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10EE with solid state DC drive - how to add reverse circuit and ELSR

jj80909

Aluminum
Joined
Sep 16, 2015
I'm hoping someone out there in 10EE land can assist in giving me some advice on solid state DC drives.

I recently bought a 1949 Monarch 10EE. The lathe was originally built with the Reliance 3 hp, open-frame motor and the motor-generator.

At some point, the generator must have been damaged and an aftermarket, single phase, DC solid state drive was installed. The drive is housed in one large Hoffman enclosure and a second enclosure houses the start / stop buttons and THE largest rheostat I have ever seen.

The spindle can only be turned on for forward motion or stopped and its speed is controlled by the large rheostat. There is no electrical cut-off or e-stop.

The lathe is equipped with the ELSR option and a 3ph coolant pump, but neither is wired for use. I pulled out the original motor generator and it looks like the generator sustained some damage to the armature at some point.

It looks like the DC drive was installed by Weaver Electric in Denver, but I do not know if they made their own drive or used one from some unknown supplier and installed it in a Hoffman box. I plan on calling them tomorrow, but I doubt it will be much help...the drive looks old and they don't mention anything like it on their website.

Anyway, the motor / drive operate well and I can vary the speed from low to 2400 rpm without any issues. When I push start, the motor starts winding up, there are two timers on the drive board and the first one goes off after a couple seconds and closes contactor AR-1. After about 10 seconds, timer two goes off and closes contactor AR-2. I really don't hear a difference in the speed or sound of the motor. It does operate very quietly.

What I would like to do is add the circuitry to allow running in reverse and at some point, wire the ELSR to operate. I was also thinking about at least mounting the large rheostat near the factory location and have the factory designed speed knob. The original rheostats are present, but the large rheostat is more than double the factory Monarch unit at 950 ohms. It does look like there is some sort of high amp voltage divider on the drive board and I wonder if it can be adjusted to the lower resistance of the factory rheostat.

Attached are photos of the motor, board, and control box.

Wiring to the drive is pretty simple with only line voltage at L1 and L2 (240 VAC), Stop (NC) at C1, C2 is common to the stop/start switches, C3 is the Start switch (NO), A1 and A2 to the motor armature, R1 is from the rheostat, F1 is not connected on the board but is connected to the wiper side of the rheostat and wired directly to the motor's F1, and F2 goes to the motor F2 field.

Any help is appreciated.
 

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You see rheostats on things like ancient centrifuges. Not the original Monarch. This is an illustration of why some of us tell people to keep the original drive if possible. You may get the spindle to turn but lose the nuances. All those relays on the panel are not there for looks. Besides a four quadrant drive, which may be the best solution now, you will also need a variable field supply because the upper speed range is achieved by reducing the field voltage. For dynamic braking you need to switch the field to full voltage and shut it off after a few seconds. I don't know about the MG machines with the big motor, which BTW is a very smooth motor and should be retained if possible, but the timer failed on a tube type 10EE and the head would get so hot from motor heat that you couldn't hold a hand on it. Of course, that was in a large shop where various people used the lathe and some would leave the main power on overnight, cooking the motor.

If you have the original relay panel, you can use the contactors for reversing, but you need to be sure the anti-plugging relay is functional.

My suggestion is that you get the factory manual from Monarch. They will sell you a manual customized for your serial number. Even if the functions are gone, you can read about them and consider implementing them in the new setup. As the saying goes, you have your work cut out for you.

Bill
 
It does run from low speed all the way to 2400 rpm (read from the stock mechanical tach). The lathe has the original motor, back-gear box and pulleys. The knob for the big rheostat does have two arrows on it: "increase voltage" and "increase speed" and it is wired into the field circuit. The lathe was used with the present, "forward only" configuration for the last 20+ years...I'm guessing that's reliable enough :)

For now, I think I'm going to create a circuit with two timers and contactors like the one I found with a Google search. I don't foresee needing to change from forward to reverse all that quick. The ELSR would be handy for threading so I'd like to wire its micro switches to control the spindle.

The lathe came with a nice 5C setup and I plan to use it for prototype work. I don't see the lathe being used to take heavy cuts and it would be nice if it was the 4000 rpm model.

In the future, I think I'll go with a VFD and large, modern motor. From what I've read, the spindle is essentially the same on the 2500 rpm and 4000 rpm models. If I find a stock 4000 rpm tach, is it a simple swap?
 
Given you are not reversing "often" and probably not in extreme haste, it would be simpler to put a DPDT switch (or relay) in the Field Power supply line and "Field-Reverse" the motor instead of Armature-Reversing it.

There is only about 1500 mA @ 115 VDC to deal with.

The reason it is not done more commonly is that the Field Coils and the laminations have a good deal of "inertia" for that relatively small power.

There are "white papers" out there covering trick circuitry for over-driving the field supply - but only briefly - on each reversal to speed up the response. I don't think you would need any such speed-up - just passive spike snubbing, if even that.

Fast enough and cheap enough to find out, yah? Switch, consumable MOV's mebbe a bypass cap and fuses "just in case". See what the 'scope tells you. Back it down to simple-dumb.

Uh uh. Reversing the shunt field makes the series fields work the wrong way and the motor does weird things. Only flip the brush leads.

Bill
 
Think the best way to do this is follow Monarch's example and install interlocking contactors and reverse polarity on the armature. Considering you don't have prints for the drive, it's asking a lot to sort this out over a forum, might be a good idea to get a pro involved.

Bill-with a 4Q drive, why did you not install a bridge rectifier ala monarch drive and make advantage of the "designed in" characteristics of the motor and the enhanced speed regulation from having S1/S2 connected?
 
Bill-no doubt that a modern 4Q/regenerative drive is a great solution, but he's asking about how to add a reverse function to his "existing" drive, not install a completely new drive. When I mentioned getting a pro involved, I meant someone on site.

Monarch went to some trouble and expense in choosing those particular motor designs, it's neither difficult nor expensive to make use of their inherent performance advantages. Can be done with off the shelf components and simple connections.
 
On the "special machine tool duty" GE KinaMatic 5HP (no gots), the Louis-Allis 5HP (no gots), the Reliance small-frame 3 HP (do have), and the rare Reliance 5 HP (too expensive for MMT to keep buying - my one is a non-MMT RPM III), with either/both of compensating or compounding, YES, there is an issue.

Predictable, not weird. Also "tolerable".

Feedback is bass-ackwards, increasing load worsens RPM drop instead of helping offset it. Even so, it hasn't been a show-stopper for typical USE when in reverse.

AFAIK, the large-frame 3 HP is classical "pure" shunt, and has no such winding issues. Life of me I can't remember why I never put it to the test, what with all the other testing I did.

Behavior depends on the balance between the shunt and series fields. It can run away to the point that the armature is trying to go infinitely fast and drawing very high current.

My motor has series poles but they are interpoles, not compound fields. My Monarch manual doesn't even show them but they are there. There is too much junk in the way where the lathe sits right now to trace the wiring to see if the interpoles are reversed. In any case, it wouldn't have severe effects in operation. Interpoles are mainly to reduce brush arcing.

Bill
 
Mechanical contactors need serious attention to detail lest they destroy his fragile SCR's.

Hi Bill
Have a single quadrant DC drive (MP25A4) here on the bench- could you elaborate a bit on this? Would appreciate any suggestions about setting up mechanical contactors for reversing (SquareD 8702s with interlock) and also adding braking resistors.
 
I have not read all the posts, so forgive me if I repeat something. I am using the Parker 514/507 setup that Bill developed, and I have wired in relays to make the ELSR work as original. I have cut two threads in the last few weeks with it, approximately 200% more threads than I have cut in the last 5 years, and the auto shut off function of the ELSR is actually kind of nice.

If this is what you are trying to duplicate I can tell you my setup.

John
 
Would be great to see your set up- did you do anything special to address potential issues with the SCRs? Interlocks, timers, braking resistors?
 
At normal max Armature voltage the 3 HP large frame, installed and belted to a spindle, will not reach stratospheric "squirrel cage" RPM, even with ZERO field.

There's too much drag. The strength of residual magnetism is degraded too soon. There's ample time for an operator to shut-down the Armature supply as well.

In any case, if people keep the original system and don't throw away all the features that Monarch went to a lot of trouble to include, they will have the field loss relay to shut it down automatically.

Re replacing the MG with a solid state supply, that makes some sense but you should keep the original control system and not have to ask questions like "How can I reverse it?" You may need some strategically placed MOVs and inductors to protect the transistors. The conversions I have seen get the spindle to run but lose all the fine points.

The field supply needs to be regulated, also. I see so many where the exciter has failed and they put in a simple bridge rectifier. The field supply needs to be steady for the spindle speed to regulate properly. This is not speculation- I coupled a 5 hp DC motor to the spindle for a dynamometer and experimented with supplies. By varying its field current, I could apply any load from almost 0 to full. If the field supply varies with load, the RPM will not be constant.

Re solid state supplies, I worked on the system supplying the trains running around in Peabody's No 10 coal mine near Springfield, IL. They had 15 miles of tunnel underground with one half supplied by "modern" solid state supplies and the other half by motor generator sets. The MGs ran on 4160 three phase and output 300 VDC, up to a half megawatt each. Despite having to do routine maintenance like changing oil in the bearings and replacing brushes, the miners much preferred the MGs because they were more reliable. The two systems had to be separated, each supplying half the overhead trolley wires because the MGs would blow up the transistors. Of course, when a contactor carrying 1000 amps opens, it generated a righteous spike.

Likewise the platers in Rock Island Arsenal. The world had switch over to solid state, but they preferred MGs, again for reliability.

Bill
 
The Mentor manuals are easy to read and pretty thorough, but do not describe using a contactor for reversing, nor the implementation for braking resistors.
Do you mean to install the choke on the output of the drive?

Thanks for your responses, those Gigavac contactors look really nice.
 








 
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