How much power do I need for 3 amps

10+ year member Elite
I'm looking to run a 300, 400 and 500 watt amps. I'm wondering if I'll need more power than just my car battery. The 300 would be powering one or 2 8's. The 400, 4 3.5's and the 500 a set of 6.5 components and maybe 2 4 x 10's (I'm not sure what I'm going to do with that slot). If I do need more power, how should I go about doing this?

Also, would you prefer JL audio TR350-CXi's or Infinity Kappa 32.5CF's?


10+ year member

ok i figure to give you some leeway a safe leeway 65 amps actually amount is 57 from what i can gather. you will deff need a new alternator most likely, other can double check as i am not positice about it, but it would be wise to get a alrger alternator


10+ year member Elite
The 300 is a Rockford Fosgate Punch 300S. The other amp I'm looking at is not the 800 anymore but rather a Rockford Fosgate Punch 500X.

The cars an 85 Pontiac Fiero.


5,000+ posts

yeah if you get a bigger alt. you'll also lose horse power and fuel economy I would go with a 2nd car battery and a farad cap bigger alternator would be a last resort
Unless you're upgrading to a HUGE alternator there should be little to no effect on power/economy. 1 extra HP driving the alt pulley should net around 700w of available power.

A 2nd battery will only improve car-off listening time.

A cap will only result in lower over-all system voltage and MAYBE help reduce headlight dimming if you have it.


10+ year member

hmmm... let's get this straigh....

you're running 300 watts to two small subs, 400 watts to 4 3.5's and 500 watts to 6.5s and 4x10s.

The least of your problems will be your electrical system. You're system's going to sound like crap. You're going to have 8 sets of full range speakers totaling 900 watts, and 300 watts to the most power hungry devices in the system...

maybe it's time to rethink this.



Junior Member
I have a Ford Ranger, and first upgraded to a one farad cap to fix the headlight diming (almost flashing) and that worked. When I upgraded my Amp to an 81000D (sub amp only) I found my truck would stall out when I was at idle with almost half bass (not cool). I asked around, and upgraded to a 200 watt alternator (peak, not RMS), and I've never had problems since. All my electronics are better, and my battery charges up faster. An alternator upgrade is by far the only way to go if your even questioning power issues. By the way, I also think you need to rethink your system. You'll never need all that power for your four ways. You'll want to run at least 500 watts to each sub alone, for good bass (I'm not crazy, that's not that much). Also, it's best to run your amps at lower capacity, i.e. buy bigger amps than you'll need, that way, you'll get better clarity with less distortion, and it will make your amp live it's life to the fullest. It sounds like your off to a good start though.


10+ year member Elite
I mentioned earlier that I was thinking of only using two amps now. Four of the speakers (3.5's) are in the headrest (2 in each headrest, they will be turned down quite a bit and I don't plan on using an amp on those anymore). Factory location. The two in the dash I'm going to try to build a plate to hold a 3.5 or 4 inch component set rather than 4 x 10's (because it seems that people think they sound like crap) and the door will be an infinity 6.5 component set. I intend to power the dash and door by a 500 watt amp. These are all 4 ohm speakers so they will actually be getting about 50 watts rms per speaker (total of 200 for the 4) so it's not 500 plus the headrest speakers. From what I've heard I'll probably go with an 800 watt amp if I'm using 2 subs.

As far as I understand, my earlier idea wouldn't have been sending 900 watts to full range speakers. 4 x 3.5's = 160 + 4 x other speakers = 200 for a total of about 360 RMS. They're all 4 Ohm speakers.

No one is currently typing a reply...
Old Thread: Please note, there have been no replies in this thread for over 3 years!
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.

Similar threads

I would suggest 80 ah of yinglong lithium and a H/O alternator. I'm running 40 ah with a 320 alternator on a 3.5K and it isn't enough.
My apologies I forgot to mention what pic is what. First is sub control the 80hx blink and I got the picture as soon it it blinked 2nd pic is hpf 3rd is sla other than that everything is at off eq...
Lmao I got built so long ago I dont remember honestly well not that long ago but it was 3 rebuilds ago lol
Buck, great idea. I did that tonight, and it actually didn't wheeze like a fat guy trying to run a marathon. I am going to put two windows that match the front 3 on each side and call it for...

About this thread


10+ year member Elite
Thread starter
Bellingham, WA
Start date
Who Replied
Last reply date
Last reply from


    Feb 21, 2024
  • 0
  • 0

Lt Ye Htun Oo

    Feb 20, 2024
  • 0
  • 0

Latest topics