I thought I would raise this subject as a discussion starter.
One of the biggest DCC draw cards for me is the use of on board power packs (keep alive, stay alives). While I have only been a recent DCC convert, It occurred to me that I have not once cleaned the wheels on any of my DCC, keep alive equipped locomotives. This surprisingly is not down to my laziness but down to the wheels remaining squeaky clean ever since the DCC conversion. I was thinking about this on the way to my club one night and thought that perhaps it was the keep alive keeping my wheels clean. I discussed it with one of the club members and we both thought the theory was plausible.
I guess there are a few factors which affect dirt accumulation on model wheels. One would have to be dirt simply picked up of the rail, another would be what the wheels are made of and another would be the amount of electrical pick up a locomotive possesses. In my DC days I have always thought the more pickups fitted to a locomotive the better your wheels stayed clean. My theory here was that if large current spikes were distributed through more parallel paths the affect of a pitting/dirt transfer spark would be decreased through a single wheel. This theory is were I think the keep alive fits also.
The TCS KA2 I have fitted to my Z13 has five 1 farad capacitors on board. This equals a total of 0.2 farads. The charging resister used on the KA2 is 150 ohms. This means that initial current draw on a completely discharged capacitor equals 0.08 amps, presuming 12 volts is present at the rails. This current draw will quickly reduce according to the capacitor resistor time constant.
During a small power interruption the keep alive supplies the motor with power and then once the interruption has passed current flows back into the keep alive at around 80 milliamperes (less usually due to the capacitor rarely being fully discharged). With non equipped keep alive locomotives, during a small power interruption the motor may stop rotating and once the interruption passes a large current will flow through the high resistance wheel contact powering the motor once again. I think this high current, high resistance path can lead to dirt building up on locomotive wheels. With the keep alive fitted the current is reduced through the wheel/rail path (buffered) thus helping to keep wheels cleaner during transient current requirements.
As I said I have not had to clean my wheels at all. They look brand new. Maybe this is just luck?
Would love to here from other capacitor users as to their experiences.