Fergus Kyle wrote:
> My question is prompted by the above. I have built a coming monster
> due to wanting to populate it with amateur radio "electro-whizzies" (as Bob
> says). This brought me to wondering how I can reduce longterm demands on
> current supply.
Here are some ideas:
1) Spend more time listening than transmitting. With a duty cycle of
25%, you need only one quarter of the alternator supply. During
listening it can charge the battery, and during transmissions the
battery can supply part of the power.
2) Go QRP. Or at least, use only half te power. 3dB less signal is
barely noticable on the other end, but cuts the power demands in half.
It has the advantages of causing less RF-related troubles in the ship as
well.
3) Use SSB with not too much compression.
> I added an SD20S but a 100watt HF transceiver can eat
> 20amps easily, I know (car history).
Yes, on constant carrier. But why would you want to do that?
With SSB with a reasonable compression power demand would go down to 5
amps average, with 3db reduction it is already down to 2.5 amps, and
with a duty cycle of 25%, your average power demand would actually be
less than 1 amp.
So what is your problem?
> This led to the idea that the master contactor wants an amp or so all its
Well, electronic shops sell relais (mainly targeted to the car industry)
capable of handling 40 amps, and using less than 200mA or so for the coil.
> My question is:
> Have I done a useful thing? What is the expected useful life of a fairly
> simple (and supposedly rugged) device compared to these usual contactors?
Well, to be honest, I don't find it useful (otherwise I would have done
something similar ;-) ). I too have a SD20S, but a split main battery so
I have fully separate electrical systems, and switch them with high
quality "car-type" relais (with good paperwork) to keep the unswitched
leads as short as possible for highest safety and have the power
switches at a logical and convenient location at the same time. And in
the very unlikely case that a relais would fail, I would always have
another independent bus going. I would without hesistation connect my
Icom-706 to this electrical system, without any other changes than
bonding all electrical parts of the airplane together and installing
bridges over all hinges and bearings to minimise receiver noise (which
is most likely going to be your biggest challenge). I also suspect that
you are going to need to do "something" to the ignition system of the
Rotax which is probably designed for max performance and reliability,
and not for best RFI-suppression on the HF-bands.
Frans
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