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2nd LSE Standby Power.

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andymeyer

Joined: 31 Mar 2015
Posts: 54
Location: SW MI

Posted: Thu Feb 01, 2024 11:44 am Post subject: 2nd LSE Standby Power.

Have a pretty solid electric system derived from the Z diagrams on my EZ.

Going to dual electronic ignition and have high confidence in 2 alternators and a battery, but want a standby "get me down" battery since my 2nd alternator is an SD8 and it doesn't make power when the RPM is pulled back. 



Switch shown here is a progressive switch. Off (down) is off. Up is normal main bus providing power to the ignition and charge current to the standby small battery. Middle position is isolating the ignition to a ~5ah 12V battery (EarthX or similar). Diode keeping electrons flowing to the ignition and not the rest of the world.



Have I missed anything? Thought was if the world is going to hell, One switch and I've got that ignition isolated and powered. Probably never use it, but...



Thoughts?



Andy

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Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Thu Feb 01, 2024 1:40 pm Post subject: 2nd LSE Standby Power.

On Thu, Feb 1, 2024 at 1:48 PM andymeyer <meyerkc135(at)gmail.com (meyerkc135(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "andymeyer" <meyerkc135(at)gmail.com (meyerkc135(at)gmail.com)>

 

 Have a pretty solid electric system derived from the Z diagrams on my EZ.

 Going to dual electronic ignition and have high confidence in 2 alternators and a battery, but want a standby "get me down" battery since my 2nd alternator is an SD8 and it doesn't make power when the RPM is pulled back. 

 

 Switch shown here is a progressive switch. Off (down) is off. Up is normal main bus providing power to the ignition and charge current to the standby small battery. Middle position is isolating the ignition to a ~5ah 12V battery (EarthX or similar). Diode keeping electrons flowing to the ignition and not the rest of the world.

 

 Have I missed anything? Thought was if the world is going to hell, One switch and I've got that ignition isolated and powered. Probably never use it, but...

 

 Thoughts?

 

 Andy

	
My personal thought process is to have engine 'stuff' isolated from airframe stuff as much as possible, so 'off nominal' operation comes closer to our training. I don't see what EI is being used, but most systems advise tying their power source directly to the airframe battery bus. That gets it away from the airframe circuitry, and keeps power available even with the Master off.

FWIW, if you have a main (big) alternator, plus the SD8, plus the main battery, adding another battery is a belt on suspenders on a belt on a.....



If I felt a real need to add battery redundancy, I'd consider a pair of diode isolated switches feeding the ignition; one from each battery. Using a single switch to select battery source creates a single point of failure if the switch fails mechanically. It also raises potential operational issues during off-nominal, because we tend to see switches as two-state devices. Might not be a big issue for the builder, but could bite anyone else flying the plane.

Hope that's of some use,

Charlie



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Charlie

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Thu Feb 01, 2024 7:07 pm Post subject: Re: 2nd LSE Standby Power.

I agree with Charlie about using 2 separate switches.

Put dots on your schematic at wire junctions.

The diode is backwards.

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Joe Gores

Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Sat Feb 03, 2024 7:40 am Post subject: 2nd LSE Standby Power.

On Thu, Feb 1, 2024 at 9:11 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



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

 

 I agree with Charlie about using 2 separate switches.

 Put dots on your schematic at wire junctions.

 The diode is backwards.

 

 --------

 Joe Gores



	
I thought the same thing about the diode, but after studying the action of the switch, I think he has the diode oriented correctly for that desired function. I still think separate switches make more sense, though. 



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Charlie

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Feb 03, 2024 11:53 am Post subject: Re: 2nd LSE Standby Power.

You are right Charlie.  I was wrong.  I mistakenly thought the battery was 

supposed to supply power to the main bus.  Below are two schematics.

The top one functions the same as the OP's.  The bottom schematic is simpler 

but accomplishes the same goal.

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Joe Gores

andymeyer

Joined: 31 Mar 2015
Posts: 54
Location: SW MI

Posted: Sat Feb 03, 2024 4:25 pm Post subject: Re: 2nd LSE Standby Power.

Lightspeed Ignition. Klaus recommends that #1 be tied to the battery - it is.

#2 can be tied to the main or essential bus. This circuit is only for #2.



Thought here is that it's a single switch (less failure points - arguable... More complex switch.) Master switch is progressive - alternator issue - click down to the center position. This switch would have the same mentality. It'd also never be a "Boldface switch flip"  unless all power went away on the aircraft (Battery dead short, took out alternator and backup alternator - too many failures in that chain for this to be boldface.)



Any circuit issues with this design, along with a diode recommendation?  



Diode reversed. Whoops - sorry about that. Fixed...



Thanks!



Andy

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andymeyer

Joined: 31 Mar 2015
Posts: 54
Location: SW MI

Posted: Sat Feb 03, 2024 5:15 pm Post subject: Re: 2nd LSE Standby Power.

Joe,



You mangled my schematic and made it better. I had the diode in the wrong spot. In you configuration, in the top switch position, the engine keeps running if the battery bus dies, runs off of the standby battery. In my drawing it didn't.



Thank you! I think that's my implementation. I want to be able to get the 2nd igntiion as far away from anything else as possible, and that configuration does exactly that.



Thank you for the diode recommendation as well - perfect.

Thanks!



Andy

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user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Feb 03, 2024 8:17 pm Post subject: Re: 2nd LSE Standby Power.

While the main alternator is running, the 5AH standby battery should be 

connected to the main bus to keep the standby battery charged.

My last schematic accomplishes that with only a diode.  There is no concern

of parasitic aux battery drain because the diode has infinitesimal reverse leakage current. 

If the switch is closed, Ignition 2 will draw current from the source with the

highest voltage, which is normally the main bus, not the aux battery.

The definition of infinitesimal is the distance that an aircraft carrier sinks 

into the water when a house fly lands on its deck.

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