Can anyone on the Europa net tell me if the Rotax 914 uses a Generator, or an
Alternator.
Garry V. Stout
District Manager, AT&T Business Services
Phone: 813-878-3929 Fax 813-878-5651
*****Please note new e-mail address******
-----Original Message-----
Subject: Re: Re :- Fuel Levels was RE:- Gates fuel
Nigel Charles wrote:
>
> Whilst the Rotax
> generator output is relatively small (about 20A max) so is the rest of the
> system. Batteries are often only 17AHr and the system load can also be
> quite small. Mine is often below 10A and only exceeds 14A for short bursts
> when transmitting. The systems might be able to keep the generator from
> cooking the battery if they can keep the output voltage below 16V but why
> risk it. A crowbar unit is relatively cheap, weighs next to nothing and is
> easily fitted. The recommendation comes from Bob Nuckolls who is a
> recognised expert in this field.
Actually his recommendation for Rotax is: "If your battery is in good
shape, a failed regulator won't drive the voltage to fire breathing
levels like a 40-60 amp alternator will. If you have a means for
timely OV warning installed, you can probably rely on your own
reactions to shut down an offending system. I would recommend both
over and under voltage lights mounted on a prominent place on the
panel."
I still generally agree with most all your comments, and my principal
point was a caution concerning wiring for a crowbar on the
mechanical-pump 912, vs. the 914 or all-electric 912, and actually
applies with or without a crowbar for the latter.
> For this reason I would prefer to use the battery as an emergency source...If
an backup
> battery is to be used there is even less reason to use the direct generator
> output.
I'm unclear as to how, if the main pump is not wired to the
alternator, that the battery becomes a backup in all fault scenarios.
What is the pump's source of power if a smoke-in-cockpit emergency
requires disconnecting the battery and alt entirely via the master
relay? One could wire it direct to battery through a switch, but that
creates other problems. Tends thus to argue that a backup battery is
really needed, not "if."
> A crowbar unit is in effect a slightly more sophisticated Zener and also has
only two wires.
A 2-wire version requires a relay to work on the Rotax. Also, re two
hookup versions I've seen (Aeroelectric and EXP BUS II), I think it
requires designing a plan B. Using the "C" terminal on the regulator
requires a leap of faith that the "C" terminal will still work in all
modes of catastrophic regulator failure. At least one of the versions
appears faulted in that the relay is always on if no OV fault. If the
relay fails, it takes out a perfectly good alternator...on a plane
with only electric fuel pumps. Followed on the ground by a lengthy
diagnosis which will find the true fault as last resort.
Regards,
Fred F.
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