2 power questions

[Drewet88]

Alright heres my question/problem. I did the Big 3 with 0gauge wire. I upgraded to an optima yellow top battery and my headlights still dim when I have my music turned up. I am running 2 pioneers 12's (not sure of the model) and my tweets/mids are alpine (again the models escape me). The speakers and the subs are both amped off of two seperate amps pulling about 1700 peak. I was told I need a Cap but I wanted to check here first because I heard they were useless.

I am sure my grounds on my Big 3 are good. I have checked and rechecked and I do notice a difference but everything still dims.

My other question isn't really a power question I was just wondering if anyone could tell me where I could find a tutorial on making an amp rack?

Any help is appreciated
~Drew~

[Krazy Jeff]

Could it be possible you need a better alternator?

[Drewet88]

Thought I put that in the original post. Its a new alternator but its not a H/O alternator. According to my local stereo shop I shouldn't be pulling that much to need a H/O.

[Krazy Jeff]

I wonder if this helps. A stiffening capacitor might improve the situation. I have read that they recommend you place the cap on the amp running your bass driver (subwoofer).

According to what I have read, Capacitors function when the power required is greater than the power used. Hence only subwoofers suck enough power to operate the capacitor.

Here is a link that might help: Car Audio Capacitors

I hope this helps, and please come back and tell us how it works after putting up a capacitor? Thanks in advance.

[PlayStation3]

u dont need a cap. what size alt does your car have?

[Krazy Jeff]

I think this site will help. click_here

Please read like the last paragraphs on the page. It does mention that your lights dim because there is not enough power coming from your alternator so it then starts taking power from your battery, and that is why your lights dim. It recommends to upgrade your alternator and it also refers to a capacitor. It's very informative.

[Drewet88]

I think it only puts out something like 130amps. Which I told the stereo shop but they said I couldn't be pulling that much and wouldn't need an H/O alt. Maybe they just wanted me to buy a cap from them.

I really dont know where to go for a H/O alt, and if I happen to get a cap what kinds are good. I know nothing about them but im guessing the more fareds the better?

[PlayStation3]

130 should be good for around 1300 watts or so maybe even more. unless it is on its way out. and do u have a muti meter?

[PaulD]

caps are useless for SPL, on occasion they do help a little with blinking lights. The only thing that matters on cap specs is the ESR, those big 25 farad block caps are worthless because the ESR is so high, so are ones with the voltmeters on the top.

The most important thing is the wiring, especially the connections to battery, fuse holder and amp(s). Just a little bit of extra resistance can effect the power transfer greatly.

[Drewet88]

I have a multimeter and I checked and rechecked all connections and cleaned them. Everything is getting tons of power I'm guessing it may have to do with my car being an 87. If I have my music on and open my doors the interior lights even dim and my dash (which is digital) also dims.

I'm guessin an H/O alt may be my only way out. I'm pretty sure my alt is not going out but I'll take it out and have autozone check it right after I click reply.

[Drewet88]

They said its fine. Old but fine.

[PlayStation3]

what is your alts voltage reading with your music 3/4 volume? up

[PaulD]

walmart/radio shack meters are not sensitive enough to measure the resistance drops you are looking for. $200+ fluke might, with the right probes ...... usually the kind that sensitive are $1000's of dollars.

The equation here is a simple one, known as ohms law. It says V=I*R, so if you are drawing 100 amps and the resistance of the connection is .005 ohms, then the voltage drop is 100*.005 or .5 volt. That's not too bad, now lets add them together - .005 at the the battery, .005 at the input of the fuse, .005 at the output of the fuse, .005 at the amp, .005 at the gnd side of the battery, .005 at the chassis gnd point, .005 at the amp gnd lead and .005 at the amp gnd point. Thats 8 if I counted right, 8 x .005 = .04 ohms total, .04 X 100 = 4 volts. In this simple example with fairly good connections (beyond what any multimeter can measure), a 100 amp current draw would cause the voltage at the amp to sag by 4 volts. This is why clean, tight connections are so critical - even if you can't actually measure them.

Even worse, if one of the connection had say 10 times that resistance, it will heat up badly when playing at full power and will eventually burn up or catch on fire.

This IR drop is also why caps with any kind of ESR are pretty much useless. The cap can only operate betwen the 13.8 - 14.4 volts of the alternator and the 12.5 V setpoint of the battery, so the IR drop can only be 2 V max before the internal resistance of the cap will prevent it from discharging. In a 200 amp system, the max for the ESR can only be .01 ohms for a max 2 volt drop (.01 X 200 = 2 V).

[Drewet88]

Originally Posted by PlayStation3

what is your alts voltage reading with your music 3/4 volume? up

Well if i'm doing this right its 13.4.

[PaulD]

you really need a meter that will capture the lows or an analog meter with a needle. The voltage will fluctuate some when the bass hits.