I’m working on my IHC SD-24 and noticed a 104m ceramic non-directional cap across the the motor terminals. What is it’s function and can motor speed be changed by changing the value of it?
The capacitor is there to reduce RF interference caused by arcing at the commutator. It does not affect motor speed, and you would not change anything by changing the value, except to increase the RF interference. Ignore it.
Unless you install DCC, in which case you would want to remove it. It will interfere with the motor drive of a DCC decoder. For DC operation, just leave it, it won’t do anything except help reduce RF emissions.
–Randy
Depending on the size, it might also help with bridging dead spots in the track by keeping a reserve power handy for the motor. But Randy and Gary are correct. It’s mostly to filter RF. And it is a definite no-no with DCC systems
Thanks! All I needed to know…
Yes, the cap. is there to limit RF interference .They are not required in the US, but because many locomotives are manufactured outside the US they are installed in all of them. The Bachman circuit board has 2 of them & one lead should be cut if a decoder is installed. Some decoders will operate well with the capacitors & some wont. Better to cut them.