HELLO MY NAME IS BEN I WORK FOR THE IC&E AS A ENGINEER. I KNOW MY ENGINES AND HOW THEY WORK BUT THERE IS ONE THING I CANT SEEM TO FIGURE OUT. THIS IS A TECH QUESTION BOUT THE DYNAMIC BRAKES ON THE EMD SD40-2 LOCOMOTIVE, WHEN YOU GET INTO DYNAMICS THE ENGINE RPM RISES TO BOUT NOTCH 4 OR SO. WHY IS THIS? IF ANY BODY KNOWS OR HAS A THOUGHT IM INTERESTED TO LEARN.
THANKS
Yes Ben you are correct, when you go to Dynamic Braking on an SD40-2 that has a DR13 you will have Notch 4 Engine Speed. You are picking up the "A" & "C" Governor Valves. The reason they do this is to provide cooling for the Traction Motor Fields. When you put the unit into Full Dynamic Braking, you will be pumping 960 Traction Motor Field Amps into the traction motor fields and you will have 68 to 72 VDC at the TH module at pins 2 to 14 which is the braking rheostat and inturn you will have 47 VDC at the RC module pins 13 to 14. Ben if you are on a SD40-2 that has a DR20 or a DR21 module, things will be a little different. When you go to Dynamic Braking, your Engine Speeds will not raise until you have applied 565 traction motor field amps to the motors. Once you have pumped in 565 field amps into the motors, then your engine rpm's will once again return to Notch 4 with the "A" & "C" valves at the governor. This is called two speed braking.
thank you that is very informative, i have noticed some of the newer sd40-2s will not raise rpm tell bout dynamic 6 or so, thats good information to know,
thank you.
Ben, those units that you are referring to about engine rpm that will not raise until notch 6 or so in that area is two speed braking. Ben if you drop the Module Compartment door, you will find either a DR20 or DR21 module in the rack of cards.
You forgot to tell him why the 645 needs to speed up: because the traction motor blower is coupled directly to the engine.
With all do respect, I took for granted that he already knew that. He told me that he knew the engines pretty well and I would say that he does. I figured that he knew the bellows on top of the traction motors were for cooling the Motors when in Motoring (he more than likley just forget about cooling the traction motor fields in braking). I will go into greater detail the next time. I have been calibrating and setting electrical limits on older EMD & GE units (been a few years since I have done a GE, but I still know how) for over 32 years and I love to talk and write about them.
Dale,
I wondered why you were being so specific on what modules where in the electrical cabinet...
Welcome to the forum!
- Erik
I probably should have not said anything about the TH & RC, I just mentioned it because at the TH module pin 2, gets the voltage feed from RH50 which is your dynamic braking rheostat which is "0" to 72 VDC. I talked about the types of DR modules because I figured that Ben had noticed going into Dynamic Braking on some Dash 2 units and was not getting engine speeds until he reached the area of notch 6 to notch 7 on his braking rheostat. That is why I mentioned the DR20 &DR21 module. I stated earlier that I have been troubleshooting and calibrating locomotives for over 32 years. To me it is not a job, it is a love that I have and there is nothing else I would rather do. I have written over 900 pages of Locomotive Troubleshooting throughout the years that I share with my co workers and the company that I work for. Erik E-mail me anytime, I will answer your ? if I know the answer.
Dale
How would that compare to an EX Southern SD40-2 with tapered extended range dynamic brakes equipped with the two speed stuff?
Dale, the applause from where I sit in the admiring Peanut Gallery deafens....That you took the inquiry to indicate knowledge and answer based from it....most appropriate. As is the clear description of functionality of "magic" results from the modules, clear.
Please, with what you've got, stay in that mode.
Taper-extended range SD40-2----with modular control and potential wire, excavating a term that commands generator field voltage, commanded by the module, to vary it based on the grids ability/stability .
Taper-extended range..... short hood trailing.....is this a trap?
Hi Dale, I think your replies are informative, so keep up the good work.
I was going to ask if you had access to a formula that would allow a calculation of dynamic braking requirements, if the inputs of gross tonnage, gradient, curvature, length of gradient, speed, etc, were available. I know there is a calculation done for subdivisions to determine tonnage grades, so assumed there must be a calc for braking as well.
I have also been doing a search to determine if there are comparative assessments for dynamic braking of B-B vs C-C locos of the same hp, i.e. GP40 vs SD 40.
Any ideas?
Cheers, GW
gordonozzie Hi Dale, I think your replies are informative, so keep up the good work. I was going to ask if you had access to a formula that would allow a calculation of dynamic braking requirements, if the inputs of gross tonnage, gradient, curvature, length of gradient, speed, etc, were available. I know there is a calculation done for subdivisions to determine tonnage grades, so assumed there must be a calc for braking as well. I have also been doing a search to determine if there are comparative assessments for dynamic braking of B-B vs C-C locos of the same hp, i.e. GP40 vs SD 40. Any ideas? Cheers, GW
Locomotive horsepower has nothing at all to do with dynamic brakes. You are limited by grid capacity (700 grid amps on the 40 series). Use 10,000 lbs. of braking effort for each axle.
I only have 27 years working on locomotives.
Randy
A 62:15 SD40-2 peaks at 60000 lb dynamic braking force at about 25 mph. Force drops along a constant-power hyperbola at higher speeds; at lower speed, if the unit does not have extended-range dynamic brake then the force is a straight line from 60000 lb at 25 mph to zero at zero mph.
efftenxrfe Dale, the applause from where I sit in the admiring Peanut Gallery deafens....That you took the inquiry to indicate knowledge and answer based from it....most appropriate. As is the clear description of functionality of "magic" results from the modules, clear. Please, with what you've got, stay in that mode. Taper-extended range SD40-2----with modular control and potential wire, excavating a term that commands generator field voltage, commanded by the module, to vary it based on the grids ability/stability . Taper-extended range..... short hood trailing.....is this a trap?
The entire 40 series has taper dynamic brakes, GEs are the flat ones.
Hey Randy, Could you please explain this more?
Sure,
Dynamic brake falls into one of two classes: taper dynamic and flat dynamic. Taper dynamic provided dynamic according to speed and controller position and were most effective. Flat dynamic provides retarding effort according only to controller operation, regardless of speed.
In other words a mixed consist of flat and taper dynamics would have the taper dynamics working much harder at higher speeds than the flat dynamics in a lower selector position. The flat engine may be in dynamic notch 3 and making 500 grid amps and the taper engine in the consist will be maxed out on grid amps.
Thanks Randy, but I still don't have my head around it.
The way I understand it the braking effort is linear from 0 mph up to the (speed about 25 mph) point where the dynamic grid is at maximum current. Then from that speed & up the current is chopped so that the grid current averages the max dissipation, but as speed increases the "chopping" is increased (thus reducing the duty cycle of the grid). So that the braking curve is not linear but drops off rapidly at first but changes lesser with speed. In other words a curve .
If I understand you right, that is flat?
Am i getting it right?
This is what I am refering to.
From Al Krug's excellent web site:
The alternative graph would be a set of curves, all about the same shape as the Position-8 curve in Krug's graph, but roughly-proportionately lower than it all the way from 0 to 70 mph. In other words, each curve climbs to a peak at 20-25 mph or so and then descends at higher speeds. So Position-5 braking effort is somewhere around half of Position-8 braking effort at any speed, instead of equaling Position-8 at speeds above 37 mph, as it does in Krug's graph.
Thanks Timz, Can you give me a graph that shows this. I'm not sure I am understanding thid right and I really want to.
Chad, didn't you post this same Krug diagram in a discussion back around 2008? Which had some very good technical detail about some of the issues being rehashed now?
[Addition -- I think it was this one.]
Hi Overmod, Yes, I have posted this link in the past. I was not aware that there is more the one kind of "curve" though. This is new to me.
Wow, I re read that thread (blast from the past) and at the time I completely missed Wabash's explaination of tapered DBs . I wold still like to see a graphical explaination if someone can come up with one to post.
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