Thread: Alternator size ?

But how loud is all of that? No one listens to their system at max wattage all the time.. so is 1000 watts only audibly 2x as loud as 100 watts?

An extra battery on the same alternator will put no more stress on the alternator, unless more power is being drawn from the batteries than when you only had a single one..which would make that an unfair comparison.

Although as you say, just because you have a 1000W amp doesn't mean you're using 1000W constantly.. you may only be averaging 100W or so.

The table above for current draw to power is laughable... so a class A amp draws the same current to reach 10W as a class D?

Funny thing is, all of this clever (and frequently misguided) maths is well and good, but I have a 55aH battery and a 100A alternator, driving a car PC, 1500WRMS of amps, a processor, headunit etc.. and my headlights don't dim at all... Maybe my alternator should read 300A?

unless I am mistaken and i can check on my 69 that car stock should have a 45amp alternator, if you have the 302 model then a alternator for a towncar will fit you can get them up to 110amps, I would suggest at least a 85amp

Originally Posted by mulletboy2

An extra battery on the same alternator will put no more stress on the alternator, unless more power is being drawn from the batteries than when you only had a single one..which would make that an unfair comparison.

Why don't you think it will put more stress? Anytime your batteries voltage is below that of the alternator, the battery is going to put a load on the alternator to get up to the alternators voltage.

Although as you say, just because you have a 1000W amp doesn't mean you're using 1000W constantly.. you may only be averaging 100W or so.

The table above for current draw to power is laughable... so a class A amp draws the same current to reach 10W as a class D?

Funny thing is, all of this clever (and frequently misguided) maths is well and good, but I have a 55aH battery and a 100A alternator, driving a car PC, 1500WRMS of amps, a processor, headunit etc.. and my headlights don't dim at all... Maybe my alternator should read 300A?

So? All that means is that you are not drawing more than about 1400wrms for any extended amount of time.

This isn't even clever math. You have 100amps X ~14 volts...Means you have about 1400watts to work with. So if you're lights aren't dimming, you are using less than that. Are you trying to say that that's wrong?

Originally Posted by XxAndyxX

Why don't you think it will put more stress? Anytime your batteries voltage is below that of the alternator, the battery is going to put a load on the alternator to get up to the alternators voltage.

Because the same music at the same levels is going to require the same amount of power, regardless of how many batteries there are in a system. Assuming a linear scale (which it's not, but it's more convenient to explain), then if a certain sequence of music made the alternator drop from 14V to 13.2, and then a single battery and the alternator together drop to 12V, then if you had 2 identical batteries in the same condition, the alternator would drop to 13.2, and then both batteries to 12.6V or so. They would take the same amount of time and require the same amount of power from the alternator to collectively reach 13.2V as the single one would from 12V. The difference being, the headlights may not have dimmed with 2 batteries because the system voltage didn't drop as low. Because the same overall power has been drawn, it takes the same time/power to recharge them.

So? All that means is that you are not drawing more than about 1400wrms for any extended amount of time.

This isn't even clever math. You have 100amps X ~14 volts...Means you have about 1400watts to work with. So if you're lights aren't dimming, you are using less than that. Are you trying to say that that's wrong?

My amps, headinit, processor, PC, inverter and other accessories have the potential to draw considerably more than 100A... what I'm saying is that just because they have that potential, doesn't mean I need an alternator that's capable of catering for that on a continuous basis.

Originally Posted by IC-C30

Unfortunatly this happens all of the time. people have -lets say- a 65amp alt and a 60AH batt.... they're comming short to feed there audio properly and buy a 100AH yellowtop and put it on the same 65amp alt.....

There's nothing wrong with that IMHO. Note the different units - Ah is the battery's reserve capacity... a 55aH battery (basically) takes as long to recharge after a given load as a 550aH one does. The only important difference is how low the battery's voltage would have dropped. Just because the alternator is rated at 65A and the battery is rated at 100Ah doesn't mean that the alternator isn't capable of recharging the battery, or recharging it fully... Replacing a battery is usually considerably cheaper than a new alternator or a re-wind. It all depends what you want and what your budget is. I'm not against an alternator upgrade by any means, but I certainly wouldn't recommend one as a matter of course for someone who's just out to enjoy a bit of music on a reasonable budget... there are better areas to spend this money, e.g sound deadening, better speakers, more time and effort in installation etc...

Just my opinion though

Mark