ESU DCC decoder + SuperCaps

Recently I have been experimenting and using supercapacitors in my model trains to compensate for dirty tracks, insulated frogs and lack of flywheel on some of my smaller locomotives. A lot of the older locos from Fleischmann (with the pancake motor) had no flwheel and their running characteristics were not so good. The hope was that the supercapacitor would act like an electronic flywheel.

The supercaps i am using currently are from Panasonic (330mf, 5.5v, 75ohms). I use 3 of these to get an effective capacitance of 110mf with 16.5v rating and ESR(DC) of 225ohms.

Caution : Charging supercapacitors is not a trivial task. If a supercapacitor’s ESR is low, then it can sink large currents while charging and destroy your source. You will need a current source to charge most supercaps. However the supercaps i am using  have a large enough ESR that current limiting occurs naturally. However this also means that current supplied is going to be quite small (12v/225ohms = 53.3mA). Sufficient to keep your LED lights ON for a long time with no flickering, or maybe run a small motor. So keep this in mind.

One commercially available supercap module for model trains is the LENZ USP. This module is a bit different. It uses a 1Farad/2.5v supercap. These supercaps have very small ESR (in milliohms). Which means that they can supply large currents. However, the capacitor’s voltage is only about 2.5v. So a boost switching inverter is used to boost that voltage to 12v and about 100ma?? of current. That’s a decent amount of current. On the flip-side, you need complicated electronics for charging the cap (current source) and stepping up the voltage (boost inverter).

I love my ESU DCC decoders. Amazing decoders with short circuit protection on both the lighting and motor drive. In the past i have used supercap backup for my DZ125 DCC decoder. I wanted to see if i could do the same with the ESU basic decoder. Below is the finished wired up decoder. End result: It works great. If the motor is not running, the supercap module kept the LED lights going for almost 2 minutes after the power was removed. You can also see the supercap module below, with the 3 capacitors in series.

20120423-102825.jpg

Close up photo of the ESU basic DCC decoder bridge section. The 2 soldered wires at the diodes are connected to the supercapacitor. ‘Yellow is +ve’ and ‘Blue is -ve’

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About

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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Posted in Electronics, Model trains

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