# Practical Application of Capacitors

1. Jun 14, 2012

### mearvk

I was thinking that a car battery is a 12v source that delivers between 300 and 900 cold cranking camps. That'd put the cranking wattage at between 3600 watts and 10,800, right?

Here's a car battery 'helper': http://goo.gl/Roo2l [Broken]

This is hypothetical at this point but what I was wondering was since a car only pulls the 3600 to 10,800 watts for about 2 or 3 seconds, would it be possible to safely use a capacitor based system to deliver this power instead of the chemical battery?

I know, I know, be careful.

Last edited by a moderator: May 6, 2017
2. Jun 14, 2012

### davenn

yes possibly, but what are you going to use to charge the capacitor ?
the car battery ? the booster thing you linked to which appears to probably have its own battery inside it ?

so you are going to complicate things by having some battery charge a capacitor for engine starting, instead of just starting the engine direct from the battery ?

Dave

3. Jun 14, 2012

### mearvk

At this point it's a theoretical exercise. Yes I agree it would be weird to have a way to charge the capacitors but not start the engine itself. You'd need a secondary generator somewhere. Which brings me to another question, how long do capacitors typically hold their charge?

4. Jun 14, 2012

### mearvk

Sort of related.

When a car battery dies is it the voltage that goes or the amperage or both?

Since we are taught to hook the jumper cables up in parallel I assume it's the amperage that is lost when the battery is drained. Can you guys chime in on this?

5. Jun 15, 2012

### davenn

That would depend on the capacitor type and manufacturing. It ( a large value one) would still hold a charge after some days or so probably. It would slowly leak across the dielectric.

Dave

6. Jun 15, 2012

### davenn

well you could say both. but principally its the voltage that goes. measure a good battery and the same type of flat battery what will you see ? .... the flat one has very little voltage

Thats a simplified way of looking at it without going into how the battery ( whatever type) produces a voltage for a start .... google will give lots of answers there :)

Just remember a battery doesnt store a voltage. It generates a voltage by a chemical reaction
So when a battery is "flat" it means that the chemical reaction is no longer occurring

cheers
Dave

Last edited: Jun 15, 2012