> I was going to "regulate" the voltage to the start battery to about 13.8 =
volts,
> either via PWM, or by the old relay-type voltage regulator
> method:  voltage over 13.8, open switch, voltage under 13,8, close switch=
..
>=20
> Anyone want to comment on the latter idea? It is basically pulse charging=
, but
> a lot cruder than PWM (and a lot easier to implement!).

Sounds a logical way to do it to me.

> Second question:
>=20
> The P-fet switch is simple to drive, but the body diode presents a proble=
m if
> the input voltage is less than the output voltage, in which case the body
> diode will conduct and current will flow FROM the start battery.
>=20
> For this reason, I might be better of to use an N-channel and then a gate
> driver.

I would look at using two FETs in series, as you will have the same problem=
 with N channel FETs. Wire the two sources together and the two gates toget=
her, then connect one drain to the source and the other drain to the batter=
y, in a similar way to what is done for AC switching using FETs.
--=20
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--=20
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