Where to attach cap?

[imstock]

I have Radio Shacks schematics, thanks to our search feature (insert applause here) and a reply by Texan several months ago. But even with it's help I am second guessing myself about where to solder my capacitor. Prior to my dis assembly it was bridging the positive and negative terminals on the motor, but I seem to remember the original cap was soldered to the motor body and the positive terminal. Does the body motor case sever as a ground? If so don't both these methods provide the same outcome?

I am bypassing the quick disconnect, and hard wiring the motor to the board using 18g wires. I am running everything stock other then the Spinbrush motor. Alkaline batteries, RWD, etc...

I wont be completing the wire job until this weekend when I am off again, so any info would be appreciated.

[texan_idiot25]

Most stock setups I've seen have the pos. and neg. tabs soldered to the cap, and one leg on the can. Think it was the pos. side...

If all else fails, copy what the stock motor had.

[Donziikid]

The main reason capacitors are used on DC motors is to cut down radio interference/noise. It's a good idea to fit at least two capacitors on your motor; generally from the positive motor terminal to the motor can and then one from the negative motor terminal to the motor can. The can will act as a ground. For extra security measures you can wire a third capacitor from positive terminal to negative terminal, but it's not needed.

Rummaging through my stock Xmods motors (for EVO) I see a capacitor is between the positive and negative terminals, but the positive end is extending on towards the can connecting all three (can, positive terminal and negative terminal). Then there is also a capacitor on the negative terminal connecting to the can.

[imstock]

That makes sense, however I am unsure how a capacitor filters out radio interference yet it creates it's own EM field. It's obvious I still have some learning to do even though I have been playing with electronics for years.

Another quick question though; what size capacitor is optimal? I have a 10µf from before, but having looked over Radio Shacks stock the original I believe was a 0.1µf or 0.4µf.

[RedSXmodder]

Not sure on the uf number, but a high frequency 104 capacitor is the best cap to use. Most companies use it on their aftermarket motors.

If you have a question on how the motor capacitors are mounted, take a look at the motors Atomic Mods, or PN sells. A cap off of the positive brush tab and a cap off the negative brush tab, then each soldered onto the can of the motor itself. That is how I do it.

Later,
RedSXmodder

[BART]

Originally Posted by imstock

That makes sense, however I am unsure how a capacitor filters out radio interference yet it creates it's own EM field. It's obvious I still have some learning to do even though I have been playing with electronics for years.

Another quick question though; what size capacitor is optimal? I have a 10µf from before, but having looked over Radio Shacks stock the original I believe was a 0.1µf or 0.4µf.

Without going way too deep, each time a brush passes from one segment to another on the comm there is an arc and a peak transient voltage produced, the caps absorb this peak (which is the primary cause of interference). one from each tab to the can stops the spike from going into ground (the can) and one from positive to negative absorbs and then distributes the spike to a segment that is in contact at that time. The flat red ceramic caps are prefered.

[texan_idiot25]

One easy way to demonstraight this is run a motor with no Cap next to a TV, will probably disturb the TV screen really bad. Now, run the motor with the cap next to the TX and there should be no interference at all.

[merc3des]

Yea, it all depends on the cap itself. Some caps don't increase speed, but keep speed consistent. These caps often make the motor quieter. Some caps just keep the motor quiet. Thats what ive learned from experience.

[BART]

Originally Posted by merc3des

Yea, it all depends on the cap itself. Some caps don't increase speed, but keep speed consistent. These caps often make the motor quieter. Some caps just keep the motor quiet. Thats what ive learned from experience.

It's not the cap that makes a difference, it's where it is installed, all caps do basically the same thing.