Where is the differnece between HP and PS?

[Supermicha]

I have a question. In a book, i found the information, that the GP 60 has a performance of 3200 KW, which are 3800 HP.

In Germany, we use PS, and 3200 KW are 4250 PS. Where is the difference?

[tree68]

According to http://www.ime.org.uk/ime/p/ps_Pferdestarke.html

PS stands for?

Ps = Pferdestärke. Literally "Horse Strength". PS differs from UK BHP, which differs from US BHP. The reason is that regulations differ from country to country about the way an engines power output can be quoted. Most engine builders quote a BHP figure at a particular revolution rate for the engine, eg 89BHP @ 5500 rpm. BHP can be directly calculated by taking the torque, multiplying by revs and dividing by the infamous "fudge factor" - a constant which is only there to keep the figures manageable.

Now. German regulations are a bit tighter than the UK regulations
when it comes to measuring the power output, hence PS tends to be
lower compared to UK BHP. US BHP is notoriously optimistic, as the
US regs allow for the fitting of special manifolds etc during the
testing. A friend discovered this after putting a Cobra copy with an
American engine on the rolling road, to find that the power was
considerably lower than expected. He did a bit of research and
discovered the US Horses problem.

I also found a converter:
http://www.onlineconversion.com/power.htm

Don't know as it answers the question, but, what the heck...

[jchnhtfd]

The differences are partly in manifolding and the like -- on naturally aspirated gasoline engines one can create quite a peak in horsepower with the right manifolds, for instance (usually at the expense of power and torque at other rpms) but the major differences have to do with what else is being driven at the time. Older SAE (United States) procedures specified that engine horsepower was to be measured with no engine-driven accessories attached -- that would include cooling fans, alternators/generators and, frequently, water pumps, never mind things like power steering pumps and the like. It wasn't done that way so much to inflate horsepower ratings as to provide a uniform standard. British and German ratings have the engine measured as installed, although there are slight differences between them. Railroad engines are usually quoted as available power to the main alternator or generator -- but it is worth noting that not all of that power is then available to the traction motors, as there are losses in the alternator and wiring and controls, as well as such goodies as traction motor cooling blowers, main radiator cooling fans and such like.

Bottom line? Specify what is being measured under what conditions!

[Supermicha]

I just found out another answer:

In the USA, the perforamnce is measured directly at the motor shaft, in europe, the performance is measured at the wheels. That means, the GP60 has 4250 HP at the engine, but 3800 "arrive" at the wheels. Thats sounds possible for me...

[oltmannd]

The US traction horsepower rating for locomotives is shaft HP into the main generator for traction. To get the diesel engine BHP, you have to add in all the auxiliary loads such as cooling fans, traction motor blower, aux gen output, etc.

The drawbar HP would be considerably less - you have to allow for main gen efficiency and electical losses and mechanical friction.

[M636C]

Michael,

The English horsepower is 745.7 Watts, while the French CV is 736 Watts. What figure do you use for PS?

This results in a small difference in locomotive power rating on conversion from kW..

As indicated above, US locomotives usually quote the power at the input to the generator and European locomotives usually quote the gross engine power.

For an SD40-2, these are usually expressed as 3300HP gross, 3000 HP into the generator. This is an approximation, with deductions for the radiator fan and the air compressor, among other things.

In Australia, our big EMD locomotives are usually quoted as having 2862 kW, or 3838HP, and these have the same engine as the GP60. I think that the 3200kW rating for a GP60 is correct, for the gross engine power, if we assume about 10% losses, as in the SD40-2.

Peter

[Anonymous]

Hi
I guess the difference is in the auxiliaries; you see, that German PS rating was higher than US HP rating. I know a lot more about SD40-2s than BR1XX electrics, but I suppose as they are electric locomotives they get power for their auxiliaries direct from the overhead, thus the tractive PS rating is the combined power of all traction motors, no power loss for compressors etc. Remember, there are no generators/alternators in those beasts. And yes, the DIN and SAE horsepower factors are different, too.

[daveklepper]

This refresher course was so interesting I downloaded it onto a floppy for future study and reference. Thanks! Dave Klepper

[Modelcar]

....And that mention of auto SAE HP rating system in the USA was changed about 1970 from gross HP which did not include accessories to a test that included accessories as installed in the vehicle. I believe the old system and the "new" rating was and is the reading at the output [crank], shaft of the engine.

[Anonymous]

Just to throw a bit of a monkey wrench into this, isn't tractive effort more important in railroading than PS, HP, or BHP (no matter how it's measured)?

Oh and the French have two terms - They use ch similarly to the way ps, hp, and bhp are used, but the term CV means chevaux vapeur. In the automotive world, the last iteration of the Citroen 2CV had an engine with around 26ch, but was in the 3CV class for insurance purposes...