Re: More grist for the battle of the battery

[Steve Leonard]

Larry Goddard wrote:
'Probably OK. However, if you are really concerned,
one option is to put a Schottky diode (of sufficient
current capacity) in line. It will introduce approximately
0.5v of voltage drop over the whole range of supplied
voltage.'

Darn good idea, Larry. Even if you aren't messing
with a higher voltage battery. And put it in ths ship's
wiring. As I discovered, not everyone will use the
same connector with the same polarity. My sailplane
was at a shop for some cleanup work. They needed to
check the radio instl in another ship. My ship had
the same style connector as a battery they had in their
shop. No problem, right?

When I got there, they said 'Does your radio work?'
'Of course it does. At least, it did when I brought
it here.' Come to find out they hooked a battery up
that used the same connector as I used, but their battery
had the plus side exposed on the connector coming from
the battery, and mine had the ground side exposed.
Net result: One dead radio, about a $250 repair bill,
and nearly two months without that radio.

If you do this to a Terra, you will hear nothing for
about two seconds after you turn it on, then there
will be a 'Pop' from inside the radio. I did this
to another one of mine when doing a re-wiring of the
panel, after a hasty first wiring job that was done
right before going off to a contest.

Steve Leonard

[COLIN LAMB]

"Darn good idea, Larry. Even if you aren't messing
with a higher voltage battery. And put it in ths ship's
wiring. As I discovered, not everyone will use the
same connector with the same polarity."

A minor problem with this approach is that there will be a constant voltage
drop in the line. This is normally no concern, except when you are down to
the low end of the battery range. Then, you have just increased the minimum
voltage by .5 volts.

You can avoid this problem by connecting the diode differently. In this
case, you would connect a diode across the radio. Connect the cathode
(banded end) across the + and the anode across the - . The current capacity
of the diode must be greater than the fuse or circuit breaker. Make sure
there is a fuse or circuit breaker in the line before the battery connector.

If the polarity is correct, the diode will be invisible - hence no voltage
loss. If the polarity is backwards, the diode will short out, blowing the
fuse or circuit breaker. Opposite polarity voltage will not exceed about .5
to .7 volts, which will not damage the radio.

Colin