How to calculate your power?

[trpkkd 0]

I was wondering if anyone could tell me or help point me in the right direction on calculating power for the system I plan on building this winter I was wondering what the math problems to figuring out your reserve(batteries), usage(amplifiers) and charging(alt.) would be? And was wondering if there are any websites or post I could check out to find this info?

[hardrock2401 8]

really is no set math, gonna differ from equipment to equipment

[S.DeYoung 968]

www.bcae1.com

[hardrock2401 8]

^ well thats a interesting site, some good reads on there

[altoncustomtech 773]

As said, there's no set calculation for it, although you can roughly estimate it. For example:Say you were planning on using a single 2kw class D sub amp on a sub at 1 ohm. Let's assume the amp is 75% efficient at full power with that 1 ohm load. It would take AT LEAST 25% more power than it's rated to make that 2kw into that 1 ohm load, so 2.5kw input power or 208 amps of current assuming 12 volts of input voltage(2500/12=208.33).

None of that math is exact, not anywhere near real world perfect at all, but hopefully it helps give you an idea on how to calculate and get an idea of the kinds of power requirements it might take to run at full tilt. There's a great number of losses and things that affect how much input power an amp is going to need to make output power. Figuring it like that is also off due to the duty cycle or dynamics of the music. Unless you're listening to nothing but Bass Boy CD's or test tones the amplifier will rarely be making that kind of current draw. There's also big debates on how accurate the listed efficiencies of amplifiers really are. I've come to expect to figure 50% for Class AB (highs amps) and about 75% for Class D just to keep it realistically, and often, a good smidge on the overkill side. It's easier to go a little overboard and have more capacity than you really need from the start than it is realize it afterward and have to buy more wire, batteries, etc. and find, build another, or rebuild a place to put it all.

[trpkkd 0]

Alright thanks alot guys will be doing extensive reading on that website thanks.

[IDGAF 0]

It's not a perfect system, but it'll give you an idea...

Take your alt and battery reserve and multiply by 10 to see how much power you can run.

i.e.- 100A alt and a 100Ah batt is 200. 200 x 10 = 2,000w.

Obviously it's not exact but it's better than guessing.

[ssh 924]

It's not a perfect system, but it'll give you an idea...

Take your alt and battery reserve and multiply by 10 to see how much power you can run.

i.e.- 100A alt and a 100Ah batt is 200. 200 x 10 = 2,000w.

Obviously it's not exact but it's better than guessing.

That's wonderful if your vehicle doesn't require any electrical power--which it doesn't.

[IDGAF 0]

It's not a perfect system, but it'll give you an idea...

Take your alt and battery reserve and multiply by 10 to see how much power you can run.

i.e.- 100A alt and a 100Ah batt is 200. 200 x 10 = 2,000w.

Obviously it's not exact but it's better than guessing.

That's wonderful if your vehicle doesn't require any electrical power--which it doesn't.

It doesn't... not? Or it doesn't?

Like I said, it's not a perfect equation. It has a built in fudge factor to account for your car's draw on the alt and amp efficiency and what not.

Would you rather me just tell him to throw in dual 500A alts and 24 G31 batts to run 2k "just to be safe"?

[trpkkd 0]

I found a video on youtube that seemed pretty helpful if I can find it again I'll post it up here for you guys. It seems pretty legit but well see what you guys think.

Didn't take too long!I found 2 that were pretty informational.

Edited December 10, 2012 by trpkkd

[ssh 924]

It's not a perfect system, but it'll give you an idea...

Take your alt and battery reserve and multiply by 10 to see how much power you can run.

i.e.- 100A alt and a 100Ah batt is 200. 200 x 10 = 2,000w.

Obviously it's not exact but it's better than guessing.

That's wonderful if your vehicle doesn't require any electrical power--which it doesn't.

It doesn't... not? Or it doesn't?

Like I said, it's not a perfect equation. It has a built in fudge factor to account for your car's draw on the alt and amp efficiency and what not.

Would you rather me just tell him to throw in dual 500A alts and 24 G31 batts to run 2k "just to be safe"?

Neither are helpful to the OP.

IE: 100A alt x 14.4v = 1440watts.

100A x 10v = 1000watts, 1440watts - 1000watts = 440watts.

So your presuming the entire vehicle requires 440watts, and the rest of the power(1000watts) can be used to power the stereo equipment. I'm sorry but most manufacturer's don't put in alternators with over three times the power requirement for the vehicle--it economically doesn't make sense. I wouldn't want to be discharging the battery down to 10v on a continual basis either.

Perhaps it would be more relevant to simply install all the equipment, and monitor the voltage before ordering alternators and additional batteries. Also presuming that if the voltage does drop severely then the OP will simply turn it down until the necessary electrical upgrades are done.

[djjdnap 78]

http://overlandresource.com/what-is-an-amp-hour-and-how-to-calculate-battery-capacity

Edited December 10, 2012 by djjdnap

[IDGAF 0]

It's not a perfect system, but it'll give you an idea...

Take your alt and battery reserve and multiply by 10 to see how much power you can run.

i.e.- 100A alt and a 100Ah batt is 200. 200 x 10 = 2,000w.

Obviously it's not exact but it's better than guessing.

That's wonderful if your vehicle doesn't require any electrical power--which it doesn't.

It doesn't... not? Or it doesn't?

Like I said, it's not a perfect equation. It has a built in fudge factor to account for your car's draw on the alt and amp efficiency and what not.

Would you rather me just tell him to throw in dual 500A alts and 24 G31 batts to run 2k "just to be safe"?

Neither are helpful to the OP.

IE: 100A alt x 14.4v = 1440watts.

100A x 10v = 1000watts, 1440watts - 1000watts = 440watts.

So your presuming the entire vehicle requires 440watts, and the rest of the power(1000watts) can be used to power the stereo equipment. I'm sorry but most manufacturer's don't put in alternators with over three times the power requirement for the vehicle--it economically doesn't make sense. I wouldn't want to be discharging the battery down to 10v on a continual basis either.

Perhaps it would be more relevant to simply install all the equipment, and monitor the voltage before ordering alternators and additional batteries. Also presuming that if the voltage does drop severely then the OP will simply turn it down until the necessary electrical upgrades are done.

I hear ya. And my advice is usually your last paragraph. LIke I said, it's just an IDEA of what you may need and the numbers sway more to the user's side when factoring in the batteries because we all know you can run more than 1,000w on a 100Ah battery since a battery of that size is probably a G31 or bigger like the XS d3100; which XS claims will support 5,000+ watts as a secondary battery.

So, 100A alt and an XS d3100 = 5,000+ watts.

Or 100A alt and 110Ah batt (d3100) = 2,100w.

Which is the more safe recommendation?