DC Panel Problems

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Chuck K

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Today I decided to fix the contacter in my dc panel. It hasn't worked for probably a couple of years. I have just been using the machine with forward spindle rotation all this time and thinking that sooner or later a parts machine would present itself. The parts machine hasn't come along, so I decided to take the coil out and see if I could get it repaired. Before removing it, I powered the machine up and and engaged the spindle in forward to make sure I had the right contacter. After running it in forward and confirming which contacter was which, I moved the drum switch to reverse. Nothing happened, as I expected, and I should have just stopped there and removed the bad contacter....but instead I manually pushed in the reverse contacter and the spindle turned in reverse. Again I should have stopped there....but I didn't. With the drum switch still in reverse I manually pushed in the forward contacter...thats when my trouble began. Something made noise at the bottom of the panel when I pushed in the forward contacter....I'm thinking the overload on the bottom left. The spindle didn't turn forward and now when i move the drum switch to forward the contacter pulls in but the spindle doesn't move. I tried pushing in the red button on the overload. You can feel the spring tesion, but it doesn't lock in. I checked the only two fuses that I know of (the one in the dc panel and the one in the panel back by the generator. This machine has been rewired with a rectifier to replace the exciter. Cal, you have walked me through this machine on the PM forum in the past. I'm hoping you can point me in the right direction to try and troubleshoot it again. Here's some pics of the front and rear of the panel. Thanks

Chuck

front.JPG back1.JPG back2.JPG
 
My monarch has a overload on the back of the Lathe by the headstock maybe that one is tripped. Arched cover with a hole and a red button inside. Robert
 
I think that's for the coolant pump if I'm understanding you correctly.
 
No it's the main power coming in to the lathe through a contactor then a overload (overheat coil) from there it goes to the motor generator. IF THE MG STILL RUNS it's NOT THIS. Robert
 
The overload in the lower left corner can be checked easily. You can remove one wire from it and ohm it out with power removed. It should have very low resistance. Or you can take your volt meter and check for volts across the two terminals with the lathe in operating mode Power applied. If You have operating volts when measuring across the 2 terminals then the overload is tripped. Do you have a wiring diagram for your lathe? If so you can check for power to both the field and armature inside the control panel at the terminals along the bottom. Hope this helps Robert
 
Robert, I don't have a wiring diagram. I downloaded the two manuals that are available online. One is for a 1965 square dial and the other is for a 1942 round dial. Mine seems to have the drive from the earlier model, but that manual doesn't have a wiring diagram. Worst case I think the manual for my machine is available from monarch. I'll check the overload in the dc panel. Thanks

Chuck

There are two wires on the front of the overload and two on the bottom. Which do I disconnect and which do I measure across?
 
OK...I'm back to my original problem. I just need a coil for my contacter. It seems when I pushed in the forward contacter with a screwdriver, sparks startled me enough to bump into the lever that selects between belt and gear drive. After checking everything I could think of (which isn't really much when it comes to electrical), I couldn't see how I could do much damage by powering it up again and trying to run it. When I engaged the spindle, the contacter pulled in and the spindle just stayed motionless. I heard some noise and shined my light down on the motor and realized it was turning. That's when I looked at the lever....Duh! So I cut the power and pulled the bad coil out. I have posted a pic of it on PM.
http://www.practicalmachinist.com/vb/monarch-lathes/spindle-drive-contacter-271630/

I'm hoping to find someone that has an extra one.

Chuck
 
Chuck K said:
Today I decided to fix the contacter in my dc panel. It hasn't worked for probably a couple of years. I have just been using the machine with forward spindle rotation all this time and thinking that sooner or later a parts machine would present itself. The parts machine hasn't come along, so I decided to take the coil out and see if I could get it repaired. Before removing it, I powered the machine up and and engaged the spindle in forward to make sure I had the right contacter. After running it in forward and confirming which contacter was which, I moved the drum switch to reverse. Nothing happened, as I expected, and I should have just stopped there and removed the bad contacter....but instead I manually pushed in the reverse contacter and the spindle turned in reverse. Again I should have stopped there....but I didn't. With the drum switch still in reverse I manually pushed in the forward contacter...thats when my trouble began. Something made noise at the bottom of the panel when I pushed in the forward contacter....I'm thinking the overload on the bottom left. The spindle didn't turn forward and now when i move the drum switch to forward the contacter pulls in but the spindle doesn't move. I tried pushing in the red button on the overload. You can feel the spring tesion, but it doesn't lock in. I checked the only two fuses that I know of (the one in the dc panel and the one in the panel back by the generator. This machine has been rewired with a rectifier to replace the exciter. Cal, you have walked me through this machine on the PM forum in the past. I'm hoping you can point me in the right direction to try and troubleshoot it again. Here's some pics of the front and rear of the panel. Thanks

Chuck
Click to expand...
Hi Chuck,

I'm glad that you solved the problem and that nothing was damaged. I was afraid from the symptoms that you might have damaged the generator. I've spend the last few hours working on a debugging post for you. I'll go ahead a post what I have so far, since it explains what happened:

When you manually closed the forward (F) contactor with the reverse (R) contactor already closed you shorted the outputs of the generator together and shorted out the spindle motor's armature. I'm not sure how you managed to do that; there is a linkage like a teeter-totter that lifts the other contactor when one of them closes.* Anyway, this would have resulted in a large current in the generator's armature.

The overload device in the lower left corner of the panel is there to protect the armature circuit: when its heater exceeds a certain temperature a thermally-operated switch opens. Note that this overload device is not like the circuit breakers found in AC breaker panels and it does not directly break the circuit. Instead, the thermally-operated switch breaks a circuit that causes a contactor somewhere to open and shut down the circuit. In this case, the overload device's switch breaks the circuit that powers the F or R contactor coil and would normally cause the contactor to open, opening the armature circuit and shutting down power to the generator's field, which cuts off the power to the armature circuit. However, since you were manually closing the contactors, the overload could not function.

BTW, thanks for all the detail in your post. It's very helpful in figuring out what's going on.

The fact that the contactor is closing when you move the drum switch tells me two things: 1) the solid state "exciter" is putting out voltage, so it's OK; 2) the armature circuit overload device's switch is closed (it may have opened, but you have taken the steps to reset it). This means that the problem is probably with the generator.

Fortunately, everything is OK. So I'll stop here, without explaining how to verify that the generator is the problem and how to check it out.

A little background on your machine, from out time together at PM: The machine is wired for 440VAC and being operated from a rotary phase converter with 240 to 480 step-up transformer to provide the 440. The exciter had failed prior to the machine coming to you and had been replaced by a simple rectifier circuit to provide the voltage to the DC panel and the generator's field. The forward contactor had a bad coil and I helped you swap the armature leads to get the motor to run forward with the reverse contactor closed. (So the bad contactor is really the F contactor). Also, you had some bad forward contacts in the headstock drum switch.

* You should have a look at the mechanical interlock between the contactors and figure out how you managed to close both contactors at the same time.

Cal
 
Cal, Sorry to put you through all that trouble. I didn't actually get both contacters to close at the same time. I had the drum switch in the reverse position when I manually pushed the forward contacter in. The fact that the reverse contacter had the bad coil in it kept it from being engaged with the drum switch in that position. I didn't real see how I could have hurt anything by pushing the other contacter in....but nothing worked after I did it, or so I thought. I was afraid at that point to just leave it in the forward position with it powered up and see what was going on. If I had done that right away I would have realized that the motor was turning but not the spindle. Mechanical problems like that I can understand. With any luck I'll come up with coil for it. I have a good lathe to use while the monarch is down now, so if I have to wait for it to be rewound it won't matter. Thanks.

Chuck
 
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