Battery Drainage! (Car Audio Gurus I Need You!)

[Toobs]

Squid is pretty much on the money.

400W = 33A at 100% efficiency @ 12V, however, most amps only run about 80-85% efficiency and most alternators give out about 13.8V under load.
So... (400/13.8)/0.8 = 36A
Add headlights @ 2 x 100W and a few hundred watts worth of engine control and ignition and you could be pulling over 60A of current.
If you only have a 50A alternator you could find yourself burning out regulators / diodes pretty quick. I assume that the MR2 has the same 80A alternator as the GT4 though so you might not have a problem.

The easiest way to test if your alternator is up to the task is to crank your system up while the engine is running and turn on all the lights... if the lights dim to the bass then either your earth needs upgrading or your alternator / battery can not supply enough current to feed your system.

Also Squid the biggest Odyssey battery you can get (PC2150) is only 100AH... and it's a huge mother (33cm x 17cm x 24cm)... are you sure your battery has 200AH capacity?

[Dale]

But an amp will never be drawing that whole 36A of current continuously, it will only be in (likely very) short spurts. I think witzl used a hills and valley theory on it once before to say that the battery supplies the power to the amp on the hills (ie louder music), and while the amp is not drawing power (valleys) it will charge from the alternator.

Mind you that's not to argue with burning out diodes or regulators!

[hamgatan]

hmmm gen III 3SGE... i hope its got the 80a alternator...

btw thanks guys this is teaching me a lot about an area i knew nothing about till friday

[Toobs]

But an amp will never be drawing that whole 36A of current continuously, it will only be in (likely very) short spurts. I think witzl used a hills and valley theory on it once before to say that the battery supplies the power to the amp on the hills (ie louder music), and while the amp is not drawing power (valleys) it will charge from the alternator.

Mind you that's not to argue with burning out diodes or regulators!

With most normal music you will never be able to continuously pull the rated current from the amp... not unless you like listening to bass mechanik or similar

[Squid]

Toobs, I better check my battery when I get home.

I have a 4*75 watt and 200w monoblock and I have run the system at ears bleeding level for 4-5 hours (while fire spinning(well away from car)) and then started it up fine.

But yeah as toobs said if the lights dim with the bass, you need a bigger alternator, or a capacitor :S I have never been convinced on using a cap in this mannar, and a 1F cap in the boot seems to me to be a pretty dangerous thing to carry charged up, could easily do someone some very nasty damage (like death)

[devolutio]

Why would running the gains on the amplifier at full make it sound any better? The quieter you have the sound source, the lower signal to noise ratio in everything leading up to the amp.

EldarO if you agree that running signal and power wires together is a nono because of worse interference, all that turning up the gain is doing is making that interference (thats getting into the signal leads) louder! Think of this, you have no music playing, but the amplifier is on and the gain is set to 0 (assuming it can be turned to 0). How much interference can you hear? None. Set it to 3, you can hear some buzzing but it's not very loud. Now turn it to 10, it sounds twice as loud. Lets say with your head units volume at max, the speakers running off the amplifier are pushing distortion with the gain set to 5... why would you run the amp at 10? you would have louder interference, run the risk of someone with no ability to perceive distortion ruin your system, and have bigger steps between levels of attenuation (assuming your cd player has a digital volume control... which is does).

[Squid]

Wouldn't you want the amp doing as much of the work as possible? the main reason you buy an external amp is that is is probably of better quality than the internal head unit one. Keeping the signal to a minimum and letting the amp do the work is the way I would go!

OK realisticly most people buy an amp for increased doof doof, but not me!

[Dale]

Squid, if speakers/sub are hooked up to an amp, the amp will be doing all the work for them regardless of gain.

Getting a bit off topic here, but running the gain control at max (for maximum doof), just makes the amp run harder, hotter, and increases the chance of killing it. That's why it's better to buy an overpowered amp that isn't running at full capacity and leave the gain control down, if you want it to last!

[BradW]

Back to the topic . The wining noise would have been your alternator working it's nuts off to recharge your battery. Did you jump start the car to get it going or clutch it.
If you can, put the battery on charge to bring it right back up to full. Driving the car will charge the battery, but if you are driving around, chances are you are listening to your new system as well so the battery isn't getting the full charge from the alternator (as it is powering the system as well). This means it will take longer to charge the battery.
If you use a (good) battery charger it will bring the battery back up to full.

[hamgatan]

yeap thats what i thought.

i drove around for a few hours last night to let it charge.. its been in the workshop all day having the clutch replaced today as well so ill get some more drive time in tonight.. starts first go now though no issues.

didnt jump start it. i just left it for an hour and came back to it and it started up after 2 or 3 secs of the starter motor ticking over.. its all good now though. alternator doesnt whine like it did yesterday now.

[BradW]

yeap thats what i thought.

didnt jump start it. i just left it for an hour and came back to it and it started up after 2 or 3 secs of the starter motor ticking over.. its all good now though. alternator doesnt whine like it did yesterday now.

The battery being able to recover and start the car is a sign of a good battery. Keep driving it and see how it goes but if you get the chance put it on a charger for a while.

[Toobs]

The reason you want to tune your amp while your headunit's volume is set at about 80% is because you want to have the line out level as high as possible to minimise any noise that may enter the RCA's...
Why not tune at 100% you say?
The answer is that you don't want the signal to get squared off before it leaves the headunit, this can happen because once go beyond 80% on most headunits the output is actually amplified above the 0dB mark which can cause the signal to get squared off (also known as clipping)

Other tips for car audio installs:

1) Avoid (as best as possible) running your RCA's past injector wires, ignition wires (e.g. IGf, IGt) or heavy power cables. The best way to do this is usually to run the RCA's along the top of the tailshaft tunnel (under the carpet obviously).

2) Make sure you increase your earth straps to match your power cables. i.e. if you have run 2G cable from the +ve terminal to your amp then run another 2G cable from the -ve to the chassis.

3) Make sure the earth on your amplifier is bolted on to a decent earth point on the car... e.g. seatbelt bolts make good earth points... self taping screws into sheet metal do not.

4) Don't skimp on the RCA's... cheap RCA's can destroy an otherwise good audio system.
Good RCA's usually cost around $30-50

5) Try to use a loom adaptor for the headunit... these are basically prewired sockets that match your OEM stereo plugs... this will make it a million times easier to put your factory headunit back in and you don't have to hack up your factory harness.

6) Don't use those awful sheet metal cradles that come with most headunits... your head unit will be much more secure if you use the factory brackets to bolt the head unit down.
Also every thief has a few of those cradle keys and can rip your head unit out in 5 seconds flat if you use the sheet metal cradle.

[hamgatan]

ok.. heh *sheepish look* ... i blew the amp

yes i really outdid myself.. didnt blow any fuses.. the the amp is toast.

tested the voltage between terminals on my battery.. holy crap, its sitting on about 15v! so that explains why it blew right there... the problem is, i know thats way too high.. i realise that my alternator must have shit itself to the point where its overcharged the battery and the voltage regulator might be stuffed..

so whats my option here. i want to regulate the voltage obviously back to 12v across the car.. does that mean

1. a sparky can fix it and put some kind of resistor in between to bring it back down to 12v or replace the voltage regulator..?

2. new alternator? how much am i expecting to pay for 3SGE alternators?

cheers guys

chris

[Dale]

I'm not sure about the alternator on that car, but I'd say it would have an internal regulator (chances are this is what is fuxxored). Is it 15v when the car is running? I really doubt 15v would be enough to kill the amp, it's pretty common for alternators to churn out about 14.8 volts

[hamgatan]

yeah its while its turned on. its sitting just over 15v. 15.1 or so..