it may just be a fluke, but i just wanna see if its happened to anyone else. yesterday i installed a more powerful amp to drive my sub. nothing out of the ordinary. today, i'm pulling up to a light, and i got a song playing with some super low, rolling bass pulses. i noticed that when the bass was hitting, the rpms were slowly falling, like btw 1k and 600rpms. the ac was on, and i didn't think to turn it off to see if it might have been causing it, but its always a possibility. anyone else ever see this happen? should i be worried? i've never had this happen before in any of my previous cars. i'm not sure if its too much current draw cause none of the lights/displays dimmed

weird, i wouldn't worry about it if in only happened once. in my old car sometimes when blasting stuff crazy loud my speedo would move with the bass hits. i don't know if it was electrical or just from the vibrations.

what amp and stuff do you have?

Fosgate p3002 bridged to a fosgate 10" HE2(?) sub

it may just be a fluke, but i just wanna see if its happened to anyone else. yesterday i installed a more powerful amp to drive my sub. nothing out of the ordinary. today, i'm pulling up to a light, and i got a song playing with some super low, rolling bass pulses. i noticed that when the bass was hitting, the rpms were slowly falling, like btw 1k and 600rpms. the ac was on, and i didn't think to turn it off to see if it might have been causing it, but its always a possibility. anyone else ever see this happen? should i be worried? i've never had this happen before in any of my previous cars. i'm not sure if its too much current draw cause none of the lights/displays dimmed

I would not get too worried, more than likely a coencidence. In 10 years audio install I have yet to see a cars audio system that pulls so much current that it affects anything other than drawing from headlights and other typical problems people run into with large amplifiers.

Just use a multimeter on your battery and measure your voltage while the car is running and make sure your not dropping voltage like crazy. You shouldnt have drops below 12-12.5 while the car is running and bass notes are playing. If you do you have a significant draw from the amp and should get a Kenetics or Optima or similar gel cell to help with that. But if im not mistaken with Fosgates model numbering system 3002 is a 300 x 2 amp right? What does its birth certificate say its RMS rating is? If its a 300 x 2 you are more than fine with the stock charging system.

it may just be a fluke, but i just wanna see if its happened to anyone else. yesterday i installed a more powerful amp to drive my sub. nothing out of the ordinary. today, i'm pulling up to a light, and i got a song playing with some super low, rolling bass pulses. i noticed that when the bass was hitting, the rpms were slowly falling, like btw 1k and 600rpms. the ac was on, and i didn't think to turn it off to see if it might have been causing it, but its always a possibility. anyone else ever see this happen? should i be worried? i've never had this happen before in any of my previous cars. i'm not sure if its too much current draw cause none of the lights/displays dimmed

I would not get too worried, more than likely a coencidence. In 10 years audio install I have yet to see a cars audio system that pulls so much current that it affects anything other than drawing from headlights and other typical problems people run into with large amplifiers.

Just use a multimeter on your battery and measure your voltage while the car is running and make sure your not dropping voltage like crazy. You shouldnt have drops below 12-12.5 while the car is running and bass notes are playing. If you do you have a significant draw from the amp and should get a Kenetics or Optima or similar gel cell to help with that. But if im not mistaken with Fosgates model numbering system 3002 is a 300 x 2 amp right? What does its birth certificate say its RMS rating is? If its a 300 x 2 you are more than fine with the stock charging system.

totally agree. 100% it must have been a fluke, had nothing to do with ur sub and amp.

Im going with it has everything to do with you amp. If you had the ac on with your system on a fairly loud level, then yes you probably put a strain on the engine.


okay. So the engine idles at around 1000. When the ac kicks the clutch on, that will knock it down another few 100 rpm. With your amp on pulling power, your alternator needs to run to regenerate the power that your sucking from the battery.

The ac and the alternator both running would cause the engine to drop rpm.

Im going with it has everything to do with you amp. If you had the ac on with your system on a fairly loud level, then yes you probably put a strain on the engine.


okay. So the engine idles at around 1000. When the ac kicks the clutch on, that will knock it down another few 100 rpm. With your amp on pulling power, your alternator needs to run to regenerate the power that your sucking from the battery.

The ac and the alternator both running would cause the engine to drop rpm.

Actually its not possible. The alternator runs all he time every time your car is running, it never speeds up to produce more current and never slows down. It is physicaly impossible for it to "kick on" and bog down your engine. When the amp pulls too much current for the alternator to keep up it just draws off of other components in your electrical system such as headlights. Thats why your headlights dim at night when the bass hits.

I'm going to agree with Wasson.
if you'd like an extreme example of how additional electrical load can cause rpm to temporarily dip, go jump start another person's dead battery. You will definitely hear your own running motor dip down before the engine management takes over and raises the rpm back up.

Before moving up to a 140A alternator in my old Honda, my Memphis Belle could stall the engine on huge bass drops. Of course, it could also draw close to 150A at it's peak.

This amp is a class AB amp, not a D class. Its rated power is 300 RMS, and thats only if he has it bridged which is probably the case. Sorry, but unless this cars alternator is on the way to the grave its probably not the amp causing this.

the alternator does not spped up to make more power, it just makes more magentic field to generate more power, putting a high loadon the engine. all a alternator is is an electric motor being driven by abelt so it makes elcctricictyu, not uses it. ALso, class AB have a high draw. class d amps hardley have a footpront, but the older ab can suck a lot of juice

the alternator does not spped up to make more power, it just makes more magentic field to generate more power, putting a high loadon the engine. all a alternator is is an electric motor being driven by abelt so it makes elcctricictyu, not uses it. ALso, class AB have a high draw. class d amps hardley have a footpront, but the older ab can suck a lot of juice

AB amps have higher efficiency and put out good power with less current draw. Mono class D Amps are current hogs. You have it backwards.

the alternator does not spped up to make more power, it just makes more magentic field to generate more power, putting a high loadon the engine. all a alternator is is an electric motor being driven by abelt so it makes elcctricictyu, not uses it. ALso, class AB have a high draw. class d amps hardley have a footpront, but the older ab can suck a lot of juice

I don't think anyone here suggested the alternator "changes speeds". They were talking about the rpm of the engine. Except MY alternator, I got a CVT transmission off an old snowmobile and hooked that bad boy up to my alternator, :silly:

And Washoutx, I agree that in this particular scenario his amp is probably NOT the cause of the rpm dip. Myself and others were simply illustrating that it IS possible in certain extreme scenarios.

I personally have experienced "oops, too much juice" engine stalls. Like Isotope, it was due to huge amps on stock charging systems. Mine was exaggerated by the fact I had a pre-runner bar and was running 4 Explorer 8" round offroad lights back in the country.

AB amps have higher efficiency and put out good power with less current draw. Mono class D Amps are current hogs. You have it backwards.

I am sorry but you are wrong.

The internal circuitry doesn't make that much of a difference at full power. Class D amps are more efficient the A/B amps but not by a whole lot. The main thing that causes the a difference in current draw is the ohm load the amp is being run at. The lower the ohm load the higher the current draw at the same voltage. It is simple physics.

would not get too worried, more than likely a coencidence. In 10 years audio install I have yet to see a cars audio system that pulls so much current that it affects anything other than drawing from headlights and other typical problems people run into with large amplifiers.

Just use a multimeter on your battery and measure your voltage while the car is running and make sure your not dropping voltage like crazy. You shouldnt have drops below 12-12.5 while the car is running and bass notes are playing. If you do you have a significant draw from the amp and should get a Kenetics or Optima or similar gel cell to help with that. But if im not mistaken with Fosgates model numbering system 3002 is a 300 x 2 amp right? What does its birth certificate say its RMS rating is? If its a 300 x 2 you are more than fine with the stock charging system.

the birth certificate says 115rms @ 4ohms. yeah, is bridged. it must have just been a fluke, but i'm gonna stay wary. i've run more powerful systems in my older cars and never seen this happen. maybe its the a/c?

haha you're overreacting. nothing out of the ordinary.

i'm running a 1400 watt that drains the batt and it does work the alt extra hard but its nothing to worry about