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Old 02-12-2013, 10:36 AM   #1
Scooby Newbie
Member#: 339098
Join Date: Nov 2012
Default Alternator swap

I have a 03 legacy L. My alternator isn't strong enough to power my Sound system. I have a couple options to help but I'm not sure what to do and what order so I can fix the problem while spending the least amount of money.
1.Big 3
2.HID lights
3.Swapping a alternator with a newer or larger sized on from a wrx or legacy gt
4.New alternator
I'm running a 12" sub with a 1000 watt amp (Sony xplod) and 2 kickers components with a 500 watt (lightning audio)
Could another option be buying a new 4 channel amp?
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Old 02-13-2013, 05:45 PM   #2
Scooby Newbie
Member#: 346952
Join Date: Feb 2013

Yu will jus need to buy a bigger alternator (higher amperage output). Yu can buy a rebuild kit for yur specific alternator. That would be the cheapest way out of it. Only if yu knw what yur doin when yur rebuilding.
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Old 02-17-2013, 04:00 PM   #3
NASIOC Supporter
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT


Higher output alternator. All the ones I've seen are "drop-ins", no modding needed.

I "think" the options are a 90amp or a 120amp. I use www.rockauto.com to compare parts/prices.
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Old 02-23-2013, 09:14 AM   #4
Scooby Newbie
Member#: 345072
Join Date: Jan 2013
Chapter/Region: MWSOC
Location: Ohio
2009 Legacy

Default common

This is a common problem any time you start adding electrical load to your car.


That is DC, there is also Mechman, Ohio Generator, Tenny, and Iraggi off the top of my head.

You want to look at your usage or future usage in watts, so assuming your amps actually put out rated power 1000+500 = 1500 watts, you divide that by 10 to get an ampere figure, so you would need 150 amps from your alt for your audio system to not drain your battery.

You divide by 10 in a 12 volt system because your amps arnt 100% efficient, so for every 1 amp they draw they dont make 12 watts of power, D class amps can often be in the 80-90% efficiency range, where AB class (most commonly found in your muliti-channel amps) are in the 40-60% range.

If your headlights are dimming when your bass hits, try the big 3 first, If its just your battery draining down, then most likely you need a new or upgraded alternator.
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Old 02-25-2013, 02:32 PM   #5
Scooby Newbie
Member#: 348166
Join Date: Feb 2013

I'm running 2 12" Rockford Fosgate subs with a 1000 watt amp. It killed my last alternator so I bought a 160 amp alternator for $190 brand new on eBay and haven't had any problems with it. I also have a 7" touchscreen headunit in the car.
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