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watt are you doing?
The equation for your lights is
Total Wattage divided by Battery output voltage equals Amperage Draw.
For your amplifiers I don't believe there is an easy equation because you
are not dealing with continuous amperage draw. You should get the specs from
For example I have two Series VIII Hifonics Amplifiers, here are the specs
(at 4 ohm load):
Amplifier Hercules 200 watt
Gemini 200 watt
Idling Current 700 mA
Max Current 40 A
Typical Current w/ Music 24 A
Note: Hercules is a Mono amp meant to run a sub, while Gemini is a 4 x 50
watt to run mids & highs.
So depending on what your alternator's output is you should be OK.
I am running H4/H1's as well as PIAA 90 Pros in the 4000 csq (90 amp
alternator). On high beam w/ driving side of 90 Pro on I am running 580
watts total, battery is putting out 12.5 volts (checked w/ Fluke as well as
gauge in car). Given the equation above, the lights are drawing 46 amps.
Accordingly, I do not listen to the stereo at full volume when I've got the
luminosity jack hammer going (I do have smaller Hifonics amps in this car).
I even took +12V switched current from the defrost switch in such a way that
when the defroster is switched on, it cuts the control current to the
fog/driving lights. For added insurance I've got an Interstate Mega Tron
All lights are hardwired to the alternator via relays and fuses.
'87 4000 csq plenty o lights & stereo
'93 S4 soon to have plenty o brakes & grip. (Test fit the Big Reds today,
>> And, uh, and you run _how_ many watts of simultaneous low-beam and fog
>I worry about my alternators ability to keep up sometimes...
>High beams: 400 watts (plus all parking lights)
>Stereo @ max: 480 watts (output... who knows what the draw is?)
>Leaves precious little to run the fuel pump and ECU when the heater fan
>is on high.
>Leaning towards an external 14.5 volt regulator and some extra ground