CAPACITORS

No capacitor needed, the only benefit would be to ride over dead spots.  Bigger is better if you're using it for that purpose.

I have on hand  1-35v 4700mf  and a couple of  40v 680mf

will both sizes work

Thanks

Yep, the 4700uf will probably be most useful.

YOU GUYS ARE GREAT

Thanks

If the capacitor gets too large, the engine will have a mind of its own when you want to stop quickly.

I use capacitors in my racing engine, and one time my son, who was supposed to catch the engine at the end of the "drag strip, missed, and the train flew off the table and scooted across the convention center floor with him running after it!!  The capacitors kept it going for quite a ways.

Exactly how much capacitance did you have on that Dale?   A 4700uf shouldn't take a locomotive too far.  4700uf barely changes the running time of a motor freewheeling on the bench, so I don't see it taking the locomotive too far.  You must have been using some really high capacitance there.

Dale:

I hope the train survived-i had to laugh it is a funny story

I had 10,000 uF in that one, running off a voltage doubler, and it was one of the small can motors in what was originally a DC set (8902).  With the capacitors charged to 40 volts, a small 12V motor can run for a while (if it doesn't blow up first)!

Yes, big difference in 6V and 40 volts, not to mention twice the capacitance.