how much voltage drop is too much?

[ppiflat10s 3]

ok, wifes car.

RF 300.1 / REX12D4, got the amp set to push right around its 300 watts at 2 ohms. its wired up with 4 gauge. no other accessories like radar detectors or other amps or anything.

the other night on the way home from going out to dinner I decided to keep the stereo cranked to as loud as it ever gets cranked to for the last ~10 minutes of the drive home. pulled into the driveway and left the lights on, stereo on, and the engine running. I busted out the DMM and it was basically staying at a steady 12.5 or so, then I killed the stereo and it took about 20-30 seconds and it was back around 14.3 and this is at idle.

as long as the voltage is always over the ~12 volts the battery sits at regularly its not going to do any damage right? and its generally gonna be quite a bit higher than 12.5V when the systems cranked but the engines sitting at 2500-4k on the road, right?

[lithium 358]

im surprised you have that much drop on that little power...

at idle do you have dimming?

[CadillacMatt 31]

From personal experience - you should be OK for starting if the battery has more than 12v, when I'm demoing at full tilt with the lights/system on I dip as low as 11.2v, but I don't turn the car off until the alt has charged the over 12v (tried it once, needed a jump.. haha)

But if you cycle a regular old battery like that then it will definitely shorten its lifespan.. what kind of battery do you have up front?

[ppiflat10s 3]

about the type of battery, Ill have to look but its just a walmart special Im guessing, nothing special. but no, no dimming at all.

Ive seen replacement alts rated at 80 amps, and seen some replacements rated at 105 but not claimed to be high output alts, so I dont know if the 105 is stock and the 80 is a cheap replacement, or maybe the V6 models had the 105.

it doesnt have the big 3 done, I might end up with enough wiring left over from my setup to do it on her car, but didnt think it would be necessary, with stock alt and only 300 watts, is it really going to be beneficial? I guess theres only one way to find out. It might be in my head, but it seems like after I start the car, get down the road and crank the stereo its loud and then pretty soon it gets a little quieter and then stays steady.

whatever the difference in power between 12.5 and 14.4 volts is, I shouldnt be able to hear it should I?

just as a theoretical figure, 300W/14.4V=20.83A

if somehow it drew the exact same amperage at 12.5 20.83A*12.5=260.375.

Ive heard I wouldnt notice the difference between 2000 and 2500 watts, so how could I hear the difference in ~40 watts?

Edited October 6, 2009 by ppiflat10s

[Kanaworm$ 292]

I would definitely get the "Big 3" done. As far as your voltage drop, I would not be that worried as long as you stay at or above 12 volts. That shows your alt is charging your battery correctly and your battery is doing an adequate job.

[CadillacMatt 31]

OldSkool is right, the Big 3 definitely will not hurt and can only be benificial to your installation... especially if you have some spare copper go ahead and bolt it right on. As for noticing a difference between 12.5 on up, if you are not already experiencing voltage issues (dimming lights, etc.) then you won't notice a difference... in fact, even if it was theoretically lower, you most likely wouldn't hear a difference but your amp would be forced to work harder to draw current and that would lessen the life of its components... but I digress... keep on rockin'

[addiction2bass 0]

dito for such low power that is odd. you must have some corroded wire connections. but the big3 upgrade should help alot. hell my old civic only had a stock alt of about 90amps or something low like that, hell the stock ground wire is only maybe 6gauge so you definatly wanna upgrade that at least. and just have the alternator and battery tested on the car to make sure they are both good condition.

but if your wife doesnt beat it up like that at full tilt then i wouldnt call it a real problem. as long as the alternator is charging most of the time it should be fine. hell i ran a solid 12.6v for awhile in my truck while stop light thumping sinc the idle was so low the alternator wasnt putting out and when i put my larger amplifier in my truck it was even worse at full tilt while driving but as long as i wasnt FULL TIL thumping from point A to B the battery always had enough power to start the truck up no problem.

[mazda6i07 0]

Well, i would try and stay above 12.5-13.0 But def. do not drop below 12.0v.

[shizzzon 461]

regardless of how much power you have in your car, i would never suggest falling below 12.5v. That's my personal threshold. If i see anyone ever drop any lower, need either larger alt and\or more batteries.

But for you, big 3 is suggested since your power draw shouldnt be all that much.

[ppiflat10s 3]

well, she doesnt listen to it as loud as I do. at least she doesnt when shes controlling the volume and Im in the car.

just got my wiring and termials from the UPS guy a second ago, so if I have any extra when I get done Ill run the big 3 in her car, just gotta get some more terminals.

[jcarter1885 995]

well, she doesnt listen to it as loud as I do. at least she doesnt when shes controlling the volume and Im in the car.

just got my wiring and termials from the UPS guy a second ago, so if I have any extra when I get done Ill run the big 3 in her car, just gotta get some more terminals.

If you dont upgrade the alternator then the wiring size from the alternator and battery may be sufficient. I would just upgrade the negative(alternator/engine block to cars frame and battery to cars frame) wires first and see how that treats you (it helped me out alot with a stock battery and alternator, with a steady voltage and less drops at full tilt).

[KU40 173]

about the type of battery, Ill have to look but its just a walmart special Im guessing, nothing special. but no, no dimming at all.

Ive seen replacement alts rated at 80 amps, and seen some replacements rated at 105 but not claimed to be high output alts, so I dont know if the 105 is stock and the 80 is a cheap replacement, or maybe the V6 models had the 105.

it doesnt have the big 3 done, I might end up with enough wiring left over from my setup to do it on her car, but didnt think it would be necessary, with stock alt and only 300 watts, is it really going to be beneficial? I guess theres only one way to find out. It might be in my head, but it seems like after I start the car, get down the road and crank the stereo its loud and then pretty soon it gets a little quieter and then stays steady.

whatever the difference in power between 12.5 and 14.4 volts is, I shouldnt be able to hear it should I?

just as a theoretical figure, 300W/14.4V=20.83A

if somehow it drew the exact same amperage at 12.5 20.83A*12.5=260.375.

Ive heard I wouldnt notice the difference between 2000 and 2500 watts, so how could I hear the difference in ~40 watts?

It's not about the difference in wattage by number, it's difference by percentage. 40 watt difference isn't much when going from 300 to 260, no, but from 80 to 40 it's a lot more. But, that being said, neither 2000 to 2500 nor 260 to 300 are significant.

[Spencerk 4]

10% of nominal is the standard....if you give to much inrush onto that bat you will burn those cells up

Edited October 6, 2009 by 144dbFiBl15

[aznboi3644 2]

My level of "low" is if it is dipping into the battery reserve a lot than that is too low.

depends on the battery's float voltage than. If the battery rests at 12 volts and the drop is only down to 12.5 than you are fine...but 12 volts flat for a battery is low anyways

[ppiflat10s 3]

If you dont upgrade the alternator then the wiring size from the alternator and battery may be sufficient. I would just upgrade the negative(alternator/engine block to cars frame and battery to cars frame) wires first and see how that treats you (it helped me out alot with a stock battery and alternator, with a steady voltage and less drops at full tilt).

havent gotten to look under the hood since she hasnt gotten beck from work, but I was under the hood of my 93 accord earlier, and my alt to battery is the longest run (obviously) and it is about half the size of the battery-frame, block-frame wiring. I didnt end up with enough extra to do the big 3 on her car, but I will order myself some wiring after I finish my setup, and then finish up hers.

[socialstealth 0]

If you dont upgrade the alternator then the wiring size from the alternator and battery may be sufficient. I would just upgrade the negative(alternator/engine block to cars frame and battery to cars frame) wires first and see how that treats you (it helped me out alot with a stock battery and alternator, with a steady voltage and less drops at full tilt).

havent gotten to look under the hood since she hasnt gotten beck from work, but I was under the hood of my 93 accord earlier, and my alt to battery is the longest run (obviously) and it is about half the size of the battery-frame, block-frame wiring. I didnt end up with enough extra to do the big 3 on her car, but I will order myself some wiring after I finish my setup, and then finish up hers.

What gauge wire are you using?

I have about 5' of red knu flex 4g wire if you'd like to buy it.

[dbjunior 0]

just curious as to where you measured voltage. you said you dont get dimming so it made me think you tested voltage at amp. if you tested at amp retest and then check at batt under hood if there is more than half a volt diffrence between the batt voltage and the voltage at the amp then you need to run bigger power wire or check your connections.

[ppiflat10s 3]

I tested it right at the battery terminals.

Ill check it at both in the next couple days.

is 4 gauge, Ill check to see if 5' is enough with what little I already have and Ill let you know if I want it, how much you want shipped to 86315

[Lucky 76 5]

do this step by step

check the battery's float voltage

turn the car on

check the voltage at the alt at idle with no load

check the voltage of the battery at idle with no load

check the voltage of the alt at 2k rpm no load

check the battery at 2k rpm no load

now do the same thing with your system on a constant tone at as loud as you normally play it

add this one step at idle and at 2k rpm

check the input voltage at the amp

this will give us a better understanding of what is going on and if there is a problem.

[ppiflat10s 3]

do this step by step

check the battery's float voltage

turn the car on

check the voltage at the alt at idle with no load

check the voltage of the battery at idle with no load

check the voltage of the alt at 2k rpm no load

check the battery at 2k rpm no load

now do the same thing with your system on a constant tone at as loud as you normally play it

add this one step at idle and at 2k rpm

check the input voltage at the amp

this will give us a better understanding of what is going on and if there is a problem.

will do, probably get it done tomorrow since shes off work.

[ppiflat10s 3]

alright, I think it must have just been bad connections at the battery. took the seats out to vacuum under them, and had to disconnect the battery so that I could disconnect the side air bags to get the seats out, and now its working much better after reconnecting the battery.

battery was sitting at 13.02 when I popped the hood (had been running about 10 minutes before though so not sure if it would drop as it sat for a while)

never even got to the 2k rpm tests because the results at idle were good.

all these were at idle.

no load:

alt-14.75

batt-14.14.41

headlights only:

alt-14.67

batt-14.28

headlights and system cranked (tones were MP3's and her deck doesnt play em, I forgot about that, but I played a lil wayne song thats pretty bass-heavy. best I could do at the time)

alt-14.41

batt-14.23

amp-(when there was a pause, it would go right to 14.15 and stay, lowest it ever hit was 13.6x)

also, no dimming of dash lights at all, no dimming of headlights at all either. dome light does dim though, but it must just be something with that circuit because it was the only light that suffered from dimming.

Edited October 8, 2009 by ppiflat10s

[Lucky 76 5]

Your dome lights will always dim unless voltage is constant. They will also get brighter if you increase voltage. The brightness of your interior lights are affected more than your exterior lighting. Your headlights remain the same brightness through a certain voltage range. Btw your alt is spitting out some crazy voltage at idle lol. I am curious to see what it puts out at 2k rpm.

Edited October 8, 2009 by Lucky 76

[ppiflat10s 3]

well, maybe Ill check that out someday, but now that its working Im gonna focus all my energy on my setup until its done.