QSI Revolution A capacitor

Model Railroader Electronics and DCC
1

Hello,

I got a QSI Revolution-A that I am going to put in my Atlas MP15 (HO). It fits… just. Now I need to find a place for that huge capacitorr. What I am wondering is if I can replace it with something smaller with the same rating (300ufd, 35 v) or possibly a different rating. I suspect if that was the case they would have already done that but I just want to make sure.

Thanks,

Peter

2

Sure, you can replace it, but it should be close to 300uf, and at least 25v. You might get away with less capacitance, but that you will have to experiment with. If you do install something else, make sure the polarity is the same as the original cap.

DC

3

So how will I know if it is working or not working? I assume the cap is to keep the decoder “alive” over dead spots or dirty rails. So if the decoder stops or the sound dies out, I would need to increase the capacitance?

Thanks for the input,

Peter

4

I believe the cap is more for the “dirty” 60Hz DC systems. Some of the DC packs have a lot of ripple in them, and the decoder will cut in and out, or won’t run at all. Basically, the amount of capacitance needed will depend on how dirty the low frequency rail power is. The cap might not even be needed if running strickly DCC since it is a lot higher frequency, but since I don’t run DCC, I’m not sure on that. You can try asking Josh at Tony’s Train Exchange. They have always been very helpful for me.

Good luck. [:)]

DC

5

Thanks DC, it looks like your input was more or less right on. Here is what QSI has to say about the issue:

Based on our testing, the 330uf cap was the smallest size that gave good
performance on both analog and DCC operation.
If the board is going to be used for DCC only, a much smaller cap
could be
used, although we would not recommend one less than 100uf at 25 volts.
If the capacitor is too small, you may have problems with the decoder
resetting while going over a switch or when blowing the horn.

Kelly Dorf
QSI

Peter