rectifiers

Hi there

I have a rather general question (which doesn't fit under any manufacturer subforum) about power conversion in locomotives.

I've heard that 645 EMD generation, uses a diode bridge in combination with a 6-phase system from the generator, without any filtration to
get a nice smooth 12-pulse DC output. I don't know if this is true or not.

But what I wonder is the older generations of locomotives, such as EMD 567, and old FM's, Alcos, GE's etc. from 40's 50's etc. before the solid state era.
Did they used mercury rectifiers or what?

And if yes, where they the bulb type or steel type, and does anyone have a picture of such a thing

thanks

Older locomotives have DC main generators.

The AR 10 alternator (used with most 645 powered locos) generates 3 phase AC currant rectified to DC via two air cooled silicon rectifier banks.

Lower horsepower locos like GP38's could be purchased with either D32 main generators or AR10 alternators. (model GP38AC)

AC main alternators seem to have been introduced widely in locomotive use around 1966.

AC excitation alternators used in conjunction with DC main generators came into use in the early 1950's. (used on locos like the Alco RS3, RS11 etc.)

Thanks

In case of older locomotives with DC generators, is there some kind of filtering involved on the output of the generator, or is the large ripple of no concern to traction purposes ?

A generator is generally smoother than an alternator and rectifier. However it also requires more maintenance. For traction purposes filtering is unneeded. For auxiliaries, internal filtering is used where needed.

How come it's smoother? I would assume that in order for the commutator (on the generator) to switch polarity, the current needs to fall to zero, which in essence gives a full-wave rectified sine, or am I wrong?

Regulating the power output of the generator is what is of prime concern. (factors such as limiting generator currant, generator field winding currant, and matching generator output in relation to engine horsepower output)

dieselsmoke wrote:How come it's smoother? I would assume that in order for the commutator (on the generator) to switch polarity, the current needs to fall to zero, which in essence gives a full-wave rectified sine, or am I wrong?

All the windings on the armature are connected, so as a brush contacts a commutator segment it sees only the peak of the sine wave, not the entire cycle. The other brush 90° away is always at the bottom of the cycle.The more bars, the smoother the output is.

ok thanks a lot everyone

And one more thing...

regarding american electric locomotives that used ignitrons, I searched the forum a bit, and so far I found a few examples, like
E44, E40, E2C, E3B, EL-C , MU trains MP54, and Washboard

I can't think of anything else right now

Are these the only units that used ignitrons in States?

Also, does anyone have anywhere a picture of the GE ignitrons used in these locomotives ?
Regarding the ones in Washboard MU's ( Westinghouse WL653B ), I assume these are equivalent to RCA 5555, and GE FG283B...
but I would really like to see how these GE GL6504 look like. I have a cross section diagram of it somewhere, but I'd like to see a nice photo (and some specs).

thanks