I agree on the zener diode because it is the only diode type that not
only forces the direction of the current (normal diode) but limits
voltage. Flooded battery better but since you already own the AGM, you
could put some type of RESISTIVE material in series. (Large resistor,
light, etc) The key would be to find the right resistance (Approx
2/15th of the internal resistance of the battery) But experimentation
would be reguired.



wrote:
On Mon, 12 Nov 2007 12:12:16 -0800, wrote:


I have an older Honda 10 hp outboard that has a charging circuit. The
small boat that it is on has a bilge pump and small AGM battery. The
outboard's charging circuit puts out over 15 volts. Can I put a diode
in the circuit to reduce the voltage? If so what kind of diode?

thanks


A very large zener diode with a substantial heat sink. I doubt you will find one
that can handle the current. Old British motorcycles had them for this purpose,
but that was a LONG time ago, and they were more likely 6 volt systems.

Most small outboards have poor, or no, regulation to speak of. Some
manufacturers have add on regulators, but they are pretty expensive - as in
$200+. It would make more sense in your case, to ditch the AGM and get a flooded
battery that is not so sensitive to voltages over 14. You will need to check the
electrolyte level on a regular schedule.