are capacitors needed for dcc conversion?

[Dan Griffin]

im going to chip my Hornby, tender drive, flying scotsman, now in preperation ive clipped off the capacitor. is this essential for successful chipping or will it be just as good without it? cheers, dan

[Oldddudders]

im going to chip my Hornby, tender drive, flying scotsman, now in preperation ive clipped off the capacitor. is this essential for successful chipping or will it be just as good without it? cheers, dan

Capacitors sometimes - but not always - interfere with the smooth operation of a decoder. Apart from the remote possibility of avoiding any contravention of radio interference regulations, I cannot think of any way that leaving the cap(s) in there would be beneficial.

[Dan Griffin]

cheers, i looked on the Hornby website and they left it in, ill chip it tomorrow and let you know how it goes, thank you

[johnd]

So far i have converted/ added decoders to in excess of 40 locos all of which have had the capacitors left in place, as yet have not had any problems under DCC operation. Decoders used have been wide and varied from Bachmann/Hornby to ESU/Zimo.

 

If you leave it in and have problems you can always remove it, removing it first you will never know, also what if you want to take the decoder out and return it to DC operation are you going to put the capacitor back.

[Phil S]

Different decoders and different motors end up with differing results 8-)

WHATEVER happens, you must not end up with a capacitor across the TRACK (red and black decoder leads, or track power connection). I note that the Hornby Javelin has its 'dc' capacitors mounted on the 'dummy plug' - so they are in circuit as they should be for dc use, but replaced by the decoder (and its components) when used for dcc. Bachmann, Dapol, Heljan all use suppression designs wich often include series inductors AS WELL ... appearing as either wound wire on ferrite, or an overgrown resistor marked Lx and not Rx on the PCB. Older decoders also used a lower-frequency motor pulse rate - which would have needed comparatively larger capacitors than used by high-frequency ('silent') decoders for the same effect.

Personally, I find it hard to believe that some of the analogue suppresion circuitry used is appropriate for the different nature of the dcc track-interface or decoder-motor interface. Those that have components mounted on the dummy plug which are removed, are most likely to have correct components elsewhere. Of course, this does not help with olde worlde locos ... but the physical removal of old bulky capacitors and /possible/ replacement with something smaller might be more convenient anyway.

A possible problem with the original capacitors on old motors - they might try to lift the brushes - which would result in interference!

Try to ensure that any connections do not adversely affect the brush holders/retainers - by ensuring flexibility is retained.

But for maximum effect, any capacitors NEED to be as physically close as possible to the place they are needed .. eg the brushes.

[noiseboy72]

I agree with the above. DCC chips may benefit in terms of noise immunity from a well suppressed motor, but as discussed, they need to be wired as close to the brushes as possible.

 

I have always left them in and find that all my locos and trains run well. On the flip side, I have 5 trains with Black Beetles and Tenshodo Spuds with no suppression and these run just as well!

[pauliebanger]

Capacitors fitted to r-t-r locos are there to reduce radio wave interference caused by sparking at the bushes, not to improve running or motor control.

 

This job is done more effectively by DCC decoders when fitted.

 

Capacitors are therefore superfluous for DCC operation. Redundant, even.

 

Mostly they can be left in place with no ill effect.

 

However, they can cause operating problems in some installations - poor slow-speed motor control due to compromising the decoder's BEMF calculations as an example.

 

As they serve no purpose, take up space (only a small amount though) and can potentially cause problems, I always remove them when adding decoders rather than possibly having to open the loco again (some are much more difficult to open than others!) and remove them later. That's just a personal preference.

 

To answer the original question, are these capacitors needed for DCC? No, they are not.

 

Paul

[Steven B]

However, they can cause operating problems in some installations - poor slow-speed motor control due to compromising the decoder's BEMF calculations as an example.

 

But this would be little worse than using a DC loco with a feedback controller - the only difference is the "controller" is closer to the motor.

 

Leaving the capacitors in place shouldn't do any harm (as long as they are between the decoder and the motor, having them on the track side of the decoder is asking for trouble). If slow speed running is affected then try removing the capacitor or tuning the feedback CVs on the decoder.

 

 

Happy modelling.

 

Steven B.

[pauliebanger]

 

But this would be little worse than using a DC loco with a feedback controller - the only difference is the "controller" is closer to the motor.

 

Leaving the capacitors in place shouldn't do any harm (as long as they are between the decoder and the motor, having them on the track side of the decoder is asking for trouble). If slow speed running is affected then try removing the capacitor or tuning the feedback CVs on the decoder.

 

 

Happy modelling.

 

Steven B.

 

 

Steven B

 

So, what you are saying is that capacitors left in place would be 'little worse' than the sort of problems that can occur in a different control method. (DC with Feedback).

 

 

1. Why should anyone be content with something 'little worse'? Surely the aim is to achieve the best possible!

 

2. That capacitors can cause problems on DC too.

 

This clearly illustrates that suppression capacitors can be detrimental to good running characteristics, whether DC or DCC.

 

Leaving them in will not improve running characteristics, they perform no useful function and by your own post you agree that they sometimes will cause problems.

 

This would seem to support my view that removing these capacitors is a good thing.

 

However, the OP asked if (suppression) capacitors were necessary in DCC. The answer is not a matter of personal preference. Or even an observation that in most cases 'it will be alright to leave them in'.

 

It is easier to think of this from the opposite direction. If you were building a loco from scratch which was to be DCC controlled, would there be any good reason to fit suppression capacitors? No.

 

Therefore, the inescapable conculsion is that suppresion capacitors are NOT required in DCC locos.

 

Whether one chooses to remove capacitors which may be present, thereby pre-empting any chance they will cause poor running, or leave them in and hope for the best is a personal choice. I have made mine, and explained here the basis upon which I made that choice. I also made it clear in my post that it was a personal decision.

 

Kind regards,

 

Paul

[Steven B]

1. Why should anyone be content with something 'little worse'? Surely the aim is to achieve the best possible!

 

Because it might not be that noticable. I DCC'd a Farish class 04 with a CT DCX75 decoder. Initially I left the capacitors in place and the loco ran just as well as it did under DC. Out of curiosity I removed the capacitor and there was no difference to my eyes. Unless you do a like for like comparison quantifying any improvement is impossible.

 

 

However, the OP asked if (suppression) capacitors were necessary in DCC.

 

No, the original posting asked if the removal of any capacitors was "essential for successful chipping or will it be just as good without it". The answer is that it's not essential. You might find that a particular decoder works better in a particular loco if the capacitors but that might not be true for all installations. Certainly from my experience in N Gauge I've never had any problems with leaving capacitors in place - the vast majority of mine have the C's still in place and still run quite happily (running a mix of Digitrax, NCE, Lenz and CT .

 

Claiming that you MUST remove capacitors is just another DCC myth that needs busting.

 

 

 

Happy modelling.

 

Steven B.

[pauliebanger]

 

Because it might not be that noticable. I DCC'd a Farish class 04 with a CT DCX75 decoder. Initially I left the capacitors in place and the loco ran just as well as it did under DC. Out of curiosity I removed the capacitor and there was no difference to my eyes. Unless you do a like for like comparison quantifying any improvement is impossible.

 

 

Claiming that you MUST remove capacitors is just another DCC myth that needs busting.

 

 

 

 

 

'MUST remove capacitors'. I made no such claim. And neither has anyone else in this thread, so why mention it?

 

I gave a reasoned arguement that removing suppression capacitors will remove the risk that they may interfere with good running. (However small that risk might be). Suggesting the removal of a souce of potential problems is not the same as claiming or even implying that it improves performance, it just prevents it from being impaired.

 

 

Here is the thead title, 'are capacitors needed for dcc conversion?' Answer, no.

 

Is it essential to remove them? Answer, no. (except in the cases where it subsequently proves to be necessary)

 

So I'm happy to agree we are both correct.

 

However, I have not suggested that they must be removed. In fact, you will see that I originally said 'mostly they can be left in place without ill effect'.

 

I simply was making the point that leaving them in may cause problems (a point which you have already agreed). On the other hand, taking them out will never cause running problems.

 

I do not deal in myths. I have been using DCC for close to 20 years and I have converted, literally, hundreds of locos over that period. I speak from some experience, therefore, when I say that, sooner or later you will come across a particular installation when you will not be able to get proper running unless you remove suppression capacitors.

 

For me, there is no logical reason to risk poor performance by leaving in a redundant component. I always take them out as it may save my time in the long run.

 

That's my opinion.

 

Kind regards,

 

Paul

[Dan Griffin]

well, 4472 is now chipped and does run, HOWEVER, there appears to be another issue, upon test it ran fine for about 3 mins on all power ranges, then the loco lost power, and ran on what looked like 25% power and would not speed up, it is the same in both directions. it stopped fine but putting it up to full power on my dynamis it just crawled along at a scale speed of around 30mph. this is a flying scotsman tender driver model, chipped ok like i said, and its chipped with a Hornby R8249 decoder. any help would be great, someone said that it could be overheating, is this the case?? cheers, dan.

[pauliebanger]

Dan,

 

There are lots of possible reasons or contributory factors in this. We will need some more info from you.

 

This decoder is rated at 500mA continous, 1 A maximum (but this max will be good for very short time periods, a few seconds at most). It is fitted with a thermal cutout. If it is overheating, it should stop supplying any power to the motor until it has cooled down sufficiently. So It should either be running well or not at all.

 

Was the loco running well on DC before you installed the decoder? Can you give us an idea about how the loco was used in the past and how often and how recently.These ringfield motors are capable of working quite well under DCC, though in my experience never quite as refined as the later can type motors.

 

However, it's possible that the motor may have a fault which is causing it to draw excesively high current. You could try a better (higher rated) decoder. There are some from the likes of Zimo and TCS and likely many other brands, capable of constant 1.5A output. These will be more expensive than the Hornby but whilst they may get your loco moving better, this may simply mask the basic problem.

 

It's unlikely to be a simple dead short as the decoder would have died instantly. The general state of the loco and your track may also have a bearing on this. Are the brushes in good condition and moving freely in their sliders? Have you inadvertantly distorted the brush housings when performing the installation?

 

What method have you employed to connect the wires to the track pick-ups and the motor? Solder? Any 'dry solder' problems?

 

 

If the Hornby decoder, when cold, does not give better running, my next move would be to revert back to DC and run some tests including measuring the current drawn by the motor. (Multimeter set to 'Amps' connected in series). There's no need to reconnect the capacitors for these tests, honestly.

 

Kind regards,

 

Paul

 

.

[Dan Griffin]

thank you for your replys. i think ive now found the answer. the Hornby chip isn't highly rated as current draw ect ( there was a very faint smell of burning plastic from the flying scotsman after running, but the decoder has not burnt out -- yet!), so im going to swap the chip for a Bachmann one, 36-553. and see if that helps. ive also chipped a Hornby (1995ish) battle of britain which stalled every 30 secs or so, indicating the decoder was overheating. i will let you know the out come, flying scotsman ran prefectly on dc and was from a reputable seller so i dont doubt the loco. ill keep you posted and i do appreciate the help. cheers, dan. :-)

[melmerby]

If you look at the spec for TCS decoders (no doubt others are similar), it states that the decoder has all necessary suppression components required to meet regulations and that capacitors in DCC systems are not required. It does not say they should or should not be removed.

A loco with a DCC chip will meet interference regulations without them.

As they are surplus you can remove them (if you want) - it may or may not improve the performance. It definitely will not make it worse!

 

Keith

[dave flint]

This thread struck a chord.

 

FWIW I've never noticed a difference in motor control with or without capacitors either. I've removed them from many hard wired installations as it often makes the job a little simpler/easier/prettier.

 

I have had a similar problem with the Horny 8249 getting hot and bothered. The Bachmann chip may be fine, but out of the box it is more suited to large motored/large flywheeled locos. Stuff with a smaller motor (like FS) may need some CV's tweaking (think CV 54/55 off the top of my head).

 

in fact, mentioned here http://www.rmweb.co.uk/community/index.php?/topic/39051-Hornby-t9-Bachmann-decoder/ and here http://www.Bachmann.co.uk/pdfs/3-function_decoder.pdf

 

As someone who has used the Bachmann chip and encounted this on a lot of small-motored loco's, you may be initially disapointed with the Bachmann chip until some tweaks have been done.

[Dan Griffin]

ive hard chipped the Bachmann 36-553 decoder into the flying scotsman, and everything works fine. no problems at all. its been running around no problems, my battle of britain is another matter and am looking for a high rated decoider for this one. things are on the up with it. thanks for all your help. dan

[Gordon H]

If you look at the spec for TCS decoders (no doubt others are similar), it states that the decoder has all necessary suppression components required to meet regulations and that capacitors in DCC systems are not required.

I am struggling to find anything on the subject in any of the decoder manuals on their website - or in the Guides - not even the one about BEMF which is where we might normally expect it to be mentioned.

Could you point to any of their documents that include this information?

 

A loco with a DCC chip will meet interference regulations without them.

This is quite a bold statement, given the almost limitless combinations of motor types, ages and qualities that could exist, let alone the loco internal wiring arrangements which they have no control over. However, if a decoder manufacturer feels able to make this claim you might think they would make it more of a selling point for their kit, given the controversy the subject attracts.

[melmerby]

I am struggling to find anything on the subject in any of the decoder manuals on their website - or in the Guides - not even the one about BEMF which is where we might normally expect it to be mentioned.

Could you point to any of their documents that include this information?

 

 

This is quite a bold statement, given the almost limitless combinations of motor types, ages and qualities that could exist, let alone the loco internal wiring arrangements which they have no control over. However, if a decoder manufacturer feels able to make this claim you might think they would make it more of a selling point for their kit, given the controversy the subject attracts.

Well, I found the information last time this question cropped up (not too long ago if I remember)

 

Had a hunt and found this:

http://www.tcsdcc.co...dwin_2-8-0.html

 

At the bottom it says suppression capacitor is on board chip.

 

(This is not what I originally referred to BTW, which I cannot now find!)

Surely the controversy you mentioned is based on lack of knowledge rather than facts.

 

EDIT this is from Digitrax:

"A more important issue is the Radio Frequency Interference (RFI) that is caused by any High Frequency (HF) energy radiated by electronics systems. In this case, this RFI is handled at the decoder and command stations. Or, to put it in EE terms at a Las Vegas convention, it is most important to slew-limit the DCC transitions, since the bit times are fixed by the DCC definitions. Basic physics. QED."

 

Keith

[Gordon H]

Had a hunt and found this:

http://www.tcsdcc.co...dwin_2-8-0.html

 

At the bottom it says suppression capacitor is on board chip.

Seems very odd that this is the only example that can now be found.

The 'Technical Explanation' implies that the decoder output stage is designed for a particular capacitive loading.

Of particular note is the value of the capacitor which they removed - said to be 105 (or 1uF). This is quite a large value to see used in such a position. Something between 103 (10nF) and 104 (0.1uF) would be more common, which a decoder would have far less trouble with.

It would be useful if manufacturers quoted a maximum capacitive loading their decoders can cope with for normal operation.

 

.

Surely the controversy you mentioned is based on lack of knowledge rather than facts.

The controversy only came about when some people started pushing the philosophy of removing capacitors regardless of any reasoned considerations, technical or otherwise. Any controversy is indeed based on lack of knowledge, where the majority seek a one-size-fits-all solution where there isn't one. Rarely does anyone advocating removal mention the effect this might have on suppression - all they care about is whether their loco runs a bit better.

 

EDIT this is from Digitrax:

"A more important issue is the Radio Frequency Interference (RFI) that is caused by any High Frequency (HF) energy radiated by electronics systems. In this case, this RFI is handled at the decoder and command stations. Or, to put it in EE terms at a Las Vegas convention, it is most important to slew-limit the DCC transitions, since the bit times are fixed by the DCC definitions. Basic physics. QED."

DCC transition rates are irrelevant here, since we are talking about the motor side of a decoder rather than track side.

If only they would quantify the capabilities of their decoders to handle motor generated RFI relative to the original suppression components, all would be well.

All it takes is a simple statement.

[GeoffW]

The debate is fascinating and I note how wizzy and clever some of the input is

The bottom line is that, on my toy trains which ran sweetly on DC, the hesitant and slightly jerky running after conversion to DCC has been resolved by disconnecting all capacitors.

Proof of the pudding?

[Oldddudders]

The debate is fascinating and I note how wizzy and clever some of the input is

The bottom line is that, on my toy trains which ran sweetly on DC, the hesitant and slightly jerky running after conversion to DCC has been resolved by disconnecting all capacitors.

Proof of the pudding?

I am prepared to believe that many decoders, in many locomotives of various manufacture fitted with capacitors, may work just fine. On the other hand, I have yet to be convinced that leaving the caps in adds any value, and as removing them may be beneficial, and most of us do not enjoy taking the loco apart again for the fun of it, removing them will remain my choice. In my DC days, my wife would sometimes tell me that I had been interfering with her tv. Once I switched to DCC these comments stopped.

[melmerby]

The debate is fascinating and I note how wizzy and clever some of the input is

The bottom line is that, on my toy trains which ran sweetly on DC, the hesitant and slightly jerky running after conversion to DCC has been resolved by disconnecting all capacitors.

Proof of the pudding?

Hardly.

It depends on the decoder, values of suppression components and motor (I have actually seen can motors with a cap across the brushes inside - hopefully not used in model railways with DCC!)

Some combinations seem to work fine, others less so, but it still boils down to trial and error but removing them definitely will not reduce the quality of running on DCC.

 

I have some locos with suppression, some without and I cannot really say there is any noticeable difference.

I have a mixture of TCS, Hornby (R8249) and a couple of old Lenz 1000s with Hornby, Bachmann, and some kits with various motors.

 

Keith

 

Edit: BTW we have to be careful not to mix up BEMF when used as a motor control system and the unwanted BEMF which causes RFI as the brushes commutate.

[Sunnysa]

I am prepared to believe that many decoders, in many locomotives of various manufacture fitted with capacitors, may work just fine. On the other hand, I have yet to be convinced that leaving the caps in adds any value, and as removing them may be beneficial, and most of us do not enjoy taking the loco apart again for the fun of it, removing them will remain my choice. In my DC days, my wife would sometimes tell me that I had been interfering with her tv. Once I switched to DCC these comments stopped.

 

Absolutely.

 

Yes, some decoders may perform Ok with caps in. a lot don't.

 

The bottom line is capacitors are not needed with DCC. There will be no detrimental affect caused by removing them.

 

This debate has been going for a long time on nearly every forum going.

 

As has been said, when fitting decoder take caps out. It saves a lot of frustration that might happen latter.

 

Re locos with decoders fitted ( OEM), I always pop the body off and remove any caps that may be lurking.

 

I must admit, as I model USA most locos I buy don't have caps fitted as they are not required by USA law. AFAIK.

 

As a point of interest, I have had 2 decoders same brand, same type. One seemed OK with caps left in the other ran like a wooly goat. Took the caps out of offending decoder, it actually ran better than decoder with cap in.

 

Go figue that.

 

Cheers

 

Ian