1942 10ee MG speed and voltage issues - Page 2
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  1. #21
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    If you were getting 350 VDC on the armature you would be getting more than 1K RPM on the motor with full field.

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    Quote Originally Posted by labeeman View Post
    If you were getting 350 VDC on the armature you would be getting more than 1K RPM on the motor with full field.
    Even with the braking resistors engaged since relay not working?

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    Quote Originally Posted by FortyFive View Post
    Even with the braking resistors engaged since relay not working?
    Yep and some HOT braking resistors.

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    Quote Originally Posted by FortyFive View Post
    Well, that was it. With cardboard between the DB contacts, it goes to full speed. I'll check into it's coil next.

    Is the 350 armature max voltage a concern? Other posts indicate 240 being the max.
    ...
    You can run without the DB relay. Dynamic braking will still work, but when you're above base speed, it doesn't work as well, since the field won't be a maximum. Just take the relay out until you figure out what's wrong with it. I don't know if Bill (9100) is still interested in rewinding DB coils; you can also do it yourself, using the 10EE to do the winding. There are several threads here that explain coil winding in great detail.

    350 VDC is quite high for the armature voltage. A number of people have reported armature voltages around 300 VDC, but 350 is a new high. My 1943 MG machine reads about 300 VDC. But I've never put a scope on it to see if some of that might be transients. If you can borrow an old school analog meter, it will be less susceptible to switching transients created by the commutator.

    You said in your first post that you have 128 VDC coming from the exciter. It should be putting out 115 VDC. If it's over voltage, the output of the generator will be high as well. You can adjust the the exciter's output by increasing the resistance of the series resistor in the exciter's shunt field circuit. The resistor is located in the generator's end bell.

    Just to clarify, the DB relay DOES NOT control dynamic braking. I've long felt that it's mislabeled: I would have called it the "Full Field" relay. The dynamic braking resistor is actually controlled by the two normally closed contacts, one on the bottom of the F and one on the R contactor. When they are both closed (i.e. F and R are open), the dynamic braking resistors are connected across the spindle motor's armature. All the DB relay does is make sure that the spindle motor has full field, so that dynamic braking works most effectively.

    Cal

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  7. #25
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    I have not rewound one of those coils but I probably can. Before doing anything rash, see if there is a spring on the relay. I have pictures of the panels I worked on but I can't tell from them where the spring is. Probably at the bottom of the relay as it sits on the panel. If the spring is missing, the relay will close on a small current, I. E. all the time. Unless someone has a sample to copy, you may have to experiment, but fortunately getting it wrong won't burn anything up, the lathe just will not operate properly.

    Bill

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    Quote Originally Posted by Cal Haines View Post
    You can run without the DB relay. Dynamic braking will still work, but when you're above base speed, it doesn't work as well, since the field won't be a maximum. Just take the relay out until you figure out what's wrong with it. I don't know if Bill (9100) is still interested in rewinding DB coils; you can also do it yourself, using the 10EE to do the winding. There are several threads here that explain coil winding in great detail.

    350 VDC is quite high for the armature voltage. A number of people have reported armature voltages around 300 VDC, but 350 is a new high. My 1943 MG machine reads about 300 VDC. But I've never put a scope on it to see if some of that might be transients. If you can borrow an old school analog meter, it will be less susceptible to switching transients created by the commutator.

    You said in your first post that you have 128 VDC coming from the exciter. It should be putting out 115 VDC. If it's over voltage, the output of the generator will be high as well. You can adjust the the exciter's output by increasing the resistance of the series resistor in the exciter's shunt field circuit. The resistor is located in the generator's end bell.

    Just to clarify, the DB relay DOES NOT control dynamic braking. I've long felt that it's mislabeled: I would have called it the "Full Field" relay. The dynamic braking resistor is actually controlled by the two normally closed contacts, one on the bottom of the F and one on the R contactor. When they are both closed (i.e. F and R are open), the dynamic braking resistors are connected across the spindle motor's armature. All the DB relay does is make sure that the spindle motor has full field, so that dynamic braking works most effectively.

    Cal
    That helps in understanding the dynamic braking. I may just run without it for now like you suggested. I don't want the higher voltages to damage anything over time. If they are in fact that high. I'll try to get ahold of a better meter. I looked at the adjustable resistor you mentioned. It would have made sense that a previous owner could have lowered its resistance to try to get more speed because of the relay issue. Doesn't seem to be the case though. Visually, the wiper is at about 3/4 of max resistance. Without disconnecting anything it measured 121 ohms. Then I disconnected the wires at A2 (information in one of your other posts) to isolate. Then it measured 155 ohms, which seems inline with others.

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    Quote Originally Posted by 9100 View Post
    I have not rewound one of those coils but I probably can. Before doing anything rash, see if there is a spring on the relay. I have pictures of the panels I worked on but I can't tell from them where the spring is. Probably at the bottom of the relay as it sits on the panel. If the spring is missing, the relay will close on a small current, I. E. all the time. Unless someone has a sample to copy, you may have to experiment, but fortunately getting it wrong won't burn anything up, the lathe just will not operate properly.

    Bill
    There is a spring at the bottom of the relay, but it is a normally closed relay.

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    OK, but I am puzzled. It seems that it would have to be normally open unless running voltage kept it energized. I have specs for three Monarch relay coils in my archives, round dial contactor coils (forward and reverse contactors), braking relay and anti plugging coils. I remember making a main contactor coil but the others are probably for square dials. The anti plugging coil is 24,750 turns of #37 wire. Takes a while to wind.

    Cal, if you have a round dial schematic digitized, I would appreciate having one. I have square dial and modular drawings.

    Bill

  11. #29
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    Quote Originally Posted by 9100 View Post
    OK, but I am puzzled. It seems that it would have to be normally open unless running voltage kept it energized. I have specs for three Monarch relay coils in my archives, round dial contactor coils (forward and reverse contactors), braking relay and anti plugging coils. I remember making a main contactor coil but the others are probably for square dials. The anti plugging coil is 24,750 turns of #37 wire. Takes a while to wind.

    Cal, if you have a round dial schematic digitized, I would appreciate having one. I have square dial and modular drawings.

    Bill
    That's how it works. The DB relay's coil is energized whenever the F or R contactor are closed, opening the contacts. It has to be energized to allow field weakening to work. As soon as the F or R open, DB's normally-closed contacts close, bypassing the field control rheostat and providing full field to the spindle motor. 45's panel uses a Struthers-Dunn 3334 relay for the DB relay. Later panels also used an SD 3334 relay for the AP relay.

    There were about a dozen different round-dial panels. I'll send you the common diagrams.

    Cal


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