Odd Voltage Alternator problem - Defender Source
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  #1  
Old June 8th, 2012, 09:22 PM
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Odd Voltage Alternator problem

So Iím driving my niece to work (one way 8 miles) and about a mile into the drive the battery idiot lamp comes on for about two seconds, and goes off. I think to myself, oh crap. Drop off the niece start heading home. I make a stop at my office; the truck is off for about 20 minutes. Start the truck up to leave, all is normal, and then the same thing happens the lamp comes on for two second the goes off. I should mention that during my entire drive my top speed is 55MPH. after another oh crap I start to finish the drive. I pull up to a stop sign to enter into the main traffic flow and the truck sputters and dies.
The only idiot lamp on is the check engine lamp as I have an oxygen sensor on the blink, I confirm this every month by pulling the code. Itís been bad for over a year. I try to get is started, check fuses, etc. (and yes the tank is full). I have my wife tow my D90 with her Kia (donít laugh) the rest of the way home.
I pull an error that says something about fuel oxygen mixÖ?!? So at this point itís going to be the fuel pump or mass flow thingamabob. Call the shop have them take a lookÖitís the fuel pump. Replace same. That leaves up with the mystery battery lamp, they check it out and tell me at 1300 rpm the alternator is putting out 13v and at 2000rpm it putting out 19v and Iím thinking how can a 12v alternator (12mnths old) put out more than itís made to generate? Take note that I have a dual optima battery configuration and have had zero problems for the year and a half since I bought it the D90. The only electrical component that has been replaced was the alternator, by me purchased from auto zone. 110a, 12v. any thoughts?
The shop said that the alternator should be replaced. Thatís what I plan on doing tomorrow. Thanks in advance.
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  #2  
Old June 8th, 2012, 10:55 PM
MonLand
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If the regulator craps out, you can get much more than the 13.5V typical output. You need to get yours repaired or replaced. Don't drive it or you risk killing circuits/pumps/etc
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  #3  
Old June 8th, 2012, 10:58 PM
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Quote:
Originally Posted by MonLand View Post
If the regulator craps out, you can get much more than the 13.5V typical output. You need to get yours repaired or replaced. Don't drive it or you risk killing circuits/pumps/etc
So you think its the voltage regulator maybe not the alternator? I will check that out thanks...
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  #4  
Old June 9th, 2012, 08:46 AM
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The regulator is inside the alternator
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Old June 9th, 2012, 09:16 AM
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Don't confuse alternator amps with alternator volts. The regulator senses voltage and if it below a certain set point it turns the alternator on until it reaches another set point and then it turns off. The regulator is constantly flipping the switch to prevent over or under charging.
The amount of amps coming from the alternator when it is in charging mode depends on many factors; engine RPM, pulley ratio, coil windings, ambient temperature, wire thickness, battery state of health, blah blah blah...
Under most circumstances the amps will be far far below the rating of the alternator. For instance a 100 amp alternator only delivers 100 amps at its top designed RPM, which may be something like 12-15K. You're never going to reach that speed in normal driving. In fact that 100 amp alternator is probably delivering more in the 30 or 40 amp range at your top speed on its best day.
Higher amps simply means that the battery is replenished faster as it discharges. That's it, nothing magic there.
So what happened to you is that you just plain old ran out of electricity. Alternator wasn't charging, you ran on battery alone until there weren't none left, which resulted in an embarrassing tow.
To avoid such future fails, install a voltmeter. When everything is humming along you should see 13.2-14.4 volts. Why more than 12? because that's the voltage being pumped into the battery by the (regulated) alternator!
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  #6  
Old June 9th, 2012, 09:19 AM
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Quote:
Originally Posted by UnfrozenCaveman View Post
The regulator is inside the alternator
yeah Not like the "old" days when it was seperate. I dont think you can buy an alternator that isnt rebuilt.
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  #7  
Old June 9th, 2012, 12:55 PM
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Sure you can. They call them new.
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  #8  
Old June 9th, 2012, 01:34 PM
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Originally Posted by Red90 View Post
Sure you can. They call them new.
few and far between on the new from what I've seen. Ordered a Bosch and it wont be here until tuesday. No one stocks anything good and I'm not doing another Autozone "rebuilt". Going to add that to my shelf inventory now...starter too.
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Old June 9th, 2012, 04:59 PM
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Find a magnito merelli [sic]. Will T got me a new one designed for a P38a I put on my LWB with a pulley swap. It is the only decent alternator I have found. Bosch sucks (died in 2 years). Rebuilts -- forget it. I rather put a used original on that a new non-MM one.
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Old June 12th, 2012, 07:05 PM
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Failing to find good local alternator (will research Merelli), I ordered a Bosch on Amazon and it finally got here today. So I have everything installed and the battery box sorted. Before I get her back on the road for the test, I have made note of a few things...
  1. The bulk purchase of baking soda at Costco was a good choice (battery acid)
  2. Batteries mounted at a slight angle minimizes leaking fluid from your over charging battery because only one vent port will pop.
  3. when the shop tells you that overcharging you battery will result in an all bad condition...they might be right.
  4. Acid resistant gloves are not an option in my garage, they are required.
Seriously it wasn't all that bad, but it could have been. Well time to see how she does on the road!
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  #11  
Old June 12th, 2012, 08:10 PM
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Switch to an AGM battery and all your acid trips will be those of your youth
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  #12  
Old June 12th, 2012, 08:47 PM
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Quote:
Originally Posted by o2batsea View Post
Switch to an AGM battery and all your acid trips will be those of your youth
Ah yes, but acid is such a pure high!

all went well, safely docked in the driveway. Charging system normal now...
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