[VAC] Re: Battery/converter questions

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx>]

Sometimes the converter is sized to handle the average load and the
battery is included to handle the peak loads and the converter charges
the battery while loads are light. The ferroresonant converter seems to
not be sensitive to battery condition and tends to overcharge the
battery running it out of water due to dissociation of the water. Once
abused that way a battery is only scrap metal.

Turning on a gaggle of lamps at the same time can knock a converter out
of regulation because the incandescent lamp draws 15 times normal
operating current at the instant of connection. At the same time
incandescent lamp life is dependent on voltage regulation. If the
converter runs a little high, lamp life will be short. The rule of thumb
is that a 5% increase in lamp voltage causes a 10% increase in light
output and cuts lamp life in half. Conversely a 5% decrease in lamp
voltage causes a 10% decrease in light output and doubles lamp life. DC
fan motors are less picky about voltage.

I've not used the Airstream ferroresonant converter to know its
characteristics, but I suspect it may depend (as Chris Bryant says) on
the battery for some control. I do know that its not especially energy
efficient, raising the electric bill. In your parked situation, I'd be
strongly tempted to cobble in some 120 volt compact fluorescent fixtures
for lighting and leave the 12 lamps off until on the road again. And use
120 volt fans for circulation and cobble one into the vent.

Or I'd add a decent digital meter to the battery voltage, or better an
e-meter, and apply 120 volts to the converter until the battery was full
charged, and then unhook power from the converter until the battery had
been run down to about 12 volts, maybe 11.8 with lights, then charge
again. That might take days between charging episodes.

Gerald J.