Practical Application of Capacitors

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Discussion Overview

The discussion revolves around the practical application of capacitors in automotive systems, specifically considering whether capacitors could effectively replace car batteries for starting engines. Participants explore the theoretical implications of using capacitors, the nature of battery discharge, and the characteristics of capacitor charge retention.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant proposes that a car battery, delivering between 3600 and 10,800 watts for a short duration, could be replaced by a capacitor system for starting engines.
  • Another participant questions the practicality of charging the capacitor, suggesting that using a battery to charge a capacitor complicates the system without direct benefits.
  • A later reply raises the theoretical nature of the discussion, noting the need for a secondary generator to charge the capacitors.
  • One participant inquires about the nature of battery failure, asking whether it is the voltage, amperage, or both that diminish when a battery dies.
  • Another participant responds that while both voltage and amperage are affected, it is primarily the voltage that decreases, explaining that a battery generates voltage through chemical reactions.
  • There is a question about how long capacitors typically hold their charge, with a participant noting that it depends on the type and manufacturing of the capacitor.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using capacitors instead of batteries for starting engines, with some questioning the practicality of the approach. There is also a lack of consensus on the specifics of battery discharge characteristics.

Contextual Notes

Participants acknowledge that the discussion is largely theoretical and involves assumptions about the operation and characteristics of both batteries and capacitors. The nature of how long capacitors hold their charge is noted to depend on various factors, which remain unspecified.

mearvk
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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

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.
 
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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
 
davenn said:
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

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?
 
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?
 
mearvk said:
... Which brings me to another question, how long do capacitors typically hold their charge?

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
 
mearvk said:
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?

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 doesn't 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
 
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