How to convert to DCC

[Allistair1964]

Hi All
I am converting all my Sons loco's to DCC when converting a standard 0-4-0 a capacitors broke so today I phoned my local model shop to be told that you don't need these capacitors for DCC is this correct?

Thanks

Allistair1964

[poliss]

Yes. Indeed most guides tell you to remove the capacitors.

[FinnerZ]

Would you recomend removing them on trains that I've already converted to DCC?

[Blackbird]

If your DCC loco runs without problems, then leave it as it is. The capacitors are fitted to the motor to reduce RF interferance from commutator/brush arcing. This can, theoretically, interfere with the back emf referance to the decoder, that is why, if

you have problems, it is recomended to remove them. The capacitors fitted to the track supplies (for the same reason, RF suppression) should be removed as they can interfere with the DCC signals to the loco.
Basicaly, a capacitor will conduct an AC current

(the high frequency DCC signal) an in effect short it, the supply to the loco. But the feed from the decoder to the motor has no DCC signal and will have no effect on the input signal.

[Allistair1964]

Hi All
This was my first post on the fourms thanks for all the help

Rgds

[rft_hillview]

Hi All
I am a Grandpa getting ready for a DCC conversion present on my Grandson's layout.
Having successfully converted R2960 - a small 0-4-0 chassis - I started to convert R2375 Virgin Shunter. It soon became apparent that the electrics are different.

The

Virgin shunter has only one capacitor in parallel with the motor and the pickup connections to the wheels are made by simply placing the motor so that the tags on the motor where the capacitor is connected rest on copper strips from the wheel pickups.

The

capacitor, which in the Hornby standard DCC instructions for 0-4-0 is in series with one motor feed, is not part of the Virgin Shunter.

Does anyone know if it can simply be ignored for DCC conversion.
If not then does anyone know what value the capacitor

is. It is not the small bit of toffee capacitor but the in line tubular one (the red one in the Hornby online instructions) which is missing.

many thanks
Ralph

[Rog RJ]

Don't worry about it. It's not needed for DCC.

[The son of Triangman]

Nope but it is needed to cure RF problems and could cause tv interferance to neighbours TV's which is illegal.

[The son of Triangman]

Removing the capacitor/s can stop reduction or prevention of RF interferance. It's highly unlikely of course but the RF supression should be there.

[The son of Triangman]

Your local shop shouldn't have offered the advice Allistair1964 without explaing why the capacitor/s are there and what they do.

[poliss]

It all depends on the decoder. Some have built in suppression circuitry so it will be quite ok to remove the capacitors.

[Flashbang]

RF Capacitors fitted internally in locos.
Theory first - The decoder uses Pulse Width Modulation (PWM) to control how the motor speed is set and the decoder's control circuit tries to measure the back-emf from the motor during the gaps in these pulses.

This allows the decoder to adjust its output in response to these measurements . Acting like a mini Cruse Control. Trying to maintain as much as possible the motors speed to that required, regardless on whether the motor is loaded or running lighter – The

loco is on the flat, pulling up hill or running down a gradient.
A RF capacitor tries to prevent high frequency - radio frequency (RF) noise, being sent back onto the rails from the arcing occurring at the motors commutator to brush connection. Where a

DCC decoder is fitted the voltage and current coming back from the motor will be modified by the capacitor. The overall effect is that the decoder cannot accurately sense the back-emf, so motor control can become poor.
The decoder will be doing this work

at quite high frequencies – typically 20,000Hz (20kHz) and some makes are doing this at even higher frequencies.

RF Capacitors, are normally little flattish round two wire devices, often a yellowish orange or brownish colour, but they can be of any

shape and any colour. They are normally connected across the motor brushes, many directly onto the motors wiring tags as often the brushes are encased is a sealed metal ‘Can’. Some capacitors are not always close to the motor, they could be fitted onto the

locos main circuit board. Be careful in identifying them when your going to remove them, there can be capacitors in locos used to help stop the flickering of lights. On some DCC powered locos larger sized capacitors are mainly used to keep the motor running

for a second when rail to wheel contact is lost. So called ‘UPS’ or ‘Stay Alive’ capacitors.

With dc (analogue) the motors RF interference is initially suppressed by the motor capacitors, but as the motor is directly connected to the rails the RF signals

from both the motor and any arcing between rails and wheels is passed easily along the rails which act like large aerials and transmit the RF interference even better! This is why RF suppression capacitor are fitted into dc power clips/power track sections

in an attempt to further reduce the RF interference.
With DCC, the motor is not directly connected to the rails. The rail power is converted into PWM via the motor control device on the decoders circuit board. RF signals will in the main stop at the decoder.

However, dirty rails and dirty pick-up wheel treads will cause arcing and this will transmit RF interference! This is not stopped by anything on a DCC layout as no power clip etc capacitors are to be used!

Much of the RF interference issues are IMO

overstated - they are required under EU / CE manufacturing laws, so the manufacturer has to comply with the regulation, but in practise they often make little or no real difference. Many ‘up market’ DCC decoder manufactures will request the locos owner or

decoder installer remove all loco suppression capacitors while wiring or installing the decoder. Cheaper budget priced decoders, which do not have such sophisticated motor control circuits built into the decoder will often will work happily with the suppression

capacitors still fitted.

My advice is, always has been and will remain so… If the loco runs correctly throughout its entire speed range, then leave the capacitors alone. However, if the loco exhibits poor running – typically surging at certain speed

steps, then remove all the RF suppression capacitors.

I've never heard of a RF detector vans staff coming round to arrest you! Even if they did call on you, they offer help not prosecution, unless you have been visited by them previously and not carried

out their recommendations! The local fast food delivery companies motorbike or someone using an old mains electric drill will probably be putting out vastly more RF interference!

[The son of Triangman]

I agree Flashbang leave the capcitors where they are, unless they give trouble, making sure the decoder has suppression built in. Detector equipment does exist, and has been used many times in the past to investigate a complaint, usually as you say advice

is offered in the first instance, but a repeat offender can find themselves with a hefty bill.

To be on the safe side leave those capacitors where they are, unless they give trouble or the decoder has built in suppression.

[The son of Triangman]

Shops shouldn't advise to just remove the capacitor/s without checking to see if the owner's decoder has built in RF supression.