Higher capcity Alternater = More efficient? - Fuelly Forums

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Old 07-07-2007, 09:17 PM   #1
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Higher capcity Alternater = More efficient?

Just a thought.
Getting my sub and amp installed tonight and was thinking of the alt and battery in my car.

Do you guys think a higher amperage alt would be more efficient for the same given electrical load? Or would it be less?

Would it be a big enough effect to notice in FE?
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Old 07-07-2007, 09:42 PM   #2
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Originally Posted by bbgobie View Post
Do you guys think a higher amperage alt would be more efficient for the same given electrical load? Or would it be less?
Higher capacity does NOT equal higher efficiency. All higher capacity means, is that it will have a higher peak load that it can generate (assuming you need that much power). In general I see little point in a bigger (then needed) alternator, unless you think you might occasionally have high electrical loads you need to power.

For example, my dad has a large capacity alternator in his van, because he occasionally needs to use the thing to charge up a HUGE (~170 pound) battery he uses for electrical power while "dry camping" (i.e. camping away from hookups). However, he clearly doesn't have the alternator for FE, and his FE does drop when charging that huge battery (which is one reason he prefers to charge that battery by plugging it in, whenever that's a viable option).

OTOH there probably is some benefit to getting the most efficient alternator you can get your hands on (although I haven't personally swapped out the alternator in my car yet). And supposedly some models/brands of alternators are measurably more efficient than standard models. But if/when you are hunting for an energy efficient alternator, hunt based upon its efficiency specs (i.e. what percentage of the mechanical work is turned into electricity), vs hunting based on "capacity". Because in many cases a "high capacity" alternator might not be any more "efficient" than a lower capacity one (and is likely physically heaver to boot)!
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Old 07-08-2007, 01:31 AM   #3
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Generally a bigger alternator would be more efficient than a small one running under a heavy load mostly due to the copper wire losses from the high current. Everything else considered that has losses in it, the copper losses are the only thing that can be improved in standard alternators. Try to get one with enough extra amps than your amp will need so you don't have to run it at 100% output too much.
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Old 07-08-2007, 04:10 AM   #4
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You should investigate power capacitors. Audio stores are now selling large ones, nearly as large as a soda can. The idea is to bank power so it's available for rapid peak demands.

I admit I don't know enough about them but if they smooth out the output demand placed on an alternator then I'd think it would let you run a more powerful amp with the same alternator
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Old 07-08-2007, 07:51 AM   #5
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Thanks guys. I was thinking the extra coils in the high capcity alternator might be more efficient.

Keeping the sound system out is not likely as I really enjoy it on my commute.
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Old 07-08-2007, 08:27 AM   #6
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from what I've seen, higher capasity alternators are larger diamiter, so you have more weight spining, this rotating weight is going to bring your mileage down.
I enjoy my CD player as well, but what's the payback from having a sub and amp installed? how long will it take for it to pay for it's self?
Either way, figure out your electrical loads, then find out what the peek output of your alternator is, and I would think 70-80% of that would be the most you would want to draw from it, of course if you drive most in the day time, then your headlights aren't on, along with the other running lights.
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Old 07-08-2007, 08:47 AM   #7
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Get yourself an underdrive pulley to decrease the load of your accesories(although it might be worse for your particular situation if you need the coolant flow and alternator output) and then get a rather massive capaciter. They have them in 5 and 10 farad sizes now wich is LOTS bigger than what most people need anyway. The large capaciter will not place a larger load on the alternator after it is charged because it only stores "voltage".
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Old 07-08-2007, 11:22 AM   #8
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I don't mind saying that it is difficult to make reccomendations regarding FE improvements when FE is a lower priority than a sound system.
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Old 07-08-2007, 06:45 PM   #9
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that sub magnet gota weigh a bunch. along with heavy wires/amps. most alts. are 100a some options are 130amp. i guess you could use under drive pulley on the 130a alt? but the high amp alts are usually used for ambulances / police / high end cars from all the add on electronics.
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Old 07-08-2007, 07:51 PM   #10
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An underdrive pully will just make the alternator run slower, making it work harder, putting more current thru the coils, lowering the peek output.
standard alternator for a 2002 RSX appears to be either a 90 or 95 amp unit.
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