Capacitors on ESC

[VinCopter]

How to know the "reaction" time of the cap.

ceramic capacitors are used to smooth out spikes like what X34 has mentioned.
Numerous smaller bipolar caps that add up to a bigger cap will give better effect than a single large cap. however, the weight and size of many small cap may not be a good trade off for the performance gain.

Also, when you buy the capacitors, you must take note of the following:

!) max operating temperature of the cap
2) max operating voltage
3) the "reaction" time of the cap.

Don't get a cap that is too high voltage, But it should have a minimum of at least 12v.

If you did install a very high farad capacitor, make sure that you handle your wire terminal with great care.

[mave]

This is a proper named for the "reaction" time of a cap.(can't remember off hand).
The only way to know the reaction time is from the manufacturer spec. Even the retailer will not know.

If you go to www.farnell.com, you will see that some caps will have this information listed

[khatiban]

ESR (Equivalent Series Resistance)
lower ESR, better 'reaction'

[Demented]

ah kong kon koh

The capacitor has an ability to store electrical charge (like a battery). The capacity is define by the value stated on the capacitor (in sub units of Farad). On the contrary to what some may had replied, the voltage limit stated on the capacitor is a limit that the manufacturer "guaranty" to operate safely.

So what does the capacitor do when put across the batteries? Well, the reason is a simple 1... When motor is not runing and sudenly you pull the trigger and the motor will try to spin. This "operation" needs lots of current and if your esc does not have a capacitor, the voltage from your battery will go down for a fraction of a sec. Now, since i mentioned on the top that capacitor is like a battery, the capacitor's charge will try to "fill the gap" (to make sure a straight and level DC level)

Well if noboby understand what im trying to say, fear not cause i type untill blur liao In layman term, "got put the cap then the car got more torque (tok) arh, song boh!!??!!"

summary:
cap's voltage rating = more than the maximum voltage from your battery at anytime. (the higher the better, but higher=heavy=big so slightly more than your batt's juice can liao.

cap's farad rating = the more the merrier once again, more farad=more weight... have fun...

[Airborne]

The capacitor has an ability to store electrical charge (like a battery). The capacity is define by the value stated on the capacitor (in sub units of Farad). On the contrary to what some may had replied, the voltage limit stated on the capacitor is a limit that the manufacturer "guaranty" to operate safely.

summary:
cap's voltage rating = more than the maximum voltage from your battery at anytime. (the higher the better, but higher=heavy=big so slightly more than your batt's juice can liao.

cap's farad rating = the more the merrier once again, more farad=more weight... have fun...

I understand what you say, but when i try the bigger ones it seems not the better? I have tried some the size of my sub-c cells or even bigger, it does not show as much punch as the small ones, and it drain the batt like crazy... two 1000 uf in parallel gives the best performance..IMO of base on no grounds just pure physical testing..

I also notice that when i leave the car stationary for a sec or 2... it get more punch than zooming about..

[khatiban]

I understand what you say, but when i try the bigger ones it seems not the better? I have tried some the size of my sub-c cells or even bigger, it does not show as much punch as the small ones, and it drain the batt like crazy... two 1000 uf in parallel gives the best performance..IMO of base on no grounds just pure physical testing..

I also notice that when i leave the car stationary for a sec or 2... it get more punch than zooming about..

The reason why bigger capacitors don't perform as well is because of high ESR(Equivalent Series Resistance). It's similar to a batteries' internal resistance which limits it maximum discharge rate.

Electric motors require HUGE amount of current when they start spinning from zero speed. The problem with most batteries is that they can't deliver that much current due to their internal resistance.
Capacitors solve the problem by charging itself up when the motor is not moving. When the motor starts moving, the capacitor throws its electrical charge to the motor all at one go, together with the current from the batt, the starting current will be large enough for the motor to pickup quickly

So capacitors with lower ESR will deliver more starting current (which means more starting torque = higher acceleration) but how long the capacitor can maintain the current will be determined by its capacitance.

My Conclusion
Many small capacitors in connected in parallel will perform better than one large capacitor because the overall ESR will be much smaller.
To calculate the total capacitance of many capacitors in parallel is as easy as adding up the numbers