Thanks for providing a working point of reference, Fred. I appreciate the
correction.
Not having the actual equipment at hand, one has to use manufacturer's
specifications, which are
often quite conservative. I did try to approximate typicals on the engine
stuff. And avionics power
drain is so variable...Those of you out there in love with the Garmin
430/530 must prepare for a
stuff is far more energy efficient. For example. And 2A typical for a fuel
pump? OWWch.
But we still have to contend with 6-8A drain for position/nav lights and
4-7A drain for strobes.
So for night flight, we'd need to add the SD-8 and call it the "night
alternator"...
On the battery front - that 7.2AH/12 RG battery sold by B&C is not
recommended by them for
cranking since the terminals are not bolt-down but fast-on and can't handle
high currents. Backup
only. This leaves the 20AH/12 RG battery at 15.3 lbs as the energy density
champ. 300CCA min,
-20C, 30 sec. B&C does discharge test their batteries, 60F/10 sec/8.5V min.
I have some numbers.
Shaun
----- Original Message -----
From: "Fred Fillinger" <fillinger@ameritech.net>
Subject: Re: Looking down the road at batteries
> You overall analysis is good, Shaun, but the actual current draw will
> not be the same as what the mfr says and is often high. Transponders,
> e.g., are spec'd at max reply rate of 500/sec. On my 2 electric
> gyros, xpondr, GPS map/comm, and monitor draw is less than 1/2 the 11A
> you've estimated, based on actual measurement. Thus, even the SD-8
> vacuum pad alternator could be enough add'l power if one shops also
> for current draw on avionics and is content with minimum goodies on
> the panel.
>
> Regards,
> Fred F.
>
> Shaun Simpkins wrote:
> >
> > The 16AH hour minimum quoted on the Europa factory schematic is Rotax'
> > recommended minimum battery size for the 914 (section 9.4.14).
> >
> > Note also that available power is not the full 18A; according to section
> > 19.5, the maximum loading from the fuel pumps, TCU, servo motor, and
> > warning lamps is 8A.
> > Typical for each pump is 2A; the TCU, probably about 0.15A; the rest are
> > intermittent. So at best, we have perhaps 15A available to us.
Airmaster
> > CS prop loads are also intermittent. Another consideration is the
battery
> > charging capacity of the system. I believe the FAA rule of thumb is
that
> > 20% of the alternator capacity should be reserved for charging. Your
> > personal specs may differ, but this is another 3.6A off the top.
> >
> > Thus, the 18A alternator is able to power about 11A of external loads
with
> > charging reserves. That's what basic electric gyros, VFR nav/comm,
xnpndr,
> > and engine monitor will eat up.
> >
> > Incidentally, this thread was last active in late 2000. Check out the
> > archives. Many are running heavy electrical loads on the factory
alternator,
> > but probably with very small charging reserves.
>
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