17MG8A1 Governor

[FCP503]

Hello all,

I am new to this forum, and I am try to locate information about the 17MG8A1 governor. (As used on the RSD12 in particular)

I have downloaded the manuals that cover the earlier 17MG3, and 17MG6 governor that are availble on http://gelwood.railfan.net however these do not provide much explanation the operating principles of these governors.

Any information would be most helpfull, thank you.

[alcodoc]

The MG8A1 governor was used on Alco locomotives equipped with Static or Type "E" control. The MG8 governor does not have a fuel limit pilot valve. Timing is provided by the cylinder head orifice and check ball. The MG3 and MG6 were installed on locomotives equipped with Amplidyne control. A second pilot valve was provided for fuel limited on said governor operated through the engine control panel. (GE 17FM110 panel)

Alcodoc

[FCP503]

OK, I could see that there is one less rheostat on the 17MG8A1 but I wasn't sure which one had been eliminated.

I didn't realize that this version did away with the Amplidyne. So the saturable reactor alone is controlling the load in the excitation generator, yes?

I can see the reasons, and advantages of this type of dc/ac excitation/load control, but I am having a little trouble betting my head around it all. It is unike everything else.

I should be getting the correct manual for the RS11/RSD12 soon, all that we have right now is for the RS3 etc. Hopefully that will take away most of the mysteries. Right now it's like looking at the manual for a 1940 era automobile in order to understand a 1960's era automobile.

[alcodoc]

The manual won't be much help to grasp how the system works. A RS11 schematic diagram is the way to go. "Static" excitation is very reliable and doesn't break down very often. It can be confusing, however, to trouble shoot if you're not up to speed. Also, you won't see the fuel limit circuit on the RS11 print as you would on a RS3 with Amplidyne and the MG6 governor. Remember it was electrically eliminated on the MG8 governor and was made an internally timed circuit operated by the govenor oil pressure system.

Alcodoc

[Alcoman]

I can't locate my RS-11 diagram at the moment, I wonder if the FPA-4 schematic would work ?
It uses the same Governor.

[alcodoc]

Yes John, The FPA4 has Static control with a MG8 Governor.

Regards, Don

[FCP503]

OK Hopfully the manuals, and schematics will help give us a place to start.

Both of our RSD12's have been sitting O/S for a number of years. One of them has an electrical issue that sidelined the unit, but it has never been looked into in any depth. (this happened before my time)

The theory that has been presented is that the batteries were in terrible condition, and the unit lost reference voltage causing the aux gen to overvolt the low voltage system. At this point we only really know two things: one, the unit that was sitting at idle with the reverser centered and it stopped operating. Two, the filaments in the headlights, both front and rear burned out. At that time there were too many other things that needed attending to and the unit was just sidelined.

Level of damage? unknown, and it will be a number of weeks before we get time to look at it in depth.

Until then I have been trying to read as much as possible to see if I can narrow my focus, and prioritize the diagnostic.

I asked about the governor in particular because that has been giving me the most trouble in trying to figure out. There may actually be nothing wrong with it, but it will have be looked into before we can even think of firing the unit up. (Along with most everything else in the electrical system!!)

There is no obvious outward electrical damage, but until we can dig into things, who knows!

If any of you have seen a simular situation, and have some ideas what it MOST likely to be damaged, that would also help us to prioritze our examination. (voltage regulator jumps to my mind)

The fact that the unit was sitting at idle, with the reverser centered, should really narrow down the areas of the electrical system that could have been damaged.

[N_DL640A]

Voltage regulator would be the first place I'd look. On every locomotive I've worked on, you can open the battery switch while the engine is running with no problem, eliminating the batteries from the circuit entirely; I can't see where bad batteries would hurt aux gen excitation. I have however seen cases where a bad VR has caused some problems; never as bad as you describe, though!

[N_DL640A]

Two other things I'd look at: check to see if the field wire leading to the aux gen is either shorted to the positive lead from the aux gen (especially within the conduit or inside the junction box on the side of the aux) or if the field lead is grounded (in combination with a separate positive low voltage ground). Either of these could cause a runaway aux gen.

[FCP503]

Thank you for the suggestions, we will certainly check those things out. (we will likely pull the voltage regulator and bench test it)

I will only have a brief chance to look at the unit this week. (right now it is buried with not so good access) We will have a chance to take a VOM to it briefly to begin to get a sense of what is up. This is a side project (I promised that it would be) so things will progress slowly for a while, at least till we can make some room closer to the service area.

Still it will be nice to get it this unit back up again.

[N_DL640A]

May I ask, what is the history and location of this unit? I've always liked the RS11/RSD12 family of locomotives, though I've never done any work on them. Plenty of time on Centuries/ MLW, EMDs and GEs, though... Best of luck!