Rockies climb throttle position question

[5280 Guy]

When I ride the Zephyr out of Denver and into the Rockies it's easy to see that it's a steep grade. Anyone know if they are running the power in the 8th notch for the climb?

 

[Siegmund]

Most likely yes, if there is no traffic ahead of you to slow you down: a quick back of the envelope calculation suggests that with ~8000 HP pulling 2 engines and 10 cars up a 2% grade with 10-degree curves, you would max out at around 35 mph.

In the F40PH days, I was on a CZ/Desert Wind/Pioneer that briefly got delayed by traffic and slowed down to walking speed. While we theoretically had the power to maintain 25 mph or a bit better, if we had been GOING that fast, we weren't able to accelerate well enough to achieve that speed, and wound up creeping along at ~10mph for a while and overheating the engines; we stopped somewhere high up in the tunnel district, before Rollinsville, and sat for about an hour, then tried again and proceeded without incident.

 

[5280 Guy]

Most likely yes, if there is no traffic ahead of you to slow you down: a quick back of the envelope calculation suggests that with ~8000 HP pulling 2 engines and 10 cars up a 2% grade with 10-degree curves, you would max out at around 35 mph.

In the F40PH days, I was on a CZ/Desert Wind/Pioneer that briefly got delayed by traffic and slowed down to walking speed. While we theoretically had the power to maintain 25 mph or a bit better, if we had been GOING that fast, we weren't able to accelerate well enough to achieve that speed, and wound up creeping along at ~10mph for a while and overheating the engines; we stopped somewhere high up in the tunnel district, before Rollinsville, and sat for about an hour, then tried again and proceeded without incident.

Thanks for the info. I appreciate it. Two other questions, if you don't mind. How loud would it be in the engine room or the cab when under full power? Also, I know that they use 2 units, as one is needed for hotel power. Does one locomotive provide the electricity and the other for motive power, or do they share it? Thanks again.

 

[Rasputin]

How loud would it be in the engine room or the cab when under full power?

Not really on topic for the California Zephyr, but I rode in the lead locomotive (an FP7A) of the eastbound CP Canadian on the steep grade east of Field, BC in 1977. I do not recall that the noise in the cab was excessive. The locomotives seemed to handle the grade very well.

 

[Siegmund]

Also, I know that they use 2 units, as one is needed for hotel power. Does one locomotive provide the electricity and the other for motive power, or do they share it?

One unit can do both (and does on shorter trains: the Portland and Seattle sections of the Empire Builder get one unit each). A quirk of the P42s is that the generator is limited to a lower RPM when supplying hotel power (it has to produce exactly 60Hz electricity, not just run flat out) - such that each unit can either produce up to 4200hp for propulsion only, or up to 3500hp divided between hotel and propulsion - so if you have more than one unit, you usually want one unit providing all the hotel power.
On a train like the CZ climbing out of Denver you would probably have one unit putting all 4200 into the rails, the other putting a few hundred into the hotel load and 3000 or 3200 into the rails.

I don't have any specific numbers re the sound. Loud enough I wouldn't care to be in it. The soundproofing in the cab has to meet OSHA limits, which are going to be somewhere around 85dB.

 

[5280 Guy]

Thanks, guys. I appreciate it.

 

[F900ElCapitan]

Not really on topic for the California Zephyr, but I rode in the lead locomotive (an FP7A) of the eastbound CP Canadian on the steep grade east of Field, BC in 1977. I do not recall that the noise in the cab was excessive. The locomotives seemed to handle the grade very well.

I got to do the same thing in ~’83 in an FP-9. Such an awesome experience for someone in 6th grade. I’ll agree, it was loud when they actually had to use full power. I really wish this was an option today.

 

[5280 Guy]

Update: We went up the hill rather slowly. At Grandby I saw the engineer walking around and he said that one of the locomotives was down and that he had been running full power. That was pretty impressive when you think that they were pulling a 2% grade and supplying hotel power at the same time.

 

[Asher]

I got to do the same thing in ~’83 in an FP-9. Such an awesome experience for someone in 6th grade. I’ll agree, it was loud when they actually had to use full power. I really wish this was an option today.

That locomotive had a Roots blown 2 stroke that could howl. Beautiful sound.

 

[railiner]

That locomotive had a Roots blown 2 stroke that could howl. Beautiful sound.

Like this?

https://www.digitrax.com/sound-depot/emd-567c-16-f9ph-non-turbo-roots-1500hp/

 

[5280 Guy]

Most likely yes, if there is no traffic ahead of you to slow you down: a quick back of the envelope calculation suggests that with ~8000 HP pulling 2 engines and 10 cars up a 2% grade with 10-degree curves, you would max out at around 35 mph.

In the F40PH days, I was on a CZ/Desert Wind/Pioneer that briefly got delayed by traffic and slowed down to walking speed. While we theoretically had the power to maintain 25 mph or a bit better, if we had been GOING that fast, we weren't able to accelerate well enough to achieve that speed, and wound up creeping along at ~10mph for a while and overheating the engines; we stopped somewhere high up in the tunnel district, before Rollinsville, and sat for about an hour, then tried again and proceeded without incident.

I'm curious why the engines overheated. At 10 MPH they weren't in run 8, but even if they were, I don't see why it would matter. I would think that, to the prime movers, only throttle position matters and not speed. 74 MPH in the 8th notch should be the same as 15 MPH at the same setting to the engine. In addition, wouldn't the cooling systems keep the temps where they should be?
I'm not disputing what you said - I'm sure you know what you're talking about. I'm just interested in the reasons behind it. Thanks.

 

[ehbowen]

I'm curious why the engines overheated. At 10 MPH they weren't in run 8, but even if they were, I don't see why it would matter. I would think that, to the prime movers, only throttle position matters and not speed. 74 MPH in the 8th notch should be the same as 15 MPH at the same setting to the engine. In addition, wouldn't the cooling systems keep the temps where they should be?
I'm not disputing what you said - I'm sure you know what you're talking about. I'm just interested in the reasons behind it. Thanks.

It may not have been the prime mover which overheated. The electrical drive system also is prone to heating up, especially when run at high power and slow speeds. I have an F3 manual from the bad old days with an ammeter chart showing the limits of what the traction motors could take. The system is different now, but I-squared-R is still the same.

 

[5280 Guy]

It may not have been the prime mover which overheated. The electrical drive system also is prone to heating up, especially when run at high power and slow speeds. I have an F3 manual from the bad old days with an ammeter chart showing the limits of what the traction motors could take. The system is different now, but I-squared-R is still the same.

I see what you mean. He said "engines," which is what threw me off. I think with AC motors it wouldn't be a problem, but I bet these have DC. ACs can pretty much take whatever you throw at them.

 

[Siegmund]

At a distance of 30 years it's hard to provide too many details --- when I said "engine" I meant those-things-at-the-front-of-the-train in general, not specifically any one component. I would assume it was traction motors overheating. As ehbowen mentioned, at low speeds the limit is on current, not horsepower. For 70s/80s era freight units, there was a minimum speed, between 10 and 15 mph, below which you couldn't continuously use full power even if the wheels weren't slipping. In a passenger-geared unit that limit might have been even higher, around 20.

Come to think of it, that may well have been the cause of the problem: we may well have been following a freight train that was maxed out at 10mph in notch 8, and forced to follow it slower than we wanted to.
I have no memory of whether we overtook a freight at the top of the pass or not.

F40PHs were DC, as was just about everything else at that time.

 

[5280 Guy]

I see what you mean. I read Al Krug's famous HP vs. TE essay and I'm not sure that they can get down to 10 MPH in run 8, but pretty close, I guess. They would sound pretty awesome in that mode.
I didn't know that about the '70s and '80s units not being about to run at full power even with no wheel slip, but it does make sense. Glad to see the AC motors of today. I will attach Al's PDF in case anyone is interested and doesn't have it.

 

[5280 Guy]

Update: I asked the engineer up in Fraser, CO, and he said that he uses notches 5 and 6, although he pays the most attention to amps. He said he runs at around 400A.

 

[west point]

When I ride the Zephyr out of Denver and into the Rockies it's easy to see that it's a steep grade. Anyone know if they are running the power in the 8th notch for the climb?

One time when Amtrak was still using road railers 2 of 3 locos failed climbing the Big Ten. Engineer even shut down HEP so he must have had to use run 8. Remember using HEP limited the loco to 900 RPM. I was worried that the DC traction motors might overheat because the train was going slow up but we made it to the Moffet tunnel. The rest of the story another time.

 

[Cal]

Update: I asked the engineer up in Fraser, CO, and he said that he uses notches 5 and 6, although he pays the most attention to amps. He said he runs at around 400A.

How'd you ask the engineer in Fraser? Did he/she open the door to get some fresh air?

 

[5280 Guy]

They seems to always climb out of the cab at that location as it is the only real stop between Denver and Glenwood Springs. I've talked to them before.

 

[Siegmund]

Tells you just how much smaller today's CZ is than they were a few decades ago, that they have that much surplus power now.

@5280Guy: if you are an Al Krug fan, and have an interest in how engineers push their units to the max at low speed, make sure you read his Kiewit, Wyoming "Tales from the Krug" story. It's with an SD9 but essentially the same story applies to any DC diesel with adjustments to the speed and how much it's pulling.

I am not too surprised that "pay attention to the amps" remains current (cough) today even on the newest power.

 

[5280 Guy]

Tells you just how much smaller today's CZ is than they were a few decades ago, that they have that much surplus power now.

@5280Guy: if you are an Al Krug fan, and have an interest in how engineers push their units to the max at low speed, make sure you read his Kiewit, Wyoming "Tales from the Krug" story. It's with an SD9 but essentially the same story applies to any DC diesel with adjustments to the speed and how much it's pulling.

I am not too surprised that "pay attention to the amps" remains current (cough) today even on the newest power.

Thanks. I am on his site now reading that. I thought "Tales from The Krug" was gone. I still have his HP/TE article.
Great stull!

 

[5280 Guy]

Also, what do they mean by 400 amps? How does that translate to throttle position and engine power? I understand the basics of electricity, traction motors, tractive effort, etc., but not this. Thanks.

 

[Siegmund]

Also, what do they mean by 400 amps? How does that translate to throttle position and engine power? I understand the basics of electricity, traction motors, tractive effort, etc., but not this. Thanks.

For an engineer's purposes, current is proportional to tractive effort, and throttle position selects horsepower. The standard tractive effort x speed = horsepower equation still applies. You watch the ammeter to see how hard the locomotive is working, and (on an old DC unit) if you draw much above 800 amps you will either spin the wheels or overheat the motor or both. (Recall that energy lost to heat is proportional to current squared.) At very low speeds -- under about 10 for freight, under about 15 or 20 for passenger -- you can't use full horsepower. At higher speeds tractive effort necessarily drops as speed increases because you are using all the horsepower you have available.

If you think back to the Al Krug essays about his SD40s pulling heavy freight trains up a hill, and you are good with your unit conversions, you can compute peak performance possible for his traction motors at about 800 amps x 480 volts ~ 500hp per axle, and compare that to the 3000hp (from 6 axles) = 90,000lb tractive effort x 18ft/sec. calculation he gave in the essay.

A passenger unit may have 750hp or more per axle available, but that doesn't make the engine any more powerful at low speed or make it able to climb a steeper grade, just means it can accelerate faster (by being able to continue delivering maximum tractive effort as the speed climbs from 10 or 12mph up to 18 or 20.)

 

[5280 Guy]

For an engineer's purposes, current is proportional to tractive effort, and throttle position selects horsepower. The standard tractive effort x speed = horsepower equation still applies. You watch the ammeter to see how hard the locomotive is working, and (on an old DC unit) if you draw much above 800 amps you will either spin the wheels or overheat the motor or both. (Recall that energy lost to heat is proportional to current squared.) At very low speeds -- under about 10 for freight, under about 15 or 20 for passenger -- you can't use full horsepower. At higher speeds tractive effort necessarily drops as speed increases because you are using all the horsepower you have available.

If you think back to the Al Krug essays about his SD40s pulling heavy freight trains up a hill, and you are good with your unit conversions, you can compute peak performance possible for his traction motors at about 800 amps x 480 volts ~ 500hp per axle, and compare that to the 3000hp (from 6 axles) = 90,000lb tractive effort x 18ft/sec. calculation he gave in the essay.

A passenger unit may have 750hp or more per axle available, but that doesn't make the engine any more powerful at low speed or make it able to climb a steeper grade, just means it can accelerate faster (by being able to continue delivering maximum tractive effort as the speed climbs from 10 or 12mph up to 18 or 20.)

Much obliged! Get explanation.