Amperage experts - How big of an alternator if 130 isn't enough

I like my steeda underdrive pullies, but yah, its time to go if your running that amp. Any alternator isn't going to put out enough at idle with the underdrives. 130 amps should be enough, but your output at idle with any alternator is going to be really low especially with underdrive pullies.
I agree totally with Mustang 5L5.

I would just get a 1 or 2 farad capacitor...I have a 1 farad cap with my 1200+ watts and had no problems with u/d pullies whatsoever..

MustangLife said:

Allright. I have a new top of the line NAPA battery and a stock alternator. But I have aftermarket headlights and foglights. A U/D alternator pulley. And a 1000 watt amp. My interior and exterior lights flicker now. So since the battery is new and good. I'm not gonna spend on a optima or similar. So how strong of a aftermarket alternator do I need.

Stock is 130 amp
PA Performance makes a 170 AMP and a 200 AMP

I'm not at all smart on amperage. But I do know that everything was fine before I added the 1000 watt car Amp with a 40amp fuse.

Thanks
Josh

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For what it's worth, in electrical-land, a watt is a volt times an amp. So when an audio amplifier is drawing 1000W, it's pulling about 72-amps at 13.8V. Keep in mind that the amp is not drawing that all the time so the average draw from the audio system is typically much less (which is why you can get away with a 40A fuse...)

Headlights are typically about 55W which is about 4A each when on. Add another 8A for two foglights. And so on. Honestly, I'd be very surprised if an alternator rated at 130A wasn't sufficient for your needs.

Lights flicker when the stereo is thumpin' due to momentary voltage drops caused by large instantaneous current demands from a high-power stereo amp. A major contributor is the battery itself. The battery has an internal resistance that shows up at other times like when, say, cranking the engine with the headlights on: the headlights dim as the starter draws hundreds of amps. The voltage right at the battery terminals can drop to 11, 10 or even 9V during cranking due to the current flowing through this internal resistance.

Still, the battery has a lower internal resistance than any alternator. Sudden large draws on the system are really drawn out of the battery with the alternator supplying recharge current. Although an alternator may be able to supply high steady state currents, they aren't that good at regulating fast transients like subwoofer hits.

So a couple of things come to mind. First, check your battery for the CCA rating. "Top of the line" may just mean its internal construction is robust so it'll last a long time but it may not speak to the ability of the battery to supply gobs of current without the voltage falling through the floor. Get one with the highest CCA (cold cranking amp) rating that will fit the tray. High CCA ratings mean lower internal resistance so the voltage won't drop as much under high current transients. They're heavier, but it's a minor penalty to pay.

Second, as 98stangv8 says, get a large cap intended for audio and install it right beside the amp with big fat lead wires. The cap acts as a very low impedance current well the amp can draw from for transients and is recharged by the system battery at a more leisurely rate. The amp will pull current for big bass hits from the low-impedance capacitor through the short leads more easily than it will from the higher impedance battery through ten or more feet of cable. The capacitor charge will be replenished at a more leisurely rate by the battery and alternator in between bass hits. You'll probably find the bass hits harder with a good cap installed and the lights shouldn't dim nearly as much.

Oh, and BTW, I'd ditch the UDPs...