I think my alt may be dead

[jeremyblevins 10+ year member]

Okay so the other day my car wouldn't start i'm like wth. so i checked my voltmeter and was getting around 11 volts so i guess my battery is dead. so i get a jump start and my voltage just up to 12.4 ish so i drive my car for a bit like 3 minutes turn it off then it starts again so i drive again for like 15 minutes turn it off and turn it on then is starts and drive alright but the voltage always seems low. so i let it sit over night and it wouldn't start and will only start when being boosted now. i checked the battery at advance and they said it was fine just low on juice. but i disconnected the battery while the car was running but the car didn't stop?

So i'm thinking the regulator in the alt is busted?

i was watching just now while it was running and the voltage would sit at 12.4ish but kick up to 12.9 when the a/c kicked on.

any suggestions?

and if my alt is busted would a 200 amp one be good? Or should i be able to get by with stock?

my system is the mustang stock mach 460 sound system with 2 10 inch type r's hooked up to an audiopipe 1500d at 2 ohms giving me around 950 rms.

is this a good place?? DB Electrical - Ford Mustang 200 Amp High Output Alternator 4.6L 96 97 98 7776

sorry for the long winded post but i'm leaving for work and wanted to get all my questions out

thanks in advanced for the advice.

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[jco1385 5,000+ posts]

why didnt you test the alt at the same time?

 

[mast240 10+ year member]

sounds like your batt has a bad cell... dont trust everything that the dudes at advanced auto say.... what exactly was he talking about when he said "its low on juice"? was he talking voltage??? it could be the regulator.... but i would go to another store and have them load test the batt first, just to be sure

also ... you may be ok with your stock alt ... depends on what it's rated at... if its over 100 amps, then i would say, you'll be alright... as long as you have your big3 done, and a decent battery... if you add more power tho... def upgrade the alt

 

[jeremyblevins 10+ year member]

yeah i think stock is a 130 amp alt. But i didn't test them both because he said he couldn't test the alt if the battery wasn't charged???

how do they load test the battery and where do i take it to test that?

 

---------- Post added at 10:45 PM ---------- Previous post was at 10:44 PM ----------

 

I got the battery from autozone it's a duralast. its less than a year old i should still have warranty on it. can they test it there?

and also if it's a bad cell in the battery why would it keep the voltage down? like when the car is running shouldn't it still be around 13 volts?

 

[jeremyblevins 10+ year member]

and now that i read the print out from the machine it never says the battery is good. It says low on charge, must be charged to determine condition. and in a box it says use midtronics diagnostic charger.

 

[VWBobby 10+ year member]

You can't do a load test on a dead/low battery. Charge up your battery until it reads at least 12.5V at rest, no charger attached. If it doesn't read at least 12.5 at rest, the battery is probably shot. Then you can take the battery in to have it load tested. If you drive the car there to have it tested, and have a bad alt, your voltage may drop down below 12.5V if its not charging the battery. General rule is at least 13.5V while the car is running and at least 12.5V at rest.

 

[mast240 10+ year member]

yea... your battery is most likely shot... usually when it says that, its either one of two things.... it wont hold a charge, or its not being charged... but, if u pulled the terminal off the batt, and the car stayed running... then the alt is putting out... do this.... pull the positive off the battery again, and then test the terminal (off the battery) with a multimeter/voltmeter) ... it should be in between 13.5 and 14.5 volts ... dont try to read the alt output with the batt connected, cuz that can distort your reading.... if your alt is putting out the right voltage, then your battery is shot.

o, and the machine they use at autozone probably wasnt a load tester... sometimes they will use an actual load tester, and sometimes they use a crappy "battery tester" ... if it were a good load tester, when it came back saying "battery requires charge" it would have autimatically charged it, and then re-tested...

if it does end up being your battery... i've got a brand new red top that i can sell you for 50 bucks plus shipping (if you want)

hope that helps bro... i'm tired as hell, and not sure if i even worded it right, lol

 

[jeremyblevins 10+ year member]

Well i don't really have a means to charge the battery myself. When my car sits over night it drops down in the 11v range but again i don't know if it's just not being charged or what. I definitely don't see 13.5v while the car is running though. 12.4v-12.9v was when i was testing it with my dmm right on the battery.

 

[jeremyblevins 10+ year member]

thanks that helps a lot and they didn't remove the battery from the car so i guess it was the crappy version, and my battery is less than a year old so it shouldn't be shot already my battery hasn't died since i bought it so i know it's not my fault. i'll try that trick tomorrow so i can just pull of the terminal then test the voltage differential from the positive terminal to the negative post on the battery?

 

[mast240 10+ year member]

yea... as long as the positive terminal isnt connected to the battery, you can read off of the negative post... mainly cuz if the battery is shot... it can distort your reading (even if your alt is putting out 13.5+ volts, it could still read 11-12) ... and a real load tester is easy to spot... it will hook up to the battery... and you will see an amperage gauge... then when it starts the test, the gauge will max out, and then step down about every 15-20 seconds, until its all the way to zero... let me know what you find out

 

[BASSMEKANIK89 10+ year member]

If you have a newer car, I would strongly advise you not to pull the battery terminal off of the battery while the car is running. It will check to see if your alternator is working, but could cause a shitstorm of other problems with the computers in the car. The battery is there to start the car and filter power produced from the alternator.

 

[jeremyblevins 10+ year member]

oh and my keyless entry and stuff still works i just used it on my car. idk if that would require much juice from the battery or not though.

 

[jeremyblevins 10+ year member]

well my car is a 1998 i don't know if you consider that newer.

 

[mast240 10+ year member]

oh and my keyless entry and stuff still works i just used it on my car. idk if that would require much juice from the battery or not though.

that doesnt really require much power bro... i've had mine work with my batt so dead that my dome light wouldnt even turn on, lol

 

[jeremyblevins 10+ year member]

yea... as long as the positive terminal isnt connected to the battery, you can read off of the negative post... mainly cuz if the battery is shot... it can distort your reading (even if your alt is putting out 13.5+ volts, it could still read 11-12) ... and a real load tester is easy to spot... it will hook up to the battery... and you will see an amperage gauge... then when it starts the test, the gauge will max out, and then step down about every 15-20 seconds, until its all the way to zero... let me know what you find out

Yeah that's not what he had. it was a computer device i don't remember seeing a gauge at all one side had the computer with buttons and the other was a small printer

 

---------- Post added at 11:30 PM ---------- Previous post was at 11:29 PM ----------

 

well i don't have a dome it's a convert but my mirror lights do come up but again could be nothing