Dual Batteries - shoot holes in my idea please!

[Claude]

... It is not about AC/DC nor high filter... etc... it is just the old way of hooking it up. In a sense... all power must go through the capacitor... not only draw power from capacitor when needed...

To help figuring out how this works just make an analogy between the electrical power system of the car and an hydraulic system:

- the battery is like the main water reservoir,
- the alternator the main source of water,
- the cable between the alternator and the battery the water pipe;
- the capacitor installed close to the amplifier is a secondary water reservoir;
- the amplifier is the load that drains current like a tap drains water;

With that model in mind the electrical power in watts that may be delivered to the amplifier (or the amount of water that could be push through the water tap by unit of time) is restricted among other things by the cabling (or the water pipe) because it introduces some electrical resistance (water flow constrain) in the system.

When the amplifier requests suddenly a great amount of power (or water) the fully charge capacitor (secondary water reservoir) installed near it will discharge in or feed the load so you avoid the effect of energy drop in the cabling (water pipe) between the battery (main water reservoir) and the load.

Because power peaks (bass punchs) are needed only part of the time, not all the time, if the system is well design the capacitor will have time to be fully refilled between those peak power requests.

Also in a well design system the battery (main water reservoir) is big enough to refill the capacitor (secondary water reservoir) between 2 requested power peaks and the generator (the water source) is itself big enough to completely refill the battery (main water reservoir) in a resonnable amount of time.

For sure it help to have the bigger water pipe (bigger cable) possible to link the different components of the system and that the secondary water reservoir (capacitor) be real close to the load (power amplifier).

That's it for my analogy.

[Tiger]

That's an outstanding anology. I totally agree with you on this.

[Ferret]

Fixed.

I think not! Lol get off my internets!

A capacitor in series is a high pass filter - IE it will let AC through and drop DC.
A capacitor in parallel is a low pass filter - it'll stop AC and smooth it out - so long as some sort of rectification is present.

At least that's what my electrical engineering degree lecturers were telling me...

Hence where Tiger's capacitor's in series I'd love to hear the results, it must screw around with the sound something awful. The amp can only charge internal caps... AFTER a massive bass beat... I'm sure that's gonna be screwed up.

EDIT : and I know the physics behind capacitor action hasnt changed in the last 15 years. Putting a cap in series is only going to cause limitation in available current. Yes your lights etc wont dim any more, but that's because you've caused a physical disconnect between battery and amp - there's actually no phsical connection between the positive and negative cap terminals - just air or electrolyte usually.

[ericbendler]

Fixed.

I see the qoute of "fixed", and wonder what is fixed? There is a lot of disagreement on the outcomes of two batteries in parallel with (or without) an isolator.

WTH - I my as well just buy two identical optima yellow tops with an isolator and do it right.

Isolator drops my line voltage .2 - .4 down, but allows me to raise the amperage of the whole system for things like (stereos, tv visors, 12v adaptors).

hmmm- $ (red tops x 2 = $150) + (PAC-200 - $60) = $210

That puts it 2nd on my list behind a new compressor. NICE!!!

[AngryPopTart]

Eh? In series with a load, a capacitor passes AC current and blocks DC. In parallel with a load, it filters out AC.

Aren't these polarized caps?

[DaveVoorhis]

Aren't these polarized caps?

With polarized caps, subjecting them to AC will damage them. In that case, replace "AC" with varying DC. The cap will filter out DC variations.

[DaveVoorhis]

Mmm... I guess it is the new way to install caps now... I have been running this way for years... like 15 years... from positive battery to negative on capacitor... and then from positive capacitor to amp positive.... amp negative is direct to bare ground.

Does the capacitor have a ground strap? Are you sure about how it's wired? If so, then it's wired in parallel, but with two positive side connectors. If it's genuinely wired in series, then it's either not a capacitor or it's shorted out. See http://www.caraudiohelp.com/car_audi...stallation.htm

[pingu]

With polarized caps, subjecting them to AC will damage them. In that case, replace "AC" with varying DC. The cap will filter out DC variations.

Almost right: subjecting polarised caps to reverse polarity will damage them.

For example, suppose you have a polarised cap connected to a voltage that varies from 12V to 14V. The cap will see an average of +13V (which should be fine, as long as the cap is connected with the correct polarity) with 1V (i.e. 2 volts from trough to peak) of AC superimposed on the 13V of DC.

If the AC were to increase to 14V superimposed on the same 13V DC, then on the troughs the cap would see -1V (i.e. 13V DC minus 14V), which it wouldn't like.

[DaveVoorhis]

Your point about reverse polarity damaging a polarized cap is true, but AC is, by definition a current varying in magnitude and direction, i.e., polarity, at regular intervals. A 2 volt P2P AC current superimposed on 13 volts DC is, strictly speaking, varying DC. 14 volts P2P AC superimposed on 13 volts is AC. See http://en.wikipedia.org/wiki/Direct_current and http://en.wikipedia.org/wiki/Alternating_current

[Felixdacat]

How many watts is he running? I would upgrade the capp before I ran two batteries. I'm running about 2500watts for my subs with one amp, and have a 5mf capp. I do however see my lights dim slightly when I have the fogs, and heat on. More amp draw from the alternator.