Train motor sound – What UK enthusiasts get wrong while Japanese enthusiasts build model VF drives

Videos featured in this video…..
Japanese enthusiasts homemade VF drive…

Homemade VF drive powers miniature railway…..

The best explanation of VF drive with oscilloscope…..

Youtuber gets facts wrong about VF drives…..

Right then just a quick video I’m just to talk about something that’s turned into a real bug bear of mine this subject matter so many people get it wrong to the point where it’s excruciating and hard to just watch and listen to people giving incorrect explanations I’m talking about VF drives

On trains so so many people don’t have a clue how it works yet they often talk about it like they understand it and I find it really excruciating one of the big things that train Enthusiast always to go on about is igbt versus GTO well

At the same time they have no idea what they’re talking about the subject cuz igbt GTO or any other forista or transistor technology used in VF drives that is not an accurate explanation of how the sound is made because well the different Technologies of the F drive

And the older the technology the more limited is in its switching capability which overall ends up with the sounds being created how they are created just saying the technology of the VF drive is not an adequate explanation the reason why trains and in particular the 1996

Train makes the sound it does is due to artificial sine wave generation this is because the motor is an AC nonsynchronous motor this motor has to have a frequency put into the motor close to the motor’s current rotating speed so if the motor’s rotating at 10

HZ and you want the motor to speed up you need to put in something like 13 14 Hertz a speed faster than its current speed to speed it up if you were to just shove in 50 HZ lights connected to the mains that’ not be efficient because the

Rotating magnetic field in the motor would be 50 HZ the motor is going 10 HZ that’s too big of a difference so you have to vary the frequency being put into the motor so the output frequency of the F Drive is close to the rotating frequency of the motor but what causes

The sound is not the output frequency it is the switching frequency it is the behindth scenes methods being used to create that output frequency this is to do with artificial sine wave generation so the output frequency is a sine wave you are making a sine wave by switching

A DC power supply off and on it is called a switching frequency because foras whatever technology you’re using rgbt or GTO is all the same thing the principle is exactly the same it cannot be half on and half off and that is the most important part of why it makes that

Sound it either has to be fully 100% on or fully off nowhere in between you’re having to pulse you having to switch a power supply on and off to make that artificial sine wave you can’t just do what a radio does cuz a radio amplifier can put in different percentages of

Power like amplifier signal which is at 50% you can’t do that with the F drives it’s either 0% or 100% nowhere in between so with the artificial sign wave generation there’s actually two main methods you can do there’s actually a few more ref than that but for Simplicity there’s two main methods the

Method which is ideally used in terms of how these things are meant to work is pul P width modulation well technically speaking all the methods are pulse with modulation but this method is going by the principle of it doing exactly what pulse modulation is supposed to do what

It says on the tin pulse width gets modulated so the switching FY stays the same while the width of each pulse changes and that’s how you change your percentage of what’s been put in the motor and that can then be used to create your artificial sign wave on this

Method there not much to be heard cuz the sound stays exactly the same all the time so if you got 1,000 HZ switching frequency no matter if the output frequency is 10 HZ or 20 HZ the sound of it doesn’t change it will just be a constant 1,000 HZ

Hum like how it stays constant even as the outp freeny changes but with older Technologies which by the way is not exclusive to GTO or LGBT in fact the fist itself is not the thing of significance other than the fact that older Foresters will have less

Tolerances but let’s say on a really the old train let’s say your maximum switch incy is just 400 htz so you’re having to make a sine wave with just 400 pulses per second but what if that sign wave needs to have a 50 HZ output so the

Output frequency is 50 HZ and the switching is 400 HZ meaning you get eight pulses per cycle or just four pulses per half cycle which is an even number and that is a problem cuz at this point the timings no longer work especially when you need your largest

Middle pulse at the top of your wave has to be the largest pulse four pulses per wave that’s an even number your biggest pulse won’t be in the Middle where it’s needed the timing doesn’t work so when your output frequency is getting close to your switching frequency which will

Happen a lot sooner and more noticeable on old trains than it does on new trains but the same thing happens on all trains it’s just more noticeable on the old trains another method has to Beed used and that method is timed pulsing so rather than the pulsing being at a set

Switchy instead it’s synchronized to the wave so as the output frequency gets faster the switching frequency also gets faster so the sound increases like that but due to the tolerances of it pulses have to be removed as it gets quicker to stop the switching frequency getting too fast for

The fista so pulses have to be removed to keep the switching frequency low within a set range so this means it could change from let’s say seven pulses per output cycle to five pulses per output cycle when that change happens it sounds [Applause] distinctive and that is what makes the sound it is pulses being taken away from the synchronized time pulses per output cycle now with that said in Japan there’s VF Drive enthusiasts who makes scale models of VF drives I think that’s really impressive cuz they actually make

These VF drives that they build they program them to simulate the sound on trains so they have these little VF Drive Scale Models re recreating the sound of their favorite trains which I think really great and make sure you check out their videos cuz they’ve got some really good [Applause] stuff [Applause] [Applause] a [Applause] And it even gets better than that cuz these Japanese BF drive enthusiast are actually building their own model Sion trains with homemade F drives this has to be one of the best homemade projects I’ve ever seen take a look at This Oh so then the next video I’m going to show is one of the best demonstrations I know of on YouTube of how VF drives work this professor shows it on an oscilloscope and it shows it really well so make sure you check out the full video here’s a

Little extract from this video which I’m showing under fair use and you may hear as we turn up the speed that it appears to be changing gear [Applause] and then we’re in top speed and off we go we can go to a very nice high speed here let’s listen to that gear changing

As we slow [Applause] down if we go up in speed now go back up we can start to see something else interesting happening so there we just changed another [Applause] gear notice that the chopping still appears to be about the same sort of uh frequency which is right the current

Waveform now is much faster and in fact does appear to have more Ripple in it well it probably hasn’t got a lot more Ripple in it but the the uh induction motor has changed its characteristics a little bit as we speed up and we are seeing a bit more Ripple in the current

But notice that this frequency is much higher than it was now something else interesting is happening now we can see something very interesting Happening Here in that we’re losing a lot of pulses particularly in the middle of the waveform there and in fact we see appear to have very few

Pulses there and in fact the Ripple frequency has gone up a lot so we’ve changed the gear again but this time we’re also dropping pulses we’ve decided we don’t actually need to have uh so much pulses in there we want more volts out of the inverter at the highest speed for the motor

Just and as we increase the speed there we go go we’ve dropped nearly all the pulses are dropped now there’s the pulses Dropping pulses coming back in a definite gear change much more noisy now those pulses have come back lots more pulses coming [Applause] in there we go very familiar sound to those people who take the train between Cambridge and London So then I’ve just shown you some really good examples of great videos about VF drives from Japanese VF Drive enthusiasts to the professor showing it on his oscilloscope but with that said there are still train enthusiasts giving out incorrect information about VF drives this has gone on for many many

Years for example the Wikipedia article on the 1996 underground train for years is it showed incorrect information on the Wikipedia article I really don’t know why this particular topic has become such a topic of misinformation a very well-known YouTuber has uploaded a video about the 1996 underground train

About what it makes the sound it does and he got his information wrong I don’t want to sound too critical cuz this YouTuber has also made some really good YouTube videos about other stuff also I don’t want to be criticizing anyone as an individual so that’s not my aim here

Take a look at this clip from his video and look at the thing he gets wrong about the F drives the supply through the inverter is regulated with gate turnoff thyers the current and the motors are what makes the noise as the current increases and the motors respond so the

Whining noise gets higher he claims the sound speeds up as the current increases that is not true not true at all if the current increases that will make the motor louder but it doesn’t affect the sound the sound is caused by the artificial sign wave generation the

Issue here is he’s got 100 96,000 subscribers and now there people commenting in the comment section saying oh now I know why the train makes that sound but the information is wrong which just was just further adds to the misinformation anyway that’s all I want to say I’m not trying to criticize

Anyone as individual people I’m more making a overall criticism I think that’s everything I want to say so that’s the end of the video not