Alternator seems to be overcharging

Battery, alternator, starter, cables, etc.
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JTalley
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Alternator seems to be overcharging

Post by JTalley »

When the engine isn't running, the battery gauge seems to stay about where it should. As soon as I start it, the gauge jumps up to just below the yellow mark. Sometimes it goes up into the yellow. If I press the brakes, it typically fluctuates up and down somewhat. Is this something I should worry about?
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

Possibly.
If the regulator is fried, you could overcharge the battery which could be very dangerous. Hopefully, your gauge is simply not showing the true voltage. To be sure, hook up a battery tester to it (it should also be able to diagnose your charging system), or even a regular voltmeter.
Voltage should be:
14V while running
12V when off.

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Re: Alternator seems to be overcharging

Post by JaxSPL »

14.2-14.8volt idling
13 to 13.8volt off

Hook up a volt meter to it.
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

JaxSPL wrote:13 to 13.8volt off
This is incorrect.
A 6-cell lead acid battery will be no more than 12.8 V at full charge in an open circuit.

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Re: Alternator seems to be overcharging

Post by Kidhauler »

My 99 shows 18 volts on the gauge when the engine is running. I hooked a multi meter to the battery on several different times and it always shows normal at the battery. I was thinking of opening the cluster and pulling the needle off and moving it back so it Shows the proper voltage.
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Re: Alternator seems to be overcharging

Post by LiftedAWDAstro »

JaxSPL wrote:14.2-14.8volt idling
13 to 13.8volt off
The idling voltage is correct but check the voltage with the engine off overnight.
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Re: Alternator seems to be overcharging

Post by JTalley »

I bet I can get a volt-meter from O'Reilly's. I think they loan those out, if I'm not mistaken.
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

I highly recommend spending the $10. These things are indispensable for any kind of electrical work.
http://www.princessauto.com/workshop/ha ... multimeter
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Re: Alternator seems to be overcharging

Post by Kidhauler »

Spend a little more and get a digital unit they are way better to read.
They are about 15-20 bucks at radio shack.
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

Kidhauler is right. The digital ones are better because you can read values with more precision. I provided the cheapest example I could find because I understand the OP is on a tight budget. But an extra $5 for the digital is good value. The current measuring function in my multimeter is good up to 20A which is good for measuring loads.

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Re: Alternator seems to be overcharging

Post by Kidhauler »

The other thing you can do is take the alt out and take it to Canadian tire, or pepboys in the states and have it tested. I know Canadian tire up here will check it for free on their machine to test the output. That was how I found I burnt a wire and my alt was still good a few years back.
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trailer tow pack with a 3:73 posi
Bucket bench seats, Rear heat, Rear Airconditioning.
teal green
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AirRide air bags in the rear to fix soft stock suspension.
Onboard aircompressor to make it all work nice.
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Re: Alternator seems to be overcharging

Post by reaper »

timelessbeing wrote: This is incorrect.
A 6-cell lead acid battery will be no more than 12.8 V at full charge in an open circuit.
Incorrect,
JaxSPL is correct
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

reaper wrote:
timelessbeing wrote: This is incorrect.
A 6-cell lead acid battery will be no more than 12.8 V at full charge in an open circuit.
Incorrect,
JaxSPL is correct
I think you are mistaken.
With the alternator going, yes the voltage has to be higher to charge the battery. But a battery on its own will never be at 13V. Not that I've seen in my lifetime.

Here are just a few web pages that support this:
http://en.wikipedia.org/wiki/Lead-acid_ ... mon_usages
http://www.scubaengineer.com/documents/ ... graphs.pdf (page 3)
http://www.pbase.com/mainecruising/batt ... _of_charge
http://www.batterystuff.com/tutorial_battery.html#6
http://www.solarnavigator.net/battery_charging.htm
http://wiki.xtronics.com/index.php/Seal ... plications

Are they all wrong?
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Re: Alternator seems to be overcharging

Post by reaper »

I am going by standing voltage IN the vehicle.
12.7 is standard thru QC with manufacturers
although there has been 13+ sent thru
& landed at retailers.
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Re: Alternator seems to be overcharging

Post by MountainManJoe »

So what you're saying is, it's an exception rather than a rule.

I'm probably buying a new battery this week. I'll start taking bets on what people think the voltage will be. :)
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