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Questions about determining health of Reliance DC motor

jim314159

Aluminum
Joined
Jun 9, 2011
Location
Atlanta, GA, USA
Hi Folks,

I'm considering reusing the existing 3HP Reliance shunt wound DC motor that came with my machine and just mating it with a modern DC Drive that can be obtained for a few hundred dollars. Before I spend on the DC drive, I'd like to make sure the motor is good!

I read up on all the electrical tests I can do without having a megger, and all looks good save for some odd behavior I'm seeing on the commutator bars.

AFAIK each pair of bars separated by 180* should have the same resistance, and each neighboring set of bars should have no continuity. When I started to measure, I discovered that 100% of the commutator bars are continuous to one another (but none of them are continuous to ground or the lamination stack).

Is the armature hooped, or am I missing something peculiar about the construction of this specific model? :nutter: Photo of nameplate and armature are below. The commutator bars I am testing are at bottom, obvs.

--jim

IMG_0492.jpgIMG_0490.jpg
 
What's serial number and build date of the machine? What type of drive did it originally have? It's hard to read the data plate, it doesn't look like that for motor/generator (MG) drive machines. In particular, it lists the RPM range as 1100|4000, whereas the typical MG machine has a motor with and RPM rating of 690|2400. I can't read the field resistance information on the plate.

There are a number of different ways that an armature can be wound and I don't know for sure which method was used on the Reliance 10EE motors. Here's a link that discusses armature windings: Monarch 10EE Motor Generator Troubleshooting

It's not true that adjacent bars will have no continuity. Unless it's a really strange winding method, you should find that all of the windings are connected together in series, in a big ring. (The above link explains this.)

Here's what I got when I did some measurements on a square-dial MG spindle motor several years ago:
  • Number of Brushes: 4
  • Number of Bars: 87
  • Resistance Bar to Bar: < 0.2 Ohms
  • Inductance Bar to Bar: 75 micro Henrys
  • Resistance at 90 degrees: 5 Ohms
  • Resistance at 180 degrees: 0 Ohms
  • Field Winding Resistance: 84 Ohms

I think the above makes it a simplex wave winding, but I'm not really sure. (The zero Ohm reading at 180 degrees doesn't make sense.) Maybe hitandmiss Bill can tell for sure what I've got.

Cal
 
Trying to read an armature with a typical digital meter usually means reading the resistance of the leads more than the armature. I have a Wheatstone bridge made by Leeds & Northrup that reads milliohms with Kelvin leads. I got it from a retired Century Electric engineer who used it on their motors. I have been contemplating doing some analysis on the armature for a different reason. As it is used, the insulation needs to withstand 250 volts between the coils and core, assuming one brush grounded and the other at full voltage. I want to see if the insulation is laid out so it can be run with one brush positive 250 volts and the other negative 250. That would move the base speed up and reduce the field weakened range.

BTW, the 180 degree apart brushes are at the same voltage and the two 90 degree away ones are at the other polarity. You could run the motor, at a lower output, of course, by only energizing two brushes 90 degrees apart.

I may try running mine at +250 and -250, but it will be with a filtered supply. I would not consider torturing the motor with a switcher.

If I just wanted to make chips and the MG unit was working properly, I would not consider changing it. There is a lot more to the system than just putting voltage on the motor. It seems to be a knee jerk response from people when they first get one of these machines to rip out all that obsolete junk and put in a "modern" supply. Unless you really know what you are doing, the odds of coming out with a better machine are slim.

Definitely check it with a megger. I have one, but St. Louis to Atlanta is a long drive.

Bill
 
Hi Folks,

I'm considering reusing the existing 3HP Reliance shunt wound DC motor that came with my machine and just mating it with a modern DC Drive that can be obtained for a few hundred dollars. Before I spend on the DC drive, I'd like to make sure the motor is good!

I read up on all the electrical tests I can do without having a megger, and all looks good save for some odd behavior I'm seeing on the commutator bars.

AFAIK each pair of bars separated by 180* should have the same resistance, and each neighboring set of bars should have no continuity. When I started to measure, I discovered that 100% of the commutator bars are continuous to one another (but none of them are continuous to ground or the lamination stack).

Is the armature hooped, or am I missing something peculiar about the construction of this specific model? :nutter: Photo of nameplate and armature are below. The commutator bars I am testing are at bottom, obvs.

--jim

View attachment 271683View attachment 271684

There is some basic errors in your thinking.
1. There should be an odd number of bars on the commutator, so there is no opposite bar at 180°.
2. There is usually an odd number of slots for the wire, and 2 or 3 coils per slot.

3. "and each neighboring set of bars should have no continuity." this is completely wrong.
"100% of the commutator bars are continuous to one another" This is correct.
See the link in post #2.

If all the commutator has an even brown color with no burns, I would put it back together and wire in the S field and Armature, along with the F leads. Observe polarity as shown on the nameplate. It should turn smoothly powered from a 12 Volt car battery.

Hope this helps,
Bill
 
2. There is usually an odd number of slots for the wire, and 2 or 3 coils per slot.

That is one reason these motors cost so much. I used to repair GE tachometer generators with a similar armature. There were three coils per slot, but they were wound one coil in a slot, move to the next and wind one coil, and so on around the armature, then wind the second coil in the first slot, go around and wind the third in each slot, each coil connected to a different commutator bar. In other words, as much work as winding three typical motors. The result was that the output had a very small ripple, like you would get full wave rectifying something like 12 phase AC.

The winding shop we sent them to would wind all three coils in a slot, then move to the next. The output would still have the tiny ripple peaks but it would staircase up three peaks, then down three peaks. I'm sure the motors in question would have the first winding pattern because the second would have a slight surging as it went up and down the coils. Did anyone say "labor intensive"?

I have a large frame 3 hp motor and if it wasn't such a monster, it would make a good servo motor. If you want to get the most performance, feed it pure DC, no ripple or pulses.

Bill

PS, most of the tach generators came from the local GE shop. They often were run until the bearings were dust and we had to sleeve the chewed up shafts and recalibrate them. I asked who was running them that hard and the reply was that they came from a pornography printer across the river in IL. I guess business was good.
 
I am the owner of Bill’s former small frame Reliance, Presently in my lathe. My original motor with the smoked armature I took to a motor rebuilding shop and was quoted minimum $1500 for a rewind, and that was from the front desk, not the man who actually does the rewinding. I would guess that once he got into the Type T armature from 1956 the cost would be higher. I can attest to the operation with Parker 514/507. Quite good.
 








 
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