capacitor debate keep it clean

3 questions about capacitors, answer them and then debate on... We will say there is a alternator with 0 gauge power wire to battery, from front battery to 2nd bettery, from 2nd battery to capacitor, from capacitor to amplifier... alternator charging at 14.4v... if you have a equation that needs more numbers, create your own simulated numbers to demonstrate, Resistance/current/power/etc... 1. How does this capacitor work in this circuit? If you know how it works I shouldn't have to add anymore leading words. 2. What are the pros of this capacitor? 3. What are the cons in this capacitor? I can't hear you!

1. Capacitors connected in parallel with this circuit will have equal voltage as shown across the power source, or in this case the battery. Batteries have been shown to have very large reserve capacity compared to capacitors. But they also charge and discharge 100's, 1000's, 10,000's times slower than a capacitor does. Which makes the case for the need of a capacitor. Say your voltage drops from 14.4v to 13.0V during a specifiv 5 second 40hz note. And your battery (HYPETHETICALLY for easy numbers) discharges and recharges in 1 second. Now if you add a capacitor that discharges and recharges 100's,1000's, possibly 10,000's times faster than the battery. What is happening is while your battery is STILL discharging, your capacitor has discharged and recharged 1000's of times. This gives you a better AVERAGE voltage with the amperage your alt and battery PROVIDES. Your capacitor can only be as good as the weakest link in your alt, battery, capacitor combination. So if you're dropping down to 10v on a 5sec 40hz note, you don't need a capacitor you need a bigger alt, THEN a bigger battery, THEN a capacitor. If you're dropping to 12.3v you could use a capacitor and a agm battery because your electrical has shown that it can handle the draw from your amps. With a capacitor you are going to have less of a voltage drop because it discharges and recharges faster, allowing that current to your amps to have a better AVERAGE out of the alt, battery capacitor combination you have. So you may only drop to 12.5v instead of 12.3v... capacitors neveeeerrrrr act like a piece of wire just drawing current because it acts as an open circuit, meaning it can't have CURRENT FLOW, it can't ONLY discharge and recharge. Pros. Better average voltage, release of high currents almost instantneously to amps with big current draws. Cons. Cheap ones on the market do not help the benefit of them since they are made of cheap material, if you see a 30 farad cap for 70$, just say no. Normally not enough capacitance for system, or way too much is expected of the capacitor. Can't wait for this debate to start, love learning new things, and peoples opinions.I can't hear you!

Batteries do not discharge slower than a capacitor - like capacitors, they supply the demand. (That's if in parallel. See below re individual discharge rates.) Similarly, capacitors do not charge faster than a battery (assuming burp and shortish overload situations) because BOTH are at the same voltage (as you stated). For long burps and overloads, it is pointless having a capacitor - they have minimal reserve time (even a 12V 1.2AH battery outlasts a multi-Farad cap). If the voltage drops from 14.4V to 13.0V for 5 seconds due to an overload (ie, the alternator is of insufficient capacity OR due to cable drops), there is no recharge involved though - ignoring surface charge - the battery is still being charged (since 13.0V is above its nominal fully charge voltage of ~12.7V). REPEAT - there is no recharging. Both the cap & batt have dropped to 13.0V. Further to that, the battery's surface charge will be far greater than the cap's capacity. The advice is usually to use headlights for 5-15 minutes to remove surface charge from a battery, or let it rest for 24 hours. That drops its voltage to its "real" fully charged voltage of ~12.7V (in theory, 12.67V). Will a cap last 5-15 minutes with headlights and only drop to 12.7V? Unless you are going into certain material or chemical issues (which are not relevant to the situations discussed), your comments -cum- assertions are simply invalid - eg: The cap voltage will be the same voltage as the battery. (I am assuming the cap is parallel to the secondary battery(s) that are next to the amp. The alternator voltage will be higher.) Charge and recharge IS current flow. A cap is not an open circuit - it is a cap. (A discharged cap is a instantaneous short circuit when voltage is first applied - hence the need for series resistance to limit the current if the short or high current could damage the supply.)    And a cap is not an open circuit (through it) for AC voltage. IE - it acts like a filter making the voltage smoother. But the battery also exhibits cap-like behavior. (Some circuits even model the battery as a very large capacitance.) There is no debate per se in the above. The inferences drawn are simply incorrect. How can a cap recharge and discharge from the same voltage? It recharges when its rail voltage is higher than itself. It discharges when the rail is lower (ie, the water and bucket model). That's no different than a battery. As to discharge rates, I don't know where that comes from. The only truth to that is that a capacitor discharges (ie - its voltage decays) much faster than a battery because it has nowhere near the same capacity - ie, capacitance. (That does depend on sizes, but if a 9V battery keeps a lamp lit longer than a 1F cap...) Ergo, why use a cap? You may see several articles that show how a small battery (eg, 12V 1.2AH) has far greater capacity than a 1F or larger cap. Hence the argument with a battery and cap in parallel becomes - for greater capacity - a battery with a small battery in parallel. That then becomes 2 equal batteries - or a larger battery - for even more capacity. The main desire for capacitors would be to replace batteries as caps do not have inefficiency (well, maybe 1% compared to ~30% recharge inefficiency for a battery). But to replace an automotive battery would require a trailer load of capacitors. Apart from the cost involved, it is simply not worthwhile. Cars burn far less fuel for the battery's 30% inefficiency than towing a heavy trailer around. Another reason for caps might be because secondary batteries are undesirable or can't be located near the amps, but that is not relevant in your case. Unfortunately I have lost the link to the original article, but have a look as Richard Clark's article as reproduced at http://forum.realmofexcursion.com/accessories-electrical/17919-why-you-dont-need-capacitor.html FYI - Ignore any mention elsewhere re "placing more load" on the alternator. The reality is quite the opposite - bigger batteries (and caps) LESSEN the load on the alternator - not that an alternator should care, though undersized batteries else alternators can cause noticeable lifespan issues. Also, despite people saying otherwise, ripple on a DC supply is AC. In this case, ripple etc is an AC voltage offset by 12VDC (or "AC with a 12VDC bias").

There is no debate.  Caps do what they do, and Oldspark has detailed that nicely.  They are not a panacea for needing additional ampacity: only a larger alternator will give you that with the engine running.  But they function just like, well, capacitors.Support the12volt.com

" The advice is usually to use headlights for 5-15 minutes to remove surface charge from a battery, or let it rest for 24 hours. That drops its voltage to its "real" fully charged voltage of ~12.7V (in theory, 12.67V). Will a cap last 5-15 minutes with headlights and only drop to 12.7V?" do this in a GM vehicle and your car probably wont start without a jump box... just saying. the reason you need a cap is because car audio companies sell them and sales and marketing teams will tell you anything to convince you that you need one. just like most people believe that a higher wattage sub woofer WILL be louder, its all about making money and capacitors are great money makers because that 10 farad cap that costs you $300 probably cost $20 to make.

But old spark then you should know that capacitor DO NOT have to fully discharge in order to recharge... and NO how can you say it acts like current flow??? The current changes at an EXPONENTIAL rate when charging and discharging in a capacitor. That is not what current FLOW is. The capacitor gives out bursts of energy MANY thousands of times faster than a battery which makes it LOOK like current flow at the amp. But it simply isn't. Since you want to talk metaphors I.e. lol let's look at your light bulbs in your home, I know its AC but capacitors act the same way in both, simply discharging and recharging. Anyway our home lights are set at 60hz, meaning it has 60 ON/OFF cycles per second. But to the human eye it looks like the light bulb is ON. That's the same way it looks to a amp. This is true, I've done a lab on it, and experiment, with results and a lab report AND graphs of the capacitors discharge and charge rates with different wave forms. I don't understand how you think capacitors and batteries charge at the same rate...?I can't hear you!

And car companies now just push 300 and 400$ batteries onto everyone. Trust me if money was an issue then they are WINNING right nowI can't hear you!

rfhvhtoo wrote: And car companies now just push 300 and 400$ batteries onto everyone. Trust me if money was an issue then they are WINNING right now

yeah but the battery costs more to make than the capacitor thus there is more profit from a $300 capacitor than a $300 battery

soundnsecurity wrote: rfhvhtoo wrote: And car companies now just push 300 and 400$ batteries onto everyone. Trust me if money was an issue then they are WINNING right now yeah but the battery costs more to make than the capacitor thus there is more profit from a $300 capacitor than a $300 battery

Its hard to even find a 300$ capacitor, 300$ for 1 battery, and you NORMALLY need 2 (one in the engine bay and one in the trunk to try an reach ideal performance) is average. And nooo, there is less profit in capacitors because they can last 10+ years. Batteries have to be bought again and again and again, AND recycled. Its a win win situation for audio companies. Because you will never see a battery outlast a capacitor in ideal conditions.I can't hear you!

If current flow is not involved in a capacitor, the WHAT is being charged? I suggest you find out how a capacitor works. Nor does a battery fully discharge. But a battery discharging 0.01V or 0.1V still has FAR more capacity than a cap. Exponential is irrelevant. They both follow Ohms Law etc wry supply and demand. My car battery is 13 years old. Most of it is recyclable, and a far higher percentage than a cap. What parts of a cap are recycled - the electrolyte? That argument is another AGAINST using a cap. And a cap up front is irrelevant. You are talking about the rear or remote performance - ie, holding up the voltage. (ie, the front cap is wasted.) Alas I have to go. And I forgot AGM protection using caps, but you have multiple AGMs as I recall. PS - are you saying a cap outlasts a battery wrt charge? If it doesn't, then what are you asking? Do the calcs!