Hornby / Triang R253 Dock Shunter Question

[Gerrard]

Hi All,

 

Can anyone tell me what the component in the picture is?

I know what the capacitor is for, but not what the component in the yellow sleeve does. Thanks.

 

Just noticed, I missed an 's' in suppression. Oop's!

 

 

Edited April 28, 2021 by Gerrard
Typo

[mossdp]

It is a choke also for supression.

[Halvarras]

Oddly enough I've also just bought one of these, also noticed this and wondered why both, as I always thought on Tri-ang models it was one or the other (bigger one = old, smaller one = new(er!)

[Gerrard]

4 hours ago, mossdp said:

It is a choke also for supression.

Thanks. Is a Choke different to a Capacitor? And does it need both or would one suffice?

 

Actually, looking at the service sheet it only shows the Yellow Choke, no capacitor. And reading elsewhere (here), I found some guidance suggesting that it's a good idea to remove old Choke's in favour of a modern capacitor. So if I do only need one or the other, I may remove the old one?

 

And from what Neil above says, it's not unusual for R.253 to have both. I wonder why?

 

Edited April 28, 2021 by Gerrard

[smokebox]

A choke (modern name is an inductor) is almost the exact opposite of a capacitor in electrical terms.

 

A capacitor blocks the flow of direct current but will allow alternating current to flow.

A choke (inductor) allows a steady direct current to flow but blocks alternating current.

Edited April 28, 2021 by smokebox

[Gerrard]

20 hours ago, smokebox said:

A choke (modern name is an inductor) is almost the exact opposite of a capacitor in electrical terms.

 

A capacitor blocks the flow of direct current but will allow alternating current to flow.

A choke (inductor) allows a steady direct current to flow but blocks alternating current.

 

Thanks Smokebox. So why does it need both?

 

[smokebox]

21 minutes ago, Gerrard said:

 

Thanks Smokebox. So why does it need both?

 

 

Not sure but having both is quite common.  Bachmann have both on most of their locos, using up to 3 capacitors on the motor and a choke in series with each motor feed wire.  I suppose they use whatever they need to use so that they pass the RF emissions requirements.

[stewartingram]

In simple terms - and no doubt someone will jump in with a more detailed explanation, but at this point I don't think it necessary - a series choke and parallel capacitor form a 'tuned circuit', which can filter out specific frequencies. My suspicion is that there was nothing too technical involved in that era that Triang when did it this way, even knowledge of electronics has improved over the years, especially away from the 'simple-users' such as Triang!

 

Stewart

[SteveyDee68]

And so I shall leap in and ask the "electronics for dummies" question...

 

Given modern DAB and FM signals, are either of the above electrickery thingies actually necessary? Would removing them cause issues with the performance of the motor?

 

Steve S

[smokebox]

Without them you would probably get quite a bit of sparking at the wheels and the commutator, as i did many years ago.

[Nearholmer]

Without the capacitor across the brushes, as  smoke box says, you will get worse sparking, and resultant damage, at the motor brushes.

 

The sparking is caused by tiny interruptions in contact as the brushes bounce around on the commutator, and the capacitor absorbs energy that would otherwise perpetuate each tiny arc for longer, then releases that energy once contact is restored.

 

Capacitors used this way are often called “suppressors”, because 

they suppress arcing, and in so doing suppress the electrical ‘noise’ generated by arcs, which is what causes interference with radio/TV receivers.

 

The inductors/coils/chokes (they go under all three names) are almost certainly provided to smooth the current flow, although I’m not certain why this is necessary - they didn’t arrive on the scene when PWM controllers became common did they?

 

This thread contains a mass of info about the dock Shunter motor unit, thanks in no small measure to RuffnutThorston. Well worth a read for any dock shunter owner.

 

Edited April 29, 2021 by Nearholmer

[AdamsRadial]

33 minutes ago, Nearholmer said:

The inductors/coils/chokes (they go under all three names) are almost certainly provided to smooth the current flow,

Possibly they filtered out the 50Hz/100Hz residual ripple from the full-wave rectified mains? As mentioned above inductances tend to block AC and pass DC.

[melmerby]

Capacitors and inductors together make a more efficient filter.

All to do with Radio Interference suppresion.

Edited April 29, 2021 by melmerby

[melmerby]

6 minutes ago, AdamsRadial said:

Possibly they filtered out the 50Hz/100Hz residual ripple from the full-wave rectified mains? As mentioned above inductances tend to block AC and pass DC.

The values are too low to have much effect on low frequencies such as 50/100Hz

[Nearholmer]

8 minutes ago, melmerby said:

Capacitors and inductors together make a more efficient filter.

All to do with Radio Interference suppresion.

Is the circuit acting as a filter, though? I’m not convinced it is, but if you explain, I might ‘get it’.

 

Does the coil slug out some particular frequency range generated at the motor, perhaps as a result of the commutation process?

[melmerby]

10 hours ago, Nearholmer said:

Is the circuit acting as a filter, though? I’m not convinced it is, but if you explain, I might ‘get it’.

 

Does the coil slug out some particular frequency range generated at the motor, perhaps as a result of the commutation process?

It's a low pass filter, the chokes will pass low frequencies but reduce high frequencies

DC (being the lowest frequency you can get!) will go straight through but high frequencies generated by commutation will be (mainly) blocked from passing back to the rest of the circuit (track, wiring etc.). These latter items could make a good aerial to radiate unwanted frequencies.

The values of capacitors and inductors used will have little or no effect on the low frequency ripple coming from the PSU.

 

[GoingUnderground]

From what I recall, and a very quick look at a couple of my Triang Locos and motor bogies, the choke was used on a lot of Triang models, including ones with the X.04 motor, not just the Dock Shunter and the other models that used the early 4 wheel motor bogie such as the Transcontinental Bo-Bos, the SR EMU and the DMU. The "6" wheel motor bogie as used on the EM2, Class 31 and 37 and its 4 wheel variant as used on the Hymek and Budd Railcar, tended not to have the choke as there was no "wiring" as such between the wheels and the brushes, just the phosphor bronze strips. These tended to have just a capacitor bridging the two strips.

 

But I'm sure Ruffnut Thorston will have the service sheets to hand to show if I'm right or wrong. 

[Nearholmer]

58 minutes ago, melmerby said:

the chokes will pass low frequencies but reduce high frequencies

I get that - I think The problem in my head is that I see the circuit as two things, doing two different jobs, a choke, and a suppressor, so I struggle to call it a filter.

[Il Grifone]

Both series inductors and shunt capacitors act as a filter to AC signals. Having both results in a steeper roll off. I won't go into a detailed description of the theory*, but basically the idea is to impede the flow of interference signals generated by the motor back down the supply line (inductor) or short them out (capacitor). The rails function very efficiently as an aerial!

Modern FM and digital transmissions are much more resistant to interference than AM, but could still suffer especially in fringe areas. (The chaotic situation in Italy on FM band II (thanks to a Constitutional Court ruling on free speech allowing unregulated transmissions) is a special case - co-channel interference is rampant and one requires a receiver with a excellent capture ratio.)

 

* AC network theory is complicated and I've forgotten most of it....

Edited April 30, 2021 by Il Grifone

[kevinlms]

4 hours ago, GoingUnderground said:

From what I recall, and a very quick look at a couple of my Triang Locos and motor bogies, the choke was used on a lot of Triang models, including ones with the X.04 motor, not just the Dock Shunter and the other models that used the early 4 wheel motor bogie such as the Transcontinental Bo-Bos, the SR EMU and the DMU. The "6" wheel motor bogie as used on the EM2, Class 31 and 37 and its 4 wheel variant as used on the Hymek and Budd Railcar, tended not to have the choke as there was no "wiring" as such between the wheels and the brushes, just the phosphor bronze strips. These tended to have just a capacitor bridging the two strips.

 

But I'm sure Ruffnut Thorston will have the service sheets to hand to show if I'm right or wrong. 

Service sheet 61 here.

 

http://www.hornbyguide.com/service_sheet_details.asp?sheetid=134

[melmerby]

4 hours ago, Il Grifone said:

 

* AC network theory is complicated and I've forgotten most of it....

I did it at college in the 1960s, used it occasionally at work and have also forgotten most of it now.

 

I did go through a period of building loudspeaker systems for my Hi Fi system and making suitable cross-over networks for them.

(I've still got the tweeters & super tweeters in a drawer/box/somewhere. The mid range units got dumped after one failed after many years use. The bass units are in a sub-woofer for my home cinema system along with a bought speaker system.)

 

 

[AdamsRadial]

18 hours ago, melmerby said:

The values are too low to have much effect on low frequencies such as 50/100Hz

I hadn't actually seen any values, but if you're right, they might be targetting the higher frequencies of 3 x Motor-RPM?

[Nearholmer]

For a three-pole motor, that would be my gut-reaction, because commutation, or possibly the mechanical action of the commutator bouncing the brushes. must be the major sources of noise.

[melmerby]

27 minutes ago, Nearholmer said:

For a three-pole motor, that would be my gut-reaction, because commutation, or possibly the mechanical action of the commutator bouncing the brushes. must be the major sources of noise.

The action of the making and breaking of contact and the inductance of the motor is a sure way to generate sparks and it's the sparks that cause radio interference.

(I don't think the number of poles on a motor is overly important.)

 

If the com is in good condition the brushes shouldn't bounce. e.g. on multipole motors the gap is usually filled with an insulator and the whole thing turned true on a lathe.

 

The very first experiments in wireless transmission involved a spark generator connected to an aerial and the receiver was another aerial a short distance away.

The "signal" was received on a simple galvanometer.

It proved the concept of radio transmission, however spark transmitters swamp many parts of the waveband. Hence the interfernce problem from devices that cause sparks.

[Nearholmer]

1 minute ago, melmerby said:

I don't think the number of poles on a motor is overly important.)

It is to the frequencies produced, although in such imperfect conditions, it may all amount to white noise anyway.