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you should be ok with the standard battery and alternater, but make sure the amps have decent sized power cable, and look towards uprating the following cables under the bonnet - batt to earth, alternater to batt, engine(alt) to earth.

This will be more effective than using a cap, cheaper, and will put a lot less strain on your battery.
 

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other_manufacturer
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yes, make sure your wiring is up for the job as JaySter said.

I'd still go for a heavy duty battery
 

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Heavier duty battery for 300W of amp power? The car battery isn't used unless 1) the engine's off, or 2) the output from the alternator drops below 13.2V(or whatever your battery is floating at - usually 12.5V-13V).

If < 25A of additional current draw in your car makes the alt output drop below 13V, you have serious problems and need to look at replacing the alternator, not the battery.

A bigger capacity/heavier duty battery will make no difference in this case, unless the engine's turned of and you're really spanking it.. in which case it'll take maybe 1 1/2 hours to drain your battery to the point you can't start the car, rather than an hour.
 

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mg_zt
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A real 300W amp will consume much more than 25A - more like 40-50A or even more. But as long as the engine is running the alternator will supply without needing a capacitor. How about a bigger alternator though? to power my ham radio set in my campervan I have upgraded the alternator from 90A to the 120A version.
 

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PaulW said:
A real 300W amp will consume much more than 25A - more like 40-50A or even more.
CAN, not will. What music have you heard that's just a constant note at maximum volume available? In reality, most music probably averages no more than 30-40% of the available output. At 12V, a 70% efficient amp (about the average) would draw 36A, IF and only if you're listenning to a 0dB sine wave. Your 40-50%assumption equates to using an inefficient class A amp (which he isn't).

How about a bigger alternator though? to power my ham radio set in my campervan I have upgraded the alternator from 90A to the 120A version.
Bare in mind that whilst upgrading to an OEM alternator from higher up a specific car model's range is a good idea (if it fits), many "high output" aftermarket alternators will be a significant step backwards. Their high output is often not realised until high up the rev range. What you want is an alternator with higher idle output than your standard one.

[edit] Crevice - lol.

HTH

Mark
 

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mg_zt
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mulletboy2 said:
CAN, not will. What music have you heard that's just a constant note at maximum volume available? In reality, most music probably averages no more than 30-40% of the available output. At 12V, a 70% efficient amp (about the average) would draw 36A, IF and only if you're listenning to a 0dB sine wave. Your 40-50%assumption equates to using an inefficient class A amp (which he isn't).
Hmm, things have moved on then. I was taught that class A amps were 10-20% efficient (maximum 25%) and class AB amps were 35-55% efficient with a theoretical maximum of 78.5% (probably very difficult at 12V). Class D (i.e. PWM) amps can be anything up to 97% efficient but with potential losses in any filtering required.

Agreed about aftermarket rather than OEM alternators.
 

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PaulW said:
Hmm, things have moved on then. I was taught that class A amps were 10-20% efficient (maximum 25%) and class AB amps were 35-55% efficient with a theoretical maximum of 78.5% (probably very difficult at 12V). Class D (i.e. PWM) amps can be anything up to 97% efficient but with potential losses in any filtering required.
Meh, you're right... I'm forgetting stuff faster than I'm learning it these days ;)

http://www.talkaudio.co.uk/vbb/showthread.php?t=83827

Anyway, I think we're agreed that music won't utilise full output constantly, so regardless of my amp classification faux pas, he still doesn't really need to worry about more than 25A(ish) average draw.

Cheers

Mark
 
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