how to calculate how much ah you need for your amp

[MACnonsence6]

is there a formula for figuring out how much battery power you need to support your amps with your alts charging amperage?

[Trey_Dog650]

Yes

[SterTheDer]

Thanks Trey, that was realllly helpful

I dont have a techical formula, but i can give advise about the basics :j

Basically, when you car is running, ALL of your energy is coming from the alternator (your voltage shiuld be above 13.6v)

At this time, your batteries are being charged, and your system wont benifit from multiple batteries (1stock walmart battery will do just as good as 100 kinetic 1800's)

BUT

things change once your current draw exceeds the limit of your alternator, and your voltage drops below 13.6.

At that point, you are asking your batteries to supply the remaining current.

This is where havig multiple batteries comes in.

Now for the math:

You must figure out how much power your system requires, then subtract how much power your alrernator can supply. This gives you a rough idea of what your batteries need to do.

For example: i have a stock 40 amp (at idle) alternator.

My sub amp is fuzed at 160 amps.

If i have subtract the two,

160-40=120amps

Playing full tilt, i would be asking my batteries to supply 120 amps.

Two 60amp/hr batteries should be able to supply enough to power this system for 1hr (while car is running) before the batteries are depleted and the voltage drop becomes terrible (dead batts = lower than 12v)

A more accurate way to calculate wiuld be totake the RMS ratings of your amps, (900rms @2ohm in my case) and divide RMS by voltage to get your current draw.

(watts/volts=amps)

900rms/ 14.4volts = 62.5amps

Subtract your alternator from that,

62.5-40= 12.5 amps.

In my case, my batteries are asked to provide 12.5amps of current, witch means i should be fine for hours.

Recap::

Your batteries supply all that your alt cannot.

Subtract your alternators ampherage from your current requirement to get how many amps your batteries have to supply.

Also, if you still have issues, let us know what you are thinking/planning/working with and we should be able to help you

I hope this helps

(If i made any face-palm worthy mistakes, please feel free to correct me, as i am tired and typing on an itouch :/)

[ZombieFatMan]

ok so this is not just one formula to get the info you need .
read up on OHM law an have a look at this guys videos, they helped me http://www.youtube.com/user/romi1rome

[ChevyBoy95]

post would have been more harm than good (confusion)

[MACnonsence6]

thank you for not being a dick and helping me out. your assistance is greatly appreciated

[skittlesRgood]

Thanks Trey, that was realllly helpful

I dont have a techical formula, but i can give advise about the basics :j

Basically, when you car is running, ALL of your energy is coming from the alternator (your voltage shiuld be above 13.6v)

At this time, your batteries are being charged, and your system wont benifit from multiple batteries (1stock walmart battery will do just as good as 100 kinetic 1800's)

BUT

things change once your current draw exceeds the limit of your alternator, and your voltage drops below 13.6.

At that point, you are asking your batteries to supply the remaining current.

This is where havig multiple batteries comes in.

Now for the math:

You must figure out how much power your system requires, then subtract how much power your alrernator can supply. This gives you a rough idea of what your batteries need to do.

For example: i have a stock 40 amp (at idle) alternator.

My sub amp is fuzed at 160 amps.

If i have subtract the two,

160-40=120amps

Playing full tilt, i would be asking my batteries to supply 120 amps.

Two 60amp/hr batteries should be able to supply enough to power this system for 1hr (while car is running) before the batteries are depleted and the voltage drop becomes terrible (dead batts = lower than 12v)

A more accurate way to calculate wiuld be totake the RMS ratings of your amps, (900rms @2ohm in my case) and divide RMS by voltage to get your current draw.

(watts/volts=amps)

900rms/ 14.4volts = 62.5amps

Subtract your alternator from that,

62.5-40= 12.5 amps.

In my case, my batteries are asked to provide 12.5amps of current, witch means i should be fine for hours.

Recap::

Your batteries supply all that your alt cannot.

Subtract your alternators ampherage from your current requirement to get how many amps your batteries have to supply.

Also, if you still have issues, let us know what you are thinking/planning/working with and we should be able to help you

I hope this helps

(If i made any face-palm worthy mistakes, please feel free to correct me, as i am tired and typing on an itouch :/)

i have to hit you on a few details.

first, if you have a 40amp alt and you believe it can provide 40 amps to your amplifier... whats running the car? I would only expect 10amps from that alt to be overhead that I could rely on stealing away.

second, you didnt factor in efficiency. 900w/14.4v would be assuming 100% efficiency. to be much more realistic, I divide wattage by 10. that'll get you close to the correct number.

so for you, 900/10 = 90 - 10 = 80. so your batteries need to provide 80amps, not 12.5

[TaylorFade]

As a general rule of thumb (and a starting point)... I always say RMS of the system divided by 10 is how much amperage you need.

2,000w = 2,000/10 = 200A

Your alt counts in there so you'd need a 100A alt and 100Ah of batt.

Obviously your alt won't provide all 100A to the system and it's not a perfect calculation, but there's a fudge factor built in and it's just a reference.

[SnowDrifter]

A lot of this depends on the music you play. Songs with constant bass all the way through like put on or thug motivation or something will put much more of a strain on your batteries than say... Rock or jazz or something.

All depends on your goals

[CJ18]

This is one of those questions that you are going to get alot of different answers to.

Personally I like to take the alternator out of the equation and figure out how much battery power it would take to run my amp/s with the vehicle off. Figuring it this way will be overkill, but that is what has lead me to 30 14v XS batteries.

With XS Power I dont pay as much attention to the ah ratings as I do the batteries wattage rating. I usually take what the company rates the battery to handle and cut it in half so I give myself extra head room for reserve capacity that will allow me to play longer.

So lets say I am planning a 5kw system and amp planning to use the D3100s that are rated for 4000w/5000w+. What I want for battery power is going to be enough to technically support double the power I am running. So taking the 5kw rating of the D3100 and cutting it in half to 2500w, I would need 4 D3100s to give me enough battery power for my 5kw system.

I know there is no math to back up what I am saying, but my experience using this method has proven to work.