Speed control capacitors.

[Taylor]

would those capacitor things help with speed control heat? they say that they take the heat, turn it into energy and then add it for extra kick on acceleration.

[Arct1k]

Yes they help with heat, no it is not about adding it for extra kick on acceleration.

It is about reducing ripple current from batteries under load - use the search on that term...

[VintageMA]

I find this thread interesting. I did a little searching on ripple current to understand it better and basically defined as the AC voltage ripple riding on top of a DC voltage. How extreme it is depends on the ratings of the capacitor and also the frequency of the AC ripple itself.

It's basically the capacitor wasting the current as heat as it charges and discharges current in response to the rising and falling AC voltage riding on te constant DC voltage.

My follow-up question is how is the ripple current generated from the batteries under load? Is it actually the batteries creating the ripple when you accelerate and brake and stop and the voltage of the cells rises and falls? In that case it would seem like the frequency of the current would be very low.

Or is the ripple current something else fired back by the ESC itself?

[Arct1k]

I believe it is the switching of the fets - It isn't really a constant pull from the bats - It is more like a AC wave...

[VintageMA]

That's what I was thinking - if you were looking at an AC ripple from the changing voltage of the batteries you would be looking at something way less than 1 Hz.

A ripple from the FETs switching could range anywhere from 8kHz up to around 32kHz or higher depending on the ESC itself. I'm not sure what the MM and the MMM are rated at, but the MGMs are switchable between 8/16/32 kHz to work better with different types of motors.

[Sammus]

I also heard someone say (or saw someone write lol) it had to do with poor quality batteries due to their voltage drop under load. Like for a split second when it starts the voltage drops substantially then shoots back up once its moving, and somehow that translates into ripple (what I was reading was actually talking about ripple voltage...not sure if they amount to anything similar...)

[Taylor]

ok thanks guys, on another forum, they had something posted about it and that most of the time they are used for bigger motors for brushless, and they have about 8-5 of them on there.