Mg drive problems

Hi all, I purchased a square dial mg 10ee a couple of years ago from a fellow pm member who purchased it from some unknown individual.
Well the machine had a few mechanical issues broken missing parts etc, and electrical issues, lately I have had some time to mess with it, when I first got it one of the reostates had a open in it I was able to source one of those, and after looking through past threads found out it had a couple of bad resistors, I replaced those this week.

So this is how the drive acts currently, when you turn up the speed knob the speed changes slowly upward till you get to about 2/3 of its travel then after that it rises quickly, till about 1200rpm then it lazily rises to its max of about 1500 rpms after several seconds of the pot maxed out.

When you turn the knob down fairly quickly speed will drop to zero then back up to speed where the pot was left oscillating the speed up and down till it stabilizes.

I have tried different brush timing on the motor (brush holder was loose btw) to gain rpm.

Voltage between a1-a2 seems low maxing out at 180 volts

This machine is missing its exciter, some previous owner added a transformer to the back of the machine, some kind of rectifier and a variable resistor on the ac side, 120 volts ac coming in 110 volts dc coming out, I tried bypassing the resistor but still have 110vdc coming out.

Any of this give clues what could be wrong with
1. Lack of speed
2. Rise of rpm not linear on speed knob
3. Osillation of speed when slowing down

Any help would be appreciated
Thanks
Mike

Mike Hill said:

Hi all, I purchased a square dial mg 10ee a couple of years ago from a fellow pm member who purchased it from some unknown individual.
Well the machine had a few mechanical issues broken missing parts etc, and electrical issues, lately I have had some time to mess with it, when I first got it one of the reostates had a open in it I was able to source one of those, and after looking through past threads found out it had a couple of bad resistors, I replaced those this week.

So this is how the drive acts currently, when you turn up the speed knob the speed changes slowly upward till you get to about 2/3 of its travel then after that it rises quickly, till about 1200rpm then it lazily rises to its max of about 1500 rpms after several seconds of the pot maxed out.

When you turn the knob down fairly quickly speed will drop to zero then back up to speed where the pot was left oscillating the speed up and down till it stabilizes.

I have tried different brush timing on the motor (brush holder was loose btw) to gain rpm.

Voltage between a1-a2 seems low maxing out at 180 volts

This machine is missing its exciter, some previous owner added a transformer to the back of the machine, some kind of rectifier and a variable resistor on the ac side, 120 volts ac coming in 110 volts dc coming out, I tried bypassing the resistor but still have 110vdc coming out.

Any of this give clues what could be wrong with
1. Lack of speed
2. Rise of rpm not linear on speed knob
3. Osillation of speed when slowing down

Any help would be appreciated
Thanks
Mike

Click to expand...

It sounds like you've got issues with one or both of the rheostats. You said that you sourced a new rheostat. 10EE motor/generator (MG) rheostats are specially wound; unless you got the right 10EE rheostat it probably won't work correctly. For example, the rheostats from a round-dial MG machine, especially a 230V exciter machine, could be a problem.

The first thing to do is to check that the spindle motor and generator field voltages are changing as expected when you vary the speed control. The motor field voltage should be 115 VDC during the first half of the speed control knob's range, then decrease steadily to about 40 VDC as you reach maximum speed. Measure the motor field voltage between terminals F2 and E1 at the bottom of the DC control panel. The terminal numbers should be marked above the terminal. Always verify that you're on the correct terminal by checking the metal tags on the wires. The 110 VDC "exciter" voltage that you report is a little low, but shouldn't be low enough to cause major problems. What make/model meter are you using to measure the voltage?

The generator field voltage controls the output voltage of the generator and thus the spindle motor armature voltage. Measure the generator field voltage between terminals GF2 and E2, at the terminal strip on the front of the MG. The voltage should be close to zero at minimum speed, then steadily increase to 115 VDC when the speed control reaches the midpoint. It should remain at 115 VDC for the second half of the speed control range. When the speed control is at the midpoint, the generator should be putting out at least 230 VDC (GA2 to GS1) and the motor itself should be turning at 690 RPM (the spindle RPM will be higher, depending on the belt ratio of your machine).

I've not encountered the oscillation problem that you describe. See if any of the relays in the DC control panel are cycling when this is going on.

Cal

The readings are as follows

At max speed
1. ga2 to gs1=174 volts
2. gf2 to e1=.07 volts
3. gf2 to e2=109 volts

At min speed
1. Gf2 to e1=105 volts
2. Gf2 to e2=4.3 volts

Readings were taken with a model Fluke 115 meter

Mike Hill said:

The readings are as follows

At max speed
1. ga2 to gs1=174 volts
2. gf2 to e1=.07 volts
3. gf2 to e2=109 volts

At min speed
1. Gf2 to e1=105 volts
2. Gf2 to e2=4.3 volts

Readings were taken with a model Fluke 115 meter

Click to expand...

The generator field voltages at each end are as expected. However you haven't told me what's going on with the spindle motor's field (F2-E2). I need to know what's happening to the generator field AND spindle motor field at the midpoint, which is where the drive switches from "normal" (full field, variable armature voltage) to "field weakening" (full armature voltage, variable field). You also need to look at how the voltages are changing through the entire speed range, as discussed above.

At maximum speed, with the 109 VDC on the generator's field, it should be putting out at lot more that 174 VDC (assuming that the M/G is running at full speed--it shouldn't slow down for any reason). The last time we saw something like that was a generator that had apparently been rewound and had it's shunt and series field windings connected improperly. Here are several of the more important posts from that thread:
Disconnect the wires from your generator's field windings at the M/G terminal panel and measure the winding resistances: GS1 to GS2 and GF1 to GF2. Please post a photo of the M/G terminal panel and some photos looking into the the end of the generator, so that I can see what the coil wiring looks like.

Cal

Thanks for the help Cal

The unfortunate thing with this lathe is I have no idea what the previous owner of this lathe did to it, you can see they took some time to prep and paint the lathe and did a decent job but there was a lot of things partially done, along with broken and missing parts.

Mike Hill said:

View attachment 304879View attachment 304880View attachment 304881
Thanks for the help Cal

Click to expand...

Someone has definitely been futzing with your generator. That variable resistor doesn't belong there. There's normally a variable resistor located in the generator end-bell, but it's connected to the exciter, not the generator. Your generator's commutator looks a little dark and might need to be touched up with a commutator stone. Have you checked the generator's brushes?

Mike Hill said:

View attachment 304882...

Click to expand...

That's a very professional looking exciter replacement. The thing in the upper right corner, above the meter, looks like it might be a variable transformer instead of a resistor. Can you find a data tag on it anywhere?

I don't know what's going on with your photos, but they are really low resolution. Are you using an iPhone?

Cal

I took the photos with my I pad

The brushes look fine and move fine in their holders, the machine is at my shop so I can get the rest of the info tomorrow, I will try to get better pics with my phone.
Thanks again Mike

For some reason, iPhone/iPad photos come in a very low resolution. Try running them through a photo editor. A while back, member sent me some iPhone photos, I had save them to another format, then convert them back to JPG to get them to post at a decent resolution. I've tried to get the Forum Lords to look into the problem, but so far, no joy.

Cal

F2-E2 is 107.5 at exactly mid crank of the reostate only spinning at 150rpm

Gs1 to Gs2 .4 ohms
Gf1 to Gf2 351 ohms
Leads were discontinued

I decided to throw caution to the wind and bypass the resistor on the end bell of the generator, the machine performed much better ran at about 2400rpm smooth speed increase from low to high on slow down speed would drop right down then come back up to the new lower rpm, only concern would be I could smell something getting warm and had excessive sparking on the motor comm

BY the way Ga2 to Gs1 was around 230 volts with the resistor bypassed at wide open

Mike Hill said:

Gs1 to Gs2 .4 ohms
Gf1 to Gf2 351 ohms
...

Click to expand...

GS resistance sounds OK.
GF resistance is high. Willray had a similar reading; it turned out that the generator windings had been improperly connected:
You should check for shorts between each winding and the case as well.

Mike Hill said:

I decided to throw caution to the wind and bypass the resistor on the end bell of the generator, the machine performed much better ran at about 2400rpm smooth speed increase from low to high on slow down speed would drop right down then come back up to the new lower rpm, only concern would be I could smell something getting warm and had excessive sparking on the motor comm

Click to expand...

I'm surprised that you're getting full generator output / armature voltage with the exciter voltage and generator field resistance that you're reporting. Best thing is to really dig through Will's thread and sort out what's going on with your generator windings.

The "something getting warm" smell may be related to the sparking on the motor commutator. There should only be a tiny pinpoint of light at each brush, no sparks. You should go back and check your brush contact and timing.

Cal

Cal the “throwing caution to the wind” part came after I took the readings I reported

The resistor I bypassed was the one you questioned in the picture of my generators end bell

Mike Hill said:

The resistor I bypassed was the one you questioned in the picture of my generators end bell

Click to expand...

Was the GF1-GF2 reading that you posted with or without the resistor? If it was with the added resistor, what is it without?

Cal

Cal the Gf1-gf2 reading was with the resistor, I failed to check the reading after the resistors removal