Conversion to DCC - Points and all !!

[Jonty66]

Good Morning all,

My layout (DC N gauge) is almost complete with just a bit of tyding up required around the control panel. I've taken the decision, even at this late stage, to convert to DCC and that got me thinking about the point connections to the decoders (I'll probably use the DCC concept ones connected to elink/railmaster). Does anyone know if the system will work OK with the diodes still in place on the Gaugemaster point motors? I wouldn't really want to remove all the points to take the diodes off, as you can imagine.

Thanks in advance,

Jon

 

 

[Chrissaf]

Jonty,

DCC Concepts & Gaugemaster do quite a range of their products. So it would be easier to help others answer your question if you stated the exact product code numbers you were thinking of using. It would then be easier for members here to research. The comments below will help you see why knowing the exact products is helpful to us.

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When you say diodes on the point motors. Are these being used to convert traditional 3 wire point wiring to 2 wire operation?

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In 3 wire operation there is a common return path and you apply a voltage to either of the other two wires to turn the point in each direction.

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In two wire operation there is a return wire (common?) and a single control wire to each point. You reverse the polarity of the two wires to switch the point with the diodes acting as electronic logic at the point motor to energise the appropriate coil.

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Most Accessory Decoders use a three wire output to operate solenoid type motors. In that configuration, they are unlikely to support 2 wire voltage reversal. Knowing the exact decoder model means that we can research whether that is the case or not.

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Where an Accessory Decoder does support 2 wire voltage reversal, then the output in that configuration is usually always on (rather than a pulse) and used to support 'stall' type point motors. Knowing the exact point motor model number you intend to use means that we can research its suitability. ie 'pulse' or 'always on' support.

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My initial gut feeling is that if the point motors are a solenoid design you will probably have to bite the bullet and remove the diodes and provide a third wire (if you currently only have two wires to the point) if you want to control them via DCC Accessory Decoders. But knowing the product details of your planned potential purchases may disprove that.

 

[Jonty66]

 Thanks Chris,

I'll take a look later at the models etc. (in work at the moment).

I fitted the diodes as I was using the Gaugemaster PCU1 to control the points and was advised by them to fit the diodes to avoid feedback across the installation i.e. not the required point would change position when requested, on several occasions another one would that was not fitted with diodes.

Thanks again, Jon

[Chrissaf]

Jonty, thank you for providing the PCU1 model number. Now that I have had a quick look at the online PCU1 manual, all becomes clear. If you have wired the diodes EXACTLY as shown in the manual, then you should have no problems leaving the diodes in-situ and just replacing the PCU1 with your chosen DCC Accessory decoder.

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The PCU1 is using a 'common positive' return, with 'switched negatives' to turn the point. This is fairly common practice and supported by most if not all Accessory Decoders.

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One thing to note Jonty. The diodes will introduce a volt drop typically 0.6 volts. Not a lot grant you, but this can be enough to cause issues with some of the lower powered Accessory Decoders on the market with less powerful internal CDUs (Capacitor Discharge Units). Fortunately, the DCC Concepts decoders are known for their good output performance, so shouldn't be an issue. Some decoders in the DCC Concepts range, if I recall correctly, have the option of using a more powerful external power source yet still retaining DCC control of the points. The potential use of the higher external power thus overcoming any power losses introduced by the diodes in the circuit.

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For others reading. The diodes in Jonty's wiring are NOT being used to convert points from 3 to 2 wire operation. They are being used in series with the point firing wires to prevent high voltage 'Back EMF' (Electro Magnetic Force) voltages from affecting the PCU1 point controller.

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For potential posters to note. The importance of providing additional relevant information along with their original posted query.