voltage drop question

[Jmw703]

I just upgraded my stock alt to a mechman 220a alt in my mazda 3. I have all 0 gauge wiring done under the hood. This helped my voltage significantly. Previously at idle i was charging at 13.2 or so at the amp, lights dimmed significantly. After the alt upgrade im charging at 14v at the amp and lights dim slightly at full tilt.

All i am running is a brz1200.D @ 2 ohms.

With the new alt and rmp at idle i tested 14v w/ no music and anywhere from 12.9 to 13.8 on full tilt depending on the song. (tested at the battery)

Ok, so heres my question, i dont know much about electrical and stuff, but should i be dropping this much on only 800 watts or so? My lights still dim slightly but if my voltage is where it is supposed to be i could care less.

Edited April 13, 2012 by Jmw703

[Guest]

where is your ground for the amp located?

[ChevyBoy95]

what is idle rpm? that unit doesnt do 220 at idle, you are probably getting something around 120a at idle, 800 watts at 12v is ~ 67 amps plus stock accessories is which probably around 30-50a, to that right there is 97-117a. I think i have the same alt rating, mine does about 125a at idle (800rpm), if your car idles lower, you get less amperage.

Plus, yes you have the alt upgraded, but an alt is nothing without somewhere to store a reserve. All alts is bad, all batteries is bad, you need to find a medium of alts and batteries.

having only alts is like having a 18oz steak(HO alt) and not having a stomach(no storage capacity), having only batteries is like having a few crackers(stock alt) and being extremely hungry(huge storage capacity).

Edited April 13, 2012 by ChevyBoy95

[Jmw703]

what is idle rpm? that unit doesnt do 220 at idle, you are probably getting something around 120a at idle, 800 watts at 12v is ~ 67 amps plus stock accessories is which probably around 30-50a, to that right there is 97-117a. I think i have the same alt rating, mine does about 125a at idle (800rpm), if your car idles lower, you get less amperage.

Plus, yes you have the alt upgraded, but an alt is nothing without somewhere to store a reserve. All alts is bad, all batteries is bad, you need to find a medium of alts and batteries.

having only alts is like having a 18oz steak(HO alt) and not having a stomach(no storage capacity), having only batteries is like having a few crackers(stock alt) and being extremely hungry(huge storage capacity).

it does 128 @ low voltage (most likely idle). Thats what the test sheet in the box said. My battery may need an upgrade, all i have is a diehard gold battery. But i mean you would think it would be fine on 800 watts. I mean honestly, dropping to 13 v isnt terrible (i think?), but it isnt great, especially with what im running.

And to answer your question kranny, the amp is grounded straight into the sheet metal on the top of my trunk ceiling. I can snap a picture if you would like.

Edited April 13, 2012 by Jmw703

[Guest]

And to answer your question kranny, the amp is grounded straight into the sheet metal on the top of my trunk ceiling. I can snap a picture if you would like.

im gonna take a guess that that's your problem. sheet metal on the trunk is thin as fuck and aterrible ground. you need to move it to either the strut tower, or the frame itself. you need to sand all the paint off where the lug touches the metal so there is maximum conductivity.

[skittlesRgood]

what is idle rpm? that unit doesnt do 220 at idle, you are probably getting something around 120a at idle, 800 watts at 12v is ~ 67 amps plus stock accessories is which probably around 30-50a, to that right there is 97-117a. I think i have the same alt rating, mine does about 125a at idle (800rpm), if your car idles lower, you get less amperage.

Plus, yes you have the alt upgraded, but an alt is nothing without somewhere to store a reserve. All alts is bad, all batteries is bad, you need to find a medium of alts and batteries.

having only alts is like having a 18oz steak(HO alt) and not having a stomach(no storage capacity), having only batteries is like having a few crackers(stock alt) and being extremely hungry(huge storage capacity).

thats actually sort of incorrect. your alt does everything until your demand is higher than your supply. once that happens, your voltage drops. it keeps dropping until you get to a voltage where your batteries start to help out. there are milliseconds between when the demand hits and the alt can react and the battery does buffer that.

by your math, he has enough alt to keep voltage up.

voltage drop does seem a little high for that power but not anywhere close to a dangerous level so its nothing to worry about.

[Decaf]

shitty ground

Edited April 13, 2012 by Decaf

[germandark]

Move ground and put your foot on the throttle, you could also install a throttle holder for demos that will maintain whatever rpm you want instead of idle. Depending on your vehicle it could be as easy as a vacuum line.

[Guest]

Move ground and put your foot on the throttle, you could also install a throttle holder for demos that will maintain whatever rpm you want instead of idle. Depending on your vehicle it could be as easy as a vacuum line.

his electrical is fine. its just his ground.

[ChevyBoy95]

what is idle rpm? that unit doesnt do 220 at idle, you are probably getting something around 120a at idle, 800 watts at 12v is ~ 67 amps plus stock accessories is which probably around 30-50a, to that right there is 97-117a. I think i have the same alt rating, mine does about 125a at idle (800rpm), if your car idles lower, you get less amperage.

Plus, yes you have the alt upgraded, but an alt is nothing without somewhere to store a reserve. All alts is bad, all batteries is bad, you need to find a medium of alts and batteries.

having only alts is like having a 18oz steak(HO alt) and not having a stomach(no storage capacity), having only batteries is like having a few crackers(stock alt) and being extremely hungry(huge storage capacity).

thats actually sort of incorrect. your alt does everything until your demand is higher than your supply. once that happens, your voltage drops. it keeps dropping until you get to a voltage where your batteries start to help out. there are milliseconds between when the demand hits and the alt can react and the battery does buffer that.

by your math, he has enough alt to keep voltage up.

voltage drop does seem a little high for that power but not anywhere close to a dangerous level so its nothing to worry about.

yea, after i read it again i saw the same thing... OOPS! my bad.

edit: and that sounds like a terrible ground.

Edited April 13, 2012 by ChevyBoy95