Headlights dimming with under 400W of power

Mast0rMason_

Junior Member
I've got a little 2005 Corsa C (unfortunately), I'm running some 600W  'rated' 4 channel amplifier bridging 2 of the channels to 300W with the gain set as normal and the gain on the other two channels are at it's lowest as theirs no speakers even connected to them. Theirs 2 25A fuses, on the amplfiier, assuming for channels 1+2 and 3+4 so I'm also assuming it's drawing less than 30A if one of the gains is set at its lowest. The guy I bought the car off replaced the alternator and the battery and they're still pretty shiny so I know it can't be them. Does this just mean it's a wank alternator? The voltage drops to 13.4ish when long low bass hits too. Or what else could it be?

Also can I throw any alternator in it if I can make up some brackets? 

 
I've got a little 2005 Corsa C (unfortunately), I'm running some 600W  'rated' 4 channel amplifier bridging 2 of the channels to 300W with the gain set as normal and the gain on the other two channels are at it's lowest as theirs no speakers even connected to them. Theirs 2 25A fuses, on the amplfiier, assuming for channels 1+2 and 3+4 so I'm also assuming it's drawing less than 30A if one of the gains is set at its lowest. The guy I bought the car off replaced the alternator and the battery and they're still pretty shiny so I know it can't be them. Does this just mean it's a wank alternator? The voltage drops to 13.4ish when long low bass hits too. Or what else could it be?

Also can I throw any alternator in it if I can make up some brackets? 
13.4 isnt bad, you need to check volts dc at the front alternator post and ground and then the front battery, and then the amp. if there's any differences its your wiring/connections. If your voltage at the amp is the same as the alternator your alternator isnt doing anything. possibly due to factory computer controls shutting it off to save gas or the alternator is junk. 

if you're clipping the hell out of the amp with the gain set too high it'll draw way over 50a at peak

 
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13.4 isnt bad, you need to check volts dc at the front alternator post and ground and then the front battery, and then the amp. if there's any differences its your wiring/connections. If your voltage at the amp is the same as the alternator your alternator isnt doing anything. possibly due to factory computer controls shutting it off to save gas or the alternator is junk. 

if you're clipping the hell out of the amp with the gain set too high it'll draw way over 50a at peak.
The gains about just under 1/3rd, it doesn't clip from what I can hear and tried it with plenty of songs. The headlights dim at 2500rpm while driving, sorry I missed that out, but only very slightly. If the battery measures 14.4V at idle with no music playing the alternator works as it will just rinse the battery as it's only 12V wont it?

 
The gains about just under 1/3rd, it doesn't clip from what I can hear and tried it with plenty of songs. The headlights dim at 2500rpm while driving, sorry I missed that out, but only very slightly. If the battery measures 14.4V at idle with no music playing the alternator works as it will just rinse the battery as it's only 12V wont it?
the stock alternator has **** output then, try looking up the model of it and see what its rated for

 
I would suggest to also upgrade your amplifier ' ground' point and also check your cars battery ground point, or you can also add another ground point to the stock location as well.

Note that in vehicles, power travels from NEGATIVE to positive hence the 12v negative ground printed in automotive 12v products.

:fro:

 
Usually with 400 watts, you should not have this issue unless;

  • your battery is on its way out;
  • poor grounding points on battery and amplifier grounding points;
  • typically, battery would last 2 - 3 years so if your battery is older, then it maybe be wise to replace the battery. check the CCA value of the battery and you can install a better rating battery as long as it fits in the designated space. :graduate:
 
Usually with 400 watts, you should not have this issue unless;

  • your battery is on its way out;
  • poor grounding points on battery and amplifier grounding points;
  • typically, battery would last 2 - 3 years so if your battery is older, then it maybe be wise to replace the battery. check the CCA value of the battery and you can install a better rating battery as long as it fits in the designated space. :graduate:
The battery is around a year old the same with the alternator. My ground for the amp the cable is about 1.5-2ft and it's screwed into the chassis under the rear seats with a screw and washer so I guess I'll have to look at the chassis to battery ground, thank you! Could it also be I'm using 

And thank you everyone else!

EDIT: Could it be that I'm using 4 gauge wire too? I know it's overkill for little power but I thought it could help incase I wanted to upgrade my subwoofer and amp in future.

 
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The four gauge power wiring should be more than adequate.  I would also suggest to use a multimeter to get a reading of your battery condition as well as I don't know where you are and that cold weather also plays a toll on the battery regardless of their age mate.

In theory, the car only needs 2 volts to start so if you are experiencing this issue, use a multimeter to probe on the terminals and let somebody start your car and if the voltage drops significantly, then it could be your battery issue here as 400 watts is not enough juice to cause this issue for you.

Another factor we do not know is how often you drive your car as that can also be an issue if you don't drive it too often. 

I have a stock battery with 1200watts RMS system being run off a stock battery.   I do drive daily , so my battery is kept charged by the alternator , like  200km / 124.2 miles per week and I travel to my remote work which is 400km / (248.5miles ) away every 6 weeks. :fro:

 
The four gauge power wiring should be more than adequate.  I would also suggest to use a multimeter to get a reading of your battery condition as well as I don't know where you are and that cold weather also plays a toll on the battery regardless of their age mate.

In theory, the car only needs 2 volts to start so if you are experiencing this issue, use a multimeter to probe on the terminals and let somebody start your car and if the voltage drops significantly, then it could be your battery issue here as 400 watts is not enough juice to cause this issue for you.

Another factor we do not know is how often you drive your car as that can also be an issue if you don't drive it too often. 

I have a stock battery with 1200watts RMS system being run off a stock battery.   I do drive daily , so my battery is kept charged by the alternator , like  200km / 124.2 miles per week and I travel to my remote work which is 400km / (248.5miles ) away every 6 weeks. :fro:
Turns out the ground terminal from my amp to the screw screwing it in is 5.1ohms, is that bad? I think I read somewhere it needs to be under 1 lol

sanded off corrosion and more paint and used a fatter screw and it’s at 1ohm when I first do it then stablizes at 0.7ohm. I’ll keep you guys posted if it sorts it! Common noob mistake I’m taking I guess!

Update, the dashboard still dims a minute amount compared to what it did, it's barely noticable, is that normal ?

 
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Mate, in 99% of the case its usually a weak ground point that causes the issue.  You will notice that stock battery ground wires are a puny 8 gauge, so with added load on the battery , the dimming in the lights is a result of voltage drop. As I stated, re-visit your ground wiring, from the head unit, amplifier and upgrade the stock ground by adding another ground wire using a truck ground wiring as they come in different sizes and this should eliminate your head light dimming issue.

:suave:

 
Oh, that reading from the ground terminal is does not sound correct.  You need to educate yourself on how to use a multimeter.  Its your best friend in car audio issues.

This is how you use your multimeter to see if you are getting a good reading with 12 v.

Set your multimeter to 12v dc, not AC.

probe the red one on the battery positive on your amplifier, and the black one on your negative one.  Should read 12v.

Ask a mate to start your car and keep the probes there to see the voltage drop.   If it drops to a few volts then you have to check your grounding points on the amp, head unit and test it again.

If the voltage still drops to a few volts then its time you replaced your battery.  Hope this helps you out mate.

 
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