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Un-hacking 10EE Motor-Generator wiring

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
 
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Maybe I'm too long-winded to get answers, but, just in case more data helps:

Here's what my MG looks like from the end:
295082d1595896075-un-hacking-10ee-motor-generator-wiring-img_8192.jpg


The wirewound variable resistor in the Generator section reads as 312 Ohms end-to-end. The slide is making a 207/105 Ohm split, with the (as configured by the previous owner) the 207 Ohm side inserted in series with the shunt field coils of the generator (between GF2 and the lower-left (shunt) field coil, the other end of which is connected to the upper-right (shunt) field coil, and thereafter back to GF1.

The lower left and upper right field coils look like they measure about 185 Ohms each, but I'm reading GF1 to GF2 as 628 Ohms. Not sure where the missing 50 Ohms went.

IMG_8192.jpg
 
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With the 207 Ohm chunk of the wirewound in the generator shunt field, the main drive motor (large-frame Reliance, I believe 3HP, though it looks like I'm missing the data plate) sees:

Lowest speed (~20 RPM): A1 to A2 = -9V, F1 to F2 = 118V
Highest speed (~1100 RPM): A1 to A2 = -150V, F1 to F2 = 22V
F1 to F2 starts dropping right around 500RPM

The FA relay does not seem to be engaging in any situation, however this is hardly making a difference with only 150V on the drive armature.

Question -- am I sane to believe that it's safe to remove the wirewound variable from the generator, and see whether it makes the appropriate 240ish volts that the 3HP Reliance is supposed to eat?
 
the resistor is supposed to be there

on second thought, after looking at the pics, you have two resistors, one on the exciter and one on the generator . i am only accustomed to seeing one. IDK what the second one is for.
 
...
That is the last style MG set, if the contacts drop out near full speed, your exiter is not putting out enough voltage to keep the switches in, it is a safety feature, the exiter also powers the field.
On the cover to the switch box should be instructions stating the commutators can be dressed using stones. The stones are available from Ideal Electric-commutator and slip ring dressing stones.
I have found, if there is any but the most tiny of arcing on the generator commutator, the machine will not reach full speed.
If the switches drop out, look at the exciter commutator for a ridge that builds up in the center from the split brushes, this cause the brushes to wedge in the holders with voltage loss.
You are in great shape the machine runs! Just some basic tuning is left. The generator set appears to be a 3v8 model
Remember what I just stated is in the instruction for the drive, it is dangerous to do, the machine is running and you have to get in to the tight spaces to do this! Not for the panty waist that tend to hang around.
Dressing the exciter with the stone glued to a wood stick, the ridge from the brushes can be see as a bright line in the photo.
04T2Fjh.jpg

I have been using the machine for close to 20yrs, and have made alot of money with it, and it a MFG model.
 
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That is the last style MG set, if the contacts drop out near full speed, your exiter is not putting out enough voltage to keep the switches in, it is a safety feature, the exiter also powers the field.

Could you possibly explain to me how the holding voltage for the F/R contractors could be affected by the drive speed/load? I've seen it claimed several times that the exciter plays a part in load regulation. Is this because the AC motor slips more, as the generator is asked to deliver more current?

I /believe/ that the contractor is dropping more frequently, when the thing is trying to accelerate, possibly specifically when it's trying to accelerate in the field-weakening region. Since my FA relay does not currently seem to be pulling in to assist acceleration, I suppose armature current is high at that point, which could drag the MG speed down. Still, it also drops randomly during steady-state unloaded running (possibly also more, in the field weakening region). I really need to get readings on both the exciter voltage and current when that's happening.

I do not /see/ any obvious ridge on the exciter commutator, though I cannot claim to have looked closely for one. I'll check that this evening.

On the off-chance that you have a machine with the same generator set, could you possibly measure the (disconnected) GF1-GF2 resistance on your generator? Cal has repeatedly documented roughly 50 Ohms per shunt-field coil in MG sets, and I'm seeing 160ish Ohms per coil. I don't know if that's a design/generational difference in the units, or if this is yet another previous-owner-modification. I do know that they were in, and rewound at least the AC section of the MG set.

Many thanks,
Will Ray
 
I am the least technical one here, but the the most experienced driver that the termite has not been able to chase off.
If there seems to be not enough line power to the AC motor and it pulls down just a little the exciter rpm drops just a little the motor contacts drop out.
At my house until recently the service was poor, and there just wasn't enough juice for the machine to start above 1200 rpms, in that case the machine will surge. But, the machine could be started at below 1200, then ramped up to full speed.
The switches dropping out has nothing to do with the big resister on the gen set.
I found top speed directly related to the generator, and condition of the commutator. The commutator can go out of true in use on the generator from heat, that is why all three commutators are to be dressed as instructed by Reliance printed on the control box.
Turn off the lights watch the commutator on the generator with spindle runnig, there should be just a faint even aching. If sparks fly around, there is a high bar causing the brushes to dance. Either you use the stones or repair the commutator in a lathe...
 
Not at all. The AC motor is not meant to slip. It is a "synchronous" design.

The Motor-generator is listed as a 3450 RPM unit, which wouldn't appear to be a synchronous motor?

If it /is/ synchronous, I'm failing to understand how the exciter output can respond to changes in load, if it's always turning the same RPM regardless of load. Certainly, its voltage output would respond to changes in current drawn out of it, but that should be reasonably replicable in a non-rotating stand-in for the exciter, so I'm struggling to comprehend how the exciter factors into load compensation in a way that a solid-state replacement couldn't.

This evening I think I will see what the generator does, with that mystery resistor removed from its shunt field circuit.

I expect that the contractor dropping is a different issue, but hopefully getting the available armature voltage up where it belongs will get more of the control system working as intended. Then I need to start sniffing for transients.

I'm really not seeing anything that would lead me to believe that the brushes/commutators need service (sparking is all but invisible), but I can't rule out the simple presence of crud that has accumulated in the years since this thing was last run
 
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Ok, I believe I have this thing sussed as far as I can go, until some kind soul with a motor-generator takes pity on me and maps out the generator internals.

First off, it turns out I was wrong about the 185 Ohms per shunt coil. It's actually 215 Ohms per shunt coil. I was an idiot and forgot to disconnect GF1/GF2 from the terminal strip, so was paralleled across part of the Generator potentiometer.

Next, removing the mystery resistor from the shunt-field circuit gets me up to about 200 volts available from the generator.

The remaining question is - is there /any/ possibility that the shunt coils are supposed to be wired in parallel rather than in series? If my two 215 Ohm coils were wired in parallel, they'd measure out at something much closer to Cal's repeatedly-reported roughly 100 Ohms GF1 -- GF2.

Could someone please, please take a look in a Motor Generator and map GF1 in to the shunt coils, and then back out to GF2?

On mine, the wiring (looking from the pulley end of the generator) follows the path shown in this image:

295185d1595984133-un-hacking-10ee-motor-generator-wiring-img_8196-copy.jpg


(yes, I know that's not the way the coils are usually represented or are oriented - I don't know the actual clocking of the windings on them, so not wanting to misrepresent an unknown fact, this is /just/ which end of the coil is where, and the presence of the coil...)

For the record, my contactor dropping looks like it was the near-ubiquitous "your 2000 Ohm resistor failed" issue, combined with a really stupid problem with the AP relay. The resistor was pretty much crap-open, which on everyone else's machine makes the thing reliably drop out above approximately 300 RPM when the AP relay pulls in and the coil voltage goes to zero.

Do I get a nice reliable failure like that? Noooo... I get a tiny little needle of swarf that's just /exactly/ the right length to wedge lengthwise between the top pole of the solenoid on the AP relay, and the moving arm. This little needle prevents the AP relay from opening its contacts reliably. The higher the running voltage, the more likely the AP relay finally overcomes the needle which gets laid down flat on the pole of the solenoid, allowing the contacts to open. When the AP relay releases, the residual magnetism makes the damned little needle jump back up straight and wedge itself under the moving arm again...

Anyway, getting rid of the needle made the problem obvious, and bodging in a roughly 2K cement resistor I had laying around made that part of the system work properly.

IMG_8196 copy.jpg
 
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Well. "Progress". Good on yah!

The resistors can be "made up" with a more common selection to get to where they need to be. Cal and others have posted which ones. There is ALSO a speciality supply house - the link is in one of my now OLD posts - that still sells the OEM EXACT values,"odd" or not. Not TERRIBLY expensive, but - physical sizes aren't assured to fit, so read on.

The resistors are the easy part. I already have a batch of aluminum chassis-mount types on the way from Digikey. (Since I have the JIC cabinet, I've got acres more room than most 10EEs have got, to mount them neatly and just bring the leads back to the DC board).

The schematics you are asking about to sort confirming the wiring connections are published ones and have BEEN seen on PM. Info is sorta scrunched-down on the basic schematic that ships with a round-dial MG manual - but factory had larger ones.

I haven't noticed any version of the schematic that depicts the two shunt-field coils separately, with the actual physical connections between them. They all just show the shunt field as a single solenoid (or IMHO bizarrely a single resistor). I don't know if that's just shorthand, or the actual intent. They don't show both field coils either, or the poles and interpoles on the drive motor, so they're clearly omitting some detail.

I am /really/ hoping that Cal does have a schematic with the physical wiring layout of the generator actually shown.

That being said, I can't think of a single good reason that switching my shunt field coils to a parallel arrangement wouldn't work. So long as I maintain the magnetic polarity properly, it ought to give me (up to) twice the shunt field strength. I can put the mystery 300 Ohm variable in series with the paralleled pair, and I should end up exactly where I am now, with the series pair and the mystery resistor removed. That will let me test to see whether I can get my 230V+ output back, and should at least at the base setting be no more stressful than the current setup.

It's hard to imagine that a maximum of about half an amp or through the shunt coils is terribly stressful. Cal's 100-ohm shunt field is either seeing 1 amp through both coils, or half an amp through each, so I believe I'd at worst be at the best that's possible in the "normal" setup.

Will
 
...

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?
Yes and no. There's supposed to be a resistor there, but not hooked up like yours. Despite what the documentation suggests, the exciter's shunt field series resistor is mounted in the GENERATORS's end bell. (Lord knows why.) Here's a diagram of how things are actually set up, with typical resistance values:

EE_2674_Exciter_Detail_Actual (w resistance values).jpg
(This diagram is for a round-dial 10EE. The actual MG terminal strip on a square-dial is different from what's shown above (even though the layout on the square-dial wiring diagram is the same as above). The square-dial terminal strip has 10 terminals instead of 12; GF1 shares the E2 terminal, GS2 shares a terminal with GA1 and the ordering is slightly different. I also haven't verified that the resistance values are correct for a square-dial MG set.)

It appears that the resistor in the exciter end-bell now handles the exciter's shunt field. We'll get to the resistor in the generator end bell in a bit.

...

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.
...

...
Here's what my MG looks like from the end:
295082d1595896075-un-hacking-10ee-motor-generator-wiring-img_8192.jpg


The wirewound variable resistor in the Generator section reads as 312 Ohms end-to-end. The slide is making a 207/105 Ohm split, with the (as configured by the previous owner) the 207 Ohm side inserted in series with the shunt field coils of the generator (between GF2 and the lower-left (shunt) field coil, the other end of which is connected to the upper-right (shunt) field coil, and thereafter back to GF1.

The lower left and upper right field coils look like they measure about 185 Ohms each, but I'm reading GF1 to GF2 as 628 Ohms. Not sure where the missing 50 Ohms went.

With the 207 Ohm chunk of the wirewound in the generator shunt field, the main drive motor ... sees:

Lowest speed (~20 RPM): A1 to A2 = -9V, F1 to F2 = 118V
Highest speed (~1100 RPM): A1 to A2 = -150V, F1 to F2 = 22V
F1 to F2 starts dropping right around 500RPM

The FA relay does not seem to be engaging in any situation, however this is hardly making a difference with only 150V on the drive armature.
...

OK. The 312 Ohm resistor is the problem.

If I understand you correctly, the 312 Ohm resistor is connected between GF1 and GF2. GF1 should connect to E2, which is the system ground. So the generator shunt field is only getting a portion (about 1/3) of the voltage applied to GF2. GF2 is the output of the "Generator" rheostat (GR). The GR is connected as a potentiometer, so that it's voltage, goes from (essentially) zero for minimum speed up to a maximum of 115 VDC (nominal) at the motor's base speed of 690 RPM.

The voltage on GF2 is what controls the generator's output. When neither the forward (F) or reverse (R) relays are closed, the GR is turned off, it's output and hence GF2, is zero. With the generator's shunt field turned off, the generator produces very little voltage, due mostly to residual magnetism. When the F or R relay close, exciter voltage is fed to the GR, which divides it according to the speed setting and provides current to generator's shunt field. The 312 Ohm resistor is dividing that voltage down, which guarantees that the generator can never put out it's full 230 VDC to the spindle motor's armature.

Take the 321 Ohm resistor out. Leave the one side of the shunt field connected to GF1 and reconnect the other side to GF2.

I suspect that the reason that the machine is faltering is that without full armature voltage it doesn't have the torque to start or run at higher speeds.

The FA relay is operated primarily by armature current. With the armature starved for voltage, the current may never get high enough for it to operate.

The Motor-generator is listed as a 3450 RPM unit, which wouldn't appear to be a synchronous motor?
No. Synchronous motor run at some multiple of the input AC frequency, the multiple depending on how the motor is wound. In this case it would be 3600 RPM. As far as I know, synchronous motor of any size require that the windings in the rotor be externally powered. I believe this motor falls in the category of induction motors. The name comes from the fact that the AC voltage in the stator windings induce current in the rotor windings. The 3450 RPM number is probably for the motor at full load and it will vary with load.

If it /is/ synchronous, I'm failing to understand how the exciter output can respond to changes in load, if it's always turning the same RPM regardless of load. Certainly, it's voltage output would respond to changes in current drawn out of it, but that should be reasonably replicable in a non-rotating stand-in for the exciter, so I'm struggling to comprehend how the exciter factors into load compensation in a way that a solid-state replacement couldn't.
Within reason, the exciter output has nothing to do with the load on the spindle motor. It's job is to provide 115 VDC to the DC control panel and the fields of the spindle motor and generator (via the big Ohmite rheostats). It's the series field in the generator that reacts to load on the spindle motor by increasing the field as the armature current draw increases. Later 10EE motors also include a series field in the spindle motor to further help out, but as far as I know, 10EE motor/generator drives don't have series fields in their spindle motors.

This evening I think I will see what the generator does, with that mystery resistor removed from its shunt field circuit.

I expect that the contractor dropping is a different issue, but hopefully getting the available armature voltage up where it belongs will get more of the control system working as intended. Then I need to start sniffing for transients.

I'm really not seeing anything that would lead me to believe that the brushes/commutators need service (sparking is all but invisible), but I can't rule out the simple presence of crud that has accumulated in the years since this thing was last run
That sounds like a plan.

What you want to see is:
  • The exciter should be putting out 115 VDC at all times. 118 VDC is close enough.
  • As you vary the speed control pot, the spindle motor armature voltage (A2 to A1) should go from a low voltage (<10 VDC) to 230 VDC at the middle of rheostat's travel (base speed). Above that speed it should stay at 230 VDC. (Your maximum armature voltage may be well above 230; I think mine runs about 300 VDC.)
  • As you increase the speed control from the minimum, the spindle motor field voltage (F2 to E2) should stay at 115 VDC until the midpoint, then reduce to about 40 VDC at maximum speed. It should never drop to zero at any point. You reported a value of about 20 VDC at the maximum speed setting; that's a bit low. There's an adjustable stop on the rheostat that can be used to tune the GR's output so that the spindle motor doesn't go above it's rated top speed (2600 RPM at the motor).

Let me know if the drop out problem persists once you've gotten the generator performing as above.

Cal
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... removing the mystery resistor from the shunt-field circuit gets me up to about 200 volts available from the generator.
...
I see that while I was off writing up my post you moved ahead.

Let me know what voltages you're seeing on the spindle motor field and armature, as requested at the end of my last post.

What voltage do you see across GF1-GF2 at base speed and above?

I don't recall seeing a point-to-point wiring diagram for the generator's windings. Unfortunately, my square-dial MG set is buried too deeply in storage for me to be able to check that for you and I don't seem to have any good photos that will help.

Here's a link that has the Ohmite and Newark part numbers for the DC control panel resistors:
Start up problem with m/G machine?

Cal
---
 
ok, done...

Let me know what voltages you're seeing on the spindle motor field and armature, as requested at the end of my last post.
Cal
----

Spindle motor field is behaving more or less as expected, 118V plus/minus a little wobble for the first half of the speed-control dial, then dropping to about 20-22V at maximum. At this point I'm only making 1600RPM (on the tach - I need to check that, but the frequency sounds about right by ear) maximum, so I'm in no danger of overspeeding the motor...

With the 312 Ohm resistor out of the GF1 -- GF2 circuit, the spindle motor armature is seeing something around 9-10V at the lowest speed, up to 200V at mid-dial, and a slight fall back to about 190V at the end of the dial travel.

I did not think to check the voltage being applied to (or current between) GF1 -- GF2 on the generator. I will do that tomorrow. That being said, the Generator-control potentiometer is behaving essentially as expected - 600ish Ohms end-to-end, and roughly zero ohms to the wiper when it's down on the terminal landing strip, so I expect to see full exciter voltage across GF1 -- GF2 at maximum speed, and the fact that I do have voltage control on the armature suggests that I'm getting an appropriate sweep up from the low voltage end.

What do you think of my idea to rewire the shunt field coils in parallel? That gets me the roughly 100ish Ohms across the shunt field that you've seen, and should put .5 or so amps into each shunt field coil, which is identical to what you've seen as well?
 
Read: An MG 10EE will perform better if one retains & repairs the OEM exciter that was "tuned" to cooperate with the main generator AND the final-drive motor. Whole rig is like unto a "team" of circus acrobats or ballet dancers.

Any "conversion" - such as to solid-state DC Drive - should be "whole hog"..with its OWN means of regulation under load (they DO have such..).... or not attempted at all.


Just to be clear Thermite, I am, and have, in no way advocated for replacing the exciter with a different source of 115VDC. In trying to understand the control and feedback system, I'm simply having a difficult time understanding how, as some have stated, changes in load on the spindle motor, are communicated to, and responded to, by the exciter.

It's easy to see how the generator senses and responds to changes in load, as the series field sees any changes in current drawn through the generator armature. Still not obvious to me how the exciter is a partner in that dance. The draw on it appears isolated from load-related changes in the spindle-motor armature current, and at higher speeds, where you'd expect more (work) load, the exciter should see lower current draw due to field weakening...

Still, that issue of my understanding of that detail is entirely secondary to the question of how the shunt field in the generator is properly supposed to be configured, which is what I /really/ need to figure out next.
 
There has been much confusion introduced up thread,
Since Cal (the moderator) has entered the troubleshooting, I will chime in.
It is too late to give Cal a call to take the info below off forum, I will put my thinking here.

Since this unit has been hacked by a previous owner,
It probably makes sense to verify if the generator wiring is correct as per Cal's drawing.

All the wires should have metal labels on them.

IF the generator series field is connected backward, it will cause the generator output to drop as the load is increased.

Another possible problem is winding faults. Lets verify that there are none before digging deeper.
Disconnect both ends of the series and shunt field wires of the generator.
Verify that there is over 100K ohms between the windings and each winding to ground.
Inter winding problems cause all kinds of problems, that are hard to find.

Once things are back together, watch the motor armature voltage from the point field weakening starts, until max speed. Yes old tachs read quite low.
The armature current increases as the motor field gets weaker.
If there is substantial motor armature voltage drop as speed is increased, just put a jumper on the terminal strip GS1 to GS2 to bypass the series field to see if the series field is the problem.

What I have not addressed yet is if the generator internal winding configuration is correct, I'm trying to eliminate as many variables as possible before digging into the internal generator connections.

If what I have posted does not make sense, Cal can flesh out the process for you.
If he needs better clarification, he will contact me.

Bill
 
Since this unit has been hacked by a previous owner,
It probably makes sense to verify if the generator wiring is correct as per Cal's drawing.

All the wires should have metal labels on them.

All metal tags are missing. The previous owner/previous motor-shop applied paper tags, but as far as I can tell, all but one of them were incorrect. As I received it, the generator had leads labeled E2, GF2, A1, and GA1.

I'm pretty sure I remapped them correctly (though looking at my pencil-sketch of the winding layout, I'm wondering if I mislabeled GA2 and GS1 on the generator, or just in my doodle), but there's certainly no guarantee of that!

IF the generator series field is connected backward, it will cause the generator output to drop as the load is increased.

I had not thought of that at all. Too much book learnin, and not enough practical experience with this stuff!

Another possible problem is winding faults. Lets verify that there are none before digging deeper.

Disconnect both ends of the series and shunt field wires of the generator.
Verify that there is over 100K ohms between the windings and each winding to ground.
Inter winding problems cause all kinds of problems, that are hard to find.

I /believe/ I checked for winding faults all around, before I started trying to apply power. My recollection is megaohms all around, however, I've been though this thing so many times now that I could be lying to myself. I will re-verify this evening.

At how high a voltage is it safe to test the windings? My previous probing was with a Fluke 87, but I can stick on the megger.

Once things are back together, watch the motor armature voltage from the point field weakening starts, until max speed. Yes old tachs read quite low.
The armature current increases as the motor field gets weaker.
If there is substantial motor armature voltage drop as speed is increased, just put a jumper on the terminal strip GS1 to GS2 to bypass the series field to see if the series field is the problem.

Please define "substantial". I do see an armature voltage drop from the onset of field weakening to maximum speed. 10-15V or so, which I wouldn't have called substantial, and I previously attributed to just additional voltage drop across the internal resistance of the generator. I have no seat-of-the-pants feel for how much I'd expect a reversed series field to fight the output though.

Also please define how the system should change in response to that jumper - I think I know, but again, too much book learnin, too little hands-on experience, so I'd like to be sure.

Jumpering GS1 to GS2 is going to be a trick, as the previous owner/previous motor shop buried the GS2 - GA1 tie point. I should be able to pick it off the brush carrier though.


I'll report back this evening.
Will
 
Ok, tonights report:

First, I labeled GS1 and GA2 in the doodle I previously posted incorrectly. My generator is currently wired as follows:

295296d1596073155-un-hacking-10ee-motor-generator-wiring-img_8196_fixed.jpg


The previous owner/motor-shop neglected to bring GA1 and GS2 out on leads, so the armature -- series field tie point is right on the brush carrier in my generator.

Next:

* Insulation tests :
** GS1 to frame 20 MOhm at 500V
** GF1 to frame 20 MOhm at 500V
** GF1 to GS1 40 MOhm at 500V
(I'm actually stunned that the resistances added there...)

Great news you even know what a Megger is, let alone have or have access to one. Yer ahead of the game on that!

My electrical and electronics diagnostic suite is not insubstantial, but my experience is more with miniature devices for the lab than with practical things like generators. Leaves me pretty certain I know what I'm looking at and how it ought to be instead, but with no practical experience with which to gauge the reliability of my intuition.
frown.gif


* Assorted voltages at speeds, polarity reported:
** Approx 15 RPM (Min speed)
*** E2 -- E1 +121.5V
(I diddled the exciter slider and haven't gotten it back down)
*** GA2 -- GS1 +8.5V
*** GF1 -- GF2 +0.5V
*** A1 -- A2 -10V
(moved the speed control and moved it back between readings.
The dummy only just noticed that while looking at his notes)
*** F1 -- F2 +119V

** Approx 650 RPM
*** E2 -- E1 +122V
*** GA2 -- GS1 +215V
*** GF1 -- GF2 +120V
*** A1 -- A2 -213V
*** F1 -- F2 +118V

** Approx 1550 RPM (current max speed)
*** E2 -- E1 +119V
*** GA2 -- GS1 +204V
*** GF1 -- GF2 +118V
*** A1 -- A2 -203V
*** F1 -- F2 23V

Shorting from GS1 to GA1/GS2 (removing the series field windings from the generation circuit) produces almost no change in A1 -- A2 voltage at either (approx) 650 RPM or (approx) 1550 RPM. What change there is, seems to be a 0.5V _increase_ (becomes more negative A1 -- A2) in generator voltage output.

I'm afraid that has me utterly confused, unless the series windings are tuned to produce essentially no contribution when the system is lightly loaded.

All these voltages are in-line with what I previously measured - slightly higher this time because I fiddled with the exciter shunt-field resistor and haven't gotten it back down to 118V where it started. At 118V, I was seeing a maximum of approximately -200V on A1 -- A2.


IMG_8196_fixed.jpg
 
My next plan, unless the assembled experts have better suggestions, is:

1st: To determine the magnetic polarity of each of the field windings. If, for each coil the side of the coil on which the terminal enters, is indicative of the winding direction for the coil, then the coils would appear to be in properly oriented pairs (Right hand rule - GF1 is positive with respect to GF2, GA2 is positive with respect to GS1 - says that North to South is SW to NE on both shunt field coils, and NW to SE on the series field coils).

2nd: To try splitting the series connection of the shunt field coils and reconnecting them in parallel.
 
Can't say I am impressed with that as a plan.

This is not a dual-voltage AC motor winding yer dealing wit' here.

Dee Cee side on an MG is a fixed situation ordinarily. Any power-source adapting done on the AC motor.. if need be.

It has been suggested the compensating coil be shorted .. or otherwise removed from influence. And no, it would NOT have much effect at low/no load. Ampere-turns thing at fixed turns but low Amperes.

Even so, contrarian effect might be in play?

Tried that yet?

Yup - that's the short across the series field coils (GS1 -- GA2/GS2). Essentially no effect on the output - which is to say, flipping them seems unlikely to do anything to get my generator anywhere near 230+ to nearly 300V output that is commonly seen.

Since you like current, I'd think you'd like the paralleling the coils :-)

Right now the shunt field current is limited to about .27 Amps in my generator. Cal and others report roughly 100 Ohms across their shunt field coils, which gives them about 1.15 Amps on the circuit as a whole. We don't know whether their coils are in series or parallel, but at the minimum they've got twice the current in their field coils (if theirs are parallel), and possibly 4x the current (if theirs are series) than I do "currently".

We don't know relative turns of their field vs mine, but my shunt coils don't appear peculiarly large, so I've a hard time believing that I've got 4x the turns, unless my coils are wound with much finer wire, and then my resistance would be much higher...

(perhaps not that) peculiarly, all the numbers look like they'd work out, if my coils were wired in parallel, rather than in series. My total shunt-field resistance would drop down to what Cal and others have seen. Given that somewhere in history someone goobered up the connections on this thing, Occam's razor suggests that mis-wiring the shunt field coils as a series pair, could be one of the things they goobered.

... plus, testing this doesn't seem terribly dangerous. The speed control pot starts off putting essentially nothing into the shunt field anyway, so it should be easy enough to see whether the generator output is behaving reasonably as the shunt field is brought up, without any serious risk of frying anything.
 
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BTW.. anything come up in your research as to "flashing" an MG's field?

I think we are way past that, but...

As far as I am aware, that's only relevant to self-excited units, like, well, the exciter, which seems to be working just fine. Since the generator side has actively driven fields, unless I'm misthinking something, it wouldn't seem to apply?

Will
 








 
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