Class 444/450 Motors

[SWRtrainfan]

You know how the 444s and 450s change sound at 20mph, having watched some videos from 2010, it seems that the speed at which this happens used to be roughly 5mph. Out of interest, why was it changed to 20mph?

 

[MCR247]

Hmm. I don’t have a source for this but I’m sure I recall reading something on here that it was the traction packages receiving an update. As I remember it the 350/2s had the new sound from new, with the older desiros getting changed a year or so later. Hopefully I’m not making this all up!

 

[Energy]

The sound is the IGBT drive, at low speeds the frequency is audible while at higher speed the frequency isn't heard by humans.

IIRC the 450s got their profile changed at some point to slow them down a little.

 

[Juniper Driver]

I don't remember it ever being changed from 5mph surely that would be when the friction brake is working?

 

[edwin_m]

Something to do with enabling regenerative braking?

 

[swt_passenger]

There’s been much discussion of this over the years. AIUI from earliest discussions the 450/444 will always sound slightly different to the 350s (mentioned in post #2) because the discrete frequencies used by the traction converters as they step up through the speed range are set up differently for the DC and AC areas of operation. That‘s to do with minimising mutual interference with trackside equipment.