Figuring amp usage from stock alternator (higher-end stereo)

[Ken Stewart]

I know the stock alternator is 130 amps. How do you figure how many amps you're drawing? I'm upgrading my stereo system and want to know if my stock setup is fine or if I'll have to upgrade:



New system:

- Two amps ... one 600watt mono amp running two subs at 300 watts RMS each, one 85watt x 4 running door speakers

- Eclipse head unit

- Image Dynamics 8" subs (2 ea at 300watt RMS)

- Image Dynamics 6.5" door speakers (70 watts RMS)



Plus, whatever the XLS model ST draws without the aftermarket stereo. Also, who knows the gauge size of the stock wiring ... may have to upgrade???



Thanks ...

 

[Blake Clark]

You should be fine as far as the stock electrical system. I would upgrade all the wiring in your system its the only way you can get full performance from your equipment.

 

[Ken Stewart]

Read other audio forums and this is what I found out, someone help out if any of my #s are wrong please Might be a little long, but may help someone out in the future:



Alternator = 130 amps, typical reserve is 40% so 52 amps left for stereo system



Figuring current draw (not my info, from forum):

RMS/.6 (60% efficiency = #watts

#watts/14v = #amps = full power test tone current draw

Typical music crest factor is at most 1/3 rms-to-peak power so for music you're looking at no more than #amps to play music LOUD



Ok, so using above formula here's what I figure for my system (again, using 52 amps in reserve):

-Amp 1 -- 600 watts RMS/.6= 1000 watts

1000watts/14v = 71.43 amps/3 = 23.8 amps



- Amp 2 -- 170 watts/.6 = 283.33 watts

283.33 watts/14v = 20.24 amps/3 = 6.75 amps



- Head unit (14watt RMS x 4 = 64)

64/.6 = 106.66

106.66/14v = 7.62 amps/3 = 2.54 amps



So, total for these three looks like I'm drawing 33.09 amps with almost 19 left over. Ok, electricians/audio experts out there please check my numbers

 

[Todd Z]

Go to sears, pay the 12 bucks, have them do a full load test.

Or buy a small amp meter.



What you do is turn everything on, lights wipers, stereo, etc.



Then have them read the amps the alt is putting out. If in the + your good. If in the - , not so good....



I also would look into running an upgraded + wire to the battery from the alternator.

Todd Z

 

[Jacob Dryer]

Another easy way is to look at the fuses on the amps and add that up. It's not exact but it's an idea of the max that they can draw.



What model amps are they? And the upgraded headunit should be an insignificant change.

 

[Robert Schroeder]

upgrade the big 3 wires



http://forum.sounddomain.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=007801



i did mine with 0/1 guage and i have 1300watts and my voltage never goes down past 13.8

 

[Ken Stewart]

Yep, read about the big 3 Robert and will do that soon, just seeing if stock is enough which it looks like it is for now. Will do soon, just always leary of messing w/electrical stuff ... even doing stereo upgrades make me nervous. Check and double-check before powering up. Shouldn't be, but I am



hoaxci ... my amps are MTXs, MXA6001 mono for sub (300rms @ 2 ohms to each sub) and Thunder 684 for speakers (60/85 rms to each speaker). Got the birth sheets for the amps and it's very true that MTX underrates their power. The 600rms for the mono sub is actually 789! The 684 came out to 579 rms (spec rated at 480 rms, 4-channel).

 

[Jacob Dryer]

You should be fine without upgrading the alt, upgrading the big 3 would definatly be a good idea though.