Diesel locomotive "Auxiliary Alternator", who can tell me all about these things?

I need to know the; output in volts and amps, phase etc...

Do they vary with the RPM of the locomotive or have some kind of voltage regualtor?

I'm thinking of making a large portable gen/alt and am attempting to learn if these bought as surplus would be useful.

This is all that I have on the subject now;

Locomotives used to operate passenger trains are equipped with an auxiliary alternator. This provides AC power for lighting, heating, air conditioning, dining facilities etc. on the train. The output is transmitted along the train through an auxiliary power line. In the US, it is known as "head end power" or "hotel power". In the UK, air conditioned passenger coaches get what is called electric train supply (ETS) from the auxiliary alternator.

I'm probably not the most qualified person on the forum to tackle this subject but I'll give it a shot none the less. Usually when you talk about an "aux alternator" on a locomotive these days, you are referring to the thing which used to do what the "aux gen" did. What the aux gen did was charge the batteries and supply control voltage. It some instances it may have supplied current to the "companion alternator" which in turn generated the current to excite the main traction alternator. There are different arrangements for these these days and whether or not it would work for what you're trying to do entirely depends on what type you're talking about. Some older units (by modern standards) like GP38-2s may still actually have true aux gens that are DC and have brushes. There probably are also drop in replacements for these whose guts are A/C but have built in equipment that should allow you to electrically hook them up without any significant modification to the wiring. Some more modern locomotives (like GEs) basically just have a big set of three phase windings in the main traction alternator (that is seperate from that used for supplying traction) and use it and various panels and diode banks, etc. to do all the various of functions of the companion alternator and the aux gen.

I'm pretty sure someone who is electrically savy could hook up a locomotive main traction alternator to provide various sorts of useful industrial power (probably most likely 3 phase 440 AC would be most likely?) , but you need to be quite savy with A/C controls, etc.

HEP generators have nothing to do with auxiliary alternators on locomotives. They generate 440 volt 3 phase A/C , usually without involving any of the electrical equipment for actually propelling the locomotive. There were examples though where HEP was tapped from the MTE, however. The early EMD F40PH and GE P42s are both examples.

Also, the general configuration of alternators for this purpose on locomotives is that they are basically a synchronous A/C generator, with a stationary set of the 3 phase windings a rotating rotor whose current is controlled and is applied to the altenator via slip rings.

In the case of F40PH's and P42's, the HEP gen's (alternators) are directly driven by the prime mover and so the prime mover runs at a set RPM, with traction voltage and current drawn off the main gen in a manner that I honestly don't know a thing about.

Basically, to get 60 Hz for HEP, the locomotives are in notch 8 or so the entire time they're hooked to the train.

-Micah

When you say "auxiliary alternator", it's a bit confusing what you mean. Every diesel locomotive has a gadget called an "auxiliary generator", which does the same thing as the alternator on your car. It replenishes the battery and supplies control voltage. On a more modern diesel it will be an alternator, hence "auxiliary alternator". This power was never used to power coaches in any way.

In the old days, passenger coaches were heated with steam heat, and air conditioned by an on-coach diesel engine (typically a "Waukesha".) Fleet operators got real sick of running ungainly steam lines (much heavier than air hoses) and Waukeshas. So they decided to make coaches all-electric, and power them from a large industrial generator somewhere on the train. They used off-the-shelf 480VAC 3-phase 60Hz, same as your electric company will provide for your office building.
Poke around this site and you'll learn a LOT about that. http://www.nwrail.com/distributed_produ ... index.html

To supply the power, several approaches were tried.

One was having an entirely separate diesel engine solely for the purpose. Sometimes that would be in a converted baggage car etc. Or it was hung off the back of the locomotive, as in the case of many commuter locomotives.

Early on, another method was employed. Add a second alternator to the diesel prime mover, and use that for all-electric-coach power (HEP). Because HEP requires constant-frequency power, the prime mover had to spin at a constant speed, and a speed appropriate to that generation. What speed? In America it's 60Hz (3600 cyc/min.) which you make at 1200 RPM (6 pole alt), 900 rpm (8 pole alternator), 720 rpm (10 pole) or 600 rpm (12 pole). Those are your only options for engine RPM. Amtrak F40PH's EMD prime-mover was obliged to spin at 900 rpm when it was built for 1000.

The F40PH had another slick trick. Its primary traction alternator had 10 poles. They could use the traction generator for HEP (giving up the ability to self-propel), allowing the engine to spin at 720 rpm instead of 900. This was called "standby mode".

The modern method depends on the huge advances in semiconductor inverters. For instance you can walk into Radio Shack and buy a 12V-120V inverter for your car, for like $30. Cheap Honda generators change the engine speed based on electrical load. That is because they are using semiconductor inverters to create 60Hz regardless of engine speed. Modern HEP locomotives do exactly the same thing. The inverter makes 480VAC 3-phase regardless of actual prime-mover speed, so the prime-mover revs up and down based on operational load. That's the state of the art today.

The HEP alternator on the F40PH is a 4 pole machine and you spin it at 1800 RPM to yield 60Hz output. There is an accelerating gearbox ahead of it.

Which is an excuse for me to ask a question I have asked all over the place for several years and have gotten no answer to:

The official RPM of an F40 in regular HEP mode is not 900 but 893 RPM. Why? Yes, any figure is just a nominal one and in reality the governed RPM varies widely (I'm told they usually are running faster). It matters little; no one is running a traditional sync motor wall clock on the HEP and if the A/C compressors and fan motors on the cars spin a tiny bit faster or slower because the power frequency is a bit higher or lower than 60 Hz it's unimportant.

But why wouldn't the official spec be 900 RPM? There must be a reason but I've yet to find it. It seems unlikely that they would deliberately make 59.53 Hz the goal instead of 60 Hz. Is it possible the gearbox takes in 893 to output 1800? Is there a combination of gear teeth that does this? I remain mystified.

Steve

The gear ratio for 893 to 1800 would be about 2.0156. An 80 tooth pinion with a 161 tooth gear would yield 2.0125. That seems unlikely that they actually did that to me. Probably someone else hit the nail on the head, the designers probably thought the circuits would only be used for lighting, heat, and air conditioning, so a frequency that was slightly off wouldn't really be important. They probably didn't envision people having all sorts of sensitive electronic gizmos (like laptops and cellphones, etc.) that people would carry with them all the time.

Actually, from a mechanical point of view, a single gear reduction of EXACTLY 2:1 , like a combination of 160 and 80 tooth gears, is quite undesirable. each tooth on the larger gear would mate with one, and ONLY ONE tooth on the smaller gear. This has the potential to cause uneven wear on the gears.

A 161:80 gear ratio is much more desirable, due to the fact that each and every tooth on each gear will mate with every tooth on the other gear, evening out any wear.

JD

Exactly why the two gears in an F40PH HEP alternator gear box have 117 teeth and 58 teeth.

PC

Trivia Quiz:

Q: What's the name for this condition?

A: "Hunting ratio" or "hunting tooth ratio".

To obtain it, the number of teeth of the meshing pair can have no common factors. It forces every tooth to mate with every other tooth at some point, thus evening out wear.

Thanks PC! (Actually with those gears 892 should be the hypothetical ideal RPM as the output would be a hair closer to 1800 but I'll quit while I'm ahead.)

Steve

There's a few things about that. First there's nothing on earth that ever cared about 60Hz being 60.0000Hz, except for clocks. Even TVs don't use 60Hz, they use 59.94. That's why at home, TV ghosts would slowly crawl down the screen, and on Amtrak the same ghosts would randomly crawl down or up, changing directions all herkeyjerkey.

Second, distribution is 480VAC 3-phase. Almost every accessory on the car runs off 480V. Each coach has a transformer which knocks 480 down to 240/120 for the very few devices on the car which actually require 240/120. For instance the Microwave, TV and VCR in the lounge. Those are the only gadgets on your side of the transformer, which reduces your exposure from spiky loads on the trainline.

Most gadgets use switching power supplies nowadays, which have gotten QUITE good, and can infamously get useful power out of all sorts of lousy input. A $15 fluorescent electronic ballast will be multi-voltage, 120-277V. Obviously it has no problem with spikes below 277V. Or the $1 "Joule Thief" circuit, which can burn a 3V LED for hours from an already-depleted 1.5V battery. http://en.wikipedia.org/wiki/Joule_thief

Many switchers don't even care if it's DC. Locomotive accessory power, 75 VDC, uses the same polarized sockets as home 120VAC outlets. Crews have plugged in laptops and phones and find they charge just fine. http://www.trainorders.com/discussion/r ... ?1,1682731

The whole thing about "Don't plug that 'expensive and therefore sensitive' gadget into train power supplies" is a throwback to when sleeper-car power actually did come off a wheel-driven generator, and truly was very, very dirty power, unsuitable for anything but a razor. Or switching power supply, but those hadn't come along yet.

Clocks, and teletype machines. My next door neighbor is a retired electrical engineer for AT&T and told about having to build a filter or some such device to refine the frequency of the 60hz signal going into a teletype machine because deviation in the frequency would cause them to lose characters which was a major nuisance. This was quite a while ago when solving this problem was a bit more daunting than today.

There's a few things about that. First there's nothing on earth that ever cared about 60Hz being 60.0000Hz, except for clocks. Even TVs don't use 60Hz, they use 59.94. That's why at home, TV ghosts would slowly crawl down the screen, and on Amtrak the same ghosts would randomly crawl down or up, changing directions all herkeyjerkey.

Sorry to disagree, I am a heating technician, one of my customers is a tourist RR that uses small residential hot water boilers to heat several cars. An employee decided to replace the primary controls on the oil burners with new electronic controls. All was fine on shore power, when they switched to the generator power, it wasn't "clean" enough and the controls went haywire. I replaced the controls with older, simpler relays, no problem. They also tried to standardize their digital thermostats to one type, these were power stealing type T-stats versus battery powered. Same thing happened, off shore power the electronics weren't happy. We switched to Honeywell battery operated t-stats and solved the problem.
Never say never, never say always :)
Fred Jordan
Deep River CT

No way to know without extensive and completely pointless trial & error testing but it probably had more to do with noise and spikes than the frequency being inexact.

Steve