DCC and resistors

[Fettster42]

As a ng modeller basic Hornby chassis are the common source. They have a bunch of resistors on them, one across the connections to the motor and one in line with each feed from the pickups. If fitting a dcc chip should these be removed or retained. The Hornby site says keep them, but I'm sure I read somewhere they are unnecessary when fitting decoders.

 

Advice please?

 

Thanks

 

Leigh

[SGJ]

My friend has a few locos some have it on, and some removed for my sins I cant tell if the locos are any different when removed !

SGJ

[Crosland]

The components across the motor are suppression capacitors and look like a short circuit to high frequency noise from the arcing at the motor brushes. Opinions differ as to whether they should always be removed. I take a pragmatic approach and remove them if easy to do so, otherwise I will see how things go. Some motor/capacitor/decoder combinations work well with them left in place, but it's virtually impossible to predict in advance. If the loco doesn't run well after you have made all the usual adjustments to the decoder CVs, then remove the capacitors.

 

The components in line with the track feed are inductors and look like a very high resistance to the high frequency noise from the motor, preventing it getting out onto the tracks that will act like an antenna and broadcsat it far and wide. Since DCC is an AC signal it will also be affected by these inductors to some extent and they should always be removed, and replaced with wire links, or otherwise isolated.

 

Andrew

[mezzoman253]

A DCC chip SHOULD stop RF interference getting out to the ether, but in a small number of cases it may not.

 

If the loco' performs ok with the components in situ then no need to remove them. If it doesn't, and after trying different CV settings, you are left with the choice of removing them.

 

This will probably fix the situation, but could lead to RFI getting out. This is unlikely but possible. You should be aware of this small eventuality.

 

Rob

[JJGraphics]

As a ng modeller basic Hornby chassis are the common source. They have a bunch of resistors on them, one across the connections to the motor and one in line with each feed from the pickups. If fitting a dcc chip should these be removed or retained. The Hornby site says keep them, but I'm sure I read somewhere they are unnecessary when fitting decoders.

 

 

 

Get 'em off!!

 

They often cause unexpected problems, especially with jerky running, as i have experienced in the past.

 

I now remove all the electronic junk from a new loco before installing the decoder and have not subsequently had any problems.

 

John

[mezzoman253]

That's rather a cavalier approach, if I may say so.

 

RFI is becoming a real problem to broadcast and amateur services with the proliferation of PLT's, SMPSU's, Plasma TV's, PC's, etc, etc.

 

We don't need unnecessary extra RFI if it can be avoided.

 

As I said, it's a small eventuality, but a real one. 

 

Rob

[JJGraphics]

My neighbour is a very experienced commercial television engineer and amateur radio enthusiast. We have discussed the issue of interference at great length after the subject was raised on various model railway forums a while ago.

 

He has carried out a number of tests and so far has not been able detect any measurable RF emissions from my chipped locos all of which have the factory-installed electronic items completely removed and have Loksound V4s fitted. I cannot offer any comment or information about other makes of decoder as I have no experience of them. 

 

This is completely in contrast to a couple of un-chpped Hornby locos tested straight out of the box and one slightly older Bachmann machine all tested on DC. All of these locos had measurable, but very slight, RF emissions. When the factory-installed electronics were removed and Loksound V4s installed, the emissions disappeared completely.

 

My neighbour says that in his experience, most domestic appliances emit measurable RF and in some cases quite considerable amounts. I have no great understanding of the issues of RF and am guided by what my expert neighbour has shown me.

 

I would be very interested to hear other views or observations.

 

John

[mezzoman253]

I'm also a radio amateur, hence my concern. It's seems MOST chips have adequate filtering to mitigate removing the original RFI components.

 

Yes all consumer electrical and electronic items emit RFI to a greater or lesser degree, and standards are in place to make sure that level is low enough not to cause interference to other services.

 

Unfortunately there are a lot of cheap items available that do not meet these standards and are, naturally, due to price, snapped up and being used.  There are also products that apparently met the standard on paper but don't meet it in practice, PLT is one case in point and LED lighting.

 

But that's going way off topic, so I'll stop there.

 

Regards,

 

Rob 

[Gordon H]

I'm also a radio amateur, hence my concern. It's seems MOST chips have adequate filtering to mitigate removing the original RFI components.

 

 

If only decoder manufacturers would take the trouble to include some kind of statement in their datasheets regarding the effectiveness of any internal filtering all this doubt and uncertainty would go away.

[mezzoman253]

That would be too easy and legally bind them to what they said, so if they don't have to do it they won't. They should comply with the EMC legislation in place now.

 

Rob

[Crosland]

I have yet to see a proven case of interference caused by a model railway installation, rather than a fault of the receiving equipment. Every case i have seen, or heard, of TV interference could be traced to faults in the aerial or downlead, often installed decades ago.

 

Andrew

[mezzoman253]

True TV coax will degrade over time and lead to loss of signal and hence the wanted signal to interference ratio will go down leading to.....interference.

 

Just making people aware of what may happen if they go down the road of snipping the components, however unlikely the chance of RFI.

 

At least you could see if RFI was being generated, rather than assuming it's not.

 

Rob 

[shibushe]

When ever I have a problem with poor & erratic  running, its usually the capacitors that's causing it, so out they go. Problem gone.

[mezzoman253]

When ever I have a problem with poor & erratic  running, its usually the capacitors that's causing it, so out they go. Problem gone.

I give up!

[Crosland]

I give up!

What do you suggest when the factory fitted suppression components are simply incompatible with the decoder?

 

Andrew

[hornbyandbf3fan]

I removed them when hard wiring a loco and it seems to have had no difference (was Bachmann though)

[mezzoman253]

What do you suggest when the factory fitted suppression components are simply incompatible with the decoder?

 

Andrew

There are decoders out there that don't exhibit these problems, and, there are others that do the job of the components removed.

 

What I'm trying to avoid is the notion that you can happily chop off the components and everything is rosy. In most cases it will be, but in some it may not and there's a consequence to that. 

 

Rob 

[S&D Man]

I agree with Rob, and others, not just in sentiment but technically.  I served an apprenticeship as an electrician, was also an electronics technician, radio and television technician.  I'm also a radio amateur, and former freelance computer engineer.  Radio frequency interference was a real problem many years ago with locos like Triang, Hornby and others (I won't go into other sources like fridges and vacuum cleaners).  The motors even when regularly kept clean (and most weren't) produced a lot of sparking which showed up on tv screens as spots or noise on radios, if close enough.  Motors today are much better designed but where the carbon brushes meet the commutator they still produce a visible sizzle.  This unfortunately is inevitable and that's why it has to be suppressed by placing across the brushes a suppression circuit consisting of usually a capacitor and choke or inductor.  The values of these components are selected so that they form a filter at interfering frequencies.  I can't see any reason to remove these.  All my locos controlled by DCC run unimpaired with them still in place.

 

Alan

[SGJ]

I agree with Rob, and others, not just in sentiment but technically.  I served an apprenticeship as an electrician, was also an electronics technician, radio and television technician.  I'm also a radio amateur, and former freelance computer engineer.  Radio frequency interference was a real problem many years ago with locos like Triang, Hornby and others (I won't go into other sources like fridges and vacuum cleaners).  The motors even when regularly kept clean (and most weren't) produced a lot of sparking which showed up on tv screens as spots or noise on radios, if close enough.  Motors today are much better designed but where the carbon brushes meet the commutator they still produce a visible sizzle.  This unfortunately is inevitable and that's why it has to be suppressed by placing across the brushes a suppression circuit consisting of usually a capacitor and choke or inductor.  The values of these components are selected so that they form a filter at interfering frequencies.  I can't see any reason to remove these.  All my locos controlled by DCC run unimpaired with them still in place.

 

Alan

 

like this bit "you still get a visible sizzle" now I want bacon butties 

In the olden  days it affected analogue Televisions, but does it affect the modern world Digital TVs ?

SGJ

[Sunnysa]

Good grief, this subject has been going round in more circles than a three ring circus and the Olympic rings put together for yrs.  It is never ending.

 

After 19yrs op DCC I have proved beyond any doubt that suppression caps left in will affect the smooth running of many decoders.

 

 More so decoders with BEMF which most have had for a few yrs.

 

 OK, some say things work OK with caps etc left in and good luck to them but how do you know loco would not run better with caps etc out.

 

 I have seen it many times with locos that seemingly ran OK with caps left in but did op better when caps have been removed.

 

 So how would one know if caps left in will affect performance, or not, until tried ?

 

 When fitting decoder why not remove caps etc at same time. It would save having to take the body off again if all is not well and save a lot of extra hassle.

 

 Removing caps etc, will not, I repeat, WILL NOT, be detrimental in any way to anything.

 

 I am sure there are some manufacturers suggest removing caps when op loco on DCC.

 

The only reason caps are left in on OEM (DCC fitted ) locos is it is law in some countries.

 

 I am a USA modeler and most locos, if not all, made for USA market do not have caps etc fitted.

 

Over the yrs I have experienced a lot of modelers that complained about poor running of DCC equipped locos both OEM and after market fitted.

 

 Removed caps and all was well with said locos.

 

 In my short experience op DCC I have adopted the belief of;  WHEN IN DOUBT TAKE EM OUT.

 

 BTW, when removing caps there is no need to replace with a bridging wire. If you do a dead short will occur.

 

 If removing inductor coil then yes, it must be replaced with a bridging wire other wise loco will not run.

 

 I must admit, when fitting decoder to any loco I completely strip existing circuit board, caps etc, out and hard wire.

 

 That way I know it is going to work unless I get careless and stuff something up. Very rare these days.

 

 Cheers

 

  Ian

[Andy Reichert]

SNIP

 

 Removing caps etc, will not, I repeat, WILL NOT, be detrimental in any way to anything.

 

SNIP

 

The only reason caps are left in on OEM (DCC fitted ) locos is it is law in some countries.

 

 I am a USA modeler and most locos, if not all, made for USA market do not have caps etc fitted.

 

SNIP

 

Or OTOH, http://online.wsj.com/news/articles/SB10001424052702304434104579378994224188328

 

Andy

[mezzoman253]

Good grief, this subject has been going round in more circles than a three ring circus and the Olympic rings put together for yrs.  It is never ending.

 

After 19yrs op DCC I have proved beyond any doubt that suppression caps left in will affect the smooth running of many decoders.

 

 More so decoders with BEMF which most have had for a few yrs.

 

 OK, some say things work OK with caps etc left in and good luck to them but how do you know loco would not run better with caps etc out.

 

 I have seen it many times with locos that seemingly ran OK with caps left in but did op better when caps have been removed.

 

 So how would one know if caps left in will affect performance, or not, until tried ?

 

 When fitting decoder why not remove caps etc at same time. It would save having to take the body off again if all is not well and save a lot of extra hassle.

 

 Removing caps etc, will not, I repeat, WILL NOT, be detrimental in any way to anything.

 

 I am sure there are some manufacturers suggest removing caps when op loco on DCC.

 

The only reason caps are left in on OEM (DCC fitted ) locos is it is law in some countries.

 

 I am a USA modeler and most locos, if not all, made for USA market do not have caps etc fitted.

 

Over the yrs I have experienced a lot of modelers that complained about poor running of DCC equipped locos both OEM and after market fitted.

 

 Removed caps and all was well with said locos.

 

 In my short experience op DCC I have adopted the belief of;  WHEN IN DOUBT TAKE EM OUT.

 

 BTW, when removing caps there is no need to replace with a bridging wire. If you do a dead short will occur.

 

 If removing inductor coil then yes, it must be replaced with a bridging wire other wise loco will not run.

 

 I must admit, when fitting decoder to any loco I completely strip existing circuit board, caps etc, out and hard wire.

 

 That way I know it is going to work unless I get careless and stuff something up. Very rare these days.

 

 Cheers

 

  Ian

The reason this keeps running on and being repeated is the "if in doubt, chop 'em out" brigade. That's rather a cavalier attitude to give a novice asking for advice without any technical explanation. In most cases there won't be a problem, and, it would be nice if manufacturers stated clearly in their documentation, what you can and can't do to improve running with regard to RFI components. Then the novice could make an informed choice.

 

It's not that I don't agree with most accepted findings, it's that there will be a small number of cases where RFI is generated and someone will suffer, both parties being ignorant of the cause. Just because your problem goes away doesn't mean you've found the correct solution, and there are receivers other than TV's.  

 

If you have the body off a loco' then do your tests before you put the body back, it doesn't need it to run (maybe on a sound model that may need the body on). If there's no improvement put the components back, or maybe that's to much of a job. Belief and fact may be two different things.

 

A quick test would be to get a receiver and bring it close to the loco' when running and see if there's any hash created. You may get some at very close range, but moved away a few metres and it will diminish. That would be acceptable. If you can still hear it some metres away then something's wrong.

 

You may feel this is being pedantic and it's unlikely to be a problem. We all like to enjoy our hobbies whatever they are. Just be aware that you could, however slight the chance, be ruining someone else's enjoyment by "fixing" your loco's running.

 

Rob

[34theletterbetweenB&D]

During the declining years of terrestrial analogue television broadcasting in the UK, some very potent bursts of interference were generated at fairly predictable times not too far from my home (by an industrial process in my completely unhumble opinion). I took this up via our MP, because it quickly became apparent that neither the BBC nor the Post Office were at all keen to investigate, let alone do anything. Long story short, the policy is to ignore RFI other than where it poses a hazard to safety critical systems such as for airspace management. Digital transmission with large redundancy and error correction just 'punches through' the RFI, so we don't need to do much to control it anymore. (Well, that's my take on the replies I received from 'please shut up and go away' section of the barely-civil service.)

 

Model railway. Bachmann's split chassis models are a completely RFI suppression free zone, and will give audible evidence of this if you place an AM radio receiver near the tracks. (Or even dampen two finger tips, place one on each rail and run loco towards said fingers at 12V.) That said even my crappiest analogue TV at the time barely suffered, you had to look hard for any visible effect. As for DCC, I have the suppression components out of most of my locos for the reasons already stated when decoder fitting. Using the AM radio test I am in no doubt that the Lenz, Zimo and ESU decoders that I have installed are more efficient at RFI suppression, than the locos as supplied for DC with a mix of inductors and capacitors.

[Crosland]

Or OTOH, http://online.wsj.com/news/articles/SB10001424052702304434104579378994224188328

 

Andy

That's a subscription only site

 

Andrew

[mezzoman253]

During the declining years of terrestrial analogue television broadcasting in the UK, some very potent bursts of interference were generated at fairly predictable times not too far from my home (by an industrial process in my completely unhumble opinion). I took this up via our MP, because it quickly became apparent that neither the BBC nor the Post Office were at all keen to investigate, let alone do anything. Long story short, the policy is to ignore RFI other than where it poses a hazard to safety critical systems such as for airspace management. Digital transmission with large redundancy and error correction just 'punches through' the RFI, so we don't need to do much to control it anymore. (Well, that's my take on the replies I received from 'please shut up and go away' section of the barely-civil service.)

 

Model railway. Bachmann's split chassis models are a completely RFI suppression free zone, and will give audible evidence of this if you place an AM radio receiver near the tracks. (Or even dampen two finger tips, place one on each rail and run loco towards said fingers at 12V.) That said even my crappiest analogue TV at the time barely suffered, you had to look hard for any visible effect. As for DCC, I have the suppression components out of most of my locos for the reasons already stated when decoder fitting. Using the AM radio test I am in no doubt that the Lenz, Zimo and ESU decoders that I have installed are more efficient at RFI suppression, than the locos as supplied for DC with a mix of inductors and capacitors.

Unfortunately you are right about general enforcement, when monies are in short supply all the bread and butter work goes out the window and only "real" concerns are dealt with. Everyone else has to suffer until the fault either goes away due to a replacement, through maintenance or the offending item fails completely. That in my opinion makes Ofcom guilty of using semantics to avoid enforcing the EMC directive, which is part of European law. That doesn't make it right, but that's where we are.

 

Your tests, on shall I say, upmarket decoders, prove that RFI suppression is indeed working. Hopefully those of a different manufacture are also OK. It would be nice to know if anyone has done any tests on other decoders.

 

Being a radio amateur I'm rather sensitive to the RFI problem, so any suggestion that removing components, as a given, without then checking all is ok in regard to interference, will raise a few hackles. It's not difficult to check and will give peace of mind that you are not causing others grief.

 

Rob