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Bronze Member Username: Bruhneedluv2Post Number: 53 Registered: May-04 | okay I have amps with an 80a fuse (220x2 rms), one 30a fuse (50x4 rms), and one 20a (62.5x2 rms) fuse. based on these figures, i would need at least 130 EXTRA amps onto my 120a stock alternator?! this ish is getting to me now. then I also looked at this calculation: 80x13.8 (average voltage of a running car)=1104 total watts, 30x13.8=414 total watts, and 20x13.8=276 total watts. all three added are 1794 total watts. All of the amps are AB circuitry, so it would be @ 60% efficiency. 1794x.60= 1076.4 total watts Now I take 1076.4 watts/13.8 volts= 78 amperes. So my question is that I would need an HO alternator that can handle 100% of the wattage (1794)or 60% (1076.4) of the wattage? AND IS IT REALLY THAT MANY AMPERES TO ADD ON? |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 3614 Registered: Dec-03 | ok first and foremost, you don't need a high output alternator unless you have a problem with lights dimming, amp clipping, etc caused by voltage rails sagging below 12 volts. this is one of those things you need to wait and see on once the system is in place. now, to calculate the current draw, first figure out if each amp is class AB or class D. then figure out how much power each amp puts out at the load it'll be seeing (2 ohms? 4 ohms?) with each amp, if its class AB, add 40% to the power it produces. for class D add 20%. this factors in an estimate for efficiency lost to heat and deisgn that all amps lose. remember an amp isn't 100% efficient so it takes more current than it produces power at the speakers. ok, now add the totals, and take the sum and divide that by 12 (volts. the idle voltage for the car) that'll be the most current the system will draw at FULL volume. now if you don't intend to drive around at peak output, going deaf, annoying the whole block, and getting cited for noise ordinance laws.... then remember this too: every time you go down in volume by audibly half, you're using a tenth of the power. so if at peak, you use 100A of current, then at half that volume, you'll only be drawing around 10A. You see how quickly the nominal power usage declines... now while amps can draw up to ten times the RMS power at peak demands, this is only momentary and for now, we're just figuring continuous draw. a capacitor can help with those brief, high demands, as long as the rest of teh charging system is adequate. good so far? more info: http://p079.ezboard.com/fcaraudiotalkfrm27.showMessage?topicID=50.topic http://p079.ezboard.com/fcaraudiotalkfrm27.showMessage?topicID=49.topic |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 3615 Registered: Dec-03 | by the way yes the system really can draw up to around 80A of current, and if you compete for SPL, you'll want an alternator that has at least that much, and a bit in reserve, in addition to whatever your car already needs to run.modern car audio systems drawing over a kilowatt of power use a tremendous amount of current. Since amps have gotten cheaper, people keep demanding more power.. The problem with that is the electrical system has to keep up. That's one of the boons of the class D amp age. when everything was class AB, nobody could afford amps larger than about 500 watts total, so total system power rarely exceeded about 800-1000 watts total, between two or three amps. Then, a 150A alternator usually did the trick, but those were still expensive, too. |
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Bronze Member Username: Bruhneedluv2Post Number: 54 Registered: May-04 | all right then. I am looking at the amps. all AB class amps all running at 4 ohms. I have amps with an 80a fuse 440 watts (220x2 rms), one 30a fuse 200 watts (50x4 rms), and one 20a fuse 125 watts (62.5x2 rms). with adding 40% to all amps, I see 440+176=616, 200+80=280, and 125+50=175. 616+280+175=1071/12=89.25 amperes. 89.25 amperes is what I need to cover those peaks at full power, right? and 44.625 or 45 amperes is what I need in addition to power my system with my 120 stock amp? I may want to push it at peak level to see how everything sound at that level but that is not an everyday thing for me to have it that loud. also in this case specifically, will a capacitor help out? |
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Bronze Member Username: Bruhneedluv2Post Number: 55 Registered: May-04 | sorry but I am bit scared that when I add all of this onto my car's current load that I will have to buy another alternator |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 3627 Registered: Dec-03 | yeah just round off so say 90A and 45A. ignore fuse sizes. those fuses are for peak output of the amp. if you run at 4 ohms, you'll never come close to the fuse ratings for current demand since you'll put out less power at 4 ohms. for caps, find the "max" or "peak" output for each amp, or take the RMS output and multiply by 3 for a rough estimate. add the figures, and then use 1 farad per every 1000 watts of peak rating. yeah the caps will help in transient response. they just don't make up for the alternator. |
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Bronze Member Username: Bruhneedluv2Post Number: 56 Registered: May-04 | in addition, my lights dimmed when the bass hits BUT I discovered that I had a bad battery and replaced it recently. Once I have EVERYTHING HOOKED UP, then I can truly see what is going on. |
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Unregistered guest | I just put a 1000 Watt amp on my stero system. I also put in a 200 Watt Boss CD Player. Where I bought my cd player they told me there that with the system I have I could get my alternator built up to put out more power or just put a capacitor on it? Would it be okay to put a capacitor on it and would it work? By the way..the alternator I have now is 105 Amp. Any info you could give me I would greatly appreciate! Thanks a bunch! |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 3920 Registered: Dec-03 | read these two pages to answer your questions: http://www.wickedcases.com/caraudio/capacitors.html http://www.wickedcases.com/caraudio/charging.html |