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

Click For Summary

Discussion Overview

The discussion revolves around a car experiencing unusually high battery voltage readings, specifically 17.2V, when running. Participants explore potential causes, particularly focusing on the voltage regulator and alternator issues, while seeking guidance on how to address the problem.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Historical

Main Points Raised

  • One participant notes that the alternator typically should not produce more than about 14.5V, suggesting that 17.2V could lead to battery damage.
  • Another participant identifies the voltage regulator as a likely culprit, sharing a personal experience of having to replace both the regulator and the battery due to similar issues.
  • A different participant mentions that modern alternators have built-in regulators that should prevent excessive voltage output.
  • One participant suggests performing a test by unplugging the regulator to check if the voltage drops to around 12V, indicating a potential issue with the regulator.
  • There is a historical anecdote shared about a similar problem experienced in a 1947 Beech Bonanza, highlighting the long-standing nature of such electrical issues in vehicles.
  • Some participants express uncertainty about the exact behavior of a malfunctioning regulator and its impact on voltage output.

Areas of Agreement / Disagreement

Participants generally agree that the voltage regulator is a prime suspect for the high voltage readings, but there is no consensus on the exact cause or solution. Multiple competing views remain regarding the specifics of the alternator's operation and the implications of the high voltage.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the alternator's specifications and the condition of the battery. The exact nature of the electrical system's failure is not fully resolved, and participants rely on personal experiences and anecdotal evidence.

Mescapium
Messages
1
Reaction score
0
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 a lot for any help provided !
 
Engineering news on Phys.org
Mescapium said:
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 a lot 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.
 
might this fit in DIY thread ?
 
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.
 
  • Like
Likes   Reactions: jim hardy
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)
 

Attachments

  • upload_2018-8-25_17-42-34.png
    upload_2018-8-25_17-42-34.png
    16.7 KB · Views: 1,004
Last edited:
  • Like
Likes   Reactions: Mescapium and davenn
Borek said:
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.
 
  • Like
Likes   Reactions: Borek
jrmichler said:
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 ?
 
jim hardy said:
Alternator should not produce more than about 14.5 volts.

Even with a malfunctioning regulator that drives the field?
 
  • #10
anorlunda said:
Even with a malfunctioning regulator that drives the field?

hmm. should have prefixed with "A properly functioning..."

will fix it

<chagrin icon>
 
  • #11
jim hardy said:
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.
 
  • #12
jrmichler said:
the FBO did not believe in spending too much on maintenance. The overcharging was a known problem,

Wow !
"Continued VFR...".
 

Similar threads

What could be draining the car battery and how can it be fixed?
  • · Replies 10 ·
Replies
10
Views
6K
Using multiple alternators at once for a power source
  • · Replies 13 ·
Replies
13
Views
10K
Seeking means of maximizing energy use from LiIon battery
  • · Replies 8 ·
Replies
8
Views
2K
Explain regulators and floating grounds to me, eg a car alternator
  • · Replies 12 ·
Replies
12
Views
7K
Real Life Car Battery Experiment
  • · Replies 9 ·
Replies
9
Views
5K
How much energy do batteries pass through an electric car
  • · Replies 6 ·
Replies
6
Views
3K
Car Alternator voltage is too high (16V+) Can it be reduced?
  • · Replies 14 ·
Replies
14
Views
85K
Auto/Motor What's Causing My Kia Stinger's Battery to Drain?
  • · Replies 28 ·
Replies
28
Views
5K
During battery charging how much is the voltage at its terminal?
  • · Replies 27 ·
Replies
27
Views
11K
Automotive Understanding 12V Car Battery Voltage Readings: Explained
  • · Replies 11 ·
Replies
11
Views
5K