Capacitors used on motors

It's a way to give a single phase AC motor a kick start at a lower voltage. Especially when the magnets have a high opposing force. Vacuum cleaners used to use these as well.

How does that work?  And, can the capacitors be used with a postwar engine that does not use the brushes with wire extensions?

Gregcz1 posted:

Hi.  I recently purchased a Postwar GP-9 and discovered the motor had been "upgraded" with capacitors and brushes with long wires extending from the top.  Can someone please tell me the significance and/or improvements this feature gives to a motor?

The brushplate shown is a newer-style as well, so it's possible the shunted brushes and capacitors came along for the ride -- or you might have an entire motor that's a few decades newer than the rest of the chassis.

The shunted brushes help with conductivity. The caps cut down on motor "noise" (electrical interference) that can effect electronics. Those brushes were first introduced in the early 1990's, whereas the caps came along with the first TMCC locomotives in the mid-1990's.

Neither will effect the operation of your loco (in fact, the shunted brushes might actually improve things a bit). If you're a stickler for authenticity, then you'll need to the remove the caps, replace the brushes and brushplate with period pieces. But if everything works OK, I'd probably leave things as they are.

TRW

I believe that Lionel first used brushes with pig tails on the 700E and 763E in 1938. 

Electrolytic (polarized) capacitors can also be used to smooth rectified AC to DC signals. I added them to some of my early Pittman can motored Williams engines and they ran and pulled better .

I'd like to understand how capacitors can help start a motor.
I found two articles on line, but neither seems to apply.
In both cases, the capacitor is only in use at startup, and is then dropped out of any active circuit.
I am pasting the links raw so people can easily see the source.

https://electronics.stackexcha...20v-ac-motor-circuit

http://sciencing.com/ac-motor-...r-start-6596783.html

The shunted brushes and small non-polarized capacitors are simply to reduce the electrical noise from the brushes.

Capacitors are used on induction motors for phase shift at start up. Their used on repulsion motors to quiet commutation noise. as do shunted brushes. Without the shunt the brushes vibrating in their guides create arcs as well as the arcs created by the brushes riding on the commutator.

JohnActon posted:

Capacitors are used on induction motors for phase shift at start up. Their used on repulsion motors to quiet commutation noise. as do shunted brushes. Without the shunt the brushes vibrating in their guides create arcs as well as the arcs created by the brushes riding on the commutator.

"Without the shunt the brushes vibrating in their guides create arcs as well as the arcs created by the brushes riding on the commutator"

I still remember getting my first set of slot cars and my Dad yelling at me to stop racing them when the football game was on.

Sometimes, removing the capacitors and shunts fixes a problem. I have several conventional classics engines which had the early production bug-prone horn/bell boards, where the bell would keep getting triggered at low speed operation. These boards were bad, and were later replaced with the Railsounds Lite boards in later conventional classic releases. It seemed that somehow the horn/bell board was being tricked by signals being received by the motor at a certain speed. So I replaced the brushes with regular ones and removed the capacitors. It solved the issue. My theory is that all that sparking and white noise scrambled the clean oscillations which had been coming off the motor which were somehow mistakenly interpreted as a negative DC offset pulse.