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Old 09-21-2017, 11:35 PM   #1
spitfireap
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2008 Astra XR
Default Low Voltage While Running - Alternator Has Already Been Replaced

I have an '08 4dr XR that's been giving me problems for the last 8 months or so with charging. I noticed a problem when the radio would shut off if I turned the steering wheel to either extreme. Then the car wouldn't start one day. I jumpstarted, headed home and checked the battery level - around 11v. Charged the battery and drove around for a couple weeks and the thing again wouldn't start one morning - again low voltage, and again charged the battery. I suspected it was the alternator so I tested it with a multimeter and replaced it with a rebuilt one due to voltage reading around 11.4 at the battery with all systems on in the car instead of the mid-high 13s. After new alternator, drove around and about 2 weeks later had the same issue. Wanting to know what was going on, I bought a voltmeter that plugs into the cigarette lighter.

If I run the car with no extra systems (radio, ac, lights, etc) on I get a reading in the high 12s. When I add lights and radio it'll drop to the mid-12s. Once I turn on the AC, the voltage drops to the mid 11s. If I don't want the battery to be dead every 2 weeks, I have to drive with no AC. Alternator is not the likely suspect due to it being replaced, although it's not out of the question. The other culprit would be the voltage regulator, but I understand its part of the alternator on this car, so a new alternator would have brought a new voltage regulator. Any idea where I might look for a solution besides replacing the alternator?

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Old 09-22-2017, 02:33 AM   #2
fdryer
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2003 L-Series 3.0L Sedan
Default Re: Low Voltage While Running - Alternator Has Already Been Replaced

In general, alternator charging circuits are simple; battery power is supplied to the fusible link wire (small gauge) from the starter terminal, connecting to a single terminal on the alternator post, One or two wire connector goes to the battery light on the instrument panel and electrical ground is the alternator case mounted to the engine block. Engine block and chassis are grounded together and connected to battery negative. Battery positive feeds the engine/interior fuse panels and starter. The starter terminal will have two cables - large battery cable and smaller fusible link wire that connects to the alternator post. A built in voltage regulator automatically adjusts output from around 13v to 15v with the average around 14.5v with or without accessories running.

The fusible link wire is basically a smaller wire gauge in a thicker insulation and calibrated to carry whatever amperage rating before burning out like a fuse except the wire runs between the starter and alternator. This wire is a direct connection from the starter (large) terminal with the battery cable. Power to the alternator is live since 12v is coming from the battery. The voltage regulator and diode pack doesn't draw any power until the alternator turns. Some quick measurements may help determine where and why the alternator isn't powering up above battery voltage (12.5v). All alternators output above 12.5v - the higher the output from alternators the higher the current to supply the car's electrical demands while slow charging the battery.

Measure, with engine off, the fusible link wire on the alternator - its a single wire on its own post on the side or rear of the alternator. It should measure as battery voltage. If no voltage is measured, either the fusible link wire is blown (as a fuse without any signs of burning) or the connection to the alternator twisted the terminal post and damaged/broke the internal wire connection between the exterior post and internal wiring. The terminal may have double nuts; the inner nut stops the stud from turning and the second nut is used to mount the fusible link wire ring terminal. The connection requires two wrenches; one to hold the bottom nut and the second wrench to tighten the second nut against the fusible link wire without twisting the stud. A little torque is all that's required for tightening. This terminal stud may be longer than the other stud to accommodate the two nuts, washer and fusible link wire. If only one nut is used, care must be used not to over tighten and twist the stud as any twisting of the stud may break off the internal wire connection and render a new alternator inoperative. The result is taking a damaged alternator back for bench testing to confirm damage as the test will show zero output when 12v is supplied and a motor/drive belt turns it. If you inadvertently did this twice......

Some alternators requires the battery light circuit and/or ecm to detect a signal before allowing the alternator to switch on. The battery light should be ON when ignition is turned on, engine off. When starting or running, the battery light should turn off to indicate the alternator is outputting. A missing drive belt means the alternator won't turn and the battery light should turn on with the engine running. The same occurs if the belt or tensioner allows belt slippage as the loose drive belt won't turn the alternator.

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Old 10-10-2017, 03:02 PM   #3
williamgcastro
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Default Re: Low Voltage While Running - Alternator Has Already Been Replaced

Have you checked the battery?

Down here in the deep south the heat "cooks" the battery every two years or so. When my battery went recently I replaced it with a new one but noticed on the way to work the next day that the dash lights seemed a bit dim. I put the DIC into test mode and the voltage was in the mid to low 12's. I figured that I had an alternator issue, so I took it to the dealer to have it checked out.

Report came back that everything was fine with the charging system. Hmmm.

Reading up on how batteries are charged by "smart" system I found that a discharged battery is bulk charged at low voltage with high current until the voltage across the battery rises to a certain level (13.4v I think). Then the computer switches to a constant voltage strategy to top off the last bit of capacity. The constant voltage prevents gassing which is the major cause of lost electrolyte which is the main reason southern batteries die so frequently.

Having already changed the alternator I would look at the battery next.

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Old 10-13-2017, 08:25 PM   #4
ulemon
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Default Re: Low Voltage While Running - Alternator Has Already Been Replaced

Sounds like a battery issue, since you already changed the alternator you could change the battery for about 100 dollars. See if that fixes it, it should.

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