kraven moorehead
read this on another forum and thought that I would share it here.


demand up to up to up to up to up to up to up to
(amperes) 4' 7' 10' 15' 20' 25' 30'
25-50 12 10 10 8 6 6 4
50-75 8 8 8 6 6 4 4
75-100 8 8 6 4 4 2 2
100-150 4 4 4 2 1 1 1/0
150-200 2 2 2 1 1/0 1/0 2/0
150-200 2 2 2 1 1/0 1/0 2/0
200-300 1/0 1/0 1/0 1/0 2/0 2/0 3/0
300-400 3/0 3/0 3/0 3/0 4/0 4/0 4/0

this chart shows minimum copper wire size acceptable for normal wire lenghts used in a
vehicle to meet normal current demands.if aluminum or tinned wire is used,the wire gauge
should be even larger to compensate.the wire size calculations are intended to allow no
less than .5 voltage drop,assuming that the wire is properly termanated.


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Wire Gauge Recommended
Maximum Fuse Size
00 awg 400 amps
0 awg 325 amps
1 awg 250 amps
2 awg 200 amps
4 awg 125 amps
6 awg 80 amps
8 awg 50 amps
10 awg 30 amps
12 awg 20 amps
14 awg 15 amps
16 awg 7.5 amps
These are the recommended maximum fuse ratings for the corresponding wire size. Using a
smaller fuse than what's recommended here will be perfectly safe.


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proper battery size
total rms watts of system minimum battery current
0-50 675
50-100 700
100-150 725
150-200 750
200-250 775
250-300 800
300-350 825
350-400 850
400-450 875
450-500 900
500-600 950
600-700 1000
700-800 1050
800-900 1100
900-1000 1150
1000-1100 1200
1100-1200 1250
1200-1300 1300
1300-1400 1350
1400-1500 1400
1500-2000 1450
2000-2500 1500
2500-3000 1550
3000-3500 1600
3500-4000 1650
4000-4500 1700
4500-5000 1750
5000-6000 1800
6000-7000 1850
7000-8000 1900
8000-9000 1950
9000-10000 2000


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proper alternator size
total rms watts of system charging system upgrade
0-100 10
100-200 20
200-300 30
300-400 40
400-500 50
500-600 60
600-700 70
700-800 80
800-900 90
900-1000 100
1000-1500 110
1500-2000 120
2000-2500 130
2500-3000 140
3000-3500 150
3500-4000 160
4000-4500 170
4500-5000 180
5000-5500 190
5500-6000 200
6000-6500 210
6500-7000 220
7000-7500 230
7500-8000 240
8000-8500 250
8500-9000 260
9000-9500 270
9500-10000 280


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when using the battery chart remember if 2 batteries are connected in parallel,the current
will combine(both batteries current added together)and the voltage remains the same.while
in series,the voltage will double and the current will remain the same.


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Here is a simple way to determine average current draw on the electrical system
(total rms continous watts * .50 / amplifier effeciency / cars voltage = average current
draw on cars electrical system).this is intended for musical signals not tone generators.
the reason for multipling by .50 is that .50 represents a musical signal driven to the
point of distortion.for bass reproduction you may use (.60).if there is more than one
amplifier used,simply combine the results of all amplifiers.
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