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Info needed: Southcon 8RG DC Drive

DaveC

Aluminum
Joined
Jun 4, 2006
Location
SF Bay Area
Hi Monarchers:

I'm just now joining the forum because I just put a bid in on a 1959 10EE. It has a solid state DC drive made by Southcon Industrial Controls, model 8RG, but apparently they are no longer in business (at least Google can't find them). Judging from the vintage of the electonics, I would imagine this is a retrofit. The controller spec plate says that it requires 240 VAC, single phase, 17A. However, the plug and wiring to the machine are all 3 phase. Can anyone point me to a wiring diagram, manual, etc. for this controller so I can determine if I can run it from my home 240 VAC single phase service?

Lacking that, can anyone recommend a good DC controller for this machine?

Thanks in advance for any info!

Cheers,
DaveC
 
Well, I bought the lathe and I started to trace out the circuitry, when I found something wierd. The lathe has a cordset with a 240V 3-phase plug. After the main disconnect switch, one of the phase leads is simply not connected to anything, so the whole thing seems to require only single phase 240V. This is good news, as that is all my home shop has. The two remaining phase wires go directly to the controller. This is consistent with the spec plates on the controller which say it uses 240V single phase.

However, there is a 1.5kVA step-down transformer (GE 9T51B11) in the base that is also connected across these two phases. Initially I thought it was to generate 120V for some accessory, but when I traced it out, its primary windings are in series and its output wires in parallel. With a 2:1 turns ratio, that would give a 4:1 voltage reduction. Normally with that configuration, the primary would connect to 480V to output 120V, but the way it is wired now would only produce 60V. If the secondary wasn't connected to anything, I'd conclude that the transformer was left over from when the (1959) lathe was convertd to solid state drive, and that the original input power was for 480V. However, the secondary has one side tied to the incoming 240V, and the other is applied to the controller (pin 4 of the input terminal strip.)

Does this configuration make any sense to anyone? Why would the controller want 60V? I don't have the controller documentation, although one list member has been kind enough to offer to send me a copy of his.

As always, any thoughts are welcome.

Cheers!
DC
 
"its primary windings are in series and its output wires in parallel. With a 2:1 turns ratio, that would give a 4:1 voltage reduction."

A 2:1 turns ratio gives you a 2:1 voltage ratio.


"Why would the controller want 60V?"

60/120 is a newly allowed (one NEC issue ago, IIRC) form of power for certain so-called "professional" applications.

The only case where 60/120 is presently employed is professional audio recording, where the combination of the fully balanced ac, plus an isolated ground system, can eliminate so-called "ground loops", and also ac induced "hum".

One of the problems which this system is intended to address is the case where an EMC/RFI filter integral with the so-called "utilization equipment", which filters are almost without exception "balanced" with respect to "ground", have one line also grounded, when operated on the North American 120 volt system.

Operating this equipment on 60/120, properly grounded, of course, can eliminate many operational problems without compromising safety.

The NEC has chapters and verse on this very new, and very specialized system.

This system is not intended for any application besides those mentioned, and any receptacles which are supplied by these branch circuits or feeders must be identified as such.

Because of the specialized nature of this new, unique system, most users buy a packaged power distribution system, one which incorporates an integral 120:60/120 transformer with very high isolation, possibly as high as 120 dB.
 
"A 2:1 turns ratio gives you a 2:1 voltage ratio."

Yes, if primary and secondary are either both in series or both in parallel. But you probably meant a "net" turns ratio of 2:1, not a 2:1 turns count ratio as I meant. Ah, semantics!

"The only case where 60/120 is presently employed is professional audio recording,(snip)"

That is indeed quite an interesting system. As it happens, I design equipment for professional audio recording for a living, so I am quite familiar with the so-called "balanced power" trend (and its shortcomings.) But it turns out that that is not what is going on with the 10EE.

Our own Tipsy was kind enough to send me big, beautiful copies of his 8RG controller's schematics (thanks again, Charles). The wiring diagram shows that the controller places the 60 VAC secondary in series with the 240 VAC input line in order to supply 300 VAC to the SCR bridge. Evidently this is required to provide full DC voltage to the armature.

So that solves the mystery of the transformer. Now I need to figure out the other controller functions. There is a “Taper Torque” circuit that applies armature current feedback to the forward armature voltage, presumably for load compensation. Then there are the other two circuit boards that don’t even appear on the diagrams. It’s a good thing this is a long weekend.

So it’s off to the garage with a DVM in one hand, and the other firmly in my pocket…

DC
 
"As it happens, I design equipment for professional audio recording for a living ..."

I operated my first Ampex in 1958, and I bought my first Ampex in 1963. I still own every one I ever bought, and that covers the 300 series to the 440 series, and nearly every professional model in between.

Member, AES, 1965 to 1995, when I retired.


"The wiring diagram shows that the controller places the 60 VAC secondary in series with the 240 VAC input line in order to supply 300 VAC to the SCR bridge."

Three-phase 240 can produce 5, 7-1/2, 10 or even 100 or 1,000 HP with ease.

Single-phase 277 can produce 5 or 7-1/2 HP with ease. Beyond 7-1/2 HP becomes much more difficult.

But, most three-phase drives are "regenerative", and these do not operate properly, if at all, when supplied by an RPC, as an RPC cannot "sink" power.
 
Nice machines, those Ampexes, although I always fancied the Nagra T. I kinda hated to help put analog tape out of business with the digital audio workstations. But I at least have lots of very talented ex-Studer co-workers now. And analog tape is not quite dead yet, although the media is now VERY expensive and hard to obtain. It is still preferred by some for tracking drums, especially for heavy metal.

"Member, AES, 1965 to 1995, when I retired."

Member, AES, 1978 (student at UCB) to present.

So the 8RG is designed to take 240 single-phase, and it is indeed regenerative. The incoming 240V is combined with the boster transformer's 60V secondary, and the resulting 300V is applied to a network of eight large SCRs organized as two full-wave bridges - one to source and the other to sink the motor power. A simple DC servo compares the speed pot's setpoint to a scaled version of the armature voltage. The resulting error signal is applied to a network of driver transistors that energize the primaries of four transformers (the SCRs are paired) that drive the gates of the SCRs. There is some form of load compensation via armature current feedback. There is also what looks like compensation for the IR loss in the motor and its wiring. And there is a kind of overcurrent lockout that I haven't figured out yet.

What I don't see yet is any mechanism for feild weakening for high speed operation. The documentation shows that a rheostat can be placed in series with the field winding, but I see no such rheostat in the unit. There are a few extra PCBs to explore, though, so I'm hoping to find automatic weakening control. There is a field loss lockout, though, so I'm hopeul.

I could probably scan and send you the schematics if you're interested. The company is now defunct, so I doubt they'd mind about the copyright.

Cheers!

DC
 
"What I don't see yet is any mechanism for feild weakening for high speed operation. The documentation shows that a rheostat can be placed in series with the field winding, but I see no such rheostat in the unit. There are a few extra PCBs to explore, though, so I'm hoping to find automatic weakening control. There is a field loss lockout, though, so I'm hopeul."

There has to be, even if the motor is always operated with full field.

If the drive truly had field weakening, then there would be a separate field regulator, most likely a half-wave version of the armature's full-wave regulator.

Oh, plus a "free wheeling" diode.

Incidentally, this kind of drive can be utilized with a compound wound motor, provided the series field is surrounded by a full-wave bridge rectumfrier, so as to ensure that the "sense" on the series field is always the same as that on the shunt field. "Cumulatively compounded" is stable, "differentially compounded" is not.


"I could probably scan and send you the schematics if you're interested. The company is now defunct, so I doubt they'd mind about the copyright."

Probably not.

Besides, it would be for a "fair use", not for an unfair use.

Sure, I'd be happy to assist in any way I can.
 
"Incidentally, this kind of drive can be utilized with a compound wound motor"

I'm not sure I know what a compound-wound motor is. I'll have to go get the Bodine Electric motor book up of the basement and do my homework...

I will try and get the documents scanned and off to you soon (holiday festivities permitting). It is a "D" size print, so I'll have to tile it with my "A" size scanner.

Over and out for tonight.

DC
 
"I'm not sure I know what a compound-wound motor is."

These have a shunt field, and also a series field.

The amount of compounding is specially selected for machine tool service.

This provides additional load compensation and enhaces the machine's performance under temporary overload conditions.

The WiaD and Modular machines have compound wound motors.

3 HP Reliance and 5 HP GE motors.

It's a nice feature to have, but most third-party drive manufacturers do not provide for compound wound motors.

Imperial did, however. Perhaps Joliet as well.

Not Monarch, however.
 
The motor looks to be original. From the spec plate:

Reliance Type 'T' Heavy Duty DC Motor
Model: (blank)
Frame: CT-255
HP: 3
RPM: 1150 - 4000
Duty: 60 Min.
Rise: 40C
Winding: Shunt
Amps: 12
Volts: 230
Field Volts: 115
Field Max. Amps: 0.95
Field Rheostat Ohms: 1000
Field Rheostat RPM: 4000
SN: L106351T44

The winding is indicated as "shunt", but I have no idea what a compound-wound motor would say on its spec plate. My machine is from 1959, so wouldn't it have been a WiaD, hence if this is the original motor, wouldn't it be compound-wound?

Anyway, I connected the controller to 240V single phase a few minutes ago and pressed the start button. The motor started up and seems to run just fine. Variable speed works, too. I have to do some more testing, but everything seems okay. The smoke, so far, has stayed on the inside of the SCRs ;)

So the restoration project is officially off and running at this point. Thanks everyone for the advice!

DC
 
"My machine is from 1959, so wouldn't it have been a WiaD, hence if this is the original motor, wouldn't it be compound-wound?"

I'm sure there were some WiaDs which were made without compound wound motors.

I've seen Reliance 3 HP motors which were not compound wound, and those which were, so perhaps this particular variation is more likely with a Reliance motor.

If the motor has S1 and S2 leads, then it is compound. These are the designations for the series field.

The shunt field leads are designated F1 and F2.

The armature leads are designated A1 and A2.

My 5 HP GE motor states "Spec. Comp." on the nameplate, but it is not otherwise identified as being compound wound.

One has to go into this motor's connection box to observe the presence of the series field leads.

Then, one is confronted with four, not two shunt field leads, with these being conected in parallel, although the nameplate states that the field is 115 volts.

I presume this means it is possible to connect the shunt field windings in series, thereby operating it from 230 volts.

But this is not disclosed on the nameplate.

Strange.
 
The motor has six wires, so it is probably compound-would as you suggest.

I've now into the first problem. The Field Loss lockout relay is kept energized by an NPN transistor in series with a 24 VDC supply (which is one of the mystery PCBs). The base drive for the transistor is obtained from the voltage drop across a pair of J600G diodes. The diodes are presumably in series with the field winding(s) somehow. Should the field current quit, the base drive disappears, the transistor turns off, and the relay opens, presumably shutting off the armature drive somehow. The problem is that the diodes are getting so hot, they melt their own solder. The diode voltage drop is low - around 0.4 V for each diode - and the datasheet shows they are not Schottky rectifiers. So I'm guessing something in the field circuit is drawing way too much current.

It turns out that the actual wiring of the machine is much more complicated than the diagrams indicate. So the next step is to make a complete and correct wiring diagram so find out what is really going on. Stay tuned...

DC
 
So I think I'm close to having this controller figured out.

The motor is indeed compound-wound. The S1-S2 field winding is placed in series with the armature via a full wave diode bridge so that it maintains constant magnetic polarity regardless of armature polarity. I can't tell what that magnetic polarity is, though, so I don't know if this is a "cumulative compound" or a "differential compound" configuration.

The F1-F2 field winding is separately controlled by a second SCR-based DC controller.

This weekend's task is to figure out the low voltage control wiring. In addition to the speed pot, the control panel has a three-position rotary switch for high, medium, and low speed operation. I would guess that the switch generates the field controller's input voltage and that the pot controls the armature controller's input voltage. Each controller seems to have current feedback capability, but I'm not sure if they are both used or not.

The field-loss relay' field current sensing diodes are still overheating. That could be due to several things:

* improper field controller input voltage

* an improperly designed feedback scheme

* the field controller is just broken

* a motor with some shorted field turns

* your idea here

Once I have the control scheme mapped out, the problem may be obvious. I will also measure the field voltage and current so I can see if the motor windings are the right resistance.

It strikes me that generating the various control voltages would be an ideal use for a microcontroller. I'm thinking that adding one would allow me to easily add acceleration and deceleration profiles, load current compensation, tachometer feedback, and possibly ELSR. Does anyone have any ideas on control algorithms?

DC
 
I operated my first Ampex in 1958, and I bought my first Ampex in 1963. I still own every one I ever bought, and that covers the 300 series to the 440 series, and nearly every professional model in between.
So solly for the inter-ruption ;)
http://recordist.com/ampex/
Ruption over


Ahh, one moe ruption..
http://www.ampexdata.com/Support/Legacy_Manuals/legacy_manuals.html
 
"The Field Loss lockout relay is kept energized by an NPN transistor in series with a 24 VDC supply (which is one of the mystery PCBs). The base drive for the transistor is obtained from the voltage drop across a pair of J600G diodes. The diodes are presumably in series with the field winding(s) somehow. Should the field current quit, the base drive disappears, the transistor turns off, and the relay opens, presumably shutting off the armature drive somehow. The problem is that the diodes are getting so hot, they melt their own solder. The diode voltage drop is low - around 0.4 V for each diode - and the datasheet shows they are not Schottky rectifiers. So I'm guessing something in the field circuit is drawing way too much current."

This is a common method of providing a field-loss function in a solid state drive.

Two silicon diodes in series would usually have a forward voltage drop of about 1.4 volts (0.7 volts per diode).

This potential difference is routed through a pair of, say, 1 K resistors to the photo-emitter portion of a four-terminal opto-electronic block, usually one from the 4N series.

The output of the opto-electronic block is, essentially, an open-collector transistor, which is input to the armature regulator's shut-down circuit.

The Emerson "regenerative" drives I have all work this way, and require no electro-mechanical relay for field-loss detection.
 
"The output of the opto-electronic block is, essentially, an open-collector transistor, which is input to the armature regulator's shut-down circuit."

Yep, although 2K in series with 1.4 volts might not turn the emitter's LED on hard enough for reliable operation. Depends on the block's specs.

Using the armature regulator's shut-down circuitry always struck me as a crummy way to implement what is basically a failsafe. A lot of circuitry needs to be working correctly in order for the shutdown to actually happen. A simple relay contact in series with the motor winding has fewer points of failure. Although relays are certainly less reliable than their electronic counterparts these days.

So I did some more tracing, and there does indeed seem to be a bug in the way the field control voltage is generated on my lathe. As I suspected, the field control voltage is generated using the three-way speed switch, but the armature controller's run/stop relay is also involved. Presumably the intent was to shut off the field voltage when the lathe is stopped, but I don't think the guy who wired it understood exactly how the run/stop circuit really works.

So on a standard WiaD unit, is the field kept energized when the lathe is stopped, or does it get shut off along with the armature drive? Besides saving energy, is there a reason to shut off the field when the lathe is stopped?

DC
 
"Presumably the intent was to shut off the field voltage when the lathe is stopped, but I don't think the guy who wired it understood exactly how the run/stop circuit really works."

This is called a "field economizer".

Usually, the field regulator is full-wave, and which is placed into half-wave mode when idling.

This reduces the field voltage to one-half, during periods of idleness.


"So on a standard WiaD unit, is the field kept energized when the lathe is stopped, or does it get shut off along with the armature drive? Besides saving energy, is there a reason to shut off the field when the lathe is stopped?"

On the WiaD and Modular, the field regulator comes on when the machine's safety switch is turned on.

It is only the armature regulator which is turned on when the CONTROL START button is activated.

Monarchs have no "field economy" circuit.

At least not 10EEs.
 
Incidentally, in a "field economy" circuit, the field voltage is reduced to one-half, under the control of the drive's "time out" circuit.

Should the drive detect that a command has come through, then the field voltage is restored to that which it was before, prior to initiating any further actions within the drive, such as turning on the armature regulator.

This begs the question as to how reliable these circuits are.

For, in a machine tool which employs a shunt wound dc motor, the field may never be turned off. The presence of a significant field flux, at all times, is the only force preventing the motor from running away, and "bird caging".

Which is why, in the Monarch cases mentioned, the fusible safety switch causes the field regulator to turn on, while the CONTROL START button effects control over the armature regulator.

Additionally, you will note that the rectifier tubes employed in the field regulator are of the type which do not need to be "warmed up", nor "formed" after a move.

OTOH, the tubes in the armature regulator are often of the type which require a 60 second warm-up period (possibly 30 minuted after a move).

Mr. Greene, Monarch's chef drive designer, considered these things when he designed these drives, and each and every detail was carefully thought out.
 
Got it.

So I rechecked my wire tracing and found that there is no wiring error after all. I had confused the wire labeled "41" with a wire labeled "HI".

So on this lathe, the field comes on when the safety switch is turned on, and stays on regardless of the state of the run/stop relay. There is no field economy feature, but if I add microprocessor control, I can easily implement one.

So this brings us back to the field sense diode overheating problem. I isolated the motor's F1 and F2 leads and measured the room temperature resistance between them to be 4.5 ohms. That seems awfully low; I expected more like 100 ohms. If the field controller was trying to put 90 volts across that winding, it would draw 20 amps. At that current, each diode would dissipate (0.7 volts * 20 amps) 14 watts!

Eiher I am missing something, or it looks like I have a motor with some shorted field turns. If true, that would be a REAL bummer.

DC
 








 
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