Western Railroad Discussion > What does the third dynamic bank give me? (GE AC DB question)

Ah yes... another one of my technical post, I'm a bit overdue for one. 

On the AC GE locomotives up to this day there has been a option to have an additional 3rd blower/grid bank. For years I had always assumed 3 blower/gird units had greater dynamic brake potential than the standard 2 blower/grid units. I've never seen anything official about what this option allows, and years ago when I was in engineers school they never touched on it. (My carrier only gets units with 3 brake option) .

On a semi-related note newer locomotives from both builders have "consist monitoring" built in. This allows you to see what trailing units are doing, if the unit is equipped with the proper hardware to transmit this data to the leader. 

Where am I going with this? well finally just here recently I had a 3 blower and a 2 blower unit in my consist that BOTH had monitoring hardware onboard. (NS ES44AC up front followed by a CP AC44CWM) I was able to watch how both units did in dynamic. It turned out that both units performed roughly the same, rarely getting more than 5klbs apart from each other. 

So my question is, what does that extra 3rd blower/grid bank do? 

Included is a small wiring schematic I did on how the DB circuits are set up on these units. 



Edited 1 time(s). Last edit at 03/28/20 20:50 by Foamductor.

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I always thought it kicked in automatically if the sustained grid temperature was at or above a certain point, such as on a long downgrade. But that is just my speculation.

The key is to go back to the original AC6000s, and their cousins the AC60/44s.  Both of them had inverters capable of handling 6000 HP, so GE had to build grids and blowers capable of handling the additional current.  The easy way was just to add an additional set of grids and a blower in parallel..

As the motors in the 44s and the 60s were the same, GE could easily offer 25% more dynamic brake capacity, and at higher speeds than anything previous.

Before I retired, the UP showed the higher rating in their special instructions, and we had to be careful not to enable too much braking on the head end of manifest trains.  As I remember, we could use three 2-blower units on the head end of a manifest with 10 loaded cars on the head end, but one 3-blower unit made the total braking effort too much, and one unit had to be isolated.

I think the braking will be about the same between a 2 and a 3 until the speed increases over about 30 mph and the control handle is in just about full position.
G



Edited 1 time(s). Last edit at 03/28/20 21:56 by ExSPCondr.

Might also be useul in higher altitude applications where additional grid area would be required for equal cooling. UP in the early days was very
specific in the dyno application as to units in dynamic and especially remotes in dynamic. I've got somewhere a whole set of instructions on remote
setup and dyno capability. 

Out 

ExSPCondr Wrote:
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> The key is to go back to the original AC6000s, and
> their cousins the AC60/44s.  

Its funny you should bring up the 60s and the 60/44s. While I've had a handful of them, I never thought to start looking at them to see how they were setup. The CSX ones had a sticker about the improved DB abilities and boy could you feel it, Those units have some insane DB.

I do NOT have a AC60 wiring diagram, but my SP AC44 wiring diagram shows a lot of AC60 stuff. (I guess they had them on order before UP got them). It appears that the AC60 an additional 3 resistor grids on the 3rd bank. 

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Would it have anything to do with extended range below 13mph? Seems amperage goes way up as the engine slows, requiring more grid to dissipate the heat.

trainjunkie Wrote:
-------------------------------------------------------
> I always thought it kicked in automatically if the
> sustained grid temperature was at or above a
> certain point, such as on a long downgrade. But
> that is just my speculation.

Looking at grid blower circuitry, the more current through the grids, the more voltage wil occur across the grid blower motor(s,) resulting in higher blower speed, and more cooling air across the grids.  ALCo, Baldwin, and EMD did it this way since the late 40s, as it works well, and the idea is to waste the current anyhow.  The more braking called for, the faster the blowers run.

Then GE comes along and starts building locomotives, and being CHEAP about it, and not using the experience they've gained from building ALCo's braking system.  On the U and Dash-7 series, GE put the brake grids in front of the radiators, and made the engine run at run 8 (unloaded) to move the air over the grids.  There was no clutch on the mechanical fan drive, so the fan ran all the time, even when the engine was idling in cool weather.  This wasted a lot of fuel and caused additional engine wear on an already fragile engine.  However, the main problem it caused was sucking up a lot of trash and holding it against the radiator screens, blocking the airflow, because the suction never stopped so the junk could fall off!.

Fortunately GE figured it out and have done well since.   The grid blowers, the radiator fan, and the air compressor are all electrically driven and don't run unless they are needed.  The air compressor is two-speed, it runs twice engine speed at idle, so the engine doesn't have to be revved up when first coupled to a large train.
G 

I'm wondering that since the first run of AC4400s had the option of running in reduced traction mode that the dynamics also wouldn't have a
similar derate ie 2 grids rather than 3. 

Out 

SD45X Wrote:
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> Would it have anything to do with extended range
> below 13mph? Seems amperage goes way up as the
> engine slows, requiring more grid to dissipate the
> heat.

In a word, NO.   (The current just comes back up to the amount it was above 23 MPH on a freight geared locomotive.)

Extended range dynamic applies only to DC locomotives, and is accomplished by shorting a portion of the grids so that the lower voltage produced by the slower turning motors can push enough current through the grids to do some braking.  There are three steps of extended range, one comes in about 18mph, two at about twelve or thirteen, and three at about tenmph.  Braking falls so low as to be ineffective at about 6mph.

An AC locomotive's computer uses the inverters to excite the AC traction motors into producing AC current, then sending the AC back to the inverters who rectify it and send it to the grids as DC to get rid of it.  See the "DC LINK schematic" posted above.  Inverters and AC motors are better at dynamic braking across varying speeds than DC locomotives, even those with extended range.

AC locomotives are able to "Dynamic Brake to a Stop, " by the computer reversing the motors at 2 or 3 mph, even though the controller is still in dynamic brake.  As the motors don't have brushes or a commutator, it doesn't hurt them, and the computer doesn't let the engine move in reverse once it stops.
G.

 

ExSPCondr Wrote:
-------------------------------------------------------
> SD45X Wrote:
> --------------------------------------------------
> -----
> > Would it have anything to do with extended
> range
> > below 13mph? Seems amperage goes way up as the
> > engine slows, requiring more grid to dissipate
> the
> > heat.
>
> In a word, NO.   (The current just comes back up
> to the amount it was above 23 MPH on a freight
> geared locomotive.)
>
> Extended range dynamic applies only to DC
> locomotives, and is accomplished by shorting a
> portion of the grids so that the lower voltage
> produced by the slower turning motors can push
> enough current through the grids to do some
> braking.  There are three steps of extended
> range, one comes in about 18mph, two at about
> twelve or thirteen, and three at about tenmph. 
> Braking falls so low as to be ineffective at about
> 6mph.
>
> An AC locomotive's computer uses the inverters to
> excite the AC traction motors into producing AC
> current, then sending the AC back to the inverters
> who rectify it and send it to the grids as DC to
> get rid of it.  See the "DC LINK schematic"
> posted above.  Inverters and AC motors are better
> at dynamic braking across varying speeds than DC
> locomotives, even those with extended range.

All good points. It should also be brought up that just about every system is wired in parallel on the DC link on the GE AC locomotives. The advantage to this is that a GE AC can tolerate the loss of a grid circuit or a traction motor/inverter and still be able to use dynamic brake using the remaining working parts. (Although you will get a reduction in tractive effort). 

EMD runs TWO DC link circuits. One for each truck. The EMD dynamic brake setup is a bit simpler. With one resistor circuit for each DC Link. The fan is wired off the rear truck's DC-Link circuit, so if you need to cut out the rear truck you will lose dynamic brake. 

Due to how DC locomotives are wired up, if you lose a traction motor or a grid. You no longer have dynamic brake. This is true for both builders. 

>
> AC locomotives are able to "Dynamic Brake to a
> Stop, " by the computer reversing the motors at 2
> or 3 mph, even though the controller is still in
> dynamic brake.  As the motors don't have brushes
> or a commutator, it doesn't hurt them, and the
> computer doesn't let the engine move in reverse
> once it stops.
> G.

I've never noticed this with a GE AC, but if you use dynamic to stop on a EMD AC locomotive as a light engine. If you don't apply the independent quick enough it will "bounce" and start rolling the other way. 

It bounces because you've built up stored energy between the grid and the motor and that's quickly disappated as the motor reverses.
Same thing in hydraulics, if you've got hose between a motor and the controlling valve, quickly shut the valve with the motor under load
and the trapped volume disappates by slightly reversing the motor.

Out 

callum_out Wrote:
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> It bounces because you've built up stored energy
> between the grid and the motor and that's quickly
> disappated as the motor reverses.
> Same thing in hydraulics, if you've got hose
> between a motor and the controlling valve, quickly
> shut the valve with the motor under load
> and the trapped volume disappates by slightly
> reversing the motor.
>
> Out 

IMNSHO, the bounces are because the computer is telling the inverters to put reverse current pulses on the motors at two or three Hz, and every pulse is felt.
G.

Highly plausible, that's very much what industrial drives do on a controlled stop difference being the effect of the dynamic braking on a locomotive drive
ie braking to a stop. 

Out 



Edited 1 time(s). Last edit at 03/29/20 18:20 by callum_out.

Both have a peak 98,000 lb brake effort rating; both have TM3 and DEAC. Those NS units have 17EA33D “standard” grid resistors whereas the CP units have 17EA33J “high temp” grid resistors. The grid blowers are the same for both: 5GY72.

EOTMOVE Wrote:
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> Both have a peak 98,000 lb brake effort rating;
> both have TM3 and DEAC. Those NS units have
> 17EA33D “standard” grid resistors whereas the
> CP units have 17EA33J “high temp” grid
> resistors. The grid blowers are the same for both:
> 5GY72.

Okay, now you've taken us down a new rabbit hole. What are "TM3" and "DEAC"? I've never seen those terms used before. Otherwise from what you post it appears that our previous posting mentioning temperature is right. Thanks!

Of all the GE motors I have ran, present day, I find no difference between the two.

I’ve often wondered the same between the 2 and 3 blower units, and I could
Have sworn the three blower units were ex-CNW.

I do know that the 44/60s have them, and never had a difference in performance.

I figured it would be due to the 60 engine, but I’m dynamics, what would the difference really be as it’s kind of mutually exclusive to a point (unless the alternators were different to handle the voltage range, but...)

In the current SSI, I think the CP or CN units (EMD though iirc) had different than standard ratings for whatever reason, especially the SD90’s.

MP683 Wrote:
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> Of all the GE motors I have ran, present day, I
> find no difference between the two.
>
> I’ve often wondered the same between the 2 and 3
> blower units, and I could
> Have sworn the three blower units were ex-CNW.
>
> I do know that the 44/60s have them, and never had
> a difference in performance.
>
> I figured it would be due to the 60 engine, but
> I’m dynamics, what would the difference really
> be as it’s kind of mutually exclusive to a point
> (unless the alternators were different to handle
> the voltage range, but...)
>
> In the current SSI, I think the CP or CN units
> (EMD though iirc) had different than standard
> ratings for whatever reason, especially the
> SD90’s.

As best I can tell. CSX, NS, CNW, KCS, FXE, KCS, IAIS and newer UP power have the 3 blower option. CN, CP, UP, BNSF, SP, CEFX all ordered the 2 blower option, some of these units are set up with the later single motor/2 fan setup. All AC6000/6044/46 units have the 3 blower setup... possibly with a extra set of resistors (haven't confirmed that yet) 

If and better since, you have a 98K braking limit why 3 blowers on the 6000 hp units when 1000 hp/motor in braklng
both can't happen and would far exceed 98K. Why would hp be a factor. I still think that db capacity vs dissapation ie
air over the grids figures into all this somewhere. On Tennessee Pass you'd need more air over the grids to even
maintain your 98K number.

Out 

The new stuff is still two fans.

Where I work we heavily use DB downgrade for about 20 miles or so. Works fine. I've personally have yet to die on me, but I know it has and does happened. Apparently was more common with flash overs with the GE DC's.

SD70ACe's are rated for 100,500lbs, and still use the single fan setup since the 50? series. 

On one of the other comments, I've never felt the bump from brake to power - but always from power to brake no matter how long you are in idle or setup. GE's like to load quickly in DB. Not so much in power on my RR. What I've been told 50th hand, is each railroad can spec how and when they can load based on experience when AC's first arrived. Apparently SP's and CNW's 4400's loaded quickly and now under the yellow flag, they can be pretty slow. This is why I like having DC's in consist as you can stretch the train somewhat until the GE's decide to do something. 

 

MP683 Wrote:
-------------------------------------------------------
> The new stuff is still two fans.
>
> Where I work we heavily use DB downgrade for about
> 20 miles or so. Works fine. I've personally have
> yet to die on me, but I know it has and does
> happened. Apparently was more common with flash
> overs with the GE DC's.

I also run somewhere where it's not unusual to be in full dyno for 20-30 mins at a time, I've never experienced a issue with anything in that regards... AC or DC. 3 blower/2 blower or single fan EMD setup. The grades I run are never over 1% but some of them are 20+ miles long, and with train lengths getting longer and longer one has to hit the dynamic fairly hard. 

>
> SD70ACe's are rated for 100,500lbs, and still use
> the single fan setup since the 50? series. 

It's not quite that simple. The EMD "Radial Grid Dynamic" (not to be confused with the trucks) setup has changed over the years. AC units typically have 4 resistor grids where DC units had 6. Some railroads even specified a larger fan IIRC. (Conrail comes to mind with the SD80MAC). 

I suspect that much how GE has various options for how DB is setup, EMD has something similar... its just not as easy to spot. 

>
> On one of the other comments, I've never felt the
> bump from brake to power - but always from power
> to brake no matter how long you are in idle or
> setup. GE's like to load quickly in DB. Not so
> much in power on my RR. What I've been told 50th
> hand, is each railroad can spec how and when they
> can load based on experience when AC's first
> arrived. Apparently SP's and CNW's 4400's loaded
> quickly and now under the yellow flag, they can be
> pretty slow. This is why I like having DC's in
> consist as you can stretch the train somewhat
> until the GE's decide to do something. 

I've also noticed this and suspected that various railroads have the manufactures tinker with how the locomotives perform.