# Unsupressed diesel



## double acting (Sep 14, 2008)

I noticed whenever a diesel train ran passes, about 400 yards from the digital radio, the signal would vanish. Once it was past back came the signal. This only happens with diesels, electric trains don't cause a problem,

I contacted the BBC and they said, I quote, "an unsupressed diesel engine was the cause" 

Problem is diesels have no electrical ignition, any thoughts on the matter?

Should this be a Radio Room discussion?


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## TommyRob (Nov 14, 2010)

I thought the diesel engine drove electric motors.


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## Dartskipper (Jan 16, 2015)

I have noticed lately I get some interference on my radio in my car when passing some HGV's on the motorway. On AM wavelength it comes over as a whistle that gets louder as I pass the vehicle, and then fades away when I am clear. I put it down to interference from an unsupressed alternator.

Roy.


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## Mad Landsman (Dec 1, 2005)

As far as I am aware 'Diesel' locomotives in the UK come in three main types of transmission:

Diesel drive direct to wheels (via auto box or similar) - Normally found on small shunting engines.

Diesel drive via hydraulic pumps and motors or other fluid couplings - On diesel multiple units etc. 

Diesel - electric - Two main types:
Diesel engine drives dynamo which drives DC motors, used where there may be an alternative 750volt DC third rail and some locomotives can run on both. 
Diesel engine drives alternator which drives AC motors. Similarly often found where overhead current is available, apparently because it makes servicing simpler?? 

Suggest that the the alternator or motor was faulty and it is that which causes the interference, not the diesel. - It may even be an offence under telecommunications legislation.


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## david freeman (Jan 26, 2006)

interesting? not up on electrical matters: How ever something in the back of my mind, leads me to the problem of generating power electrically? Modern generation is 'AC' and then 'chopped into bastardised 'DC'- by computer lead conversion- I am not sure whether the generation is with a standard AC Voltage with variable current or a variable voltage with constant current by the diesel driven generator, and then '' chopped'' into a dc output on the recipient slave motor, for the required power out put.
As stated it has nothing to do with diesel engine thermodynamic cycle.


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## Mad Landsman (Dec 1, 2005)

david freeman said:


> interesting? not up on electrical matters: How ever something in the back of my mind, leads me to the problem of generating power electrically? Modern generation is 'AC' and then 'chopped into bastardised 'DC'- by computer lead conversion- I am not sure whether the generation is with a standard AC Voltage with variable current or a variable voltage with constant current by the diesel driven generator, and then '' chopped'' into a dc output on the recipient slave motor, for the required power out put.
> As stated it has nothing to do with diesel engine thermodynamic cycle.


Take what I said as being just off the top of my head, from observations and conversations while in loco workshops etc. - Now you mention it the term 'chopped' does sound familiar...


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## Hamish Mackintosh (Jan 5, 2006)

Thought the AC output on an alernator was DC'd thru the diodes


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## david freeman (Jan 26, 2006)

Hamish Mackintosh said:


> Thought the AC output on an alernator was DC'd thru the diodes


Oh dear history here, ac diodes, and dc commutators and ac slip rings: induction motors etc. I am but an old Fart, and maybe miss informed??


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## Mad Landsman (Dec 1, 2005)

Are there any real railway buffs on here? 
Obviously I am way out of depth, but doing my best.
The permutations of generation/traction are limited only by the technology available when the locomotive was designed.
However, it remains that the 'electricery' is the problem - and may even be illegal!


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## Dartskipper (Jan 16, 2015)

I think that may be one reason that BR Western Region opted for Diesel Hydraulic power for their Warship and Western classes. The Maybachs built under licence weren't terribly reliable, but they made a wonderful sound.


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## howardws (Aug 15, 2009)

I sometimes drive this on the Kent & East Sussex Railway. Allen diesel, BTH electrics, 4 x 25 hp motors. Built 1931, I doubt that it is suppressed!


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## D1566 (Sep 7, 2009)

howardws said:


> I sometimes drive this on the Kent & East Sussex Railway. Allen diesel, BTH electrics, 4 x 25 hp motors. Built 1931, I doubt that it is suppressed!


Like it  My forum I/d is the number of the beast (!) that I used to drive at Llangollen. Also all unsuppressed DC and never knowingly a cause of TV or radio interference. I wonder if the OPs problem may have been caused by a particular train having issues, either with its variable voltage drives, or even with its comms equipment?


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## Long gone (Jun 20, 2009)

Dartskipper said:


> I think that may be one reason that BR Western Region opted for Diesel Hydraulic power for their Warship and Western classes. The Maybachs built under licence weren't terribly reliable, but they made a wonderful sound.


No, that was the old GWR people in charge being their usual 'different' selves


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## YM-Mundrabilla (Mar 29, 2008)

Here in Oz most 'modern' diesel-electric locos produce AC from the diesel driven alternator which may be converted for use in DC traction motors in many locos but some of the more recent locos have AC traction motors as well. 

It is a source of considerable academic argument whether AC or DC traction motors are better for specific applications.

AC traction motors have been known to upset some electronic signalling systems.

In our particular location (all of 7 miles from the GPO in Melbourne) digital radio is Rat S**t and a waste of money for some reason known only to the boffins!


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## Varley (Oct 1, 2006)

Through one of those often repeated stories in TSD of a sunny afternoon I understand that the issue of the railway train motor is simple. The wear and tear on the permanent way is much, and adversely, affected by the 'unsprung axle weight' (apparently we are allowed axle in locomotive engineering).

It is difficult to provide the final transfer of motive power to the wheels without that final transducer being on the bogie and so on the wrong side of the suspension - 'unsprung'.

Technology changes then influence the choice of lightest motor available as train design also advances (usually electric, I had not heard of an hydraulic option until this thread).

Once the choice of motor is made we then have the choice of providing it's supply in controllable form.

It is fashionable to produce electrickery with one waveform and voltage and then to bugger it around with electronics. This comes from the grid based problem of servicing the end user without affecting the other users. The earliest electronics had only on off devices (mercury arc, then thyristors) to effect the necessary embuggering to suit the end user.

On/off devices (to control, necessarily doing so other than at zero volts of an AC grid supply) produce harmonics (there being no wave other than a sine wave, all apparent breeches being the sum of many different sine waves) easily producing radio frequency interference and unnecessary heating in many components.

Modern power electronics has proportional devices, MOSFETS etc. which can do the job with much less in the way of harmonics.

I see no reason why a diesel road vehicle should have power electronics. The alternator (if Googling is to be gone by) may well have switching electronics but only on the excitation much like a ship's alternator. Most are shown with slip rings'though and simple sparking of worn rings will make RFI just as well as Mr. Marconi managed. With emission control and multivalve configurations there must be an 'engine management computer'. All computers produce RFI locally (its a non-existent square wave thing again).

What I have found difficult to swallow is that at sea (an Island Network it might be called ashore) the economics would seem to favour modification of the supply when the principal use of that supply is to bugger it about for something that needs to be controlled. This can be done very much more simply with low power electronics acting on the excitation (like it does now only to provide a variable instead of constant output) with any smaller auxiliary load system being catered for with electronic conversion (lower power the smaller the harmonic content) or even separate generation.

For instance a relatively late build vessel with DC propulsion motors (which I don't question here) was provided by dedicated but conventional AC generators driving only the propulsion motors via a thyristor converter much like a steel furnace might require when supplied from a national network. Separate auxiliary generators were provided for the domestic and other normal supplies (and if I remember the DC motor field supply).

A significant additional capital block (which had other implications as well). A more imaginative solution would have been to have the alternator excitation controlled.

The model applied to trains being that the ones carrying their own power plant as with diesel electric might benefit from a similar 'Island' solution. Those running from overhead or third rail being tied to developments of the grid customer solutions. 

Hope this isn't too far off topic.


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## david freeman (Jan 26, 2006)

it aint half intriguing? great read.


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## sternchallis (Nov 15, 2015)

Yes it was, if I could have only understood it.
Chiefs Electro did not go that far, but then there wasn't diesel electric cruise ships in those days.
We always said that if it has got a wire going to it , call the lecky.


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## Varley (Oct 1, 2006)

Oh! but it did. It is only that you didn't practice that you think it a dark art. In terms of learning (should it have been learned) a Chief's ticket beats my C&Gs any day you like.

(The same thing, although tried, did not work in reverse. My first C/E as engine room staff, John Benn, was not beyond connecting a wire to some piece of sick plumbing when he wanted me to help out).


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## sternchallis (Nov 15, 2015)

I remember sitting in a lecture on BH curves when the lecturer said to a gentleman from Nigerian National Line, 'Dat's White Man's magic'!
Uo, Ur and all that jazz.
Think I know enough to separate BH from BS.


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## Varley (Oct 1, 2006)

I can only think, immediately, of magnetic hysteresis scheming against jolly jack.

The older echo sounder transducers were magneto-strictive but, rather like an earphone, required a magnetic bias otherwise it would 'ring' at twice the frequency of the applied signal.

To confirm that the transducer was magnetised (done when performance was poor), on a DC ship, the transducer was connected to the mains supply through a fuse. When switched on the fuse would blow. There being no way of knowing at the outset what was the polarity of any residual biasing magnetism one shock might have only succeeded in de-magnetising the item so the operation was always tried twice using the same polarity of voltage.

I was tagging along with the technicians of East Ham during one long leave (I had done a long turn about to allow Frank Murphy, my Opo on Stonehaven, time to marry and honeymoon). The task was just as outlined above and the staff man performed the first part of the trick. Unfortunately the second attempt resulted in no blowing of the fuse the connection between feeder and transducer having melted instead. Fortunately I was not insured to go tank diving so the staffer had to return and remake the connections in the transducer cofferdam.


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## R.kearsley (May 14, 2012)

have same problem as per #3 but think it may come from the hgv/logging trucks cb radio's,have also found that some mobilhomes cause a whine on my radio which may be caused by the inverter they have on there solar panel battery charging system


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## RayL (Apr 16, 2008)

In a TV do***entary I watched a few weeks ago on the topic of diesel pollution, the researcher was surprised to discover that the pollution measured in a train carriage was far, far worse than that in a busy city street (I'm guessing that it enters the carriage through the roof vents when the train is passing through tunnels and bridges).

I was aboard a Grand Central/Virgin train the other day and particularly noticed the fumes in the vestibule during the approach to the terminus. This, I'm sure, was due to the old fashioned 'pull-down' window in the door, many of which won't stay fully up during the journey. Given the power of a diesel locomotive engine, I'm not overly surprised that its dense output of particulates and nitrogen dioxide has the effects described in the OP.


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## david freeman (Jan 26, 2006)

still intriguing, hysteresis: what a come back, I must get those books out again


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## Varley (Oct 1, 2006)

David, if there were anything difficult about it how could I have made a living? The books would read easier if read again - unlike hysteresis!


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## sternchallis (Nov 15, 2015)

I remember when taking ONC electro of doing an experiment with a coil and measuring Flux Density against Magnmotive force as the voltage was increased then decreased. After plotting the figures you ended up with something like the sausage we got when taking cards.
The bit between the curves (ip) was the hysteresis loss, I suppose copper and iron losses. Probably akin to latent heat.

How am I doing Varley for a plumber? 
With that knowledge and a bus pass I can get into town for nothing.

All very interesting but when is a chief engineer or a superintendant going need that knowledge.
Any former supers out there want to comment.


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## Varley (Oct 1, 2006)

Very well. Although that is the first link with latent heat that I have heard and copper losses have nothing to do here either.

(I don't know about the indicator cards. Pa visited a steam up and downer in Gibraltar during the war to find the Chief had cut brass templates to make up his office returns!)

Perhaps hysteresis should only trouble the battery stacking super with magnetostriction troubles (or perhaps worrying about removing the rotor of certain tachogenerators into a cylindrical keeper lest its permanent magnet lose strength) but the superintendent of plumbing would do well to understand the most serious of the iron losses (or that least easily countered in construction) - Eddy current.

We experts normally allow the pig iron polishers to do mundane things like motor rewinding without our oversight. In this we can err.

Should a burnout also manage to weld together one or more of the laminations sadly even well known repairers may rewind without checking and this can result in rapid failure of the new insulation system.

The Eddy current losses in an AC stator or (also DC armatures? - here my expertise fails) with short circuited laminations can dramatically increase this 'iron' loss. The heat generated being local to the damage, a hot spot can be rebuilt-in, not obvious in the cooling outflow but easily capable of cooking the insulation close-by. Mostly this is insidious, more premature ageing so failure is some months after repair (and of course any guarantee) however in my last year in the job (and one where a core pack integrity check had been specified) a bow thruster motor overheated so badly that it was detected during a post delivery check - by smoke signal (the motor had an electronic soft starter and so 'obviously' this was blamed first!)

If a rotating electrical machine is worth rewinding then it is always also worth making magnetic integrity check of the laminated parts. Do not use the term magnetic flux test, as the battery stacker operating alone might, as this can be confused with a test for detecting cracks in improperly polished pig-iron.

And do so every time. Even if the burn is obviously in the overhang (it is most likely here when NOT for this cause I am told, Hr. Muller of Siemens, fabulous workshop) you are unlikely to know if it has been rewound before.

(And now I find myself casting Pearls without getting paid for it, woe, woe etc. But I do like the sound of my own keyboard).


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