Electronics 2000

Hi
What do I need to discharge a capacitor very slowly. I am using it on my model railway to go on my locomotives to keep them running on badly layed track or dirty track, but I need the caps to discharge slow.
Can some one out there help please.

Ray

It is by no means easy to devise a system which will work well in every instance, but basically you need large value capacitors to act as a short term supply to the motor. I expect that your locomotive will draw somewhere in the region of 1/4 - 1/2 amp, and such a current will exhaust a 1F cap completely in a couple of seconds. Look online for suitable caps - remember that the working voltage has to exceed the supply voltage to the track. For a small loco supplied with 12v DC I would guess that you may well need something of the order of 10F or more @ 16 VW (if you can find any such - you may have to make up from smaller ones) to carry the locomotive over some dirty track. This ideaonly applies to DC supplied track - if you use a modern system where the track is energised with 25vAC, it must not be used. Diodes should be used to protect the caps from incorrect polarity of track or derailment short circuits.

BTW, surely the best solution is to relay badly laid track, and clean dirty track?

What about putting a battery in the loco instead of a cap.