Electric motors on DMU's

[MatthewRead]

On many DMU's I've traveled on I sometimes here what sounds like an electric hum however it's only in a particular part of the train. Having said that I've never heard it on a Class 159 or on a Pacer unit could somebody explain why?

 

[61653 HTAFC]

Presumably it'll be electrical equipment managing the "hotel power" supply (lighting, PIS etc.)?

 

[ForTheLoveOf]

On many DMU's I've traveled on I sometimes here what sounds like an electric hum however it's only in a particular part of the train. Having said that I've never heard it on a Class 159 or on a Pacer unit could somebody explain why?

Certain DMUs are actually DEMUs - that is to say, the engine is merely used as a generator, and everything else is driven as it would be on an electric train, off the electric power provided. Thus you would have electric motors, which could be responsible for the noises you're hearing (although, on most diesel units, the engine is far louder than the electric motors).

 

[MatthewRead]

Certain DMUs are actually DEMUs - that is to say, the engine is merely used as a generator, and everything else is driven as it would be on an electric train, off the electric power provided. Thus you would have electric motors, which could be responsible for the noises you're hearing (although, on most diesel units, the engine is far louder than the electric motors).

How come you don't hear that sound on 159's or Pacer units though?

 

[twpsaesneg]

How come you don't hear that sound on 159's or Pacer units though?

Because Sprinters and Pacers have hydraulic transmission, therefore no traction motors to make the noise.

What class of DMU were you on when you heard the electric hum sound?

 

[anamyd]

MatthewRead if the class number begins with a 1, it has hydraulic or mechanical transmission, but if it begins with a 2 it has electric transmission

 

[randyrippley]

Defective fluorescent light tubes on trains often have a habit of humming - though nowhere near as bad as they used to be

 

[Geeves]

You can sometimes hear what sounds just like that old school 3rd rail electric hum on on DMUs, going over lines that have just had the rail grinding train over them.

 

[apinnard]

You'll hear the electric motors on a 222 quite easily. They're even easier to hear when one engine is isolated as is sometimes the case. Had this recently one a 222 at Bedford.

 

[TRAX]

Some tracks can make any train sound like a classic DC-motored EMU.

 

[MatthewRead]

Because Sprinters and Pacers have hydraulic transmission, therefore no traction motors to make the noise.

What class of DMU were you on when you heard the electric hum sound?[/QUO TE]
A lot here's a list:
Class 150, 153, 156, 158, 165, 166, 170, 171, 172 and 180 so quite a few classes there!

Because Sprinters and Pacers have hydraulic transmission, therefore no traction motors to make the noise.

What class of DMU were you on when you heard the electric hum sound?

I could give you a large list:
Class 150, 153, 156, 158, 165, 166, 170, 171, 172 and 180.

 

[apk55]

Ventilation and air conditioning could be using electric motors. Also engine (radiator) fans and possibly transmission cooling.

 

[big all]

just a though
"sounds like an electric hum"
could be unusual airflow causing resonance or just mechanical vibration ??

 

[MatthewRead]

Have a listen to this example, you quite clearly hear what sounds like an electric motor:

 

[rebmcr]

Could be an air compressor for the braking system. Could also be the air conditioning.

 

[AM9]

Have a listen to this example, you quite clearly hear what sounds like an electric motor:

Sounds like the transmission, bear in mind that there are gears connecting the cardan shafts to the driven axles, so the gear teeth will produce a whine at a frequency proportional to the axle speed and the sound level will vary according to the load on the drive. Listen to the clip at around 1:35 when the torque converter hands over to the fluid coupling. The engine power is lowered and then resumes at a lower level. The class 165s have relatively lightweight bodies and it is likely that a low level transmission noise like the final drive is not shielded that much from the vehicles' occupants.

 

[Andy25]

You will also have an auxiliary alternator driven off the diesel engine to generate electrical power for lights, hvac etc.

 

[37057]

It could be the sound of a transmission or final drive bearings. It can sometimes be more noticeable when power is reduced at speed when the 'driven' wheel becomes the 'driver' (of the driveline back as far as the transmission).

It's quite common on buses etc.

 

[MatthewRead]

It could be the sound of a transmission or final drive bearings. It can sometimes be more noticeable when power is reduced at speed when the 'driven' wheel becomes the 'driver' (of the driveline back as far as the transmission).

It's quite common on buses etc.

But how come you don't here that noise on Pacers have a listen to this

 

[swt_passenger]

But how come you don't here that noise on Pacers have a listen to this

Numerous different types of engine, gearbox, transmission, final drive, and auxiliary power alternators are fitted to the wide range of DMUs, all capable of sounding different.

Why not just accept that if the class number has a 1 at the front it doesn’t have traction motors...

 

[37057]

Numerous different types of engine, gearbox, transmission, final drive, and auxiliary power alternators are fitted to the wide range of DMUs, all capable of sounding different.

Why not just accept that if the class number has a 1 at the front it doesn’t have traction motors...

Plus it could be down to the condition of the bearings etc and whether they're due oil/greasing for example.

 

[swt_passenger]

Plus it could be down to the condition of the bearings etc and whether they're due oil/greasing for example.

Yes, and maybe the track condition, eg if it’s just been ground or milled...