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Old 05-24-2016, 11:18 PM   #16
geolemon

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Quote:
Originally Posted by loganbeckstrom View Post
ive also heard about adding a 4th wire to the big 3... which is one from the alt case to chassis ground. anyone know if this is truly beneficial? i will probably be doing it with mine this week, just in case, but wasnt sure if there was any truth behind the matter.
Do the big three first.
Live with it for a little bit.
When you add more grounds - sure, it can help. Sometimes.
You can also create a "ground loop" sometimes, which does the opposite of helping - it introduces noise.

Essentially, it's from having two grounds at different ground potentials (kinda sorta "resistance" - in an absolute sense). As this article shows - not all grounds are equal.
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Old 05-24-2016, 11:55 PM   #17
geolemon

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Quote:
...and explain why everyone in the industry who tries to sell you a $100 capacitor is an azz hole.
Well - to be really fair, this is just as false as the guy who tries to sell you a capacitor as your starting point.
Capacitors absolutely DO play a role. If you don't have external ones, the ones on the supply side of your amp are going to have to do all the work. And even great amps with tons of capacitance aren't designed for that.

That other link you put up on capacitor info is OK, but think of them for what we want to use them for - shock absorbers.

You might have a monster amp, over a thousand real RMS watts. You might have an upgraded alternator - or maybe there's no chance in hell of finding one for your model car. Either way, when that bass hits and you've got it up so loud your window glass is waving at you, you WILL be exceeding the current capability of your alternator.

When that happens:
...the voltage drops - until your battery voltage level is reached, where it can start supplying whatever remaining current the amp is sucking up that the alternator can't provide.
As soon as that bass note stops, the amp stops needing that much current, the voltage level rises back to that of the alternator, and everything recharges.

But here's what's key:
A battery is slow. Chemically slow. Literally. And God help you if you have a deep-cycle battery, with it's thicker, more durable, but slower-to-respond-to-transients plates.

As electrons are being summoned to flow literally at the speed of light, your battery is choking itself - it isn't meant to respond to such fast-draw dynamics, it's meant to start your car. Slow charge, slow discharge, good to supply power over a loooong time period.

By contrast, a capacitor is an amazing thing. Theoretically, it charges infinitely fast, and can discharge infinitely fast. In reality, internal resistance keeps any capacitor from being theoretically perfect, but you can still weld with a capacitor - it can flow current, and instantly. You even need to take care charging and connecting to a capacitor just so you don't spark 'n arc your ring terminal leaving black spots or welded rings!
Super fast charge, super fast discharge, and definitely not good to supply power for more than moments before being discharged.

But that's OK...
All we need it for is moments.

Slow motion:
Without capacitor.
The bass hits.
The alternator can't supply all the current needed by the amp.
Voltage drops drops drops.... there's the battery.
It's trying... struggling... can't supply the current that fast...
Voltage still dropping... lights still dimming...
Battery is going "I think I can, I think I can..." Some current is flowing now...
Voltage still dropping... until the battery rises to the occasion.
Now voltage is rising back up - at least to the level of the battery.
Now the bass hit stops for a few seconds.
Voltage rises back to the capacitor level.
Battery charges at least for a few seconds, probably comes close at least to recharging what was lost.

In this "Without" scenario, you'd see violent headlight dimming... even sub-12v headlight dimming, and the lights would be just ripped down to that 12v level - and even beyond, since the battery is slow, and it takes a moment to begin delivering current - it's dropping the whole time - even below battery voltage level. This kind of headlight dimming looks downright violent.

With capacitor.
The bass hits.
The alternator can't supply all the current needed by the amp.
Voltage drops... Instantly the capacitor starts supplying some of the needed current... It's own voltage will drop as it supplies current...
Down the level of the battery - come on battery, wake up...
Capacitor is still supplying current as the battery responds...
Once the battery is supplying current the capacitor not only doesn't have to anymore, but can't because it's voltage can't keep dropping any more. It's already recharging, at least to the 12v battery level.
Bass note stops.
Battery didn't discharge as much as the "without" scenario, so needs to recharge less.
And the capacitor recharged as fast as the voltage rise back to 14.4v.

In the "With" scenario, you'd see the lights dim to the 12v battery level, but not as dramatic, softened by the hand-off from alternator to battery thanks to your electrical shock-softening friend, the capacitor. It's more of a dim fade down and up, than violent drama.


An analogy would be like a Jeep, offroad. Sure, with stock shocks it'll go offroad. But if you put some shock absorbers on that can really take big hits and slams it becomes no sweat.

Remember - it's called a "system" for a reason.

Last edited by geolemon; 06-15-2016 at 05:28 PM. Reason: slight rewording
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