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Alternator amp size?


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I have 0 Gage, big 3 ( big 4 really, have ground on back of alt to battery also) , regular battery up front, 2 smaller sealed high amp hour batteries in back,  Rockville db16, jbl gto 1000.4 , a Sony 4 channel ( like 50x4), 6 way electronic crossover, pioneer headunit, and a gravity 7 band eq/line driver. Have a generic 250a alternator and after about 5-6 minutes of high volume volt Gage drops significantly and even wipers slow down. I know my batteries are good, I charge them every few weeks and test them with a carbon-pile tester usually same time. The alternator just cant charge them quick enough. My biggest problem is that I live 5 miles from work so my truck only gets driven like 20 miles a day! After a good charge on my batteries, I get a good week before I get dimming again. I have a cheapie volt meter that is currently unhooked , but when it was hooked up it never dipped below 12.5v at idle with stereo wide open. At 2500rpm, stayed over 13.6 v with stereo wide open.  How big of an alternator do I need to get to keep this thing charged with the little amount of driving I do?

2009 Silverado 1500, 7.5" lift, 37x12.50r17s, Built Gen 4 5.3L ( 4.8l flat pistons, decked 243s, SS2 Cam, Pac 1218 springs, ported intake, 120mm TB, Long tubes, 3" duals HP tuner software tuned by me), 4l80e swapped and 4.56 gears. All done by me. stereo is Pioneer avh 600ex, all stinger rca, jp23 v1.5, skar rp150.4, and hertz hpd4. 2 SHCA 6.5 8ohm, 1 SHCA 3.5", and 1 DS18 tw120pro in each door. The 3.5 mid and 3.5" tweeters are powered by the skar rp150.4, the 6.5s are powered by the hertz bridged @4 ohms. Dual runs   of 3/0 welding cable, 300a alternator, 2 Vmax AGMs up front. current sub is a AB XR 12 ( dual 2 ohm) with bottom spider cut out in 2.25 cubes at 32hz

 

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Maybe 2700 watts rms total

2009 Silverado 1500, 7.5" lift, 37x12.50r17s, Built Gen 4 5.3L ( 4.8l flat pistons, decked 243s, SS2 Cam, Pac 1218 springs, ported intake, 120mm TB, Long tubes, 3" duals HP tuner software tuned by me), 4l80e swapped and 4.56 gears. All done by me. stereo is Pioneer avh 600ex, all stinger rca, jp23 v1.5, skar rp150.4, and hertz hpd4. 2 SHCA 6.5 8ohm, 1 SHCA 3.5", and 1 DS18 tw120pro in each door. The 3.5 mid and 3.5" tweeters are powered by the skar rp150.4, the 6.5s are powered by the hertz bridged @4 ohms. Dual runs   of 3/0 welding cable, 300a alternator, 2 Vmax AGMs up front. current sub is a AB XR 12 ( dual 2 ohm) with bottom spider cut out in 2.25 cubes at 32hz

 

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$150 on eBay, don't even know who made it lol. What's a reliable cheap brand that'll do the job? And how big of an alternator should I get

2009 Silverado 1500, 7.5" lift, 37x12.50r17s, Built Gen 4 5.3L ( 4.8l flat pistons, decked 243s, SS2 Cam, Pac 1218 springs, ported intake, 120mm TB, Long tubes, 3" duals HP tuner software tuned by me), 4l80e swapped and 4.56 gears. All done by me. stereo is Pioneer avh 600ex, all stinger rca, jp23 v1.5, skar rp150.4, and hertz hpd4. 2 SHCA 6.5 8ohm, 1 SHCA 3.5", and 1 DS18 tw120pro in each door. The 3.5 mid and 3.5" tweeters are powered by the skar rp150.4, the 6.5s are powered by the hertz bridged @4 ohms. Dual runs   of 3/0 welding cable, 300a alternator, 2 Vmax AGMs up front. current sub is a AB XR 12 ( dual 2 ohm) with bottom spider cut out in 2.25 cubes at 32hz

 

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a 240amp should be fine, look up Mike Singer (singer Alterntors), mechman, DC power. They should be able to help. dont expect 240 rice tag though. Probably 300-400. Quality cost money. 

I have bought an alt from mechman that never gave me an issue, same for my singer alt. Both work perfect

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Dropping to 12.5, especially at idle, isnt a big deal, at all, this is car audio, just tossing that out there. That is after all,  where the battery rests.  Looks like you have a shit load of equipment, none of which pulls much amperage or has a high demand at all. 

I'm on board with Eric, and his comment about the Ebay alt being a paper weight, for sure. Your OEM alt would probably actually be better in this case, but if your charging at 13.6 at rev, and seeing that wide open on the loud knob,..that is feeding the demand needed, and charging your bank soooo what is the main concern here? Dimming lights is your main concern? 

Put new sciency, future bulbs in. (LED or whatever) Or add a actual working cap bank, for speed. 

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so not to jack the thread or anything, but on the topic of voltage dropping, if i'm running ~3krms and my voltage drops from 14.6 to 13.8 on hard, off tuning bass drops and instantly goes back to 14+ on the next notes, that's nothing to be too concerned about  right?  kind of just been curious.  i'm sure there's not really anything i can do to make it stay at 14.4 when pulling full power, i just wanted to make sure my setup is performing decent

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i will play clear down to 12.2 and not worry, even on sustained notes. But its my gear, my money. Most amps are rated 9-16v,not that i would recommend dropping to 9v. 

And unless you have a bank of supercaps youre gonna have voltage drops on kick drum notes. there is gonna be a slight delay from the current demand to when your alt ramps up output. its a mechanical device after all.

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8 minutes ago, bmwking said:

so not to jack the thread or anything, but on the topic of voltage dropping, if i'm running ~3krms and my voltage drops from 14.6 to 13.8 on hard, off tuning bass drops and instantly goes back to 14+ on the next notes, that's nothing to be too concerned about  right?  kind of just been curious.  i'm sure there's not really anything i can do to make it stay at 14.4 when pulling full power, i just wanted to make sure my setup is performing decent

Fuck no. Half a volt, to a daily, at full rip .. meh.

Some see more loss, with just wiring resistance. And sure, there are things you can do, to maintain/keep it stable, but,  again for a daily, I wouldnt sweat that in the least homes. Let it eat...

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12 minutes ago, Kyblack76 said:

Fuck no. Half a volt, to a daily, at full rip .. meh.

Some see more loss, with just wiring resistance. And sure, there are things you can do, to maintain/keep it stable, but,  again for a daily, I wouldnt sweat that in the least homes. Let it eat...

cool man, thanks for that!  hopefully it wont sag too much more when i swap my 2k for my 5k :)

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