High Voltage (charging system problem)

[antpic]

2004 Xterra SE S/C 110,000miles

Car died - got a new battery because it was 5 years old

(1 week later) Battery & brake lights come on when I accelerate - had an auto parts store test it and it said it was charging at too high voltage - got a new alternator

Car worked fine for about 2 weeks (400 miles) now, when I accelerate the battery & brake lights come on and sometimes the radio stops working ( all issues generally stop when I let off the gas) Also, the battery dies almost every night.

Tested again and the charging system still has high voltage (16.7+ no load, 15.9+ loaded)

When I took the old alternator back for the refund, I had them bench test it in the store and it passed, so i don't think it's an alternator issue at this point. Also, they wouldn't exchange the battery because that is testing good.

Took it to the dealer and they found a 5amp draw from the battery even when the car is off, they pulled each fuse to see which one would stop the draw and none of them made a difference.

They wanted $100 per hour after that to run more diagnostic and thats out of my budget so here I am, stuck, desperately hoping you guys might be able to help.

On a side note, since before I replaced the alternator, both of my interior cabin lights have not worked when opening the door or manually putting them on.

Thanks

[rjr162]

Going fuse by fuse (under the dash and under the hood) is the only way really to figure out where the draw is happening. Do you have any after market items in the car? (Stereo, amp, alarm, lights, etc?)

As for the over-voltage.. that's just weird. I'm pretty sure the regulator on our cars are in the alternator (but I've never paid attention)... and it should be doing around 13.8V-14.4V (typically 13.8 at idle and 14.4 revved up some)

[intender]

The voltage regulator on the xterra is built into the alternator from everything I have read and heard. The only reason you should have voltage that high coming from the alternator is if the regulator is bad. If you had the wrong alternator installed the pulley size could have been wrong and would cause it to put out too much voltage, which would have eventually burnt out the regulator. but then it should have tested bad if they bench tested it, unless they were spinning it at a the proper speed for that alternator, then it would have probably tested good. if they had spun it faster and the regulator was bad it would have put out too much voltage. So unless you have changed out any of your pulleys in the past with a different size pulley you either got a bad alternator, or the wrong one for your truck.

[kms1990]

i agree with intender try pulling the alternator's fuse and relay and see if there is any draw after that, you ant trust the dealers word, as most every car dealer just wants a quick buck off of you. also check for any crossed wires anywhere, but a good, correct fit and form alternator with a built in voltage reg. should not be putting out voltage that high. as intender said you may have the wrong one did they say the amperage on the one you bought? your s/c truck needs 100amp the non s/c need 80amp also i would get the part number of the alternator you were given and go to a website like rockauto.com or one of the local parts store's website and cross it, then once you get their part number for the one you have, look up your truck on that same site and see if the numbers match. also check your belts. but man electrical stuff is a bug to trouble shoot, if i were you i would find a mechanic (not dealer) and ask him of his opinion, and how much he might charge to diagnose and/or fix the issue. but thats just me as i am not excellent at diagnosing electrical issues, i would rather leave that up to a pro. i an diagnose a bad battery or alternator but when it comes to constant current draw all i can think is shorted wires somewhere.

[intender]

5 amps is a fair amount to be pulling when the vehicle is off. Is your truck stock or have you added anything. aftermarket radio, cb, etc. Does your truck have a rockford system in it? i am still leaning towards the alternator being you issue. Alternators have diodes built into them that stop the alternator from pulling charge off the battery when the vehicle is turned off. If those diodes are bad, that can cause parasitic drain, they allow current to drain out of the battery and back into the coil of the alternator where it is dispersed as heat. even occasionally you can hear a high pitched whine coming from the alternator when the car is off when the diodes are bad. Bad diodes in an alternator can also cause too high of a voltage to be produced from the alternator. both of this things are issues you seem to be having. Not all testers are capable of checking for bad diodes, so even though it may have tested good for them on the bench, doesnt mean its not bad.

Also would be curious to know how they measured the parasitic drain on your battery. there are a lot of things in our trucks that can still draw current for up to 30 minutes after the car shuts off. I have seen as high as 3amps pulling off my xterra up to 10 minutes after its shut off, but after about and hour its down to almost nothing. If they tested the drain of your car before everything powered down into sleep mode you could easily have 2A or more of draw in the first 10 minutes or so, plus the drain from the alternator would put you in the range your seeing.

[Itsme]

I think the most important thing here is, Are you sure your voltage tester is reading correctly? I doubt this has anything to do with the shorted lights and the radio shutting down.
Try to use another volt meter, to test the output voltage. I'll bet it is normal!
I don't have any good things to say about finding the electrical leak, but most of the things not working for you are influenced by the alarm/unlocking system, which also influences the radio. I would start there.

[antpic]

Thanks for all the help guys!

The old alternator which I believe was 80 amps was the one they had bench tested and passed. The new aftermarket one I got is 100 amps, the looked up the one needed for my truck at the store but I will double check that it is the right one. All belts look good and are tight.

The truck is completely stock other than the factory installed Rockford Fosgate system. I also thought the zener diodes could have gone bad since that senses the voltage but is there a way to check them?

I had never noticed a draw on the battery until the dealer brought it up. I'll check tomorrow to measure it after I turn the truck off and an hour later, I'll also disconnect the alternator fuse and see if that eliminates it.

[kms1990]

the 100 amp is for the supercharged one yours is not if you had the 80. i bet if you get an 80 all this will clear

[intender]

The amps of an alternator should have nothing to due with the voltage that its putting out. I have put higher amp alternators in a couple of my cars in the past with no issues at all. Its like a charger for your phone, get one thats too small and it either takes forever to charge or you will burn out the charger. If you have an 80 amp alternator you can pull a 960 watts at 12v (it really should put out 13.6v to 14.4v) from it without issue. 100 amp would give you 1200 watts. if you have 4 100 watt lights on you truck they pull 33 amps. Add in 2 head lights and the stock fogs and you are using about 55 amps. Add in your truck running and you are getting close to about what your stock alternator can provide which means you are not going to get enough to charge your battery while running. A winch alone will pull 2 to 3 times what a stock alternator can provide under a moderate load.

A good alternator will put out proper voltage no matter what the amp rating is.

[RacerXXL]

This ^^ I have a 180 amp Mean Green in mine and it still charges at the normal voltage rate.