Having voltagw issues

[cows0136 10+ year member]

I have two batteries and a 1500 watt amp. i tested both batteries and they are 12.6v with the car off and i have a 270 amp h/o alternator. well when my bass is hitting the volume at 10 and my heater on setting 2 out of 4 my voltage is dropping to 13.5V i thought a second battery would fix lights it didn't so i got my high output alternator and the lights are still dimming and the voltage is pretty low at such a low volume what is going on? im driving a 95 grand prix

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[dgaf 10+ year member]

what's your resting voltage without subs and heater on?

 

[cows0136 10+ year member]

I didn't check let me run out and check right now

 

[cows0136 10+ year member]

14.0-14.04v

 

[double 07 10+ year member]

What gauge wire are you using? Have you done the big 3?

 

[cows0136 10+ year member]

The shop when they put it in ran 4gauge and yes iv done the big 3 u can't install a h/o without doing the big 3 u could but it would **** up the wiring

 

[daboyfrumdabx 10+ year member]

Have you disconnected the batts from each other and measured resting voltage independently?

 

[cows0136 10+ year member]

They are running through a battery isolator if i disconnect the front one the rear one wont be getting a charge

 

[Kangaroux 5,000+ posts]

You shouldn't be getting any dimming period with a 270A alt. A 1500w setup at the most will pull around 110A of current and that is full tilt on a test tone. What kind of alt do you have?

 

[cows0136 10+ year member]

Mechman alternator The shop ran 4 gauge wiring i don't know if doing the big 3 in 4 gauge wiring would have any effect but i don't know what the hells going on

 

[cows0136 10+ year member]

I think i located my issue but need some advice. Before i had the new alternator put on my belt never squeaked well after i put it on the new belt squeaks (well after the shop did) it squeaks on take off then stops when i get going. but also my lights get brighter and my heater fans speed up (i would assume means a loose belt I have a serpentine belt.) i don't know much about cars soo any advice would be needed the **** shop that put it on for me said its as tight as it needs to be so im going to have to pay another mechanic to tighten the **** thing (just so i don't over tighten it)

 

[cows0136 10+ year member]

Okay well the belt is fully tight so i have no idea why my lights are dimming and my rmp meter is dipping. i'm so lost and pissed iv put about a grand it to try and help with this and nothings working not deep cycle batteries not a a 270 alternator ugh

 

[cows0136 10+ year member]

if anyone is still willing to help me and needs to know my voltage drops to 13.5 while bass is playing

 

[RangerDangerV2 5,000+ posts]

what guage wire are you running to your second battery and amp???

 

[lionfamlee Premium Member]

The shop when they put it in ran 4gauge and yes iv done the big 3 u can't install a h/o without doing the big 3 u could but it would **** up the wiring

Kind of suprised they used 4 AWG and not 0 AWG. ???