# COMMUNITY : FORUMS : TECH

## Charging BoostCaps

I recently got a few of the 3000 farad 2.7 boost caps from electronic goldmine.  I have a quick question about charging them.  Applying a higher than rated voltage before the capacitor is charged all the way would be fine, right?  The voltage drop should cause the source voltage to approach 0, thusly below the 2.7 volt rating.  As an extreme example, lets say you simply hooked up a 9 volt battery to it.  Since the battery can only supply like 200mA, the voltage drops to nearly 0 as the capacitor appears to be a dead short.  The dielectric (or ion exchange or napheon membrane or whatever it is in a ultracap, lol) should be fine, correct?

My main goal is to later hook up one or two of these for a regenerative brake system of something like a small gokart or bike or something.  Stopping at 30mph is like (assuming 200kg total mass) 20k joules, and each one can hold about 10k joules, and assuming a max efficiency of like 30 or 40% (I think itd be much lower, though), these capacitors could brake a gokart going fairly several times without having to be discharged inbetween cycled (but of course they would be).  For braking, could these essentially be hooked up directly (of course with pwm, and other things, but in essence:) to the motor with a little protection circuitry to prevent overcharging the capacitors?  Or would the higher voltage instantly puncture and destroy the boostcap?

tantris5 years ago
I guess, you would want to do two things with the pwm: define the maximum amperage, so the motor doesn't overheat, and the maximum voltage to protect the boost caps. I would add kind of a "soft start" for the maximum break power, so it feels more like a mechanical brake engaging and not like putting a stick through your front wheel ;)

guyfrom7up (author) 6 years ago
More the question is that the voltage will drop to a nonharmful voltage immediately and safely charge the capacitors, assuming you break the connection when the max voltage for the capacitor has been reached
Electronics1116 years ago
In order for the capacitors not to appear as a dead short when braking you would need some sort of high wattage resistor to stop the inrush or current making the capacitors appear as a dead short. If you overcharge the capacitors by a few (i.e. 2-5) volts, it shouldn't destroy the capacitors but may reduce their lifetime.
6 years ago
You need an active chopper really