[T3] gas mileage, voltage, etc.

[Jim Adney]

On 20 Jun 2017 at 19:03, Daniel Nohejl wrote:

> B+ on the regulator is between 13.8V and 14.1V at
> idle and it measures the same at the battery. 

It's important to understand that measuring the voltage at idle 
doesn't tell you anything about the health of the voltage regulator.

Here's how the system works:

At low rpm, the charging system is 100% enabled, putting out as much 
as it can. As the rpms increase, the charging system is able to put 
out more and more voltage. This increase will continue until the 
voltage reaches the threshold where the voltage regulator (VR) 
reaches it's set point. 

The set point is that voltage where the VR starts to limit the 
charging system output. Watch what happens to the voltage as you 
increase the rpms. It will increase to some point, then it will peak 
and then settle to some level value which is the regulating voltage. 
This regulating voltage is where the VR is active.

You have to read the system voltage when the VR is active. At idle, 
it's far from active. When active, the voltage at B+ should be 14.1 - 
14.4 V. Under the same conditions the voltage at the generator will 
be somewhat higher and the voltage at the fuse box will be somewhat 
lower, but you can't depend on any particular voltage difference, so 
only the voltage at B+ is meaningful.

I wouldn't worry about your battery at this point. As long as it 
starts the car, it's probably good enough. It doesn't control the 
voltage; the VR does.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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