EMD Fan

[QuietGuy]

The radiator cooling fans have AC motors powered by the Companion Alternator. I think that the frequency of the AC power from the CA depends on engine speed, throttle 8 is 900 rpm, 7 is 750, etc. so there will be a variation of the sound based on engine speed, plus the fan motors are two speed. The fan operation is controlled by the engine computer which senses the water temperature. More fans and speeds are cycled on and off to maintain temperature of the cooling water, based on a temperature sensor in the water line.

Just remember, the locomotive engine speed is not contiously variable like automobile engines, it has only five or speeds from idle to throttle 8.

I still say you don't really hear the turbine whine, just the noise of the entire engine as it grinds out more power.

[mbta1051dan]

Here's a question for Mike from trainiax. During this recording,

http://trainiax.net/recordings/crec-slr ... 05-805.wav

it sounds like the dynamic brake fan from the 3206 is spinning much higher than the others (est. between 2100 and 2600 RPM), and fluctuating. Is there a reason for this? Is it a dirty DB inlet air filter?

Also, why do the road slugs, the 800 series on the SLR, look like they have DB fans?

-Dan

[conrail_engineer]

The dynamic brake fan speed does fluctuate on some models; particularly older EMDs with DBs modified for heavier braking at slower speeds. It depends on the model and on how it's set up...some have a fan that kicks on and stays screaming; some have a fan that varies with speed or with need.

Can't speak for the road slugs you refer to; but yes, many/most slugs do have their own DB circuitry. It's not hard to conceive; it's just a reversing of the circuitry on the traction motors and the dynamic brake equipment mounted.

The excitation the circuit needs, it gets the same way it gets power to the traction motors - through the high-voltage cables to the mother unit.

[trainiac]

Here's a question for Mike from trainiax. During this recording,

http://trainiax.net/recordings/crec-slr ... 05-805.wav

it sounds like the dynamic brake fan from the 3206 is spinning much higher than the others (est. between 2100 and 2600 RPM), and fluctuating. Is there a reason for this? Is it a dirty DB inlet air filter?

I wondered that too, and I asked the same question here 2 years ago when I heard the sound myself. Here's the excellent response I got from ExEMDLOCOTester

The Control Cabinet of the straight 40's is a box full of wire, wire wound resistors with taps, & relays. After listening to the sound byte again & again, knowing its not a -2, what I am hearing is the DB cooling motor overvoltage relay picking up and dropping out. The relay circuit is designed to prevent a flashover of the motor. Why that is happening is the source of the problem and is a long list of possibilities....

In other words, it's kind of like the motor is constantly being brought back from overspeeding. The fan only did that in full dynamic braking--not at lower settings. I might also add that the 3200-series initially lacked dynamic brakes (they're former Rock Island units) and the system retro-fitted is visually the same as that of a GP35.

Also, why do the road slugs, the 800 series on the SLR, look like they have DB fans?

...Because they do! They are former GP38's and GP40's, and except for the diesel engine and accessories, they have all the capabilities of the mother units--cabs fit for leading, fuel tanks, dynamic brakes. Since dynamic brakes work off the traction motors and the slugs are linked to the mother units, the removal of the diesel engine did not affect the use of the dynamic brakes. Also, fuel from the tanks on the slugs is transferred back to the mother units, effectively doubling fuel capacity.