Voltage Drop
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This is a discussion on Voltage Drop within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; MY friend and I just installed High Output alternators in our Suby's and were running a few tests with a ...

  1. #1
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    Voltage Drop

    MY friend and I just installed High Output alternators in our Suby's and were running a few tests with a multimeter and a voltmeter on my radar detector(8500). My friend has an 04 FXT auto and when he is parked his audio system runs fine, but when he put it in drive, his system will cut out after a few bass hits. He even has the 15 farad Alumapro C.A.P. We measured the voltage and when he is in park it averages 14~14.3 volts with the system on and everything. But when he puts his car in drive, the voltage drops by an entire volt to 13`13.3 volts. It then slowly bounces voltage with the music until it drops below 12 volts and then cuts out at the amp. The amp has a protection circuit that causes it to cut out. What could cause the voltage to drop so much by putting it into drive. This happens even on the highway, so it is not an RPM related problem.

    I drive a stick WRX and it does the same thing to a lesser degree from neutral into a gear, and overall has a lower average voltage.
    Our alternators should be identical, and have the same output, so there must be some other players in the voltage stability. Hopefully someone can give me some insight as to what the heck is going on.

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    Registered User Jack's Avatar
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    YOU ever notice when its dark out and u have ur headlights on and rev the engine all the ligths get dim?

    i GUESS the same thing is happening with ur amp.

    USe the search button..i remeber reading about getting a bettere smaller battery or a groudning kit,
    -My name is Tom not Jack

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    "I wanted to put a bullet between the eyes of every panda that wouldn't screw to save its species" Fight Club

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    Yeah, my friend will be getting a new battery and upgrading the "Big 3" along with grounding mods, but this only seems to be a problem for him when he is in any gear besides park. The lights turn on when he puts it in drive, and I could understand a small dip, but not a huge drop...

    I myself have grounding mods as well as an optima group 35 red top. I am seeing less voltage than him, and I just have the factory stereo. I drive the 5 speed, so I haven't seen any resemblences of the park/drive switch and voltage drop. My voltage drop seems to occur on engine warm up....so that makes some sense, I just cannot see that my car would be that much hotter than his....but maybe it is. I'll have to check into fabbing a heat sheild for my turbo/downpipe again.

  5. #4
    Registered User Jack's Avatar
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    my voltage gauge drops from 14.0 to 13.2 when ijust turn on the car, then they go from 13.2 to around 13.0 with lights on. I think its a weak battery..

    good luck with it
    -My name is Tom not Jack

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    "I wanted to put a bullet between the eyes of every panda that wouldn't screw to save its species" Fight Club

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    Registered User billdo's Avatar
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    Angry

    im having prob;ems too i ahve an 03 wrx. i have an apexi ground kit and turbo timer that reads volts. when i turn the ket it will be 11.2 ill start it it will rev for the worm up and go to 14.4 then after it revs down the volts will drop like 14.2 14.0 then if i drive for a long time like i am worm it will be 13. 7 with lights and heat it will go 12.1 and some times lower. i had my altinator checked the said its fine i think i might swap out my battery to see if this works but its pissing me off and dont know what to do. any ideas

  7. #6
    Registered User ryanwrxduksa's Avatar
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    its gonna sound weird but use your meter from the post to the battery case and check for voltage drop, you can get static drop from any dirt on there. also check from the post to the terminal on both pos and neg. bes case scenario there should be none at all. if there isnt go but a hydrometer and check you cells, unless you have a avg or maintence free.
    07 white STi in CT

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    Registered User Xantos's Avatar
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    I have been experiencing a similar problem, although in the opposite conditions you are talking about. My battery will not charge at idle if anything more than the stock radio is running.
    When it was Texas hot outside for the past few months I had to have 3 jumps, and needed to plug it into a trickle charger at night. When I'm getting above 1k RPMs it charges just fine, so my "trick" has been before turning off the car rev it to 2k for a few seconds and then turn it off. Once I learned this, no more dead charges and no need for the trickle charger.
    However, things like rolling down the windows with the lights on will almost always drastically dim the headlights, and on one occasion when I rolled them down after idling in traffic for a while caused the ABS light to come on, the headlights to completely turn off, and the idle got very rough. I of course immediately fixed this by revving in neutral for a few seconds, but this is very troubling.
    My question is, should I replace the battery, or is this a need for a new alternator?
    Christine the silver 03 WRX wagon
    Brought unto the world on 6/6/06
    May your evil be known around the world

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    Registered User billdo's Avatar
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    yeah im seein that if i am stoped and idalling my volts will drop and flash at me apexi turbo timer and when i have my heat or ac on its goin down i cant fugure it out and its pissing me off

  10. #9
    Registered User billdo's Avatar
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    yeah so its not the battery tryed that today so i ordered an altanator well see how that does ill keep you informed

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