Colyn,
Yes, the backup battery is only for one ignition and the sole main battery
is 28 AH. The voltage will drop to about 7 VDC (knocks out stuff that
needs 9-32 VDC). "Why?" You might ask.
1. Battery is behind co-pilot seat. Cable run is about 7 feet to
starter motor.
2. Cable is #4, not #2 in order to reduce weight. At hi amp draw even
a small resistance in the cable/system leads to big voltage drops.
3. Engine has a CR of 9:1, thus a bit harder to turn.
4. Mstr Sw lights up certain things - Master relay, RMI Microencoder, S-Tec
turn coordinator, gear locked lights and EPI 800 engine monitor.
5. B&C starter that does not draw more power as voltage drops unlike
Sky Tec. This is good.
6. Heavy prop and damper is a lot of weight to get going although usual
start commences by 1/2 to 1 revolution.
Scott
In a message dated 4/27/2013 8:21:35 A.M. Central Daylight Time,
colyncase@earthlink.net writes:
Scott,
Did you get voltage drop on when starting off the main battery?
I usually start on the main battery with the crossfeed off while my
engine monitor is running (through diodes ) from both batteries.
I wouldn't expect the voltage at the engine monitor to drop lower than
the backup battery, even while cranking.
I have the ability to use both batteries to crank but if I'm going to do
that I manually shut off all avionics, one at a time.
Colyn
Fred,
with a very low voltage drop (.2 to .3 VDC), other diodes may have drops
of .5 to .7 VDC or greater. I also saw a hefty voltage drop when
engaging the starter - enough so that the engine monitor ceased operating and
then rebooted itself after engne start. The monitor was hooked
up through the Essential Bus..
Scott
Interesting MVP 50 indications.
Occasionally in recent flights I get an alarm that oil pressure
is high after start up, reads 100+ psi. Do a run up and it
clears even before oil temperature changes. It comes and goes,
and seems independent of RPM on the ground, so I put it down to
instrument error instead of a stuck oil pressure relief valve.
Possibly important note: My MVP 50 is on the essential buss along
with my PFD, back up horizon and a few other things, which means the
buss is hot when I turn on the master and do the start. So the
voltage sag at the start may cause the MVP 50 to lose its brains
momentarily. I have lots of voltage spike protections
built into that buss, but not much one can do about voltage
sags.
Fred
-------Original Message-------
Date: 27/04/2013
4:02:26 AM
Subject: Re: [LML]
Re: Prop overspeed???
Angier,
Your prop did not over speed. Note that while the pump was
running the voltage was lower than during the time the pump was not
running. While 13.2 VDC is not that low, the MVP may be
sensitive to that or to an unusual ground loop relative to the pump
ground. The same may be true for the fuel flow
sensor. Check it out.
I like the hydraulic pressure included in the data logging.
Scott
PS do not worry about 2710 rpm.. You may want to change the
limit values slightly. Then again, why did the mstr wrn go away
or did you reset it.
In a message dated 4/26/2013 2:10:57 P.M. Central Daylight Time,
N4ZQ@VERIZON.NET writes: Today's 2hr flight was normal in all respects with the
single exception that immediately after liftoff, the MVP-50 began
screaming 'check RPM'. The RPM display was close to 4000 and fuel flow
spiked.
Nevertheless engine sounds remained normal. Sure got my
attention.
At 6:29:28 and just as the gear started to come up is
when the RPM indication spiked for all of about
5 seconds. Haven't
seen this before.
What would the common, everyday prop
overspeed sound like?? not that I ever want to hear
it....
Angier
Ames
N4ZQ
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