Hello Martin
The prime cause of the voltage drop when additional load is drawn is from
the resistive loss in the whole of the circuit. The circuit resistance
includes the internal resistance of the source (alternator/battery), contact
resistances of all circuit breakers/switches in the current path, and all
the wiring resistance in the current path.
A secondary cause may be the "drooping characteristic" of the alternator,
where the voltage output drops as the current increases. The Rotax 912
internal alternator is capable of a maximum of 19 amps, but I'm not sure how
rapidly the voltage regulator can compensate for rapid changes in load
caused by the pulsing of strobe circuits. The original regulator circuit
recommended by Rotax took its voltage reference from the battery or the bus
bar, but they later recommended a direct connection to the regulator output
to prevent any possibility of the reference becoming disconnected (e.g. via
a circuit switch). Any resistance in the circuit between the regulator
output and the bus bar could lead to a fluctuation in the bus bar voltage --
and this is why a heavy-duty cable should be used.
If the voltage fluctuation occurs equally when operating from the battery as
with the engine running, then you should look first at the wiring and ensure
that your cable gauges are adequate. Do not neglect to check the ground
return path, as any resistance here will be common to all circuits. You
could try using jumper leads to make a direct connection to the strobe
circuit to find out whether the cause of fluctuation is a load on the
voltage source or a common resistance drop in the wiring.
Hope this helps.
Fly safely
Mike
Europa Club Safety Officer
-----Original Message-----
From: MJKTuck@cs.com
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