Inter-City 125 - Conversion from DC to DCC

[RDS]

2 questions please.

1) I converted the above Loco (running number 43010) to DCC a few years ago and I have hardly used it since. I recently decided to take the body off to see if it had directional lights fitted and noticed that I have not removed the

 

capacitor across the motor terminals when I converted it to DCC. Should the capacitor be removed?

2) I have read many times about 3 pole Ring Field motors. Is that the type of motor that is fitted to this Loco?

[Fishmanoz]

The capacitor may degrade DCC performance, not just be redundant.

[Flashbang]

Hi

The Radio Frequency (RF) capacitor(s) fitted across the locos motor terminals can safely be removed for DCC operation. No DCC loco has ever been recorded as running worse with the RF capacitor(s)removed!

My advice is test the loco and if its ok

 

leave them, but remove them if performance issues are noted. They can if left in place with some makes of decoder effect the way the decoder tries to read the Bemf from the motor and can in some circumstances case erratic running.

 

Manufactures like

 

Hornby will be unable to advise you to remove them, this is because they have to comply with legislation when selling or dealing with a model they produced, that legislation specifies RF suppression must be fitted to any item that can produce a spark (or RF

 

interference). Therefore they can never be sure you wont convert it back to dc operation which then needs the motors RF capacitor to be fitted!

 

The removal or leaving of the motor RF suppression capacitor(s) has no effect on the DCC signal in any form.

 

 

 

But if a dc rail connecting clip or power track section is used on DCC its essential the clip is opened up and the internal capacitor removed. These capacitors will effect the DCC data signals if left in place.

 

[RDS]

@Flashbang

I was a little surprised to find that I had not removed the capacitor because I thought I always took them out, unless I converted this model to DCC before learning about the need to remove it.

 

 

[Fishmanoz]

Flashbang, a single loco with a capacitor may be ok but what about 10 locos all with capacitors all on the track at the same time? That means 10 times the capacitance across the track.

[Fishmanoz]

Oops, maybe not as the motor and capacitor is effectively isolated from the track by the decoder. Forget I said anything.

[RDS]

@Fishmanoz

I have now removed the capacitor and .... it hasn't made any difference whilst running the loco on my newly acquired Rolling Road.

[Flashbang]

Hi

As I stated in my post above....

The motors RF capacitor(s) - suppression capacitor(s) and there may in some locos be more than one, can effect the way the some decoders try to read the Bemf being produced by the motor with RF cap(s) fitted.

 

 

If the Bemf is turned on and the decoder is unable to fully read what the motor is doing it can cause erratic running including 'lumpy' slow running.

 

The motor capacitor has no effect on the quality of the DCC data or DCC information being received

 

by the decoder from the rails. But they can effect motor control and performance. :-)

[RDS]

@Flashbang

The thing that did impress me was how smooth it ran at very low motor speed and it did not (appear) to make any difference with the capacitor in or out.

I emphasise motor speed because this was on a rolling road as I do not have my track

 

down at the present time.

[Augustus Caesar]

The capacitor was there to supress noise to tv's and radios and no more really but only on analogue systems. Zero 1 allowed removal or non removal and as stated above the capacitor makes NO difference to DCC at all. So you can remove them from ANY DCC

 

loco at any time. If you convert back to analogue in the future you may wish to hang onto the little pesky beasties...

[The son of Triangman]

Worth remembering is that the capacitor is there also for legal reasons. Most DCC decoders do have inbuilt supression but it is wise to leave the capacitor unless it is causing problems wht the decoder.

[The son of Triangman]

As for direction lighting, replace the old bulb with LED's fitted with suitable resistors and linked up to the first two Hornby decoder functions(assuming you are using the standard Hornby decoder), this will give you directional lighting without the fancy

 

extra boards you can buy if memory serves me correctly.

[RDS]

@The son of Triangman

That is interesting. Thank you.

I thought though that directional lighting normally changed from white to red depending on direction. Does your Tip cover that aspect?

 

 

[RDS]

@AugustusCaesar said

..... If you convert back to analogue in the future .....

 

 

There is one thing that is very certain - I will not be converting back!

[Fishmanoz]

SoT's tip will certainly work for directional lighting. After all, AC's PCB is just a way to conveniently wire up the LEDs and resistors that SoT mentions. The directional aspect works by using the white and yellow decoder outputs operated on F0 and F1

 

but with them connected white red respectively at one end and red white at the other. That way you then have white at one end and red at the other with one function on, and the other way around with the other function. The PCB also has the facility to swap

 

sides on the white light for day and night running using a third function.

 

As SoT says, you can do all of that wiring yourself if you wish then mount the LEDs behind the appropriate lenses. The PCB does it all for you though (look at the pictures of

 

it, it's just LEDs and resistors) with only the function wires to be soldered and double sided tape mounting it such that the LEDs are all in the right place. You pay your money for the convenience of a simpler job doing it.

[RDS]

@Fishmanoz

Thanks very much. I think I am going to give that a try.

Am I right to assume you are referring to a red/white LED in one LED, i.e. 3 wires?

 

Also though, is there no way to simply let the direction of the loco define the red or

 

white, rather than having to switch functions. That is what my Blue Box Class 37 and 47 do automatically.

 

[walkingthedog]

DC locos have had directional lighting for years using rectifiers that only allow DC to pass through them in one direction. Easy to use. I have used them on a dpol diesel to switch the cab lights on and off depending on direction.

[Fishmanoz]

RDS, sorry for the confusion in my post. For a start, the red and white LEDs are separate. You can see that by going back and looking at AC's article again. In the motor car, the white LED cathode is connected to the white wire and the red LED's to the

 

yellow wire. Each has a resistor in series with it to limit voltage drop across the LED. The blue wire is the +ve common and connected to all anodes. In the dummy car, the white LED connects to the yellow wire and the reds to the white wire, blue again the

 

common. On the PCB, all of that wiring is part of the board such that you only have to connect the white, yellow and blue wires at the appropriate points and all LEDs and resistors are wired.

 

On switching, the function key or keys, depending on your

 

decoder type, decide whether the lights are working or not. The change to direction is done automatically by the decoder when direction is changed.

 

Hope that is clearer.

[Fishmanoz]

For further explanation and the actual circuit to do it yourself, take a look at http://www.brian-lambert.co.uk/DCC.htm#Basic%20decoder%20connections in the lighting diagrams. The pictures are worth 1000 of my words above.

[RDS]

@Fishmanoz

Thank you, that is very clear.

One other thing though, I assume there must be some form of electrical connector between motor car and dummy car, that was not required before conversion to DCC.

 

[The son of Triangman]

You will need a second decoder for the rear car and for the rear LED's or have a permanently coupled rake with power car, coaches and dummy car wired straight through.

 

 

[The son of Triangman]

THe tricky bit is geeting the leading unit to have white lights showing and the rear unit to have red lights showing at the same time. Programming the doecders to do this can be awkward at times.

[RDS]

@The son of Triangman

Thanks. I prefer a separate decoder to a permanent connection. I like the sound of a challenge of something difficult to set-up!

 

[walkingthedog]

Surely it would be easier to use the DC system unless you want to turn the lights on and off digitally.

[RDS]

@walkingthedog

I agree it does look like in this instance, DC would be easier but I am committed to DCC. I don't want to be able to turn the lights on and off digitally, just directionally. The only reason for another decoder is because I don't want

 

to run a permanent connection between motor and dummy car.