alternator/battery question??

[1min.shuffle]

i've got 3 amps (2 amps at present and one one the way...) to be installed. These are to drive the following:

a.) 4 channel - to drive 2 pairs of seps ratde at 40 and 50 watts RMS resepctively.

b.) 2 channel amp (2 ohm stable at 120 watts) to drive two pairs of seps in series at 50 watts RMS per pair.

c.) class D amp - rated output at 750 watts RMS at 2 ohms to drive a pair of 12'ers at 300 RMS (2ohms) each.

question is, what should the alternator give out in terms of amperes?....what battery should i install.

I've got a Power amper PB3D cap (3 farads)....will this help if i use my existing 70 ampere alt and a 3sm battery?...thanks!

[-cardo-]

eto pre, i managed to save this doc sa PC ko. i downloaded it from a site(kalimutan ko na URL). naka hilite yun answer sa tanong mo. compute mo na lang, mahina ako sa matematiks e   gudluk  


Upon reading and answering questions about car audio, one question always pops up:
"Do I need a high output alternator or just a capacitor"?
If you want a killer system, you may think that all you need are big amplifiers and huge speakers. Not so! Adding a bunch of car audio components to your vehicle without the proper charging system may lead you to disappointment, distortion and damaged equipment.

Let's say you install a 1,000 watt amplifier in your ride. Your rides charging system must produce enough electrical current to run the amplifier. Now how do you know how much current is needed? Simple: divide the RMS power rating of the amplifier by the amount of voltage your cars electrical system will produce.
Most vehicles electrical system will crank out around 13.8vdc with the engine running. So, 1,000 watts divided by 13.8 volts equals 72.46 Amperes of current. This means that the electrical system of the vehicle will need to produce an extra 73 Amperes of electrical current to power your amplifier and subwoofer at a reasonable level. Keep in mind that the factory electrical system is designed to produce enough charging power (alternator and battery) for the vehicle's stock equipment, and does not accomodate high-powered audio systems.

The biggest mistake made by consumers and (some) installers is failing to beef up the charging system to handle the extra load of the audio system. First, you need to understand how the electrical systen operates. This must be one of the most mis-understood systems of the entire vehicle. So here's a brief summery:
Turning the ignition key begins the process of cranking the motor. The battery supplies the power to get things started. Once the engine is running, the electrical burden is shifted over to the alternator. The alternator uses the engine's mechanical power to produce electrical (AC) current. The AC current is passed through a rectifier and changed to DC current which is what powers all of the electrical devices in the vehicle. The alternator also has the duty of recharging the battery after starting the vehicle.
Everything works perfectly so long as the power requirements of the vehicle do not exceed the output of the alternator's capacity. If the output is exceeded due to excessive load, then power will be pulled from the battery. If the alternator and battery combined cannot meet the demand, then the vehicle's electrical devices are diminished (dimming lights, spark plug misfires, audio distortion and amplifier clipping). Keep in mind that as voltage drops, amperage draw increases and that creates heat in components. This is the reason that loud bass play sometimes will damage components if the charging system is inadequate.

The first place to look to determine if your charging system is up to the task is the alternator itself. If possible, look for the HOT RATING on the alternator. IF you can't see it easily, call a local auto-parts store or car dealership and ask them to look up the stock alternator size, or rating for your vehicle. The hot rating will tell you the amount of power the alternator will produce once the engine reaches it's operating temperature (this is a lower rating than the cold rating). Once you get this info, you can then determine if the charging system is going to do the job. Allow your alternator about 10 Amperes credit or buffer area. If your power draw will be more than 10 Amps over the hot rating of the alternator, you may want to consider a high-output alternator. If only a little extra current is needed (say 10-12 Amps), the easiest way to enahnce the charging problem is to replace the existing battery with a larger one and add a capacitor to stiffen the voltage rails.

(some commentary was added or enhanced in this article by the moderators of this forum, to clarify and correct data given.)

As a note, when calculating your required current for your audio system, this is an easy way to do it:
calculate the total RMS wattage of your system based on how the amplifiers are wired (2 Ohm load, 4 Ohm load etc)
take that total RMS rating, and divide by 12.
This is how many Amperes your audio system will require in addition to what your car already needs (stock alternator rating.)


For more information on charging systems and alternators, see here:
http://www.eatel.net/~amptech/elecdisc/charging.htm

[1min.shuffle]

Thanks a lot!!!  maraming maraming salamat pre'.....now i have some solid foundation to start with.

thanks ulit!!

[be989]

Gurus, how do I know how much current my car needs kapag naka on lahat (except for sounds) para ma-calculate kung kaya nga ba ng alternator yung added load ng sounds. Meron bang "more or less" number ito? Let's see, headlights, foglights, tailights, brakelights, blinkers, interior dome and maplights, dashboard gauge lights, aircon,... Kung lahat yan naka on ilang amps yun?

[Swordfish]

Gurus, how do I know how much current my car needs kapag naka on lahat (except for sounds) para ma-calculate kung kaya nga ba ng alternator yung added load ng sounds. Meron bang "more or less" number ito? Let's see, headlights, foglights, tailights, brakelights, blinkers, interior dome and maplights, dashboard gauge lights, aircon,... Kung lahat yan naka on ilang amps yun?

for a standard car with all the lights on, stock stereo, horns and airconditioning, and then some...it usually consumes around 40 amps
if you put more accessories, like foglights, sirens, sun roof, etc...this consumption will increase
its a bit tedious, but you can actually compute the current consumption of your stock car accessories.
the formula goes....rated power divided by 13.8 volts equals amperes consumed
ex: your HU produces 20watts x 4ch = 80watts; 80watts/ 13.8v = 5.79 or 6 amperes...this is what your HU needs from your alternator
do the same for your other stock accessories like your headlights and aircon, and sum them up...this should be your current consumptionfor you stcok accessories alone
when it comes to your sound system, on the other hand, get the rating of the amp and apply the formula
deduct this value from the surplus amperage of your alternator
by this, you would have found out if your electrical system is deficient or not  

[be989]

Thank you sir. Last question, are 90 - 120 amp alternators aftermarket parts or meron oem nito. I'm going to need one for a 4G63.

[Swordfish]

Thank you sir. Last question, are 90 - 120 amp alternators aftermarket parts or meron oem nito. I'm going to need one for a 4G63.

most stock alts are rated anywhere from 65-70 amperes
there are a few high output alts that have come out on stock cars that are available locally
for mistsu...90 amperes for the galant, 100 amperes for the pajero gas, 125 amps for the pajero GDi, 140 amps for the evo (i think, but theyre rare)
for nissan...110 amps for the cefiro, 125 amps for the x-trail
you can buy orig bnew alts but its freakin expensive
what most enthusiasts do is buy surplus or rebuilt alts and bolt it on or adapt it to their existing alternator mounts/brackets
several friends of mine have inastalled cefiro alts to their CRVs to beef up the electrical system  

[be989]

You have been a lot of help sir. Thank you very much.