Nostalgia & History > Extended Range Dynamic Braking

In another thread, exhaustED Wrote:

https://www.trainorders.com/discussion/read.php?11,4652835
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> What does extended range mean with respect to
> dynamic brakes?

Each dynamic braking resistance grid is limited to 700 amps, with some high capacity dynamics being rated for 920 to 945 amps. Standard dynamic braking, with resistance grids interconnected only at each end of the grid, became ineffective below 200 amps, or about 13 mph.

Using a combination of shorting contactors, and center taps on the resistance grids, extended range dynamic braking keeps the resistance of individual grids constant, in steps that depend on train speed. All of the grids are used at speeds above 25 mph; 3/4 of the grids are used at 18 mph; 1/2 of the grids are used at 12 mph; and 1/4 of the grid surface is used at 6 mph.

At each reducing step, and as individual grids and portions of grids are shorted out by the contactors and center taps, amperage can return to the maximum 700 amps at each of the three step-down speeds: 18 mph, 12 mph and 6 mph.

The combination of shorting contactors and center taps gave locomotives with four axles a total of eight dynamic braking sections, and six axle locomotives had twelve sections. The lowest speed used the fewest number of sections, allowing maximum braking effort and amperage from the traction motors to be dissipated.

The GP30s delivered in 1962 were the first on UP with extended range dynamic braking and high capacity resistance grids. All EMD locomotives delivered after the GP30s also came from the factory with extended range dynamic braking.

I think the GP50s were the last on UP with the grids located above the engine space, a location that made interconnecting of the grids and center taps difficult, and the cabling subject to engine heat problems. The SD50s were the first on UP (I think) that had their grids in a circular wagon wheel pattern, making interconnecting easier. All since the SD50s have used the wagon wheel pattern.

Don Strack



Edited 2 time(s). Last edit at 10/20/18 04:12 by donstrack.

Nice write-up Don.  

Extended Range DB was an option, and thus not all units delivered after the GP30 model received the Extended Range feature. Also, for what it's worth, the dynamic brake feature was NOT "basic" on GP models,i.e. it was an extra cost option, as was the Extended Range feature. Dynamic brake was "basic" on SD models.

You have done a better job making this clear than I could, Don. Want to give it a go on flat vs. tapered dynamics?

EO

We can add that the GP60's, GP60M's and GP60B's were the last EMD units to get the dynamic
brake "blister" over the engine compartment.  

Nick Tharalson,
Marion, IA

>
> Extended Range DB was an option, and thus not all
> units delivered after the GP30 model received the
> Extended Range feature.

Yup, the bell ringing GP35s on AT&SF did not have extended range DB.  They were tapered also.  Next to worthless, like everything else about the engines.

donstrack Wrote:
-------------------------------------------------------


> --------------------------------------------------

> > What does extended range mean with respect to
> > dynamic brakes?
>
> Each dynmaic braking resistance grid is limited to
> 700 amps, with some high capacity dynamics being
> rated for 920 to 945 amps. Standard dynamic
> braking, with resistance grids interconnected only
> at each end of the grid, became ineffective below
> 200 amps, or about 13 mph.
>
> Extended range dynamic braking reduces grid
> resistance in steps as track speed decreases below
> 25 mph, allowing maximum amps to be maintained
> until the locomotive slows to approximately 6 mph.
>
>
> Using a combination of shorting contactors, and
> center taps on the resistance grids, extended
> range dynamic braking increases the resistance of
> individual grids in steps. All of the grids are
> used at speeds above 25 mph; 3/4 of the grids are
> used at 18 mph; 1/2 of the grids are used at 12
> mph; and 1/4 of the grid surface is used at 6 mph.
>
>
> At each reducing step, and as individual grids and
> portions of grids are shorted out by the
> contactors and center taps, amperage can return to
> the maximum 700 amps at each of the three
> step-down speeds: 18 mph, 12 mph and 6 mph.
>
> The combination of shorting contactors and center
> taps gave locomotives with four axles a total of
> eight dynamic braking sections, and six axle
> locomotives had twelve sections. The lowest speed
> used the fewest number of sections, allowing
> maximum braking effort and amperage from the
> traction motors to be dissipated.

>
> Don Strack

One slight little error:
Everything is well described except that the grid shorting contactors REDUCE the resistance of the brake grids because the traction motors can't push as much current through the grids at full resistance when they are being turned slower.  By reducing the grid resistance, the current stays higher and gives more braking force, although at slightly less total effort because the resistance is lower, giving less wattage.
G

Both the EL and the N&W did not specify extend range DB. However, NS was the first to specify 945 amp DB on the "SOU" SD50's IIRC.

Posted from Android

Thanks, great descriptions/info!

I believe that Mr Strack was talking about the UP and the UP only when he made the comment about everything after the GP35's had extended range DB's.

PHall Wrote:
-------------------------------------------------------
> I believe that Mr Strack was talking about the UP
> and the UP only when he made the comment about
> everything after the GP35's had extended range
> DB's.

I for one realized that. It was a railroad by railroad decision.

Posted from Android