I've noticed that some diesel locomotive models have them and some of the same model locos don't. Any particular reason for this?
It all depends what the actual railroads stipulated when they ordered the locomotives. Off course what with take overs, hand me downs etc theres no set pattern. whoppit
Storm: Dynamic Brakes (DB) were primarily used by and for down grades. They function by essentially turning the traction motors in the trucks into generators. The electricity produced this way is conducted to grids (heating elements) located in the roof, where fans are used to dissipate the heat. Using the traction motors as generators produces a retarding or braking effect on the locomotive. The fact that they are mostly used for downgrades is why some roads (such as MoPac) that saw their track profile as essentially flat passed on the installation.
Eagle2, More and more the railroads are useing the dynamics for slowing down going into a town or yard even on the flat (saves on brake shoes). The area I live in the UP and BNSF both use the dynamics to slow from the 60 mph track speed to the 40 mph track speed in town. I love the sound of the dynamics, sounds like the loco is singing. Shannon WP LIVES ATSF LIVES
You ought to hear a 16,000-ton coal train on a 2% grade whine...... The mountain RR's; SP, DRGW, ATSF, GN, NP, UP, etc, all ordered many locos with dynamics. As stated, increases braking effort, and lowers wear on brake shoes and wheels. The flatland RR's skipped on DB also as a cost-saving measure.
Yea, I figured it was just an option like power brakes on cars used to be an option years ago. I guess though that running between Omaha and Cheyenne or Kansas City and Denver or similar terrain you would not encounter too many steep grades. Makes sense to me.
Shannon: I think some of it also depends on era. A lot of the equipment I have is '60's and '70's, prior to the introduction of extended range dynamics, which I believe is what you're referring to (not trying to rivet-count, even if it sounds like it). And a lot of the non-DB roads primarily ran through the midwest (Kansas, Oklahoma, Missouri for example). I have to think that any railroad even thinking about Denver would need DB's.
Strangely enough, the B&O's first order of GP7s didn't include dynamic brakes... and we're talking the Allegheny Mountains here! But the GP9s they ordered sure did. They often would put diesels on front as helpers for steamers since their DBs could help on descents.
I've often wondered why PRR Geeps didn't have dynamic brakes. Were they bought by the seacoast divisions?
On a DC locomotive, extended range dynamic braking uses contactors to transistion the dynamic braking resistor grid from parallel to series as locomotive speed decreases. This allows the grid to work at a lower speed range. It's very similar to how a DC locomotive has to transition from series to parallel when current is being applied to the traction motors as speed increases...
