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Dual Alternator, Dual Battery, Single Bus

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dbrown2(at)nycap.rr.com
Guest

Posted: Sun Jan 25, 2015 7:59 am Post subject: Dual Alternator, Dual Battery, Single Bus

Hello Bob,

My project will have a dual electronic ignition and an all-electric panel. I intend to have the two battery and individual battery buses per your Figure Z-30. I will have a single power bus that is supplied by a 60 amp main alternator (Plane Power AL12-C60) with a 30 amp backup alternator (Plane Power FS1-14). The B-leads from both alternators are connected through a Maxi fuse block to the hot side of the starter contactor which then goes through the firewall to the bus. 

I have some questions:

<![if !supportLists]>1)      <![endif]>The 6 AGW B-leads from the alternators can easily carry 80 amps. Can I protect the both leads with 80 amp Maxi fuses? I believe I might have read that this is okay in the List FAQs.

<![if !supportLists]>2)      <![endif]>According to Hartzell Engine Technologies (new owners of Plane Power alternators) the main alternator puts out 14.2 v and the backup puts out 13.6 v so if the main drops below 13.6 v the backup takes over.   Their wiring diagram does not show a diode in the circuit to stop the flow of electricity from the bus to the B-terminal of the backup alternator. I thought that this may affect the backup alternators life but the technician at HET said not to worry about it. If I was really concerned I could turn the field off on the backup under normal operation and turn it on in the event of a low voltage indication. I prefer the automatic takeover of the backup so my question is this,  do I need to have a diode in the circuit to block the reverse flow to the backup alternator or is the 0.6 v potential no big deal? If it is prudent to add the diode what type of diode do you recommend?

<![if !supportLists]>3)      <![endif]>I also think I remember reading in the List FAQs (but can’t seem to find it) that in the event of the battery contactor opening and disconnecting the battery from the bus, a load on the bus could cause precipitous failure of the alternator. It would be nice to have a battery contactor open indicator light. What is the best way to add such a device to your dual battery circuit?

Thanks,

Dan

   [quote][b]

dbrown2(at)nycap.rr.com
Guest

Posted: Mon Jan 26, 2015 3:24 am Post subject: Dual Alternator, Dual Battery, Single Bus

Thanks Bob,

 

 	  Quote: 	
		    As long as you don't have 250w incanescant landing lights

  or an electro-hydraulic pump system, transient loads

  capable of stalling a self-excited alternator don't

  exist. Further, since you're running dual batteries,

  you'd have to crap two contactors to set that scenario

  up.

I do have an electro-hydraulic pump for the landing gear but I get your point about the two battery contactors. I will make sure I do a contactor check during run-up to ensure that I am not flying around with one of them failed.
	


 

 	  Quote: 	
		    What does your power distribution look like. What electro-whizzies

   from which which busses?

I am still working on that but basically its electronic ignition, fuel pump, clock and system memories, cabin lighting and 12v outlets split between the two battery buses and everything else on the main bus. The last time I tried to estimate the total load I came up with about 40 amps with everything I plan to equip my plane with on at the same time. If my estimate is correct I could probably run my full suite of goodies with the 30 amp aux alternator. If I find that my system want much more than 30 amps during normal cruise will install a contactor that cuts the power to non-essential equipment and reduces the load to <30 amps.
	


 

This brings up another question. I already have a contactor, that I have named avionics contactor, conveniently locate by the power bus. Traditionally I believe its intent was to turn off all the sensitive and expensive avionics during engine startup and such to protect them from power spikes or surges. At least that’s what I was told. I was also more recently told that modern avionics, with their internal protection, do not need such isolation. If that is the case I would like to use my avionics contactor as the non-essential equipment switch cited above.  Is it true that the avionics switch is a thing of the past?

 

Thanks again,

Dan

   [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1933
Location: Riley TWP Michigan

Posted: Mon Jan 26, 2015 10:19 am Post subject: Re: Dual Alternator, Dual Battery, Single Bus

 	  Quote: 	
		  Is it true that the avionics switch is a thing of the past? 	


Here is a quote from SkyView Pilotâ€™s User Guide - Revision Q

 	  Quote: 	
		  SkyViewâ€™s robust power protection allows it to be powered on during engine start. 	


And here is a quote from the Dynon D-180 user guide:

 	  Quote: 	
		  It is acceptable to have the FlightDEK-D180 turned on during engine start. 	


My RV-12 does have an avionics switch, but only because I had to build the plane exactly per the plans in order to register it as E-LSA.  But I never shut it off, even during engine start.  The Garmin SL-40 and GTX-327 and GPS496 and Dynon D-180 all still work fine.  I probably should exercise the avionics switch occasionally to remove corrosion on the contacts.

An avionics switch is a single point of failure.

Joe

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1933
Location: Riley TWP Michigan

Posted: Mon Jan 26, 2015 10:46 am Post subject: Re: Dual Alternator, Dual Battery, Single Bus

Here is link to Bob Nuckolls article about the avionics master switch.

http://www.aeroelectric.com/articles/avmaster.pdf

_________________
Joe Gores

dbrown2(at)nycap.rr.com
Guest

Posted: Mon Jan 26, 2015 1:21 pm Post subject: Dual Alternator, Dual Battery, Single Bus

Thanks Joe,

That article rings of a familiar tone. Maybe that where "I was also more

recently told that modern avionics, with their internal protection, do not

need such isolation."

Dan



--

ARGOLDMAN(at)aol.com
Guest

Posted: Tue Jan 27, 2015 1:46 pm Post subject: Dual Alternator, Dual Battery, Single Bus

Actually,

  

 That information came from a conversation that I had with Dynon's Tec.  When I asked him how do I monitor my oil pressure ect on startup he told me  about starting the engine on the backup battery.

  

 So if you start the engine with the skyview attached to the system bus and  you get the electronic glitch that would reboot your system, by the time it  reboots and is able to give you an oil pressure reading you may have toasted  your engine. Are they just talking about the starting draw decreasing the  voltage to the point of resetting or the transients caused by starting when they  talk about the use of auxiliary power on startup. My understanding, possibly  wrong is that the dynon battery is automatically connected in the case of low  voltage. If low voltage is the case, does the switchover happen quickly enough  to prevent the reboot? If a transient situation does the small aux battery have  the capability to filter it out?

  

 Additionally the installation/operation instructions for the ICOM A-200  (not really an ancient radio) state,

  

 "Do not turn the power on until after the aircraft engines  have been started. This is important for the protection of the  circuit."

  

 If you are concerned about single point failure, nothing stops you from  having a duplicate avionics switch. I have duplicate fuel pump  switches (located in different places).

  

 Rich

  

  In a message dated 1/27/2015 9:50:01 A.M. Central Standard Time,  fransew(at)gmail.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "user9253"    <fransew(at)gmail.com>

 	  Quote: 	
		   TO MINIMIZE THE CHANCE OF THE SYSTEM    RESETTING DURING ENGINE CRANKING, THE OPTIONAL REDUNDANT (DIODE OR'D) POWER    INPUTS MAY BE CONNECTED TO AN AUXILIARY BATTERY . . .OR STABILIZED POWER    INPUT. . .


	


The Garmin manual does not recommend using backup power    during engine start.  It says that OPTIONAL backup power MAY be    used.

Both Garmin and Dynon say that having optional backup power will    prevent rebooting during engine cranking, which I think is a good idea because    rebooting is annoying.  But neither company says that not having backup    power will damage their units.  And neither company recommends    disconnecting their units from the aircraft electrical system during engine    starting.

  The point that I am trying to make is that an avionics    master switch to protect avionics is unnecessary.  Installing an avionics    master switch introduces a single point of failure.  If that switch    fails, avionics go dark.

Joe



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 [quote][b]

jmjones2000(at)mindspring
Guest

Posted: Tue Jan 27, 2015 2:09 pm Post subject: Dual Alternator, Dual Battery, Single Bus

I would be interested in looking at the circuitry of the standby battery from dynon. Does anyone know if there is a diode that allows current to flow from the standby battery to the dynon but not back into the battery? 

Seems that you would either have a need for a replacement standby battery, or you would have a need to recharge the dynon battery somehow (if it were rechargeable) when the standby battery dies. 

Justin



 



On Jan 27, 2015, at 12:44, ARGOLDMAN(at)aol.com (ARGOLDMAN(at)aol.com) wrote:

[quote]     Actually,

  

 That information came from a conversation that I had with Dynon's Tec.  When I asked him how do I monitor my oil pressure ect on startup he told me  about starting the engine on the backup battery.

  

 So if you start the engine with the skyview attached to the system bus and  you get the electronic glitch that would reboot your system, by the time it  reboots and is able to give you an oil pressure reading you may have toasted  your engine. Are they just talking about the starting draw decreasing the  voltage to the point of resetting or the transients caused by starting when they  talk about the use of auxiliary power on startup. My understanding, possibly  wrong is that the dynon battery is automatically connected in the case of low  voltage. If low voltage is the case, does the switchover happen quickly enough  to prevent the reboot? If a transient situation does the small aux battery have  the capability to filter it out?

  

 Additionally the installation/operation instructions for the ICOM A-200  (not really an ancient radio) state,

  

 "Do not turn the power on until after the aircraft engines  have been started. This is important for the protection of the  circuit."

  

 If you are concerned about single point failure, nothing stops you from  having a duplicate avionics switch. I have duplicate fuel pump  switches (located in different places).

  

 Rich

  

  In a message dated 1/27/2015 9:50:01 A.M. Central Standard Time,  fransew(at)gmail.com (fransew(at)gmail.com) writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "user9253"    <fransew(at)gmail.com (fransew(at)gmail.com)>

 	  Quote: 	
		   TO MINIMIZE THE CHANCE OF THE SYSTEM    RESETTING DURING ENGINE CRANKING, THE OPTIONAL REDUNDANT (DIODE OR'D) POWER    INPUTS MAY BE CONNECTED TO AN AUXILIARY BATTERY . . .OR STABILIZED POWER    INPUT. . .


	


The Garmin manual does not recommend using backup power    during engine start.  It says that OPTIONAL backup power MAY be    used.

Both Garmin and Dynon say that having optional backup power will    prevent rebooting during engine cranking, which I think is a good idea because    rebooting is annoying.  But neither company says that not having backup    power will damage their units.  And neither company recommends    disconnecting their units from the aircraft electrical system during engine    starting.

  The point that I am trying to make is that an avionics    master switch to protect avionics is unnecessary.  Installing an avionics    master switch introduces a single point of failure.  If that switch    fails, avionics go dark.

Joe



--------

Joe    Gores





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  	  Quote: 	
		  

	


[b]

ARGOLDMAN(at)aol.com
Guest

Posted: Tue Jan 27, 2015 7:45 pm Post subject: Dual Alternator, Dual Battery, Single Bus

Dynon--personal contact with the dynon tech rep when I was designing the  electrical of my craft.

  

 Icom from the installation manual

  

 Rich

  

  In a message dated 1/27/2015 5:47:12 A.M. Central Standard Time,  fransew(at)gmail.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "user9253"    <fransew(at)gmail.com>

 	  Quote: 	
		   The below not withstanding, Dynon    recommends starting and stopping the engine with the /Skyview not connected to    the ships buss. They recommend starting the engine on the skyview backup    battery so that you can see the engine instruments and connecting to the ships    power after start. What do they know that we don't? 

 Rich


	


Where    did you read that?  Please post a link to Dynon manual and page.    



The Dynon SkyView PilotÃ¢â‚¬â„¢s User Guide - Revision Q  page 2-1    says, "SkyViewÃ¢â‚¬â„¢s robust power protection allows it to be powered on during    engine start."

According to Bob's teachings, there are no high voltage    spikes during engine starting.  The only concern is a brownout.     Dynon's SkyView automatically switches to its own backup battery during    brownout conditions.  No action is required by the pilot as the power    transfer is automatic.

Joe

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 [quote][b]

ARGOLDMAN(at)aol.com
Guest

Posted: Tue Jan 27, 2015 7:46 pm Post subject: Dual Alternator, Dual Battery, Single Bus

Puts my mind at ease about the dynon-- now just to think of the icom

  

 Rich

  

  In a message dated 1/27/2015 6:13:28 A.M. Central Standard Time,  fransew(at)gmail.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "user9253"    <fransew(at)gmail.com>



Below is a quote from SkyView System    Installation Guide - Revision R page 2-5.

 	  Quote: 	
		   SkyView Can Be On    During Engine Start SkyView units incorporate robust power protection that    allows them to be powered on during engine start for full engine monitoring.    SkyView displays require a minimum of 10V, and during engine start, itÃ¢â‚¬â„¢s    common for the electrical system to temporarily drop below 10V. If an SV-BAT-    320 backup battery is not installed, SkyView may shut off / reboot. If you    wish to monitor your engine prior to engine start, an SV-BAT-320 backup    battery should be installed so that the SkyView display can switch to the    SV-BAT-320 when its power inputs are not receiving at least 10V. The SkyView    display will switch from SV-BAT-320 to shipÃ¢â‚¬â„¢s power when its power inputs    receive voltage above 10V.


	




--------

Joe    Gores





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 [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1933
Location: Riley TWP Michigan

Posted: Tue Jan 27, 2015 8:33 pm Post subject: Re: Dual Alternator, Dual Battery, Single Bus

Here is a link to the http://tinyurl.com/SkyView-User-Guide

Kellym gives a good explanation in a separate thread.

It is not an electronic glitch that reboots the SkyView, but is low voltage caused by the heavy starter load.  Aircraft system voltage during engine cranking can drop down to 8 volts or so.  The Dynon needs 10 volts or else it shuts off.  The SkyView then reboots when the aircraft system rises above 10 volts.  But if the SkyView has a backup battery, it automatically switches to that instead of rebooting.  The switch over is instantaneous.  The SkyView, like any electrical load, will draw current from the highest voltage source that is available.  There are no significant voltage spikes (transients) caused by engine starting that would cause the SkyView to reboot.  The Skyview backup battery is isolated from the aircraft electrical system and is recharged by the SkyView.

Joe

_________________
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