Car reading 17V+ in the battery when running, how to fix?

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Hi, I have a 2004 Toyota Matrix with 270 000km. It's working great but today when i started my car the battery was going up to 17.2V (i have a battery voltage reader in the car at all time). It's the first time it went up there, it usually stays in the 13-14V. I know something is wrong and I want to fix it before it breaks something. I made some reasearch already and i read it could be the voltage regulator circuited between the alternator and battery. I don't know much about car's electrical system and my electric classes are a little bit far (still i am supposed to have some basic knowledge). So i'd like to know precisely what's the problem and how to fix it. Or some help or guidance, thanks alot for any help provided !!
 

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Hi, I have a 2004 Toyota Matrix with 270 000km. It's working great but today when i started my car the battery was going up to 17.2V (i have a battery voltage reader in the car at all time). It's the first time it went up there, it usually stays in the 13-14V. I know something is wrong and I want to fix it before it breaks something. I made some reasearch already and i read it could be the voltage regulator circuited between the alternator and battery. I don't know much about car's electrical system and my electric classes are a little bit far (still i am supposed to have some basic knowledge). So i'd like to know precisely what's the problem and how to fix it. Or some help or guidance, thanks alot for any help provided !!
Note the alternator’s make and model. Most modern units have a built-in regulator that should cut off above 14.4V or so.

17.2V, if correct, will be boiling your battery and causing untold electrical havoc - best not to use the car until you have it sorted.
 
  • #3
jim hardy
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might this fit in DIY thread ?
 
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Borek
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In my experience voltage regulator is a prime suspect. As Guineafowl wrote if it is a lead battery high voltage can mean heating it till it the acid starts to boil, it stinks like hell and corrodes the metal around.

At least that's what I had to deal with about 15 years ago, in the end I had to replace both the regulator and the battery.
 
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jim hardy
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EDIT When it's working, an..
Alternator should not produce more than about 14.5 volts.
It has an internal voltage regulator to control its output voltage.
It should look like this
upload_2018-8-25_17-42-34.png


and be mounted on the alternator. probably on end opposite the pulley.

Try unplugging the wire that plugs into that receptacle then start the car.
Voltage should read around 12 .

One can replace just the regulator but it'll probably cost you nearly the same as a whole alternator.

good luck

old jim

(Sorry)
 

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  • #7
jrmichler
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At least that's what I had to deal with about 15 years ago, in the end I had to replace both the regulator and the battery.
Me too, about 1974. The exact same problem. In a 1947 Beech Bonanza over Wyoming. Flew from there to Southern California with the electrics shut off. Fortunately, airplane engines have magneto ignition, so can run forever without a generator.
 
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jim hardy
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The exact same problem. In a 1947 Beech Bonanza over Wyoming.
Ahhh Nostalgia. My good friend and mentor had one of those... Amazing machine.

did yours have the Jordan-Flanagan truss mod ?
 
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anorlunda
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Alternator should not produce more than about 14.5 volts.
Even with a malfunctioning regulator that drives the field?
 
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jim hardy
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Even with a malfunctioning regulator that drives the field?
hmm. shoulda prefixed with "A properly functioning..."

will fix it

<chagrin icon>
 
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jrmichler
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did yours have the Jordan-Flanagan truss mod ?
Probably not. It was a rental on leaseback, and the FBO did not believe in spending too much on maintenance. The overcharging was a known problem, and I was told to just add water to the battery.
 
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jim hardy
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the FBO did not believe in spending too much on maintenance. The overcharging was a known problem,
Wow !
"Continued VFR......".
 

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