There are adjustable voltage regs available for our Bosch alternators
for not much money if you want to set it to the high end of "normal".
You can choose from internal type with an adjustment pot on the brush
assembly or an external type with long wires from the brush assembly to
the remote reg and it's adjustment pot for easier fiddling. You might
consider the external type with an added switch to allow a dropping
diode to to be added or removed from the sense wire circuit. This would
let you easily boost the charging voltage when really needed and return
to normal charging voltage the rest of the time, all with the flick of a
switch.

http://bartonharness.com/AdjustableVoltage.html

Mark

Otmar wrote:

> .............
> I had forgotten that these alternators are usually only running at
> 13.8V. And it's true that at such a low voltage it's very hard to get
> a fast charge.
>
> As I understand it, this is where a AGM type battery will shine. The
> do have very low internal resistance and so will charge much faster
> at low voltages.
>
> It is possible to turn up the voltage, and even implement real good
> charge algorithms, but that get's pretty complicated (or expensive).
> I remember now that I had turned my alternator up to 14.5V when I was
> doing a lot of charging.  But that could damage a battery when it's
> hot, so that's where it gets complicated.
> --
>  -Otmar-
> 82/86 Stretch Vanagon Westfalia GTI. "Power of two" Soon to be TDI.
> http://www.evcl.com/vw
> 1 914 EV, 1 Insight Hybrid
>