Its' an alternator
Dave Simpson
----- Original Message -----
From: STOUT, GARRY V, CSFF2 <garrys@att.com>
Subject: Re: Re :- Fuel Levels was RE:- Gates fuel
> 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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