? about caps

[rchippie]

Im getting ready to solder some caps on my 9920 to help it out. Is the side with the white strip the negitive side of the cap ?.

[What's_nitro?]

Yes it is. There is usually a dotted, black line through the white stripe to further signify the negative terminal. If the case of the capacitor were light in color, it would have a black stripe with a white, dotted line on the negative end.

[rchippie]

thank you i just wanted to double check .

[What's_nitro?]

NP man. Better safe than sorry.

I sounded like my parents right there...

[rchippie]

I just added 2 extra caps to my 9920, because people have said they help the esc out. Can anyone please tell me how exactly they help the ESC ?.

[What's_nitro?]

The capacitors take the stress off of the main battery during time of high current demand, like acceleration. A higher total capacitance means they can supply this high current for a longer period of time. All the while taking more stress off of the main battery. The caps have a voltage rating which needs to be greater than or equal to the fully-charged voltage you run in the vehicle. You may have heard the term "Low ESR", which stands for "Low Equivalent Series Resistance". A good analogy would be "LiPo batteries have a lower ESR compared to NiMH or NiCD, which allows them to produce much higher currents with less heat. The same is true for capacitors. Lower resistance means higher currents at higher efficiency. The lower resistance also allows for faster current-rise times meaning that the time it takes for the capacitor to go from outputting 0A to say 150A is much less. In a nutshell: Capacitors + LiPo = Lots of PUNCH!

[rchippie]

Originally Posted by What's_nitro?

The capacitors take the stress off of the main battery during time of high current demand, like acceleration. A higher total capacitance means they can supply this high current for a longer period of time. All the while taking more stress off of the main battery. The caps have a voltage rating which needs to be greater than or equal to the fully-charged voltage you run in the vehicle. You may have heard the term "Low ESR", which stands for "Low Equivalent Series Resistance". A good analogy would be "LiPo batteries have a lower ESR compared to NiMH or NiCD, which allows them to produce much higher currents with less heat. The same is true for capacitors. Lower resistance means higher currents at higher efficiency. The lower resistance also allows for faster current-rise times meaning that the time it takes for the capacitor to go from outputting 0A to say 150A is much less. In a nutshell: Capacitors + LiPo = Lots of PUNCH!

They are 35v 330uf esr caps that i got from brian . Do they help the esc at all while braking ?.

[What's_nitro?]

Oh yeah, forgot that part.

The low resistance lets the caps absorb energy more quickly as well. During braking there are huge voltage spikes sent back to the battery through the ESC. The caps take in the spikes but let most off the current flow into the battery to slow the vehicle. Now, this is only if the ESC uses regenerative braking. I think most ESC's do. There is also another way called "shunt braking" in which the motor phases are effectively shorted out by the FET stages of the ESC. The shorting is controlled by a PWM signal sent to the FET so as not to allow a "dead short". This type of braking does not benefit from additional capacitors.

[Serum]

the older nimh/nicd batteries can't stand a pulse load. their voltage drops when they get this pulsated load. I don't know how lipo's handle this, but according to all the experiences others have shared about the added capacitors i expect them to do the same.

Since the batteries voltage drops, current needs to increase to get the same power, this is why caps are able to help out; they can handle a pulsating load, and the battery doesn't 'see' the ripple because of the capacitor.

[rchippie]

Thank's for the info guys .