[T3] Battery voltage with headlamps on ?

Jim Adney jadney at vwtype3.org
Thu May 5 15:24:36 PDT 2022

It's important to understand that our generators don't do much of anything 
when the engine is at idle. At that point, you're just running on the battery, 
and that's fine. Getting down to 11 volts sounds lower than I'd expect, but 
you have to keep in mind that it depends on where you're measuring the 
voltage. The system voltage will be lower at the fuse box than it is at the 
battery. The difference will be larger if your headlights are on.

The 12.45 you measured in the morning sounds fine. The hardest thing 
you'll ever ask your battery to do is to start the engine. As long as it can do 
that, it's okay.


On 5 May 2022 at 14:32, William Jahn wrote:

> Yesterday I was driving 3 miles home at night. At low RPM idle 800 RPM auto
> trans in drive. The voltage would drop only at stops in gear most of the
> time if I sat long enough it was 12 volts then once I began to move it read
> near 14 volts. The last stop was a bit longer, had  the Turn signals on and
> noticed they were flashing fast at that point the battery voltage was
> around 11 volts . I placed it in neutral then they went back to normal .
> Once I was moving it was fine. Checked the battery voltage this morning at
> 12.45 volts. It always starts fine  cranks fast . Drove it a few weeks back
> with the same route headlamps on and it was fine.
>  The generator and regulator are both fairly new , Battery about 5 years
> old interstate which is not really new.
>  I used to drive 7 miles back and forth to work at night on the way home
> and never had this issue yet there was not as much traffic back in 2004 .
>  I feel this may be normal, just not sure. What I mean is sitting in
> traffic with the headlamps on will allow the system voltage to drop .
> William
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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