i need some help

heres the breakdown.
just got my 99 porsche c4 back from the car audio shop
4th visit due to them not doing things right the first time
installed 2 amps for car audio system, prob total of 600 watts
system sounded great, but after about 2 hours battery light comes on
i was driving while this happened, not sitting idle
i figured battery was shot, went and bought a new one
same problem, def not the battery

i want to be sure its the alternator that needs replacing
im thinking it could be a bad ground, by the car audio shop
i pulled the fuse for the amps, not sure if that matters
problem still exists

battery level pulses while car idles
goes from 13 down to 11, dash lights come on and go off
pulses about every 10 seconds, with stereo off, new batt, amp fuses out

did pulling the fuses for the amps eliminate the bad ground theory?
anyway to check to see what is causing the problem?

sorry for the long post, im lost, dont want to buy something i dont need
thanks for the help, best porsche site on the net

 

If you're only getting 11 volts with no load, then it's probably the alternator. You really should be getting at least 12.5V (probably >13V). I can't think of another reason for the voltage to be low. Even with the amps running you shouldn't have such a low voltage.

 

the voltage is not steady, it goes from about 13v to 11v holds for 10secs, then back to 13v.

i am really thinking it is a bad ground.

 

If you pulled the power fuses for the amp and the problem still exists, it probably has nothing to do with amp grounding.

Are your battery terminals in good shape and does look like the cables are still making full contact? Does everything start working correctly at higher revs?

 

terminals good, cables are making good contact.
high revs does nothing to improve the situation, still acts the same?

 

pulling that much current from a stock alternator/battery set up without increasing the size of the wires and the alternator has probably fried the voltage regulator in the alternator and/or burned wires where you could have a partial short...I'm surprised your audio shop did not caution you about drawing that much additional current...600w at 12 volts is 50 amps and the alternator is probably not much more than 100/150 amps...a fuel injected car requires substantial current as well...my experience is that the alternator/battery setups in these cars is barely enough to keep the battery charged as it is...certainly not enough capacity to add a sound system like that...you need to get it to an alternator/electrical expert to determine that you haven't started a short that will lead to an electrical harness fire down the road...you also should see if you can upgrade the capacity of your alternator

 

sounds like you need to replace your alt

 

its weird cause i just replaced my older amps which were drawing even more power. kind of ironic how the smaller amps caused the final strain.

has anyone upgraded their alternator to a higher amperage model? if so, what did you use and where did you get it from?

thanks

 

you may have to have it custom built by an alternator shop...I know there are quite a few companies that make special high amp alternators for hot rods but don't know about a Porsche fitment/wiring model...need to talk to your P-car parts guy..there could be a Porsche alt that will fit and is a higher current model

 

I'm not positive, but I think the 1999 996s had 120 amp alternators. While a 600 watt amp *theoretically* can draw 50 amps, they almost never even come close. Unless you're running at full blast for an SPL contest, I doubt you'd draw more than 20 amps. I've been running a 1000+ watt system off of a 75 amp alternator in my 94 Integra for years--the headlights only dim if I crank it up (I've been too lazy to install a capacitor).
I don't think a custom alternator is necessary--IMO. Good luck.

 

As another member posted, it's probably not the ground wire, but to be sure, ask the audio shop where it is grounded. Also, drive it with the 12V amp wires DISCONNECTED from the positive battery terminal. Does it behave the same?

On a drive over the weekend, I noticed big voltage drops on bass hits. Sometimes I lose all output from the subwoofers. This could be an amplifer safety mechanism, though. I contacted Rod Birch at http://www.caraudioinnovations.com/ to find out his take. I may be in the same boat, looking for a higher capacity alternator. May not hurt to contact him as well.

 

i disconnected the fuse between the battery power and amps, problem still exists.

i have to agree that i dont think i need an upgraded alternator. the stock alternator is 120 amps. if the price was only a little higher i would prefer to upgrade, but it seems to be a lot more and probably custom.

it seems that porsche used crappy electrical parts and components. batteries and alternators seem to all be below average. i bet if i get a bosch alternator it will do the trick even at the same 120 amps.

i guess i killed the cheap stock alternator. it is probably the same one that came on the car 11 years ago so i guess i cant really complain all that much. i hope im not posting again in a few weeks talking about my new alternator being dead as well. my audio system is not all that crazy really.

love this forum, thanks for all the help and such.

 

Ask your audio guy to get u a stiffing cap that's to store power cause the amps are pulling too much power this cap will store it and stop the surge when bass hits did they run a new power wire with a fuse from the battery post for the amps?

 

i was thinking about a cap. they did run a power wire with fuse to the battery.

another question if anyone is still around. i think i might purchase a reman bosch alternator. do i need to also purchase the pulley? it states it is not included. i am planning on getting a new belt just not sure i need the pulley.

 

wanted to add one more thing. i found an autoline reman alternator that has a refund for the old core unit that is almost the same price as the new part. kinda crazy but i might give this a try. if the alternator dies again, i will only be out the installation costs.

or should i just buy the Bosch reman unit?