Fitting DCC to Locos with Capacitors

[Rowley]

I would like to fit DCC controllers to a number of Hornby locos that I purchased some 20 years ago.

I can follow and understand the standard circuit diagram on the Hornby website, however when looking at the instructions for the Flying Scotsman Tender it appears that the wiring differs if a capacitor is involved.

Is there a diagram for locos with capacitors available?

[poliss]

What's the R number of your loco? Is it tender driven?

With modern decoders the capacitor can be discarded.

[2e0dtoeric]

The function of the capacitors on the old loco's was to prevent the 'snow-storm' on your (parent's) tv when the loco was running, but as the old analogue tv's that were affected no longer exist, it is pretty academic whether the cap's are there or not, with dc - and with digital they are serving no purpose whatsoever, and can even 'confuse' the decoder if it reads the motor speed and load via back emf.

[poliss]

My old East German DC locos still caused plenty of snow on my screen and I was using a digital Freeview box 2e0. No capacitors fitted to them.

[walkingthedog]

I agree poliss.  I was trying to get an old loco going (think it was Trix) and it certainly affected our TV, not so much snow more a fuzzy line.

[Fishmanoz]

Poliss, if your box is fitted to an older non-digital TV, the hash can still be picked up, as you've found. 

 

WTD, a line, even if fuzzy is much more interesting than hash/snow.  It means that the interfering signal must be in synch with picture frequency, be it frame or line rate.  That's a conundrum given it is originating from DC plus hash, although the 50Hz from the AC can intrude all over the place and is the same as the frame rate.  Takes me back to valve jockeying days when a short developing between heater and cathode (heaters were fed from low volt AC) caused the screen to go half black and half white. 

[Fishmanoz]

Rowley, just to finish up on capacitors, the Hornby guides sometimes leave them in and, when the do, they remain across the motor connections where they were in the first place and the rest is just a standard DCC conversion with orange and grey going to those connections too.  Then sometimes they suppression component is an inductor which is in series with one motor connection. If this is left, it stays where it was in series with either the grey or orange to the motor.

 

But again, much better to avoid all potential trouble, remove all such components and do a standard conversion.

[walkingthedog]

I was a bit surprised by the interference fishy, it was/is a modern TV but I was quite close to it. 

[Teedoubleudee]

Remove them. Not required as decoders are fitted with them any way.

 

Please move to DCC section Admin.

 

[Blackbird]

Capacitors, or otherwise termed, suppressors, were/are fitted to DC motor powered model locos to reduce the RF (radio frequency) emmisions which interfered with TV transmissions. This is now not required as analouge TV has ceased. The problem with capacitiors arises with DCC control. One of the properties of a capacitor is to smooth the current flow through the circuit, and as DCC signals are transmitted via a high frequency alternating current, any capacitors will influence that signal. That is why Hornby have a designated DCC track connector, which is the same as a standard track connector but without the suppressor (capacitor). In practice, the effect of the motor or track suppy connector suppressor is minimal, but in theory, could cause problems.

[poliss]

Haven't had my old Piko loco running when my new digital telly on so far, so don't know if it affects the picture.

The old analogue steam wireless is still going strong with no plans to turn it off yet, so a DC loco without capacitors will certainly interfere with it.

[Rowley]

 

3.

thanks for the feedback,

However the feedback has confused me slightly by throwing in the googly of whether a capacitor is needed in the first place. None of my TVs are analogue, however my layout is in my attic and sections of the track will only be a couple of metres from the aerials.

 

All said and done, if I need to retain the capacitors and as I have more than one Loco to convert that is more than likely fitted with a capacitor am I right in thinking that I can take the Hornby’s  Tender Drive Flying Scotsman Decoder Installation as the guide as the prime example of how to rewire i.e. splicing in the red and black wires from the decoder to their respective pickup to motor cables and attaching the orange and grey wires to the capacitor?

[Fazy]

I remove the capaciter as a matter of course as I have been told and read that the capaciter can interfere with the running of a dcc chip fitted loco. Along with that dcc chips have capaciter built inthe board anyway.  After testing a loco with and without a capaciter fitted I observed better slow running with it removed. Plus being only 6 feet away from a TV never noticed any interference.  

[poliss]

As fazy said, modern decoders have TV suppression built in. There's no longer any need to keep them on DCC converted locos. If after conversion you do get intererence, then you can easily refit the capacitor, but try without them first.

They're only really necessary on DC locos these days.

[Fishmanoz]

Rowley, just checking back on this thread, you now have one or more posts from 7 different contributors who have thousands of posts on the forum and who are all telling you to remove all suppression components.  That includes capacitors across the motor contacts and inductors in series with one motor contact (these are sometimes fitted instead of or in conjunction with a capacitor).  Do not follow any guide that tells you to leave them there, remove them all.

[Metradio]

Problem of interference still exists with people who use an analogue Video Sender to relay Sky to other parts of the home..

[ColinB]

Interference is still an issue with digital TV, if I am running the trains the more obscure channels tend to lose data and you get a picture that freezes. As for the capacitor across the motor if it is a Hornby, remove it as they have a habit of going short circuit and taking out your DCC decoder.

[Fishmanoz]

If we are only talking DCC locos here on the DCC forum, then no external suppression components are needed, suppression is included in the decoder circuitry and the advice remains to remove any external components. 

DC is another matter. These require the suppression components to avoid interference to older TVs and radios. 

[ColinB]

Yes Fishmanoz you are right and yes if it is easy to remove it then do it, but if if means hacking at the loco wiring then don't, not that the capacitor is needed it is just that you are risking damaging something else. As I say if it is on a Hornby loco try and remove, they are lots of posts saying where the capacitors give issue ( I think they must have purchased a duff batch), but it is such a small value, all it will do is slightly round the PWM edges that get fed to the motor.

[Rog RJ]

........ all it will do is slightly round the PWM edges that get fed to the motor.

 

 

It also affects the back emf feedback which can cause problems.  Some makes of decoder are more sensitive than others.  Hornby and Lenz decoders don't seem to be affected much though.

[The Duke 71000]

Capacitors and Suppressors are two totally different pieces of electrical equipment. 

 

 

Capacitors are used to temporarily store electricity. In a model locomotive adding a capacitor reduces jerking when the locomotive negotiates a piece of track where the electrical supply is interfered with, such as in "Dead Frog" points, dirty patches of rail etc. The same applies for carriages with internal lighting, a capacitor will effectively prevent the lights flickering, by supplying the missing power for up to a few seconds, or until the capacitor has fully discharged .

 

A suppressor is a legally required addition, normally fitted across the motor contacts. Because DC motors set up static fields that can interfere with a number of other electrical items including TV's, Radios, and Telephones. It's still a legal requirement or Hornby wouldn't be still fitting these items !  

 

Adding Capacitors to locomotives and carriages can however cause other problems. If the supply in the rails is intermittently interfered with, the Capacitors try to fill the shortfall by discharging. But they, the Capacitors, are not intelligent. So they do NOT apportion the difference necessary, they simply start discharging. This can result in power surges. If you have a train load of coaches with lighting the combined effect of more than one Capacitor discharging simultaneously can trip out the controller. Because you can get a back feed to the controller, as the Capacitors suddenly add to that being provided by the controller. These sudden surges can also damage other sensitive electronics on digital chips, or elsewhere in your system, causing various types of chaos !!! 

 

Modellers using both Analogue & DCC are experiencing problems with Capacitor fitted models whether locos or other items of rolling stock. There are three solutions. Either you ensure you have no dead or intermittent bits of track, which means "Live Frog" points, and more thorough track and wheel cleaning. Or you bin the Capacitors. Or like me you do both !!!

 

 

The Duke 71000