Improve the DZ125 DCC decoder by adding supercapacitors

The DZ125 dcc decoder from digitrax is a neat little decoder that i use in my smallest HO locomotives. This decoder is not one of the best (my favorite is lokpilot) but its biggest advantages are (1) Price and (2) size.

One of its biggest issues seem to be the nonexistence of a decent capacitor after the diode bridge to smooth things out on the tracks, especially when they are dirty or at turnouts when the frogs are insulated.

So i figured, why not add my own capacitor bank. And while i am doing that, why not “Supercaps”??

Now supercaps are a new technology product that came about due to advances in dielectric medium.  Since capacitance (C) is directly proportional to the dielectric strength, the new advanced dielectrics have given us supercaps in 100’s of Farads.

I found a really nice Panasonic supercap at digikey which had a decent capacitance : 330mf (that is millifarad) @5.5v and was pretty small. So i bought some and put three in series to make effective supercap of value 330mf/3 = 110mf @ 16.5v (capacitors when put in series have lower effective capacitance, but higher voltage rating).

Panasonic supercaps

As you can see, 2 mounting types are offered, horizontal and vertical.  At the left is the soldered set of supercaps insulated with liquid-tape

So now that the supercap is done, where to connect it up on the DZ125?  Here are some close up shots of the DZ125 with its wrapper removed. Those are some really tiny 0402 footprint SMD components. Looks like the board is using a micro-controller from microchip. I cannot see any big storage caps.

Side1 of DZ125 DCC decoder from digitra

Side2 of DZ125

Marked in the picture above are the locations where the +ve and -ve wires of the supercap are to be soldered. You will need a fine tip soldering station for this. I am using a Hakko 693.


I am a computer engineer living in the beautiful city of Austin,TX. While my day job is designing computer chips, I love to dabble in woodworking, metalworking, r/c and electronics.

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2 comments on “Improve the DZ125 DCC decoder by adding supercapacitors
  1. Ken Kondo says:

    Nice mod report!! I would like to try the same, but like to see performance report. Do you have any?

    • rkovvur says:

      Sorry I don’t have any performance report. But having used these capacitors i can say that their internal resistance is quite high. So they definitely cannot drive a motor.

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