Battery choices

[JackG]

Originally Posted by edevlin

"As you point out yourself, the battery is ~12V, while the alternator produces ~13.6V. An accurate analogy of voltage is water pressure in a pipe. If you have two pipes connected together in a "Y" that then go to a sprinkler, and one pipe has a higher pressure than the other, which pipe will be feeding the sprinkler? The one with the highest pressure, of course! The lower pressure pipe will in fact reverse it's flow until the pressure equalizes, which is how the battery charges!"


So, based on your discussion, if I wanted to provide more current to my outboard audio amps which are wired directly to the to the battery) the best strategy would be:


1. Get a higher output alternator

2. Get a larger battery

3. Stick a large cap in the circuit from the battery to the amps


I am especially curious about the third case. My current setup seems to be working fine, but when I had a smaller battery (11 lb Braille) in the car, when I was driving with the headlights on and the music playing loud, you could see the dash lights dim in rhythm to the music at high (very) high volume levels. With my current 15lb Braille battery everything seems to be working fine, but I am still curious about a large cap in the circuit.

Ed

:dance:

What you were seeing is voltage drop across the resistance in the car's wiring, and also internal resistance inside the battery. The more current you pull, the larger the voltage drop.

Since you are wired directly to the battery, you're seeing the drop in the wiring from the alternator to the battery. You old, smaller battery also likely had a higher internal resistance, so it was less able to keep up with the dynamic current demands of your audio setup. You new larger battery probably has less resistance, and while replacing it you may have created better connections at the battery as well, which would help.

The big capacitors are placed as close to the amp as possible, and are there to provide a low resistance path for providing those short peaks of high current that the amps need for musical peaks. Capacitors are basically energy batteries that can release and recharge their energy very quickly and easily. The end results is you will have less distortion during peak power demands. Whether you'll hear the difference depends on your equipment, musical taste, and ears.

[Jaxonalden]

Unbelievable...have you ever owned a recreational vehicle that didn't have a battery? At idle the headlight is dim, rev the motor and the light brightens up. That's what happens in a system with no battery (remember constant voltage?).

So in your scenario the same thing would happen, quote "the alternator supplies *all* the current to run the car". The alternator is not run on a constant speed. Explain that one.

[JackG]

Originally Posted by Jaxonalden

Unbelievable...have you ever owned a recreational vehicle that didn't have a battery? At idle the headlight is dim, rev the motor and the light brightens up. That's what happens in a system with no battery (constant voltage).

So in your scenario the same thing would happen, quote "the alternator supplies *all* the current to run the car". The alternator is not run on a constant speed. Explain that one.

Your first one... apples and oranges. And a system with no battery is NOT "constant voltage". That's why the headlights dim.

Your second one... That's what the voltage regulator is for. I already explained it as well.

Take a look here: http://www.bcae1.com/charging.htm

Look at the second paragraph: "As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle. "

I really don't have time to educate you on this. Please do some searches, and some reading.

[blue2000s]

JackG doesn't really need my help, but he's 100% right.

[Jaxonalden]

Then why does the OEM use the battery it does? Being the sports cars these are they should have a lawnmower battery under the hood.

[JackG]

Originally Posted by Jaxonalden

Then why does the OEM use the battery it does? Being the sports cars these are they should have a lawnmower battery under the hood.

Because Porsche designs the cars to suit 90% of the buyers. Most people buying Boxsters don't want to eek out the last 1% of performance that a lightweight battery would provide. They'd rather have a battery that will last through a week or two of non-use and still start the car; a battery that will start the car when it is negative 18 degrees out; a battery that will last more than 15 minutes of leaving the lights on before it's dead.

If you replace the OEM battery with a lawnmower battery, those are the kind of issues you'll have to look forward to. And Porsche, along with the vast majority of the buyers, just don't want that.

[Lil bastard]

Well, it seems that in terms of losing weight for ax, it's not all or nothing.

Dedicated ax'ers regularly spend time prepping their cars for an ax or track event, swapping wheels/tires, brake pads, some even pulling the passenger seat. Why not add a battery swap to this regimen if the results warrant it?

Instead of removing the battery terminals, you could just as easily remove the cables at their other ends (still a single nut) and install a pair with terminals dedicated to the smaller battery. Even a lawn mower battery would be sufficient for the day and could then be removed and kept on a tender until needed again. It's not a lot of $ or effort, if you're dedicated enough.