Car power usage

**wirelessdreamer** · 05-17-2008, 02:59 PM

Car power usage question:

I've got experience with computers and electronics, but not as much practical experience with car electronics, so posting this question.

my alternator is rated at 85amps ('05 chevy aveo) so assuming it was only giving me 12v (really its more like 13.8, but playing it safe on the numbers side) the max my alternator can give is 1020 watts (85 x 12). I have a DSatx power supply, rated at a max of 220 watts, so once again playing it safe with numbers, i'm going to assume i'm maxing it out.

1020 85 x 12 Alternator
-220 Carpc
800

So now I'm trying to figure out how much the integrated electronics can draw (heat, ac, low/highbeams, etc) so i Know what the max I can put into my sound system is, without having to worry about a capacitor bandaid. I really don't want to have to replace the alternator in this car.

I originally wanted to go with a Kicker ZX700.5 5 channel amp, run everything at 2ohm, a MB Quart RSH 252 10" in the trunk, start with 2 Infinity Kappa 63.9I's, and leave the other 2 channels for if I want to add some fill to the back.

so 800 - 700 (Max) would leave 100w, which being a pessimist, I'm thinking I should be leaving 300w for the car to play with. this is of course assuming that everything is drawing max, which is seldom the case, and a capacitor bandaid could easily fix a small problem.

I've also been looking at running a Alpine PDX-5 with a similar setup to reduce my power useage requirements. Anyone here have experience with each amp by chance?

Anyone have feedback on what i'd expect? Ideally I wanted to stay with one good 5 channel amp in the back, but this post is more about power requirements.

**DarquePervert** · 05-17-2008, 10:09 PM

I have stock bettery & alternator in my truck.
I've added the PC, two amps and an inverter.

I have no charging issues or battery drain issues whatsoever.

GRANTED, my truck is pretty bare-bones. No power windows, seats or mirrors.
Honestly, I don't think you should have a problem unless you're going all-out with the audio system. Based on what you mentioned in your post, that doesn't appear to be the case.

**wirelessdreamer** · 05-18-2008, 12:18 PM

Originally Posted by DarquePervert

I have stock bettery & alternator in my truck.
I've added the PC, two amps and an inverter.

I have no charging issues or battery drain issues whatsoever.

GRANTED, my truck is pretty bare-bones. No power windows, seats or mirrors.
Honestly, I don't think you should have a problem unless you're going all-out with the audio system. Based on what you mentioned in your post, that doesn't appear to be the case.

did you look up how many amps your alternator provides, and what are your 2 amps ratted at for max watts?

I don't want to just guess, I want all my numbers happy before I buy any audio equipment or install anything.

The formula that should work for finding out what your alternator can drive is

P = I * E

P = Power (Watts)
I = Current (Amps)
E = Energy (Voltage)

**Bugbyte** · 05-18-2008, 01:42 PM

I know you are trying to be conservative, but use the 13.8 number when calculating the total wattage (in this case 1173). Add in the safety buffer when deciding the full draw.

Remember also that a 220 watt power supply only draws 220 watts when fully loaded, which you should not be doing. In any case, the battery can supply some power briefly if it is a simple spike in startup draw. Also, the amplifiers won't draw the full 700 watts except in cases where you really ought not to be in the car without hearing protection.

I think you are fine with the setup you have spec'd. Figure the nominal load of the PSU at 150 watts (I don't know what your system is, but let's say 150) and the amp at 400 watts and you have 1173 - (150 + 400) = 623 left over.

Capacitors can help smooth out spikes but they still have to be charged in between discharges, so your alternator still has to output the total required. They work for times when you need a peak for a brief time and there is a longer period to recharge them. I don't think you'll find a problem with your setup.

**DarquePervert** · 05-19-2008, 07:52 AM

Originally Posted by wirelessdreamer

did you look up how many amps your alternator provides, and what are your 2 amps ratted at for max watts?

I don't want to just guess, I want all my numbers happy before I buy any audio equipment or install anything.

The formula that should work for finding out what your alternator can drive is

P = I * E

P = Power (Watts)
I = Current (Amps)
E = Energy (Voltage)

Thanks for the lesson in basic electrical calculations.

No, I did not look up my alternator's output rating. I didn't feel the need to. I figured that I would look into it if I had a probably with my battery not charging up once I got everything installed.

I just looked it up and my truck has an 80A alternator. AS I said, I still have the stock battery.
The amps are listed in my worklog.

**greatwhite** · 05-19-2008, 08:13 AM

As mentioned, the rating you are basing your calculations on are teh max rating.

You'd have to be running the DSATX and your amps at full capacity to achieve that power draw.

Unless you're going to run a dual core and some heavy graphics processing while sititng at idle in the parking lot with the stereo at full gain, you should be ok for normal driving.

Keep in mind, most cars can outstrip alternator output sitting at a light on a rainy humid night (enigne idling, wipers going, lights on, fan blowing to defog windshiled). This is when the battery kicks in that little bit extra........and they don't drain the battery or die at the light.................

**wirelessdreamer** · 05-22-2008, 07:58 PM

i'm actually running an e8400 core2duo 45nm ( 65 watt proc) and integrated geforce 7150 on board, (thinking about changing the board out for an intel x3500 based board. also thinking about a lower snr pci-e soundcard.

**rybitski** · 09-14-2008, 02:05 AM

Just a little note from experience: I have an '07 aveo with the same alternator as your car. I have a 1,000 watt amp, 200 watt stereo, 250 watt M4-ATX, power windows, etc. I always have these running simultaneously with no problems. I have had this setup for about 3 months now and my car has never failed to start due to the battery not getting charged. As everyone else mention these ratings are all peak. In reality my amp is only consuming about 450 watts with the gain turned all the way up. My stereo only consumes about 80 watts turned all the way up and so on. This reply is coming a little late, sorry.