EMD Field Loop Dynamic Brake Control

[Pneudyne]

Baldwin’s introduction of an optional compatible control system, including field loop dynamic brake control, was mentioned in a Railway Locomotives and Cars 1954 October article, attached below. The option was said to have been introduced within the last year. It was said that Baldwin units fitted with this control system would MU with EMD units in motoring and braking, and with Alco units in motoring only. That tends to confirm that only field loop dynamic braking was available, not – at that time anyway – the potential wire type.

Presumably the Wemco system used by Baldwin was essentially the same as had been used by Fairbanks Morse in its Consolidation line. As far as I know, in that case, the exciter battery fields were connected in the loop, each being shunted by a lowish value resistor that diverted most of the loop current. But from the viewpoint of the loop, as it were, the shunted exciter field looked like a similar impedance as an EMD main generator battery field.

RLC 195410 p.75 BLH MU.png

Cheers,

[Pneudyne]

Also from RLC 1954 October, an article on Fairbanks Morse locomotive improvements mentioned the availability of what it called the “dual-circuit dynamic brake control”, which allowed leading F-M units to control trailing units with either field loop or potential wire DB control.

That would appear to put a date on the advent of the dual DB control case.

Presumably this was done with the WEMCO electrical and control equipment, although that is not explicit. One may also assume that GE, as the incoming supplier soon thereafter, would have been required to match this capability. And that having done this, it was then able to offer the same facility for Alco locomotives.

RLC 195410 p.77.jpg

RLC 195410 p.78 F-M Dual-Circuit Dynamic Brake Control.png

Cheers,

[Typewriters]

Baldwin’s introduction of an optional compatible control system, including field loop dynamic brake control, was mentioned in a Railway Locomotives and Cars 1954 October article, attached below. The option was said to have been introduced within the last year. It was said that Baldwin units fitted with this control system would MU with EMD units in motoring and braking, and with Alco units in motoring only. That tends to confirm that only field loop dynamic braking was available, not – at that time anyway – the potential wire type.

Presumably the Wemco system used by Baldwin was essentially the same as had been used by Fairbanks Morse in its Consolidation line. As far as I know, in that case, the exciter battery fields were connected in the loop, each being shunted by a lowish value resistor that diverted most of the loop current. But from the viewpoint of the loop, as it were, the shunted exciter field looked like a similar impedance as an EMD main generator battery field.


RLC 195410 p.75 BLH MU.png



Cheers,

I think BLH at that time is just reinforcing its position; Erie had all of its Baldwin road switchers built to allow multiple unit control with both EMD and ALCO units (dynamic brake was field loop only, and worked with EMD only) and this began right at the end of 1949 with the 1100 class DRS-4-4-1500 units. The word on the street was often that Baldwins would not MU with other makes and BLH was probably just reminding everyone at that date that this wasn't the case.

See this handy chart at Fallen Flags for MU compatibility of Erie / EL first generation diesels.

http://www.rr-fallenflags.org/el/loco/el-mu-comp.html

[Typewriters]

Also from RLC 1954 October, an article on Fairbanks Morse locomotive improvements mentioned the availability of what it called the “dual-circuit dynamic brake control”, which allowed leading F-M units to control trailing units with either field loop or potential wire DB control.

That would appear to put a date on the advent of the dual DB control case.

Presumably this was done with the WEMCO electrical and control equipment, although that is not explicit. One may also assume that GE, as the incoming supplier soon thereafter, would have been required to match this capability. And that having done this, it was then able to offer the same facility for Alco locomotives.


RLC 195410 p.77.jpg RLC 195410 p.78 F-M Dual-Circuit Dynamic Brake Control.png



Cheers,

It is my understanding (from reading an interview of an F-M employee years back) that the Universal Dynamic Brake (the official name for this option, and that's what you'll see it called in operating manuals and wiring diagrams) didn't happen until GE equipment was being used. So far, I have only one operator's manual in my collection for units that had this option; this is for the very late Baltimore & Ohio H16-44's 6705-6709. I have also recently seen a wiring diagram for Reading 807-808 stating clearly that these two units had Universal Dynamic Brake. I am sure there are others, but have no idea which.

Baldwin offered field loop dynamic brake on units with electric throttle; it was not compatible with ALCO-GE units and I have no evidence anywhere that BLW / BLH ever offered a comparable Universal Dynamic Brake to Fairbanks-Morse's setup. The setup was cooked up by Fairbanks-Morse, not by either of its electrical contractors.

[Pneudyne]

Thanks for that, Will.

It could have been that the change from Westinghouse to GE electrical equipment presented F-M with something of a problem, given that GE used the potential wire dynamic braking systems whereas Westinghouse used the field loop type. Preferably, future GE-equipped units should be fully backward compatible with those that were Westinghouse-equipped. Thus F-M more-or-less had to develop its Universal Dynamic braking system.

Possibly this was done by more-or-less overlaying a field loop system on the potential wire system. This would have required that GE-equipped units could both provide and respond to field loop control. The first part was probably easier, for example requiring a heavier duty braking control rheostat that could pass up to 15 amps. The second part looks as if it might have been more difficult. Possibly it could have been done by using a current measuring reactor to detect field loop current and convert this to a control voltage signal for the amplidyne or amplistat. Alternatively, a voltage measuring reactor might have been used to detect the voltage across a “dummy” resistor (say 1.2 ohms) in the field loop trainline.

This was somewhat different to the Western Maryland case mentioned upthread. There the modified Alco units could provide a field loop output, could act as a “dummy” field loop unit by means of a 1.2 ohm pass-through resistor, but could not respond to a field loop control input.

I can’t trace that F-M ever patented its “Universal Dynamic Brake”, although patent searching is not an exact science. But it did have some patents in the locomotive control field, for example its MU hump control, US2908852.


Cheers,

[Typewriters]

I have locomotive manuals with wiring diagrams for Universal Dynamic Brake and I will take a look to see if I can figure out what they did. I'm trained as a nuclear electronics technician / reactor operator but it's been a LONG time since I traced wiring diagrams.

Off topic for an EMD thread here but F-M also adapted GE control equipment to use an air throttle. That's actually pretty straight forward except in the case of amplidyne excitation they had to add an air operated step controller to set current (excitation) limits progressively as the throttle pipe pressure increased since they couldn't get that signal another way.

[Pneudyne]

I have started a new thread for further discussion of Fairbanks-Morse control systems, see: https://www.railroad.net/fairbanks-mors ... 75123.html.

F-M appears to have been quite “inventive” in this area, evidently working out how to derive Amplidyne control voltage inputs from unexpected sources, i.e. the field loop dynamic brake current level in one case and air throttle pressure in the other.


Cheers,

[Pneudyne]

Given what F-M did in respect of dynamic braking control when it made the transition from Westinghouse to GE electrical equipment, a concomitant question is what did Baldwin choose to do in similar circumstances, given that it is known to have done the engineering design work for the substitution of GE electrical equipment case, even though in the event it made very little use of such.

I have found but one reference, at this web page: https://www.geocities.ws/newjack56/as416.html.

It is probably unwise to place too much stock in a single source, although the fact that it quotes from a Baldwin operating manual adds some weight. From that one may infer that for Baldwin developed both pneumatic and electrical control systems around the GE equipment, but that only the former was offered with a dynamic brake option, presumably broadly following the precedent of Baldwin’s established pneumatic system.

For the purposes of this thread, it looks as if Baldwin had initially not offered electrical control with a field loop dynamic brake option with the GE equipment, even though it had done so with the Wemco equipment. Or maybe that would have been a subsequent development to meet likely customer demand. More general discussion of the Baldwin/GE combination would, I think, belong in the Baldwin forum.



Cheers.

[Pneudyne]

It could have been that the change from Westinghouse to GE electrical equipment presented F-M with something of a problem, given that GE used the potential wire dynamic braking systems whereas Westinghouse used the field loop type. Preferably, future GE-equipped units should be fully backward compatible with those that were Westinghouse-equipped. Thus F-M more-or-less had to develop its Universal Dynamic braking system.

Possibly this was done by more-or-less overlaying a field loop system on the potential wire system. This would have required that GE-equipped units could both provide and respond to field loop control.

That the F-M Universal Dynamic Brake system allowed GE-equipped units to respond to a field loop input may have been an unwarranted assumption.

A look across the various dual DB control systems mentioned in this thread suggests that the customary approach was to equip units so that when they were in the lead, they could provide both potential wire (PW) and field loop (FL) DB control outputs to trailing units.

FL-only trailing units would respond to, and pass on if appropriate, the FL signals. They would also pass through PW signals via trainwire #24 of the MU bundle. So, as long as the MU bundle followed standard practice, they would not require modification to operate in a mixed DB consist.

PW-only trailing units would block further passage of the FL signals, but of course would respond to and pass on the PW signals.

Dual DB trailing units would generally respond and pass on to the PW signals, and would also pass through the FL signals. In some cases they were fitted with a series resistor (usually 1.2 ohms), so that they could act as a dummy FL unit, and so be included in the FL unit count. But it would appear that this was not always done. In some cases, only actual FL trailing units were included in the FL count.

The above commentary derives largely from a rereading of Typewriters’ early posts in this series, namely https://www.railroad.net/emd-field-loop ... l#p1208783, and https://www.railroad.net/post1210700.html#p1210700.

Possibly then the F-M Universal DB system was not so different from the later individual railroad, Alco and GE developments.


Cheers,

[Typewriters]

From Fairbanks-Morse Bulletin 1502F, Engineman's Manual for operating NYNH&H 1600-1614, section 110A (Dynamic Brake) page 3, item 18.

18. Operation in multiple with field loop-controlled units

a. For multiple operation with units using the field loop system of dynamic braking control, units can be equipped on railroad specification with a field loop circuit. This circuit is designed to energize simultaneously with the voltage control of the GE braking system in the braking range of the controller. From big B to little B on the controller, field loop amps vary from zero to fourteen (14) amps plus or minus 10%. The field loop circuit controls only the excitation of trailing units loop equipped.

The field loop contactor "FL" closes when the controller selector is placed in the "OFF" position. Loop current begins to flow just beyond the big B (minimum braking) position.

b. IF FIELD LOOP JUMPERS ARE USED, place the unit selector switch in the position corresponding to the number of units in the locomotive.

IF UNITS ARE EQUIPPED FOR FIELD LOOP JUMPERS AND NO JUMPERS ARE AVAILABLE, it is possible to operate the dynamic brake on all units provided they are equipped with the GE braking system. In this case, place the unit selector switch in position one (1) on the controlling unit. DO NOT PUT THE UNIT SELECTOR SWITCH IN 2, 3, or 4 POSITION UNDER THIS CONDITION OR THE FIELD LOOP WIRING WILL BE SERIOUSLY DAMAGED.

.... Here are a couple other things. The unit selector switch is only equipped on units equipped with the Universal Dynamic Brake, which directly implies that there was no option at all for field loop-only design.

The wiring diagram for these units specifies, under MU DATA, models ALCO DL-701 and EMD GP-9. The units were fitted with standard 27 point MU plugs and cabling and the standard field loop jumpers plugs and cabling.

[Pneudyne]

Thanks for that.

It would appear that the Fairbanks Morse Universal Dynamic Braking system was broadly similar to that later adopted by Alco and those developed by the railroads, e.g. Western Maryland as detailed upthread.

That is, locomotives equipped with the FM universal system provided control signals for both the potential wire system (voltage) and the field loop system (current), so could lead consists with either type of braking. I think that mixed consists would also be possible provided that any trailing potential wire units were also equipped with field loop through wiring and 1.2 ohm dummy resistors.

I suppose one would reasonably expect that a GE control system would anyway cater for potential wire dynamic braking, with the universal option adding field loop (for trailing units), but with no provision to delete potential wire. Although in theory at least it might have been possible to adapt a GE system (say Amplidyne or Static) to respond to a field loop dynamic brake control input, for example by using a current measuring reactor on the field loop line to develop the appropriate control signal.

Regarding the possible damage to the field loop wiring system if the selector is in other than position 1 when no field loop jumpers are connected, I imagine that in position 1, there would be a total of four 1.2 ohm resistors in the field loop circuit, which would limit the current to around 15 amps even with the full 74 volts applied. In positions 2, 3 and 4 there would be respectively three, two and one 1.2 ohm resistors in the circuit, allowing much higher than the design maximum current.




Cheers,

[Engineer Spike]

As to the question of how Baldwin handled the dynamic brake control after the exit of Westinghouse, it seems that Baldwin was well on the way out. I don’t think many GE equipped units were ever built. Many of the last were switch units where DB was a moot point.

[AllenPHazen]

Re: Engineer Spike's comment.
Only two 1600hp road switchers were built with GE equipment: AS-416 for the Norfolk Southern. (Trivia quiz: how many railroad corporations have borne that name?) Given that the NS was a low-speed railroad (think about what ordering A1A trucked road switchers in 1956 implies about their track!) operating in non-mountainous territory, I suspect they were not d.b. equipped. (But someone in Typewriters's family -- son or brother -- made a blog post a few years back about these two locomotives. So Typewriters probably has access to some document that would confirm or refute my suspicion.) ... There were also eleven S-12 switchers with GE electricals (according to the Baldwin volume of Kirkland's "The Diesel Builders"), and -- though switchers with dynamic brakes have been built -- there is no indication that any of these 11 were anything but standard. So maybe Baldwin never made a definite decision about what to do with dynamic braking on GE equipped units.
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But why did GE bother with this minuscule bit of Baldwin business? Baldwin was evidently still planning to stay in the locomotive business when they got the bad news about Westinghouse's decision to stop making heavy traction equipment, but Baldwin's position by that time was pretty marginal: GE's management wouldn't have thought electrical equipment for BLW locomotives was likely to be a big market! And there were costs: 752 traction motors (used on both the switchers and the roadswitchers) were an off-the-shelf item, but the Baldwin engine, with its very low r.p.m., required GE to design new generators: the 591 for the switcher and the 590 for the roadswitcher.
Possibly it was advice from the legal department: GE was serious about locomotive building, and probably already thinking of maybe someday fielding what turned out to be the U25B: the 4-unit set locomotive with CB engines at an appropriate rating was built in 1954. So maybe it was thought important not to do anything that even looked like conspiring to put a potential competitor out of business!
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But there was surely a limit on how much development work GE would have been willing to put into the project: my guess is that the generators GE provided for Baldwin were close cousins of existing GE generator designs, with some parts commonality. The 590, for instance, probably looked a lot like the 567 (for FM) or 586 (for six-axle Alcos, and used later on six-axle U boats). (That is, of course, speculation: comments welcome.)