resistors were? Presently it measures 385 ohms in it's damaged condition, but this seems too high. if I am correct.

    Thanks for any suggestions.

    Henry Weiland
     
  2. swolf

    swolf Registered User
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    Nov 24, 2002
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    Henry, the lowest voltage that your clock will normally should acctuate on, (say 95-100 volts) would define the value of the appropriate series resistor.

    You could use a Variac to obtain the starting voltage and use an adjustable resistor of about 10 waTTS dissapation in series with the clock to establish what value of resistance will just reliably run the clock.

    The increment between 95 volts and 120 volts is the margin needed to provide reliable clock operation in the event of line voltage fluctuations. While the clock is running you can measure the voltage drop across the resistor to calculate the wattage requirements.

    This drop will only be present while the clock coil is energized. Now this is not the wattage that is actually required because the duty cycle or average current heating the resistor is much lower.
    What I would do is use a handful of resistors of the correct resistance value but different wattage ratings and empirically find an acceptable rating that did not runn too hot to the touch. (Your call when your finger gets blistered).

    Sherm
     
  3. glr1109

    glr1109 Registered User

    Jun 2, 2002
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    could you post a photo of this clock?

    greg
     
  4. H.Weiland

    H.Weiland Deceased
    Deceased

    Thanks for the suggestions Sherm. The present resistor is only a 2 watt size, and since it is behind the dial, I am limited in the size resistor I can install in a single resistor.

    The variac is a good idea I had not thought of. Today I am off to the electronic parts house to get some resistors. Last night I cleaned the movement. Since all the parts are very small, I put clean naptha in a mason jar which then I put in water in the ultra sonic. The movement would only run 8 swings before it tripped the release. Before starting actually I had some doubts if this was needed, since the movement looked so clean. After all the parts were cleaned, I was surprised how dirty the naptha had become, and a surprising amount of residue was laying of the bottom of the mason jar. The cleaning was followed with standard work of pegging out the holes. and so on until everything was very clean and oil free.

    I had read in the Bulletin article that many of the professional clock guys do not want to disassemble the movement. Now it is not difficult to reassemble but is very exasperating. The key is that the entire (almost) movement must be assembled at one time. For instance you can not put the train together, then add the pallets, and so forth. Unfortunately complications exist, the gravity arm hides the plate under it were the pivot holes can be seen and the gravity arm has a wire attached. Just a word to the wise, it helps to have pictures or another movement handy for reference. Then please take your time, and you will be able to get it together. Remember everything needs to be assembled more or less in one operation. Put all the parts were they go, "piled up" in place then start locating the arbors, and be sure to watch the small click on the top of the movement. I will warn about the gravity arm wire below.

    I did not fully understand this intially, and after a couple assemblies and disassemblies, it was completed.

    Now after the movement is clean and back together, the clock swings for about 35 swings before it trips again.

    After the clock was back together, I experimented with a old General Radio decade resistor box subsituting for the original resistor. With some detective work, (asking the neighbor what the resistor colors were) found it was most likely originally a 330 ohm 2 watt resistor. What I am going to do is parallel two 680 ohm resistors together, making a resulting 340 ohm resistor but 4 watts capacity. I will take a ohm meter to the electronic house to find the best resistors to come as close to the correct value I can. This is acceptable since the original had only a 10% calibration. Since the current is on only for the shortest amount of time, the contacts just really tap for an instant, this should be more than sufficient, and twice as good as was there originally. The resistors are not visible behind the dial so nothing is disfigured.

    The wiring for the 120 volt Barr is different than used for the standard battery clock. The movement for the battery clock is part of the circuit, for the 120 volt clock it is not. Here wires thread though the movement. Take very careful note of the ROUTE the wire to the gravity arm follows, as it winds through the movement. If you do you will save much exasperation.

    The contact block is insulated from the dial assembly, as is the contacts on the gravity arm. Otherwise the entire metal movement would be at line voltage. If you set the hands and the movement were live this would be unacceptably dangerous. As it is to get a shock you would specifically have to touch the contact block or depending on how the plug is in the wall, the gravity arm contacts. This is not as seriously dangerous, but should be born in mind. The only time one could get hurt is standing on a (damp) cement floor with no shoes or socks and sticking you finger into the contacts.

    I will report how the new resistor turns out shorty and will try to post a picture too.

    Henry Weiland
     
  5. eskmill

    eskmill Registered User
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    Aug 24, 2000
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    Barr 120V.
     

    Attached Files:

  6. glr1109

    glr1109 Registered User

    Jun 2, 2002
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    Although I've seen a couple of designs of these clocks...I've never worked on one. Of these two I like the one with the drawer for batteries. You could buy as an accessorie a transformer that fit into the drawer.

    While making adjustments, I use a "universal transformer" set to 4.5v. Just clip the red onto the top-cap-holder and black onto a plate.

    greg
     

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