Hallo, i was wondering how much powerful are dynamic brakes vs the traditional air brakes on a single locomotive (first gen diesel as such). I am not familiar on how it is measured in the US, but in Italy where i live, all locomotives and cars have at least two sets of data relative to braking power vs weight example total weight: 80 tons, "braked" weight: 70 tons (that is for locos that do not have a huge %) total weight: 40 tons, braked weight 65 tons (high speed passenger cars) and all in between for freight cars which also set an empty/loaded braking power as much as the braked weight is in % of total weight (of the train this time) there are speed restrictions, especially on grades My question is, assuming a first gen diesel (F3/C420 with dynamic brakes), how much braking power ("braked weight") (%) do I have to consider for the dynamic brakes? That should add to standard brake power up to wheel locking, but mostly be used to keep the train from picking up too much speed. Thank you
An interesting question. I have never given this much thought. I do wish someone had an answer, as your inquiry has made me curious.
This could be complicated comparison because the amount of dynamic braking depends on the locomotive speed and air brakes do not. I imagine the braking power would be limited by the traction motor horsepower rating. I doubt the motors are rated to produce more power when braking than they produce when running.
An easy way is to count each braking axle as making 10,000 lbs. of braking effort at 23 mph with 62:15 gearing. At speeds above and below 23 the brakes fade. An EMD F-7 therefore will have 40,000 lbs of braking effort at 23 mph with 62:15 gearing. The effort depends more on the brake grid capacity than motor capacity, 700 amps being the old norm for brake grid current limits. Randy Stahl
Thanks for the answers, I was looking for the max braking effort, which I assume for 4 axle is then 80Klbs, I understand it is only for slowing down. The line I model is quite steep 2,5 to 3 % that is why I was thinking about that to see if the dynamic brake is enough to get to the train braking effort required to avoid the speed restrictions imposed on lower braking% trains or frequent use of the air brakes which will void the purpose of the dynamic braking.
A 4 axle engine is 40 K. For a 2.5%- 3% grade you would need 100% retainers as well as dynamics. If you model the 50s-60s this was the common practice. If you model today you are in luck because the locomotives of today have strong dynamics 20,000 lbs per axle or 120,000 k per locomotive.
Randy, got the message of air brakes, my post referred in what is common practice here in Italy on steep grades, to use only DB to keep the train from picking up too much speed (if they are powerful enough), and apply air brakes only when more braking action is needed. If DB are not enough then the air brakes are applied as usual, albeit with reduced frequency. The use of DB (on regular non high speed trains) on grades is mainly to avoid wear and tear of the brake pads, and reduce noise.
