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

On Apr 27, 2013, at 7:03 AM, Sky2high@aol.com wrote:

Fred,

 

Yep. Usually the Essential Bus is isolated from the Main Bus by a diode.  I used one as described at http://periheliondesign.com/powerschottkydiodes.htm 

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

 

In a message dated 4/26/2013 8:15:33 P.M. Central Daylight Time, frederickmoreno@bigpond.com writes:

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-------   From: Sky2high@aol.com Date: 27/04/2013 4:02:26 AM To: lml@lancaironline.net 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 <426131.jpg> -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html

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