Hi Terry,
> for several hours with the engine off. We have since flown with the
> engine off for about an hour max, and had the voltage to the instruments
> drop to the point where they started dropping out (we were consuming
> about 2.5 amps). Our problem is that there are small voltage drop at
> many locations that can add up to as much as 2 volts. So when the
> battery drops to 12.0 volts, the instruments see 10.0 V, and have
> problems operating there. We have spent some time looking for the
> voltage drops. They come from each connection (spade lugs, etc.), each
> switch, and each circuit breaker. The biggest drops are in the
> individual circuit breakers in the switch panel we bought from Aircraft
> Spruce.
2 Volts of loss appears pretty much to me. As I don't have the engine
running yet, I'm playing/testing with the avionics on just the (scrap)
batteries, and as far as I can tell I have nothing near 2 Volts of
voltage drop.
What you could do here:
1) Use regular fuses, they have less voltage drop than circuit breakers.
2) Make sure not to use too small wire sizes.
3) Run one heavy ground wire, as every avionics item needs ground, this
saves half of the wire losses with just one wire.
4) Use as few connectors as practical. I have one connector that
connects the instrument panel to the rest of the ship, the rest is soldered.
5) For voltage sensitive equipment, use a DC-DC-converter, which accepts
any input voltage and always puts out 12 Volts.
6) A rarely used trick, but worth considering, is to use a 7 cell
battery. This will give you a nominal voltage of 14 Volts.
--
Frans Veldman
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