GE -7 dynamic braking troubleshooting

[CHECKIT]

Well, I hate to admit it, but even after several years of working with -7 locomotives, and having access to many shop manuals, I still have not found a good reference for troubleshooting dynamic brake systems.
Many of our units have low loading braking, or in some cases, virtually no loading, when operating.
Assuming good braking grids and cabling, would anyone have methodology in place to logically diagnose braking problems? Again, there seems little in the way of publications dealing with DB.
Also, references I have indicate that many of the -7 models had three speed events to progressively increase engine speed, determined by DB throttle position, to provide adequate fan (mechanical) velocity for grid cooling. I believe its Idle/N1, Notch 4, and Notch 8. This seems to make sense for fuel conservation, but our fleet of B23-7's, ex CR, ex Southern, and ex CSX all throttle right up to N8 as soon as DB is asked for. Seems like a waste of fuel at times. Anyone ever "re-install" speed event panels or can maybe offer insight as to why engine speed is maximized right away?
Thanks!

[WVU]

When troubleshooting Dynamic Braking on a Series 7 unit, to start with make sure your traction motor field amps is set correctly for exciting the motors. On a CHEC II unit like a B36-7 the field amps are set for 1260 amps (set this with the independant brake released). If the unit is a basic Series 7 unit like a C30-7 or a B30-7 or a B23-7 you want your field amps set at 1165. If you have a area to track test the unit, you can get a Grid Current Measurement at the BCCR which is 100 amps per volt. You should have atleast 6.8 to 6.9 VDC at the BCCR in full dynamic braking at the peak of extended range or if you are over 19 to 21 mph. If your loadmeter in braking does not match the 6.8 or 6.9 at the BCCR you have a loadmeter resistor that needs to be adjusted to 19 ohms underneath the engineer side. If you have Grids that keep Burning up, make sure they are turned in the proper direction with the correct cable hooked to them (it is easy to install a Grid backwards on a older GE). If you have Extended Range Contactors Burning Up ( I promise you that you have an Open Grid in the System)

Now for Engine Speeds in Dynamic Braking. Some GE's Have it and some do not. From my experience, units that have a VSR1 relay when energized at 43.5 VDC from the braking rheostat with 465 Grid Amps will give you 773 Engine RPM's. The VSR1 also has a relay with in the relay called MGR which stands for Medium Grid Current and it has interlocks marked MGR. You will also have a VSR2 relay that will pick up at 56.6 VDC from the braking rheostat with 600 Grid Current Amps and you should then have 1050 Engine RPM's for cooling the traction motor fields. The VSR2 also has another relay within the VSR2 called the HGR which stands for High Grid Current and it also has interlocks within the Governor circuit to raise engine speeds for cooling. The EMD 40 series units basically did the same thing with the DR20 and DR21 module.

Again from my experience I have noticed that units that have the VSR1 & VSR2 Relays also have what they call an EDDy Current Clutch that runs the cooling fan to cool the water in the Radiators. You have a ECR1 and a ECR2 relay. When cooling the engine if the temperature is not very high the ECR1 (Eddy Current Clutch Relay #1 will be picked up via WTS1 ) and the cooling fan will turn1/2 the speed or so. When the Eddy Current Clutch Relay #2 via WTS2 picks up the fan for cooling the engine will run at high speed. When you put the unit in Self Board Load the ECR2 reay picks up and puts the fan in high speed for cooling the grids as well. When you put the unit into Dynamic Braking, the BKA relay will pick up and go staright to the ECR2 and put the fan in high speed for cooling the grids in braking.

Some of the older Series 7 units had the engine cooling fan directly hooked to the drive shaft and there was not no varible speed control on the engine for cooling the traction motor fields, it went straight to 1050 enginer RPM's. Units mostly with the VSR1 & VSR2 did have the Eddy Current Clutch Relay. So if you have the VSR1 & VSR2 mostly located in the left hand corner a couple of feet above your CHEC Panel you should have Engine Speed Control for the Braking Rheostat.

[CHECKIT]

WVU,
What a great post. You sound like you have ALOT of knowlege of GE electrical. Not my strong suit, unfortunately.
Our units (B23-7s) do not have eddy current clutches. The cooling fan is drive shaft powered. Engine revs up, fan speeds up.
Could you explain more about how the grids can get put in "backwards"? They pretty much look the same either way, to me, but it might explain the seemingly high failure rates of our grids. Thankfully, I bought a bunch from a scrapper. But, if they are getting put in wrong, we are not helping ourselves any.
I'm printing out your post, and will talk it over with our electrician. He's pretty good, although more trained on older EMD units.
As far as DB engine speeds, it just seems like a lot of fuel being expended to operate in dynamic braking with the relatively short (20-30 car) trains and moderate grades (1%) or so. Just wondered if there wouldn't be a way to modify engine speed to react to braking resistence, in steps, instead of all or nothing, or something along those lines.
Thanks for the info!

[WVU]

To start with, I agree, GE Grids do look alike and can be confusing to work with. For Grids being turned the wrong way, the GE Grid you have to be careful with is the one that can be used for a 1/4 Tap. Hear is a list of Grids and replacements.
17EA21H109B muliipurpose grid is the grid that is used for (17EA7C43 {NO Center TAP})
17EA7C109 (Center Tap) when using 17EA21H109B the multipurpose grid for 17EA7C43 (No Center Tap) for .025 ohms, do not hook to the center tap.
When using 17EA21H109B multipurpose grid in place of 17EA7C109, you want to use the center tap for 0.12 ohms.
GE uses the multipurpose grid for 0.25 ohms & it can be used for the 0.12 and 0.13 ohms (center tap) be careful howhis grid is turned. The other grid they use is for a quarter tap, 17EA7C134 and another grid is 17EA21H134B, the quarter tap is 0.19 ohms & 0.06 ohms.
I have had B36-7 unit show up with grids that keep burning up and the problem was the people that was replacing the grids kept putting in the same grid and hooking it up the way they found it. The grids was either the wrong grid or turned the wrong way.
I once had a C-36-7 that had two grids turned the wrong way in it also. When we went to calibrate dynamic braking using the BCCR tester on it at AG & AF on the CHEC Panels bad was bad. We found that the FL1310 Card was bad. This is where your ACCR and BDCCR and VCR feed. We applied a new card and brking regulated fine.

[WVU]

Checkit, I wanted to follow up on the BCCR Tester. To start with we want to make sure the unit has the proper Traction Motor Field Amps for Dynamic Braking. The B23-7, B30-7 and C30-7 should have 1165 traction motor field amps in Notch 8 Full Dynamic Braking with the Independant Brake released. You can check this at the FL Card at the ACCR test point and on these units it will be voltage X 600 and you should have around 1.942 VDC. On the B36-7 and the C36-7 units that are CHEC 2 units, you should have 1260 traction motor field amps and you will get that reading at the FL Card at the ACCR test point and you will X the voltage by 1000 at the ACCR test point and that should be 1.26 VDC. To adjust your your traction motor field amps you will go to Pot # 6. Turn Pot Clockwise to raise traction motor field current.
Now to check your Grid Current. You can simulate it by using a BCCR Tester. You will hook your tester to the IDEF wire that is connected to terminal AF and to the EDG wire at terminal AG at the bottom of the CHEC Panel. With your unit in Notch 8 Dynamic Braking and you have the proper traction motor field amps for your unit with the Independant Brake released, start turning your knob on the BCCR tester and when you reach 6.8 to 6.9 VDC at the FL card at the VCR/BCCR (100 amps per volt) test jack, you should start seeing your traction motor field amps start to bleed off. By the time you get to 7.0 to 7.20, your traction motor field amps should be gone. That is your regulation point. If you have no regulation in the braking circuit you will melt the grids right out of the unit. To adjust Grid Current, go to Pot #5 at the CHEC Panel and to raise grid current regualtion, you will turn the Pot counter clockwise. If you have a test track, hook your meter to the FL card at the VCR/BCCR test jack and keep an eye on it. If it goes over 7.2, you need to go to Pot #5 and adjust it.

[CHECKIT]

WVU,
Man, I wouldn't mind trading brains for awhile. I mentioned that I'd take this up with our electrician, and now he's been ill, and using up vacation time! I can't wait until he's back to show him this stuff.
Anyway, I have a basic understanding of the information you are so generously sharing, but the other guy is alot better. I'll be sure to print all this stuff out for when he is back.
I really appreciate your willingness to help out on this.
Were or are you on an Eastern road, or from out West?
Finding dash-7 electrical help is not as easy as with EMD, so having your input is great.
All in all, though, the CHEC system and -7 layout is pretty good. The B23's have been generally very reliable. We just need to continue to learn their quirks.
We are considering an aftermarket control syatem to try on a unit to modernize all control functions. DB, excitation control, and wheel slip detection/correction will all be microprocessor controlled. Meanwhile, we will continue to support all our other B's as usual.
Thanks again for the help. I'd be appreciative of any thing else you care to share. These are good units that get overlooked too often as far as medium horsepower lokies go.

[WVU]

Checkit, I am on the Eastcoast and I love working on the old GE units eventhough I don't get the chance to hardley do so anymore. For the rail company that I work for, we don't have all that many left. To start with I cut my teeth on the EMD units and I love working on them also but the old GE units have a special place in my heart. For years I have told the people that I work with that the GE Excitation System was light years ahead of EMD and the guys I worked with looked at me like I was from Mars. The reason why I say that GE was ahead of EMD is, At that time back in the 60's and 70's GE had a perfect excitation system, it was called CHEC, CHEC stands for Constant Horsepower Excitation Control. GE excitation system was montoring Volts, Amps and KW and the Load Pot was designed to run in full maximum field at 5:30. On the other hand the EMD had the static excitation system that only monitored Volts and Amps and it is common for the Load Regulator to run out of the whole at 9:00. EMD did not come out with a perfect excitation system until they produced the SD50 in the early 1980's. The SD50 excitation system is the same thing as a CHEC, they finally started monitoring Volts, Amps and KW and the Load Regulator should be in full maximum field. On a CHEC system, the reason why the Load Regulator is designed to be in full maximum field rather it be a GE or EMD is, that when the load pot backs out, it weakens the KWref. When the KWref is reduced the unit will not make full HP. So to maintain KWref, you have got to get the load regulator in the whole. Even the newer GE units are still basically a CHEC engine, They are controlled thru the computer and it is called Micro CHEC.