Capacitor for amp

I don't think you'll need a cap. I'm running around 500 watts RMS right now between my 2 AMPs and have no problems. I have had them installed for a few months now and they have been thoroughly worked for hours at a time. On my 8 hour cruise through BC's interior, the music was pretty much cranked constantly with no dimming. However, when the car is off or in ACC then you'll notice the lights dimming, but that's too be expected from a small 12V battery.

 

Stiffening capacitors serve three purposes:

1) Enhance the appearance of your install

2) Generate high-margin sales for the parts manufacturer and retailer

3) Demonstrate to the world that you don't know anything about electronics, and are easily fooled by marketing propaganda

None of those three interest me, so I don't use them.

If you do the calculations on how much energy is actually available from a capacitor, you'll find it's just a fraction of it's rated capacity. This is because the voltage on the cap drops as its energy is drained, and it is only useful as long as its voltage is above the level that the amp shuts off. So the actual energy you can get out of it before the voltage drops below a useful level is around half of its total capacity. If you really feel the need, your money is much better spent on a second battery rather than a capacitor. A car battery holds thousands of times more energy than a 1 farad capacitor.

Also, as the previous posted pointed out, unless your stereo is designed to annoy people in their homes rather than actual listening, you'll never play it loud enough to dim your lights. My two amps, tested at 700 watts combined, don't even get warm to the touch when played at normal listening levels (below the level at which permanent hearing damage occurs). Unless you've turned your Prius into a "Bumpin Ride" with multiple 12" or larger subwoofers, I don't think you have anything to worry about.

 

All a capacitor does is smooth out voltage fluctuations and make it more like the amps are hooked straight to the battery rather than a distance away and therby smoothing out voltage fluctuations as the amperage pulses would normally move the voltage up and down in the long travel of wire.

but with a small battery.. its worthless anyway..... the capacitor cannot create any more power than the battery has to give!.... you can't run an amp without the help of the car inverter! If a capacitor smooths out voltage.. what good is it.. if the the "smoothed" out voltage is only 10 volts?...

 

That's not it at all - just do the math and you can see that there is no significant voltage drop along the wire as you claim.

4 gauge copper wire has a resistance of .000292 ohms per foot. Let's assume it's an 18 foot run from the battery to the amp (in a Prius it's less than 18 inches), and you're powering a 1000 watt amp, which we'll assume is 55% efficient.

1000/(.55 * 12) = 151 amps

151 * .000292 = .04 volts

So the voltage drop in a 18 foot piece of 4 gauge wire is 0.04 volts with 151 amps of current running through it. There is no significant drop of voltage along that wire, so your assertion is completely wrong.

What the capacitor manufacturers would like you to believe is that your battery and alternator cannot supply sufficient current to prevent a voltage drop, and a cap will store energy in reserve to prevent a voltage sag when your amps draw a lot of current. The reality is that a one farad capacitor stores so little energy it's completely useless. As I stated before, a battery stores thousands of time more energy than a capacitor, so it's a better way to spend your money.

 

I agree.. without a load on the battery there is no voltage drop because there are no amps to drop it.

 

in my firebird, i had three 10's runnng off a 1000w amp. capacitor really helped there. i did NOT buy one from a store for $100+ though. my cousin is an electrician who rigged me up one for about $10. they do work, but the price is way too high.
now in a prius, with the energy coming from not only the battery, but the inverter also, there may not be a need for one. i'd say hook up the sysem, and if you notice there is a lot of diming, then get one.

edit * as stated earlier, better off getting a full size battery first.

 

Its hard to "Hear" the difference.. you have to have a really hard punch from the bass side.... ... in reality.. having the amps close to the battery is the best you can do... other than having a bigger battery and alternator "which is fixed" in the prius.
Good amps have the capacitors built in.. usually rated as a "dampening" factor... "if I'm getting my terms right". Those are the ones that can deliver the full bass punch without fading. I have amps in my sound system at home that are rated at 2500 watts and they don't do as good a job with my 18 inch sub as the 1500 watt that is a better quality!... its the guts that count.. not the watt rating!

Simliar to a bullet.. one thats moving at 3000 ft per second may not do the same damage as one thats doing 1500 ft per second but weighs five times more! More energy is involved in the second illustration. Even so with car amps... Watt ratings are not the whole story... not by any stretch of the imagination.

If your wire travel was really long "and it shouldn't be in the prius since the 12V is in the back...", but based on where you mount... and if your bass "did" really pull the volts down, an extra battery near the amp would suffice much better than the measley capacitance of a cap. There is a reason they use 4 guage wire!
In my car, I can turn the bass up and make your skin itch and crawl as it vibrates with my 4 amps and voltage drop is not an issue and I don't use caps. The air is moving the molescules so vehmently that if you try to speak "out loud" it sounds like you are talking in a fan as the sound waves chop up your voice! If I turn the car is off and I don't have the added power from the alternator, then voltage drop is more noticable... eh.. but who cares.. I don't.

Go and borrow the biggest cap you can find and alternate between using it and bypassing it... there is not much difference on the bass... "none" on the other frequencies! Capacitors are largely over rated!.. and way overpriced!... along with all the gold plated "do=dahs" they sell!... If your doing it for show.. go for it!

 

In any high-powered amplifier for cars there needs to be a voltage boost circuit, otherwise your limited to (at best) a measly +/- 6 volt swing out of the amplifier. The voltage boost circuits require significant capacitance in order to retain the "headroom" needed for audio reproduction. Basically, this is reserve current needed to deal with instantaneous current draws. Capacitors on the battery side are really not going to help very much, if at all. If you need to draw more current from the battery side, then you would need a huge capacitor to make much of a difference.

It reminds me of the monster cable debate... People swore that spending $10/ft on cable was the only way to go. All sorts of exotic cables sprung up, many reducing the capacitance (but effectively increasing the inductance) properties of the line. Finally, a truely blind study was done by Pass Labs, where they discovered that the only correlation between quality and cable characteristics was the wire gauge. In addition, at 14 gauge, there was statistically insignificant improvement. So instead of spending $10/foot, I spend significantly less by using 12 gauge low-voltage lighting cable (the stuff that looks like lamp cord on steroids).

Without a true scientific study or significant engineering metrics to prove that anything works, I would never listen to anecdotal stories.

 

I've read some of the capacitor debates on the car audio sites, and it always seems to be that the people who do measurements and power calculations think capacitors are not useful, and the people who rely on non-quantitative theories and "impressions" are the ones who think capacitors are worthwhile.

Honestly I haven't delved into measurements and calculations enough to be able to speak authoritatively, but my sense from those who have investigated them is that capacitors are generally not very useful for car audio. They might have some applications in really high powered cost no object systems, but even there adding more batteries seems to be a much more cost effective upgrade than capacitors. For a daily driver system I don't think there is any need for them.

BTW I just recently took the 12V battery out of my 2004 prius while I was working on that area. The well the battery is in is much deeper than you might expect, and the battery is much taller than you might expect. I'd say it was about 2/3 the size of a standard car battery overall. So the Prius battery is not as wimpy as you might suspect.

 

If the lights are blinking to the rhythm of the music, a cap will help.
The blinking shows that the power draw is not continuous, otherwise the lights might dim when the audio is turned on, but otherwise remain steady. The cap can compensate for the voltage fluctuations due to wiring resistance AND battery/alternator internal resistance.

 

There is some debate as to whether the cap will solve even the situation where the interior lights dim to the beat of the music. Note that the xenon headlights shouldn't dim even in this case since they have voltage regulators.

But it is a good point to make: If you can play your stereo loud with the hybrid system on and the interior lights don't dim to the beat of the music, then you can be sure you won't benefit from a cap.

 

I concur the last two posts as accurate!.... the beat gives the clue.. usually you won't see that unless the car is off and your running off battery alone with no alternator support.
But if your voltage is smooth... smooth is smooth.. a cap won't help anymore!

I only notice fluctuation when my car is off.. on batteries alone, AND I kick the power and the bass up high... I have a dash knob that control the bass amp output.