120a Alt upgrade

Electrical mods for the hi-end modder. Such as wiring harness hacks, swaps, etc...

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sixsracing
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Re: 120a Alt upgrade

Post by sixsracing »

SoCal, a 120 amp unit is on the way, they are standard issue on Mk3's. 8)
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Re:

Post by gull »

Briano1234 wrote:While that is true, about doleing out. if you have a 600watt amp running your sub woofer as some do, then according to ohms law P power in amps equals I amps times E voltage.

so 600 divided by 12vdv = 50amps.

Ricers wonder why they blow out batteries and alternators because of thier big honking Stereos or Subs....
Your math is fine, but it's important to remember that it will only draw that much for brief periods of time. Music has lots of peaks and valleys; unless you like listening to test tones at full volume, the average consumption will be a lot lower, and that's what the battery and alternator care about. (Indeed, the amp itself would likely not survive putting out 600 watts continuously for long; neither would the speakers.)

Those peaks can cause voltage drops in the wiring, though, which can cause other problems -- like distorted audio, and headlights that flicker on bass peaks. The usual fix for that is a "stiffener capacitor" to supply extra current on peaks and smooth out the overall power draw of the system.

For alternator sizing purposes, you want to pay a lot more attention to heavy, continuous loads -- headlights, the heater blower, the rear window defogger, etc.
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CalAltaDubber
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Re: 120a Alt upgrade

Post by CalAltaDubber »

Spykce wrote:I installed a 800 watt amp to power the 6.5" component polk speakers I installed in the front doors, as well as an 8 inch sub. This is obviously causing an issue so I have not yet played it very loud, especially at night. I am going to relay the headlights sometime this week but I'm thinking I will go with a 90 amp also. The car has manual steering and no A/C so it has few strains on it.

An 800 Watt amp will consume 67 Amps (when operatiing at peak power), Average power will still be right up there probably still 50 Amps.

First I need to dispell some sales crap that car sound sales people talk. The output of an amp is NOT added, a head unit that is 50 Watts per chanel has an output of 50 (Fifty) Watts. The term 4 X 50 W means four chanels with a fifty Watt output, it is only one amplifier.


The question becomes is your amp. a true 800 Watts or is it a two chanel amp with a 400 W output?

The quick answer is to look at the fuse for the amp. If it is a 35, 40 or even 50 Amp fuse your amp is 400W. In that case the 90 Amp alternator should surfice.

If your fuse is rated at 70 Amps (or more) you do indeed have an 800 W amp. and will need to do more aside from the alternator upgrade. I would suggest the installation of a large capacitor. Car stereo folks install these for two reasons:

1, they act as a backup battery for the sound system to keep a constant potential available for the amp. This will take some of the strain off the alternator, but needs to be done in conjunction with the alternator upgrade; and

1, they filter out ignition noise.

The 90 Amp Alternator output is only 300 Watts more than the 65 Amp. (operatiing at max output) and would not be enough to operate an 800 W mono amp.
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Spykce
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Re: 120a Alt upgrade

Post by Spykce »

Great information! The amp is an 800 watt four channel amp. I have it hooked for 2 channels driving my polk speakers in the doors, and the other 2 bridged for the subwoofer. I was considering a capacitor as I had to install one of these on a past car, but it had a much larger stereo system in it. I'll hopefully be relaying the lights next week sometime to help with that. I have 2 - 25 amp fuses in the amplifier, I would assume one for front and one for rear. All the information has been very helpful!
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Re: 120a Alt upgrade

Post by CalAltaDubber »

Spykce wrote:Great information! The amp is an 800 watt four channel amp. I have it hooked for 2 channels driving my polk speakers in the doors, and the other 2 bridged for the subwoofer. I was considering a capacitor as I had to install one of these on a past car, but it had a much larger stereo system in it. I'll hopefully be relaying the lights next week sometime to help with that. I have 2 - 25 amp fuses in the amplifier, I would assume one for front and one for rear. All the information has been very helpful!
Having two fuses suggests to me that the unit is consists of two independant, two channel 200 W amplifiers. The actual power consumption of the unit is probably 400 W (Peak). To handle 800 Watts the 2 fuses would have to be at least 40 A.

I would think the 90 A. alternator will be enough, but the capacitor is still a good idea too. It will help.

On a side note, to clairify, relaying your headlights only has them take their power source directly from the battery (in effect putting them in parrellel with the rest of the car's electrical system), They still will be a load on the electrical system. The advantage to doing this is to allow more electrical current over heavier wire to the headlights.
Phil

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Spykce
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Re: 120a Alt upgrade

Post by Spykce »

Yup, I just want to get them putting out as much light as they can. I went from an A4 with HID's to the cabby. While I know it won't be the same more output will help.
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Re: 120a Alt upgrade

Post by kamzcab86 »

Spykce wrote:Yup, I just want to get them putting out as much light as they can. I went from an A4 with HID's to the cabby. While I know it won't be the same more output will help.
I finally relayed my car's headlights last year (as detailed here http://cabby-info.com/Files/RelayingTheHeadlights.pdf ). The stock lights ended up being a lot brighter; should've relayed 'em years ago! Because the left light was bad, I replaced both headlamps earlier this year with crystal clears using H4 bulbs. I didn't get a chance to use them until a recent road trip to Northern AZ where it was pitch black... those lights were like spot lights!! :shock: :lol: So, if you're used to HIDs, consider upgrading to H4's (which will definitely require relays). :beer:
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Re: 120a Alt upgrade

Post by Calimus »

Nothing (except HID's) beats relayed H4's. Hav ebeen using a relay setup on the rocco for year as well as the crabby cabby.

It's amazing what you can see at night.
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