A more intriguing question about ESC caps

[Basstronics]

I have had some college coursework in electronics and I understand some of the fundamentals and what things do (more common components).

What I cant figure out is this: Why do the caps in our ESC's discharge?

I know a capacitor is kind of like a battery but it discharges was faster. I know it takes 5c to charge for that 1c burst.

However, when you are running your boat the caps should always be in a charging process. In the DC operation they should help to stabilize voltage during peak spikes (hard acceleration) as the ESR is less than that of the Lipo. Now we never run our batteries fully dead, we bring them in and 70-80%. Which means the caps should be charged 100% before we get the tape off the hatch and unhook them.

So why the big zap when you hook them up? Is it just the small voltage difference between the fully charged lipo and the stored voltage in the caps? Or is there residual bleed off in the circuitry? Im aware the cap will self discharge slowly but that dont explain the big zaps that happen after only a week or two of sitting...

Inquiring minds would like to know.

Paging Dr Wayne!

[sundog]

Capacitors don't hold very much current to begin with. You couldn't light an led more than a few seconds with a fully charged cap the size used in esc's. And they are not perfect storage devices - they self discharge due to materials used and manufacturing processes. But the reason they discharge so quickly in an esc is because the resistors (and coils) in the circuit act to short out the cap giving off a minute amount of heat in the process.

[egneg]

In an RC boat the load is not constant. A sudden increase in load will cause a voltage drop below what the cap has stored so it discharges as it tries to keep the voltage constant. When the load decreases and voltage goes back up the cap charges back up again thus helping to stabilize the ripple. Now to address the cap/ led scenario. Say the cap holds 50 volts but the led only needs 5 volts to operate. The appropriate resistor in series with the led will give off light for quite some time. I have a wind up key chain led light that will hold a charge for days and will give off light for several minutes.