Alternator output question
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Senior User
Joined: Nov 2006
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From: Phoenix, AZ
Alternator output question
I've been looking to replace the factory 60 amp alt in my 77 for quite some time now and it's now moved to the top of my "fix it" list as it is going out now and making a strange whizzing noise. My question is would a new 70 amp alt be sufficient output for a stereo with a 760 watt amp and 600 watt sub? I've considered a higher output but am unsure of the higher price tag that goes with it. What does everyone think?
Elder User
Joined: Dec 2007
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The smart answer would be "Turn that down".
How is everything working out with the stock alternator? (before it started to 'sing' on its own). As in...with everything working, do your lights dim and the charge gauge start to dip into the 'D' (discharge) range?
The extra 10 amps, provided everything bolts up correctly wouldn't hurt in my opinion--Just wondering how the system is currently working with the loads placed onto it.
S-
How is everything working out with the stock alternator? (before it started to 'sing' on its own). As in...with everything working, do your lights dim and the charge gauge start to dip into the 'D' (discharge) range?
The extra 10 amps, provided everything bolts up correctly wouldn't hurt in my opinion--Just wondering how the system is currently working with the loads placed onto it.
S-
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
To the OP - the 600W on the sub doesn't mean that it continuously outputs 600W. It means it is capable of outputting 600W peak without blowing. For the amp - assuming you're at idle when the alternator output is at its lowest and the battery sits at 12V and your amp is pulling its maximum current, that means you are drawing 760 / 12 = 63 amps for the amplifier alone. It depends how you're going to configure your amp, and what other loads are on the system, but if you plan on having your amp pretty loud, a 70 amp alternator is going to be a little weak.
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Joined: Dec 2007
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I might be reading what you meant incorrectly, so I apologize if I am. But a 70 amp alternator doesn't mean that it continuously outputs 10 extra amps than a 60 amp alternator. It means that it is capable of supplying 10 more amps if it is called upon, without draining the battery.
To the OP - the 600W on the sub doesn't mean that it continuously outputs 600W. It means it is capable of outputting 600W peak without blowing. For the amp - assuming you're at idle when the alternator output is at its lowest and the battery sits at 12V and your amp is pulling its maximum current, that means you are drawing 760 / 12 = 63 amps for the amplifier alone. It depends how you're going to configure your amp, and what other loads are on the system, but if you plan on having your amp pretty loud, a 70 amp alternator is going to be a little weak.
To the OP - the 600W on the sub doesn't mean that it continuously outputs 600W. It means it is capable of outputting 600W peak without blowing. For the amp - assuming you're at idle when the alternator output is at its lowest and the battery sits at 12V and your amp is pulling its maximum current, that means you are drawing 760 / 12 = 63 amps for the amplifier alone. It depends how you're going to configure your amp, and what other loads are on the system, but if you plan on having your amp pretty loud, a 70 amp alternator is going to be a little weak.
Depending on how much everything draws? It may or may not be enough..It all depends as you say, how loud it's gonna be blasting.
S-
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From: Phoenix, AZ
THe stereo isn't going full out all the time...only when I wanna make an entrance. It's usually at a pretty steady and reasonable volume. I can't run the stereo at night with my headlights on cuz I know it'll draw too much. The alt was running pretty smoothly before it started singing. Never really had many problems. I think the problem is just that it's probably the factory alt and is showing it's age lol. How do I determine how much total power my stereo and any other accessories are drawing?
Elder User
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That's a question for the aftermarket audiofiles. While my backround is in electronic repair/automotive tech area? It's not in the design arena as much as I'd like it to be.
Keep in mind it (the increase demand) might have accelerated the current alternators demise. Heat is the enemy of all electronics, and the more load? The more heat is generated. (why I suggested bumping up to the 70 if possible, built for more 'kick' at the odd times).
There is a formula for figuring out the demand/load totals to come up with the correct true amperage you require. It might be around the net for a basic search? (I can't remember it offhand. I'm lucky enough to remember Ohm's Law some of the time)
Summit shows their largest alternators for our truck as being 140amps with internal regulator. It comes with a large price tag as well at almost $200! Also a 200 amp one that runs about $325.
I'm not even sure how they would work out on our trucks. But I figured it was worth a mention.
S-
Keep in mind it (the increase demand) might have accelerated the current alternators demise. Heat is the enemy of all electronics, and the more load? The more heat is generated. (why I suggested bumping up to the 70 if possible, built for more 'kick' at the odd times).
There is a formula for figuring out the demand/load totals to come up with the correct true amperage you require. It might be around the net for a basic search? (I can't remember it offhand. I'm lucky enough to remember Ohm's Law some of the time)
Summit shows their largest alternators for our truck as being 140amps with internal regulator. It comes with a large price tag as well at almost $200! Also a 200 amp one that runs about $325.
I'm not even sure how they would work out on our trucks. But I figured it was worth a mention.
S-
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Elder User
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Most aircraft alternators are the Ford style big case 70 amp models I believe-they can handle the environment and vibration due to design.
My ol 40 amp stocker gave up a few years back due to age, so I did some research and put in a 75a IAR(internal alternator regulator) alternator(late 80's) for awhile-until I found out they have design flaws(the wiring plugs mainly)
So after more google searches, then I found the FTE-I installed a 130a alternator(called a 3g) from a later model mustang-and it rocks.
I can't remember atm what year of car it came in, but the case has the same mount patterns so that it bolts up into my stock 70's engine bracketry.
The wiring was easy after the research, it looks very trick, the fan is internal, so its just the alt. with a pully and minor wiring, and no external regulator. Plus it is all Ford.
The newer stuff is more expensive, but I found mine at a pick n pull for cheap.
So whatever you do, make sure you know for sure it will work for you, and be comfy with it.
Good luck!
My ol 40 amp stocker gave up a few years back due to age, so I did some research and put in a 75a IAR(internal alternator regulator) alternator(late 80's) for awhile-until I found out they have design flaws(the wiring plugs mainly)
So after more google searches, then I found the FTE-I installed a 130a alternator(called a 3g) from a later model mustang-and it rocks.
I can't remember atm what year of car it came in, but the case has the same mount patterns so that it bolts up into my stock 70's engine bracketry.
The wiring was easy after the research, it looks very trick, the fan is internal, so its just the alt. with a pully and minor wiring, and no external regulator. Plus it is all Ford.
The newer stuff is more expensive, but I found mine at a pick n pull for cheap.
So whatever you do, make sure you know for sure it will work for you, and be comfy with it.
Good luck!
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From: dallastown pa
Well I would say with head lights and AMPn ot being able to be on at the same time is a no go then add A/C or heating wow dead in the water I bet. There are 90 AMP and larger made to bolt in place of your stock and run around 90 to 140 depending on size. Good luck buddy!!!!!