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Dynon EFIS & EMS power on the main bus

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jeffrey_davidson(at)earth
Guest

Posted: Mon Oct 27, 2008 8:45 am Post subject: Dynon EFIS & EMS power on the main bus

Background:  I tried to start my Jabiru 3300A yesterday.  It didn't start because of a lack of fuel.  I can address that.  At the same time, an electrical system question has come up.  The battery is a 2-3 year old 17 Amp Hour motorcycle battery.  It was charged up and eventually spun the engine fast enough to start under normal circumstances in my opinion.  I intend to replace it soon.  The ship's wiring diagram is a combination of Jabiru's design from their installation manual augmented with Aeroconnection techniques like the forest of ground tabs.  As such, with the Permanent Magnet alternator, I followed Jabiru's advice that Over Voltage protection is not needed.  



Question: My question here is about the wiring of the Dynon EMS and EFIS to the main bus.  They are powered up when the Master Switch grounds the Battery Contactor.  The starter contactor is downstream of the battery contactor.  When the starter is engaged by grounding the starter contactor with the ignition switch, both Dynons lost ship's power and came up on the backup battery.  When we had tried this several times, the Dynon backup battery was exhausted and the Dynons simply went off.  Again, the engine never started so all this was happening while the starter was engaged.  My question is whether or not the Dynons should be moved to the Avionics bus.  Yes, I have an Avionics Master and understand the concern about it.  The functional problem is that the tachometer and oil pressure are displayed on the EMS and nowhere else.  In the certified planes with glass panels that I'm familiar with, the glass panels are similarly connected to the Master Switch and stay on when the engine is started.  I need to be able to check oil pressure as soon as the engine starts.



Thanks for any light you can shed on this.  Next time, I'll move the fuel selector from the Off position!



Jeff Davidson (still an electrical newbie)

CH601-HD w/Jabiru3300A

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nuckolls.bob(at)cox.net
Guest

Posted: Tue Oct 28, 2008 7:18 am Post subject: Dynon EFIS & EMS power on the main bus

 	  Quote: 	
		  Question: My question here is about the wiring of the Dynon EMS and EFIS 

to the main bus.  They are powered up when the Master Switch grounds the 

Battery Contactor.  The starter contactor is downstream of the battery 

contactor.  When the starter is engaged by grounding the starter contactor 

with the ignition switch, both Dynons lost ship's power and came up on the 

backup battery.  When we had tried this several times, the Dynon backup 

battery was exhausted and the Dynons simply went off.  Again, the engine 

never started so all this was happening while the starter was engaged.  My 

question is whether or not the Dynons should be moved to the Avionics 

bus.  Yes, I have an Avionics Master and understand the concern about 

it.  The functional problem is that the tachometer and oil pressure are 

displayed on the EMS and nowhere else.  In the certified planes with glass 

panels that I'm familiar with, the glass panels are similarly connected to 

the Master Switch and stay on when the e!

  ngine is started.  I need to be able to check oil pressure as soon as 

 the engine starts.



Thanks for any light you can shed on this.  Next time, I'll move the fuel 

selector from the Off position!


	


   The spirit and intent of avionics master switch

   was to "protect sensitive avionics from hazardous

   spikes generated during engine cranking."



   In years since, it has been discovered that while

   there was significant brown-out during the first

   few milliseconds of starter operation similar to

   that shown here:



http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1_2.gif



   there were no high-voltage excursions that could

   not be easily handled by simple components in the

   potential victim's power input conditioning.



   Further, the industry tapped a huge experience base

   by forming RTCA and inviting all interested parties

   in aviation to participate in quantifying and documenting

   the magnitude and type of stresses a piece of avionics

   should shrug off.



   Based on our current knowledge and skill in crafting

   airplanes and their accessories, there is no need

   for an avionics master switch to "protect" anything.



   I believe you stated that all batteries involved in

   your test were of questionable condition either by

   reason of age or state of charge. I'll suggest

   then that what you experienced was not worthy

   of generating concerns. You need to repeat the

   experiment with a known-good ship's battery and

   fully charged stand-by batteries.



   It's doubtful that anything was damaged. Everything

   you observed appears to be the byproduct of soggy

   batteries.



   Bob . . .

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Wed Oct 29, 2008 8:07 am Post subject: Re: Dynon EFIS & EMS power on the main bus

 	  jeffrey_davidson(at)earth wrote: 	
		  

Thanks for any light you can shed on this.  Next time, I'll move the fuel selector from the Off position!



Jeff Davidson (still an electrical newbie)

CH601-HD w/Jabiru3300A 	




I'm not going to address the whole avionics master switch issue. What concerns me is what sounds like a limited life on the Dynon internal battery.



I've heard stories of people getting them, taking them out of the box or testing them during the building process and then not turning them off properly and when the plane's power is disconnected  they think there is a power outage and just drain the internal battery.

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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

DaveG601XL

Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh

Posted: Wed Oct 29, 2008 9:23 am Post subject: Re: Dynon EFIS & EMS power on the main bus

Yeah, I wonder if your Dynon battery was fully charged prior to this exercise.    On a typical Jabiru start with a charged main battery, my Dynon D180 does not even see low enough main voltage to go on the internal battery.  This is mainly due to the rapidity with which the Jabiru normally starts.  Now that it is cold, and I did not richen up my idle mixture screw, it took me about 6 cranks to get started the other day.  Towards the end, my Dynon told me that it was going on internal battery during the cranks.  Even without an internal battery, Dynon emphatically says that it is no problem to have it hooked live to the main bus during cranking.



Good luck,

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_________________
David Gallagher
Cincinnati, OH area

longg(at)pjm.com
Guest

Posted: Wed Oct 29, 2008 12:14 pm Post subject: Dynon EFIS & EMS power on the main bus

My Dynon cable has 3 power leads which I assume is done in an effort to

alleviate this issue. Cable is from http://approachfaststack.com/



1. Main bus (DC primary power switch)

2. Essential bus (or alternate backup source)

3. Battery bus (or always on connection)



I have not experienced this behavior. If I start the Dynon while sitting

with the power off, I get the message, but If I add ship power I do not

get another message that it is on ship power. By pressing any button

then Next->Next->Info you can monitor the battery charge and the ships

battery level. 



Did you connect the always on lead to your battery bus?



--

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jeffrey_davidson(at)earth
Guest

Posted: Thu Oct 30, 2008 6:31 am Post subject: Dynon EFIS & EMS power on the main bus

I USE THE DIGEST VERSION OF THE LIST SO I’LL RESPON EN MASS.  THE CAPITALS ARE NOT SHOUTING, JUST SO YOU CAN EASILY FIND MY RESPONSES.  THANKS TO EVERYONE FOR THEIR INPUT.

Jeff



Gig wrote:

“I'm not going to address the whole avionics master switch issue. What concerns me is what sounds like a limited life on the Dynon internal battery.  I've ….. just drain the internal battery.”  NOT THE SITUATION HERE.  THE DYNONS ARE FINE.



Dave wrote:

“Yeah, I wonder if your Dynon battery was fully charged prior to this exercise.  On a typical Jabiru start ……., Dynon emphatically says that it is no problem to have it hooked live to the main bus during cranking.”  THE DYNON BATTERY WAS NOT FULLY CHARGED.  



Longg wrote:

“My Dynon cable has 3 power leads which I assume is done in an effort to alleviate this issue. Cable is …….. Did you connect the always on lead to your battery bus? THE DYNON KEEP ALIVE IS NOT CONNECTED SINCE I’M JUST FINISHING BUILDING AND NOT FLYING REGULARLY.  THE MAIN IS ALSO NOT ON A LOT SO THE DYNON BATTERY IS ONLY CHARGING SPORADICALLY.



Bob Wrote:

“You need to repeat the experiment with a known-good ship's battery and fully charged stand-by batteries. It's doubtful that anything was damaged. Everything you observed appears to be the byproduct.”  SOUND ADVICE.  WITH A LITTLE FUEL I EXPECT IT TO RUN!

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