Willray
Aluminum
- Joined
- Jan 30, 2011
- Location
- Central Ohio, USA
Greetings all,
I'm in the process - closing in on the home stretch - of returning #41868 (1956 Square Dial MG, ELSR) to service. I'll worry about something that smells like a restoration later, right now I need it to make chips.
I've a few lingering conundrums about the Motor-Generator at this point, largely due to the efforts of some previous owner, who rewired a good bit of it, had the MG rewound as 440V only, and mislabeled pretty much every wire in the thing.
I've sorted a lot of the mislabeling, and the fact that I can now get her to start and run and change speeds suggests that I got reasonably close.
However:
1) My MG has what seems to be an undocumented wirewound resistor mounted at the bottom of the generator (NOT the Exciter - that has it's own wirewound resistor). GF2 goes to one end of this resistor, and the slider goes to the pair of field windings that come back on GF1. Why didn't I measure the resistances on this thing yet? Good question...
Question - Is that resistor _supposed_ to be there? If so, what is the proper slider setpoint?
Diagnostics to date:
I'm wondering whether it belongs, because I'm not getting full top-speed out of the machine (yeah, I know the standard answer is the FA relay and field weakening - I can't rule that out, but this resistor affects the system too.
With the slider where I found it, which is applies about 2/3 of the resistance of the whole resistor I get something vanishingly close to zero RPM up to maybe 1050 RPM. If I disconnect the slider so that the whole resistor is in the circuit, I get about 800 RPM top speed. If I swap the leads so that the (previously unused) 1/3 section is in the circuit, I get about 1600 RPM.
I'm wondering if some previous owner added this as a way to restrict the top speed of the machine. I have the JIC cabinet, and the 270-degree-sweep from walking-pace to full-speed with the JIC-mounted speed-control is rather abrupt!
2) My DC motor contractor(s?) randomly drops out and pulls back in instantly. Not the MG contactor, the F contactor (I assume the R contractor does as well, but I haven't spent as much time with it in Reverse yet). Sometimes it does this "repeatedly", other times it seems to just be a random clunk and then another 10 minutes of running without a hitch. The issue /may/ be load dependent. I believe it does it a _lot_ more when it's trying, for example, to start with the lathe at the higher end of the speed range. I'm not 100% confident in that assessment.
I believe I saw a flicker on the E1-E2 voltage once when it did this, but I can't say whether it was a reduction in exciter output, or a momentary higher current drain.
I can't think of any reason that higher load would affect the exciter output (it's running 118V), or affect the F/R contactor's ability to stay pulled in.
Do those symptoms mean anything to anyone with more experience with these drives than I have?
Thanks in advance for any assistance!
Will Ray
I'm in the process - closing in on the home stretch - of returning #41868 (1956 Square Dial MG, ELSR) to service. I'll worry about something that smells like a restoration later, right now I need it to make chips.
I've a few lingering conundrums about the Motor-Generator at this point, largely due to the efforts of some previous owner, who rewired a good bit of it, had the MG rewound as 440V only, and mislabeled pretty much every wire in the thing.
I've sorted a lot of the mislabeling, and the fact that I can now get her to start and run and change speeds suggests that I got reasonably close.
However:
1) My MG has what seems to be an undocumented wirewound resistor mounted at the bottom of the generator (NOT the Exciter - that has it's own wirewound resistor). GF2 goes to one end of this resistor, and the slider goes to the pair of field windings that come back on GF1. Why didn't I measure the resistances on this thing yet? Good question...
Question - Is that resistor _supposed_ to be there? If so, what is the proper slider setpoint?
Diagnostics to date:
I'm wondering whether it belongs, because I'm not getting full top-speed out of the machine (yeah, I know the standard answer is the FA relay and field weakening - I can't rule that out, but this resistor affects the system too.
With the slider where I found it, which is applies about 2/3 of the resistance of the whole resistor I get something vanishingly close to zero RPM up to maybe 1050 RPM. If I disconnect the slider so that the whole resistor is in the circuit, I get about 800 RPM top speed. If I swap the leads so that the (previously unused) 1/3 section is in the circuit, I get about 1600 RPM.
I'm wondering if some previous owner added this as a way to restrict the top speed of the machine. I have the JIC cabinet, and the 270-degree-sweep from walking-pace to full-speed with the JIC-mounted speed-control is rather abrupt!
2) My DC motor contractor(s?) randomly drops out and pulls back in instantly. Not the MG contactor, the F contactor (I assume the R contractor does as well, but I haven't spent as much time with it in Reverse yet). Sometimes it does this "repeatedly", other times it seems to just be a random clunk and then another 10 minutes of running without a hitch. The issue /may/ be load dependent. I believe it does it a _lot_ more when it's trying, for example, to start with the lathe at the higher end of the speed range. I'm not 100% confident in that assessment.
I believe I saw a flicker on the E1-E2 voltage once when it did this, but I can't say whether it was a reduction in exciter output, or a momentary higher current drain.
I can't think of any reason that higher load would affect the exciter output (it's running 118V), or affect the F/R contactor's ability to stay pulled in.
Do those symptoms mean anything to anyone with more experience with these drives than I have?
Thanks in advance for any assistance!
Will Ray
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