Capacitors, batteries, alternators, and myths


This topic comes up a lot in here and I'm just going to go ahead and clear up some confusion. High-powered mobile audio systems are power hungry beasts. If you want your system to perform as the manufacturer intends, you have to provide ample power.

-How much power does my system need?
Look at all your components (amps, head unit, x-over, changer, etc..) and write down the OEM fuse rating on each device's power line. Add them all up and figure about 50% of that number as what your system will need to be reliable. If one of your amps has two 20amp fuses, count each of them individually. This is not the most accurate method but you will get the ballpark...I doubt most people have the tools to get more specific.

-How much battery do I need?
Enough to start your engine. This is what the battery does, nothing more. Period, anything you hear to the contrary is a myth. The competetion vehicles with banks and banks of batteries use them because they do not run the engines in their vehicles and they listen for extended periods... they INTEND to drain their batteries, you don't.

-How much alternator do I need?
After you figured 60% of your system's demand above, add about 30-50amps (depending on need here, these are not concrete numbers) and that's what your alternator needs to produce to keep up with your system. If you don't have enough alternator, you are taking it out of the battery and you'll end up stranded somewhere.

READ THIS CAREFULLY: If your alternator does not produce more power than the sum of the electrical systems in your car demand, you will hate life. Either upgrade the alternator or downgrade the system. You can't fly without wings.

-What about a capacitor?
Capacitors have one quality that the audo community likes: fast discharge. A capacitor is similar to a battery; they don't make power, they store it. A capacitor holds a large jolt of power on tap and can dump it into the amplifier when a hard bass hit comes about. Then the capacitor slowly (it's actually quite fast but much slower than the discharge rate) charges back up and sits waiting for another surge in demand. If your headlights slightly dim ONLY on big bass hits or if your big bass hits seem a little mushy but you have NO OTHER POWER PROBLEMS, you will find a benefit with using a capacitor.

Summary: More batteries don't help and adding capacitors don't help...adding either of these to an already taxed charging system only perpetuates the problem. Again, your charging system must produce more than your total electrical demand or you are draining your battery.


Dominic L.
good job on info ;)

hehe, i just saw the link to this on a dif. post, good job moto, i was thinkin about writing something similair becuase it comes up so often. i had to write one like that for my other forum. helps a lot instead of typing the same thing 100 times eh? :)

No joke Derek, I get so tired of explaining series and parallel that I'm about to puke. I don't even bother linking to particular posts anymore, I just send them to the accessories board to do a little research. If they can't find this one they have no business trying to install audio equipment.


stupid ppl talking about hey i'll just get another battery. or i'll just get a cap. they need to realize that a cap used on a drained charging system will just make things worse than they already are, bahhhh, i just made a link to this site from my other forum, im so tired of this crap, damn.

Hey guys Just a quick question. Im not a noob but im not a pro my last system was 2 hx2 punch 12" and 2 501s amps and a cap it sounded great but i ened up with 2 blown subs. Im trying to keep my knew system simple with one jl w7 12" and jl 1000/1 mono i was just wandering would i need to replace my stock alternator or get it rewound? And if so about how much would that cost?
Thanks guys

hey jason, first i would trade down to a 500/1 for that sub, it will burn up with the 1000/1, second, Ohio Generator can help you with your alternator needs. as far as your question on wether or not you need a new alt?, i would say yes IF you play it often at high volumes, but NO if you play only an hour or so at high volunes each day, your battery needs time to recharge if your system draws more current then what your alternator puts out, so leave your tunes turned down for a while let it charge. in my opinion i think you should be ok with your factory alt as long as your not just drivin around all day long bangin, good luck w/your system
ps the best i've heard that sub is in slot ported enclosures, sealed has very weak output

Well i have seen w7s with this set up and it seems to work fine. I have heard that a w7 sub can handle all you can give it. Ive also heard that its better to give a little more power rather than underpowering it. The rms is 750 rms and thats underated as most top of the line subs are and according to jl it is still close to the optimum settings (yellow) The sub will be in a vented box. But i think a 500/1 will be a waste.

i found this site that sells factory alternators but im not sure what to get. I know that it should be over 100a and i found one that is 140 but it sais letf mount straight mound. What is this? I drive a 1996 fourd taurus and her is the site if some one could help me find the right alternator i will purchase it and have it installed by a friend. Thanx
Please e-mail me if you can offer me some help thanx again!

xjasonx, i've serviced countless blown w7's, they can be burned up. we sold jl at colubiaaudiovideo and i've hooked up and sold tons of these subs.
the 500/1 slams this sub very hard, if you dont think its enough and you stay with the 1000/1 then i urge you to keep your infrasonic filter turned up and keep the gain levels minimal.
you can blow it up, and my opinion on the rms rating differs from jls, at about 700rms with a sign sweep the sub begins to overxcurt(distort).
i'm not trying to talkdown your sub, i think they are one of the best, however i just don't want to see ya fry your sub.

Well i don't know but like i said im not a pro and i don't want to fry my sub but almost every w7 ive seen i have seen it with the 1000/1 but anyway if i do get the 500/1 will i need to replace my co-exesting alternator?

Also one more thing, I went to the jlaudio website and it sais recomeneded amps 500/1 or 1000/1
So im just curious to why jl would advise this amp if its risky?

my main point is that the 12w7 will slam slam slam so hard with the 500/1, listen to one w/that set up and i promise you'll agree, now second, the 500/1 puts out over 600 rms, so we know that the 1000/1 is underrated as well, you must know that 1000rms+ is to much for that 12. save your money, trust me friend.

Ok Im gonna go with the 500/1 and see how that sounds. should a cap acompany this setup i had a cap with my last system and it didn't do Sh*t. Also what size amp kit. I was thinkin 4 awg.
Thanks for your help zac.

Unregistered guest
hey thanks man. i have been trying to figure out what i need to upgrade. So many people i have talked to just say get a battery or a cap. Thanks for clearing up the crap. You are the man.

New member
Username: Glasswolf

Post Number: 288
Registered: 12-2003
also see here for more information on this stuff:

that should tell you absolutely everything you ever wanted to know about charging systems and capacitors.
and probably then some.
I wrote two of those articles myself.

New member
Username: Motoman22

Post Number: 7
Registered: 12-2003
xJasonx, the 1200/1 will work fine with a W7 sub... just make sure the enclosure is tight and proper for the sub (and use your brain with the settings because you CAN blow pretty much anything with that amp.)

Saying you can't use the 1200.1 on that sub is like saying you can't go the speed limit in a Porsche. It's all about control.

New member
Username: Glasswolf

Post Number: 291
Registered: 12-2003
a JBL P1200.1 puts out a little over 1200wRMS @ 2 Ohms.
The JL 12W7 is rated for ~750wRMS peak power without voiding the warranty on it, and who wants to waste a 3 year wararnty?
The 12W7 is a 3 Ohm sub though (dual 1.5 Ohm coils) so the 1200.1 will put out less than it's rated power for 2 Ohms, making the combination a pretty good match.
You'll actually be feeding the sub about 900wRMS.
That's over the rated amount of power for that sub, but if you have a sub level control on the crossover, or head unit, leave it turned down so the amplifier never delivers full power and you'll be fine.
The ideal recommended amp for a 12W7 is the JL 500/1
that delivers a little over 650wRMS of real world power.

New member
Username: Motoman22

Post Number: 70
Registered: 12-2003
I'm not bumping

Unregistered guest
I have 2 Kenwood +db 12's with a 1000 watt Kenwood Excelon amp. I also have a 45x4 Excelon headunit with a 10 disk Kenwood changer. My problem is whenever I play my music really high it plays for about ten minutes and then the amp shuts off. If I let my truck sit for a couple of minutes and turn it back on than its fine until I turn it up again. I got a .5 farad cap thinking that would help but it didnt't really. What could this be?

Gold Member
Username: Glasswolf

Post Number: 1165
Registered: 12-2003
1: weak alternator
2: overheating
3: typical kenwood poor reliability and performance.

Bronze Member
Username: Zen936

Post Number: 55
Registered: 01-2004
And I thought the excelon really looked good... :-)

I think the first two were reasons were more legit.

Unregistered guest
I'm looking into starting a new system. In the car I'm driving now, I have alot of Diamond products, ie TDX subs and Hex speakers. But I was told by a reliable source that 12W7 subs are better than TDX and that Focal Utopia componets are better than hex by diamond. Which way should I go?

Step one: read topic
Step two: realize that this thread discusses power needs
Step three: Find thread on topic or start new thread.

Thank you

Unregistered guest
hey guys,
im kind new to this stuff, but i have a 2000 camry and 2 10"eclipse ti, running off of an autotek stealth1500. i also have the eclipse 55090 deck which runs off of my other eclipse amp. both amps draw around 120-130 amps. my camry probably only produces around 90. should i get a red top battery, cap, both, or just new alternator. do u know who makes good alternators?
i was also going to up my subs to probably 2 12"w6. i was told go with the w7, but i've heard great things about the w6. what do u suggest?

Bronze Member
Username: Wj94

Post Number: 14
Registered: Feb-04
Also one more thing, I went to the jlaudio website and it sais recomeneded amps 500/1 or 1000/1. So im just curious to why jl would advise this amp if its risky?

to answer that question......which one costs more money? there's your answer. =)

Unregistered guest
I'v just bought a 10w7 in a prowedge box. I also bought a 500/1 jl amp, do i need a capacitor???

Bronze Member
Username: Alpinepower


Post Number: 20
Registered: Jun-04
If your lights are dimming:

First upgrade alternator
Still outta luck?
isolator to optima yellowtop in trunk (deep cycle battery)
Still outta luck? HAHAHAHAHA
Try a decent sized cap, but if the other 2 suggestions dont help you, buy a new car!

Bronze Member
Username: Motoman22

Dallas, Texas USA

Post Number: 80
Registered: Dec-03
I'm not bumping
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