power cable size recomendations for 800w

Hi, I currently have a JL a4300 , 45w x4 4ohm. and alpine F450 driving 12" type r wired at 2ohm 400w RMS.

I'm planning to upgrade to 4 speakers with 100W each (mbquart or alpine speakers)driven by MBquart amp 4ch PAB4100 4x 100W RMS.so i wonder if i need to upgrade my power cable to 4gauge kit?.

Another question is is that amp gonna drain my car's battery soon? I don't want to end up having a dead battery due to heavy power sound system.


In the next few weeks i'm dynamat my car, nearly the whole thing ,so I don't think i'll push volume level to nearly 80% like now.

Do the math... We'll figure 60% efficiency, across the board. This will allow a bit of a buffer if your sub amp is Class D, as it will have a better efficiency.

100 X 4 = 400
400 X 1 = 400
400 + 400 = 800
800 / .6 = 1333 watts IN
1333 / 14.4 = 92.5 A

In theory, you could safely use a #8, but I'd never run that much power through a single #8. Your #4 amp kit will be perfectly adequate. Fuse within 18 inches of the battery for 150A, and NO LARGER.

Since the power ALL comes from the alternator, if your alternator cannot support that additional 92 amps of current demand, yes, you will drain your battery in very short order, and potentially damage many parts of your car, including ECU and alternator.

You will ABSOLUTELY have to upgrade your alternator.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thank god, my M450 ( not F450 is class D), the mbquarts ones are Class AB so what's the difference?

From the old set up of 45x4, and 400w, I'm using a 30A fuse, so is it ok or needs adjustment?

hmmm i wonder how many volts my civic running now 12 or 14... kinda confusing. And how do i know how many amps my alternator can drive up to?

man.. it's kinda sucks when we found new problems when upgrading to bigger system. May be i'll just dynamat my car for better sound quality now.

where's the edit button on this thread.. anyway.. i'm i'm running current set up, it'll be 70w x 4 +400W = 680W .... and calculate like what you did above, it'll be around 80 AMP.... man i think my car battery gonna run out soon...

haemphyst wrote:

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100 X 4 = 400
400 X 1 = 400
400 + 400 = 800
800 / .6 = 1333 watts IN
1333 / 14.4 = 92.5 A

Since the power ALL comes from the alternator, if your alternator cannot support that additional 92 amps of current demand, yes, you will drain your battery in very short order, and potentially damage many parts of your car, including ECU and alternator.

You will ABSOLUTELY have to upgrade your alternator.

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ABSOLUTELY false.  A standard 80-100A alt will have no problem powering a system of this size unless full volume test tones are played constantly.

Real world music at a reasonable volume you're looking at 15-20A.

...IN A CIVIC!!! Having owned SEVERAL Hondas, (1986 Civic Si, (-60A) a 2001 LX, (-65A) and a 2007 Fit (-60A)) I can tell you that the stock alternator in my 2001 coupe wasn't even happy about running the headlights (up to 32A on high beams...) and the AC (as much as 42A with the fan on high...) at the same time... I've done my research. Have you?

Honda, while they build the very best car that money can buy, (and I don't care what everybody's opinions are regarding that statement, so keep 'em to yourselves...) doesn't allow too much buffer in the alternator arena. Even "real world music at a reasonable volume, you're looking at 15-20A" is more than the stock alternator in a Civic was ever designed to run.

khanhfat, do yourself a favor, and upgrade the alternator.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Those are also cold ratings... You need to derate from cold by at LEAST 15%

75A cold rating - 15% operating temperature de-rate = 63.75A hot rating

That being said, the guy is asking the question as though he has EVERY INTENTION of running that system WFO... He says he's only going to run it up to 80% or so "for now". Even 80% of the required maximum input of 1333 watts will still be 74A. The system, the way the OP has every means to run as loud and as hard as he possibly can, will be using the ENTIRE cold rating of the stock alternator. Also, last time I checked, Vietnam is not exactly a COLD place, so now he's using EASILY 35 of the OEM alternator's 75 (cold) amps just to run the climate control system. Now, add headlights... (relatively continuous 18A current demand, 24A on high beams... add another 15A if he has foglamps) Now add brakelights... Now add (transient, I'll grant you) turn signals... Now add 9.5A (continuous) for the ECU, engine, and OEM battery charging requirements. Now run the car until it reaches normal operating temperature, and then de-rate the alternator's output. (These numbers, BTW, are ACTUAL current readings from the current meter in my dash, which I installed to monitor the current output of my alternator... They are not just "anecdotal" numbers.) Now, dump an 800 watt stereo system into the car, and run it "at about 80%".

khanhfat, do yourself a favor, and upgrade the alternator.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

OMG... so much opinion here, i never thought of upgrading the thing , i only thought about the battery needs to replace earlier than usual when running system. Seems like this cost me extras.

HOwever, which alternator is good though. i've been reasearch after reading about the alternator last night til 2AM. People would recommend to use stock ones which at average of 80-90Amp. NOt many of them using the aftermarket alternator.


I'm living in Houston, the weather here probably as hot as vietnam in summer.

I think i might hold back buying the amps until i find the right component to protect my electricity.