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Is my math correct?
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<blockquote data-quote="n2audio" data-source="post: 4061685" data-attributes="member: 540940"><p>Your result is within reason, but getting there is a lot more complex.</p><p></p><p>From a couple very good and experienced mechanics I've dealt with you can generally assume about 40% of a stock alt's output is head room.</p><p></p><p>So at 130A, about 50A is unused.</p><p></p><p>So let's say you run 1000w class D, and 400 class a/b</p><p></p><p>Class D at around 75% efficient, a/b at 60%, call it 1400w at 70% just for simplicity...</p><p></p><p>1400/.7 = 2000w</p><p></p><p>2000w/14 = 143A</p><p></p><p>Now the big variable - Crest Factor...</p><p></p><p>That 143A assumes the amplifiers are operated at full output playing sine waves. Music draws a LOT less current than sine waves -- 1/3 at the most. So even at full volume you'd be drawing about 45A. Depending on the music type and your typical listening volume you might not even draw 20A most of the time.</p><p></p><p>Crest factor (and low demand listening habits) explain why people can run 1000w+ for years on relatively small stock charging systems and never have a problem.</p><p></p><p>The big 3 is never a bad idea, and you might still see some dimming at high volume - but 1400w on a 130A alt shouldn't be a problem.</p><p></p><p>FWIW - I have a 2000 contour with a 130A alt. I'm running 1100w with no upgrades to the stock wiring and have only minor dimming at full volume.</p></blockquote><p></p>
[QUOTE="n2audio, post: 4061685, member: 540940"] Your result is within reason, but getting there is a lot more complex. From a couple very good and experienced mechanics I've dealt with you can generally assume about 40% of a stock alt's output is head room. So at 130A, about 50A is unused. So let's say you run 1000w class D, and 400 class a/b Class D at around 75% efficient, a/b at 60%, call it 1400w at 70% just for simplicity... 1400/.7 = 2000w 2000w/14 = 143A Now the big variable - Crest Factor... That 143A assumes the amplifiers are operated at full output playing sine waves. Music draws a LOT less current than sine waves -- 1/3 at the most. So even at full volume you'd be drawing about 45A. Depending on the music type and your typical listening volume you might not even draw 20A most of the time. Crest factor (and low demand listening habits) explain why people can run 1000w+ for years on relatively small stock charging systems and never have a problem. The big 3 is never a bad idea, and you might still see some dimming at high volume - but 1400w on a 130A alt shouldn't be a problem. FWIW - I have a 2000 contour with a 130A alt. I'm running 1100w with no upgrades to the stock wiring and have only minor dimming at full volume. [/QUOTE]
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