Amperage Calculations


New member
Username: Phreezerburn

Post Number: 1
Registered: Jun-06
In order to figure out the size of alternator I need, would this way of thinking work:

I take the values from the manuals of the amps and deck that read "Current Consumption" and add them all up and get 107 amps

How much would the rest of the electrical system in a typical car be? Say 20-40 amps?

Then would a 150 amp alternator do just fine for my needs? Right now I have a stock 105 amp Alternator in a Cavalier and the sound system isn't installed yet, still doing fiberglass work. My older system which drew about 80 amps ran with some heat issues, amp would turn off at high volumes, so I figure it was the electrical system.

--------------System Specs------------
Premier DEH-P980BT
Premier PRS-D4000F
Premier PRS-D5000SPL
Premier TS-C720PRS
Premier TS-W5000SPL

Silver Member
Username: Highstone

Post Number: 214
Registered: Mar-06
how many RMS are the amplifiers?

New member
Username: Phreezerburn

Post Number: 2
Registered: Jun-06
Premier PRS-D4000F is 300w RMS
Premier PRS-D5000SPL is 1500w RMS

Gold Member
Username: 54danny54

Betsy layne, Kentucky..GO... USA duh

Post Number: 2709
Registered: Nov-04
150 might go 180 to be safe

Gold Member
Username: Illuminator


Post Number: 3222
Registered: Apr-05
To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 2 channel amp rated at 300 watts RMS per channel would be 600 watts). Double it to account for amplifier inefficiency (600 watts X 2 = 1200 watts), then divide by the average output Voltage of an alternator, 13.8 volts (1200 divided by 13.8 = 87 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (87 amps divided by 3 = 29 amps). The result is the amplifier's approximate average current draw.

Multiply the amount of current your alt puts out by 40% and that's how much current you have to play around with.

Silver Member
Username: N2audio

Lawrence, Ks USA

Post Number: 891
Registered: Mar-04
Amps running hot probably isn't an electrical system issue.

But I think A 150A alt would work nicely.
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