Back to the original question :-) Let's do some simple math--

You have a total of 300W + 1000W = 1300W of amp output. Assuming you run continuous 1300W and assuming your amps are 50% efficient, you'll be pulling about 2600W from the electricals. Assuming you have a 120A alt, it can only supply about 1400W. The other 1200W has to come from the battery. A standard battery will be sucked dry in a few minutes at that rate even if your engine is being reved continuously to keep the alternator at full output. Also remember the 50% amp inefficiency will be dumped as heat somewhere; they will be glowing hot!

Reality check -- you'll never come close to running continuous power like that unless you're running a continuous tone. Assume you're rocking the neighborhood with an average power of about half (1300W), your alt will be running near full capacity spec. As long as the alt is really spec'd to pump out 120A continuous, you "should" have no problem as long as your engine is running.

No stiffening cap will help you in this situation. There's simply not enough joules capacity to make any difference assuming your wiring is robust. If the cap really had that much capacity, you should be able to start the engine with the cap alone. Not the case! The battery will be doing most of the work of AC ripple filtering.

 

snoman's got a good point here. I've also played with scopes in my car in my earlier daze. A lot of the bounce you're seeing is due to the drop across the power cable and the drop across the internal battery resistance. However, does it matter?

It depends... most car amps I've looked at have a boost inverter in the front. It chops the 12V and bumps it up to something a bit higher inside the amp where it is again rectified and filtered into DC. If that inverter is well-designed, regulated, very high current output, and has fast transient response (meaning costs more $$), that output should be tightly regulated under all loads within spec regardless of what the battery and alt are feeding its input, bouncing or not.

If there's a stiffening cap that needs to be placed anywhere, it should be there feeding the transistor power supply rails inside the amp between the inverter and audio amp stage, not outside of the amp. A cheapy Walmart zillion-watt amp will most certainly be a nonregulated low current design, and the audio amp section would certainly be starved of juice on deep bass notes. So the quick fix it hanging a huge cap at its input. Well, why not just spend the cap money on a better amp that doesn't need one?

There's also a lot of switching noise/harmonics from the inverter itself which can be cleaned up fairly easily.

 

I will second his statement that its splitting hairs. For all practical purposes it does travel at the speed of light. I'm sure that most people on this forum have no idea what you guys are even talking about (skin effect, reactance, velocity factor, EF and EMF etc.) and don't care, probably wouldn't understand anyway because it does get awful technical. College wasn't all fun and games. Besides, it really has no application here anyway.

No point in arguing about the value of caps. Say your peace and Live and let live.

 

Aquaman's got that one pegged - I have a horrible AC line where I live, and the answer for the computers is an inverter setup. AC line is rectified, converted to DC and fed to a cap. The DC is then inverted back to AC (choice of 50 or 60 cycle), and highly regulated in the process. The cap alone will hold up the AC output for something like 200 milliseconds with complete loss of Ac power. I had a battery backup unit, but it wouldn't switch over in time to prevent the computers from rebooting. It now feeds the inverter , and the inverter holds the line up until the BBU switches over - best of both worlds.

In all actuality, I wouldn't be suprised to see a quality amp bucking the 12v input up to something like 50 or 60 volts or even higher within the unit.....