The Filsner is unlikely to have a problem through the diode setup you
have now. (not that I like the diode setup but it should work - BTW you
should be able to find lower voltage drop diodes).

For the Microair I would not read too much into a nominal voltage spec.
It is hard to tell wether the manufacturer is quoting a real absolute
voltage range or the nominal voltage. On the other hand I'd not want to
inflict anybody with a Microair radio (oops I can feel the flames
already). They have a very bad reputation where I fly. The several I've
seen installed have had problems, especially apparent heat related
problems with the displays getting garbled and then finally the whole
radio going out to lunch (and I'm not talking really hot days). Other
brands seems to be much more reliable. Why not go with Becker?

Personally I'd stay away from trying to get too fancy with regulators
etc. I want the supply to be as dumb and simple as possible. Just
batteries and circuit breaker or fuse and master switches. As few
connectors or solder joints as possible. And I personally I like
running one battery at a time - I want to see the health of each
battery and know about how much capacity I have in both batteries and
know I can switch in a reserve if I run a battery down -- which I may
not notice until it is too late. Like many of us in the Western USA I
fly over pretty desolate areas and I really want to know roughly what
battery capacity in reserve.

If you are goigg to install a transponder, have lots of avionics toys,
expect long cold flights it may well be you need to look at moving up
to larger capacity batteries or installing solar panels.

Darryl Ramm


Martin Gregorie wrote:
COLIN LAMB wrote:
Most diodes have about a .6 volt drop, which may be significant. Therefore,
you will need diodes with a low threshold. Schottky diodes should be about
.3 volts drop. You can measure the actual drop using a digital
volt-ohmmeter. There is a diode test range and it will show the voltage
drop.

I'm flying with the diode setup. The best diodes I was able to find in
the UK were Fairchild MBR1035 Schottky diodes. These handle 35 amps and
come in TO-220 packages. Their spec quotes a 0.57 v drop, which seems
about right: with 2 x GPS II+, EW-D logger, SDI C4 and B.40 varios all
on the C4's internal voltmeter shows 11.6 v on two fully charged 7 AH cells.

I need to fit a radio and am thinking of fitting a Filser ATR-500. Can
anybody tell me if that will be OK on the end of the diodes or would I
be better to discard the diodes and use one battery to drive the ATR-500
and the other to run the GPS, logger, and varios?

Another reason I'm wondering about rewiring to separate the batteries is
that if we get landed with transponders I assume I'd be better off using
one for radio and transponder and reserving the other for the
GPS/logger/vario setup. Comments?

The other choice of radio would be a Microair 760. I assume that, as its
rated for 12-14v it would be quite unhappy on the end of the diodes and
just barely usable on a separate battery. I see that Maxim sell a range
of solid state voltage boosters (there is a model that can output 14v at
2 amps). Has anybody tried using one of these to drive a Microair radio?
If so, how well did it work?




Colin Lamb




--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |