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EFIS backup battery switch wiring

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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Nov 17, 2009 10:26 am Post subject: EFIS backup battery switch wiring

Hello 



I have an MGL Enigma EFIS and will put in a backup battery. In regular operation, both the main and backup battery are to be wired to the EFIS. The Enigma automatically switches to backup when it senses a main battery low voltage.



I was thinking of maybe some wiring of a 2-10 that would do the following:



Down position: main buss to EFIS. 



Middle position: backup battery to EFIS (for backup battery check)



Up position: both batteries to EFIS.



Or maybe just a two position switch, one position would be for both batteries, the other just to the backup. The backup check position could be a momentary on, I suppose, that just takes the main battery offline. Hold it in this position and see if the EFIS still works, then release.

_________________
Dan

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Nov 17, 2009 10:47 am Post subject: Re: EFIS backup battery switch wiring

Well, I got one possibility figured out using a 2-10. Figure attached.

Enigma EFIS backup switch wiring with 2-10.pdf

Description:

Download

Filename:

Enigma EFIS backup switch wiring with 2-10.pdf

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_________________
Dan

edleg

Joined: 11 Jun 2009
Posts: 14

Posted: Tue Nov 17, 2009 11:47 am Post subject: Re: EFIS backup battery switch wiring

With one switch you are putting all your eggs (and faith) in a single point of failure. What use is having emergency backup power if you can not use it if the only switch is broken?

dsvs(at)ca.rr.com
Guest

Posted: Tue Nov 17, 2009 12:25 pm Post subject: EFIS backup battery switch wiring

Dan,

Turn the master on, turn the EFIS on .  Turn the master off.  If EFIS remains on the systemn works.  

Don VS  RV7 flying

---- messydeer <messydeer(at)yahoo.com> wrote: 

 	  Quote: 	
		   

 

 Well, I got one possibility figured out using a 2-10. Figure attached.

 

 --------

 Dan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p 73310#273310

 

 

 

 

 Attachments: 

 

 http://forums.matronics.com//files/enigma_efis_backup_switch_wiring_with_2_10_162.pdf

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Nov 17, 2009 12:56 pm Post subject: Re: EFIS backup battery switch wiring

Turns out I had the wiring to the EFIS wrong. There are separate terminals for the backup and main power inputs, so I've redrawn it. It looks like if I forgot to turn off the EFIS switch, my backup battery would run dead. But I suppose I otta notice that my screen is still powered up. I would think that would be pretty obvious.

Enigma EFIS backup switch wiring with 2-10.pdf

Description:

Download

Filename:

Enigma EFIS backup switch wiring with 2-10.pdf

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 17, 2009 3:55 pm Post subject: EFIS backup battery switch wiring

 	  Quote: 	
		  I have an MGL Enigma EFIS and will put in a backup battery. In 

regular operation, both the main and backup battery are to be wired 

to the EFIS. The Enigma automatically switches to backup when it 

senses a main battery low voltage.



I was thinking of maybe some wiring of a 2-10 that would do the 

following . . .


	




   What does the manufacturer of the EFIS system

   recommend?

        Bob . . .



         ---------------------------------------

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

         ---------------------------------------

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Nov 17, 2009 4:28 pm Post subject: Re: EFIS backup battery switch wiring

Thanks, Bob.



From the manual: 



"...One power switch for the main incoming 12 or 24 V feed (switch in positive supply lead),

another for the backup battery.

In flight, both switches would be “on” allowing the charging of the backup battery.

Preflight check would involve switching main power on, then battery power on. Check of

battery power would involve switching main power off and verifying that Enigma continues

to operate. Voltage on the backup battery should be measured by means of the backup

voltage readouts which can be placed on any display..."



Imaged referred to attached.

MGL Enigma Odyssey installation.bmp

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2.42 MB

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_________________
Dan

edleg

Joined: 11 Jun 2009
Posts: 14

Posted: Tue Nov 17, 2009 7:11 pm Post subject: Re: EFIS backup battery switch wiring

In simple terms... if the backup battery is not on its own switch it won't charge. Two switches is simple. Trying to find a special switch to do all things at once leaves you with a non-common fix if it fails away from your home airport..... 



Two switches lets you troubleshoot power problems, and lets the EFIS be powered fully during a voltage drop, like during an engine start.

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Nov 17, 2009 7:36 pm Post subject: Re: EFIS backup battery switch wiring

Thanks, E., for bringing up the issue of single point of failure.  Hadn't thought about that, which makes me ask some questions about DPDT vs SPST switches.



 Looking at the schematic of a DPDT switch it looks like there are two circuits, an upper and a lower. Their terminals are separate but contained in the same housing. They also use the same lever and the mechanism the lever connects to that makes and brakes the contacts. 



If the only way a switch failed was through these shared components, then a DPDT would have the same reliability as a SPST, so there would be a single point of failure.



And if DPDT's never failed at these shared components, then having one DPDT would be just as reliable as having two SPST's, and there wouldn't be a single point of failure.



I'm sure the truth lies somewhere between these two extremes. If it turns out that a DPDT has 90% of the reliabilty as two SPST's, I might stick with just one DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider going with two switches.

_________________
Dan

retasker(at)optonline.net
Guest

Posted: Tue Nov 17, 2009 8:09 pm Post subject: EFIS backup battery switch wiring

The issue is not so much about what the relative reliability is.  The 

issue is that if the DPDT switch fails you may not be able to connect to 

either source of electrons.  If one of the SPST switches fails, you 

always have the other one.



Dick Tasker



messydeer wrote:

 	  Quote: 	
		   



 Thanks, E., for bringing up the issue of single point of failure.  Hadn't thought about that, which makes me ask some questions about DPDT vs SPST switches.



  Looking at the schematic of a DPDT switch it looks like there are two circuits, an upper and a lower. Their terminals are separate but contained in the same housing. They also use the same lever and the mechanism the lever connects to that makes and brakes the contacts. 



 If the only way a switch failed was through these shared components, then a DPDT would have the same reliability as a SPST, so there would be a single point of failure.



 And if DPDT's never failed at these shared components, then having one DPDT would be just as reliable as having two SPST's, and there wouldn't be a single point of failure.



 I'm sure the truth lies somewhere between these two extremes. If it turns out that a DPDT has 90% of the reliabilty as two SPST's, I might stick with just one DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider going with two switches.



 --------

 Dan





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 73392#273392

khorton01(at)rogers.com
Guest

Posted: Tue Nov 17, 2009 8:49 pm Post subject: EFIS backup battery switch wiring

What are the consequences of failure of both poles in that switch,  

given how you will operate the aircraft (day/night and VFR/IFR) and  

the backups you have installed?  If you are certain that you will be  

able to safely get the aircraft on the ground with an acceptable  

workload, then the potential single point failure is acceptable.



Kevin Horton



Sent from my iPod



On 2009-11-17, at 10:36 PM, "messydeer" <messydeer(at)yahoo.com> wrote:



 	  Quote: 	
		   

 >



 Thanks, E., for bringing up the issue of single point of failure.   

 Hadn't thought about that, which makes me ask some questions about  

 DPDT vs SPST switches.



 Looking at the schematic of a DPDT switch it looks like there are  

 two circuits, an upper and a lower. Their terminals are separate but  

 contained in the same housing. They also use the same lever and the  

 mechanism the lever connects to that makes and brakes the contacts.



 If the only way a switch failed was through these shared components,  

 then a DPDT would have the same reliability as a SPST, so there  

 would be a single point of failure.



 And if DPDT's never failed at these shared components, then having  

 one DPDT would be just as reliable as having two SPST's, and there  

 wouldn't be a single point of failure.



 I'm sure the truth lies somewhere between these two extremes. If it  

 turns out that a DPDT has 90% of the reliabilty as two SPST's, I  

 might stick with just one DPDT. If it has only 20% of the reliabilty  

 of two SPST's, I might consider going with two switches.



 --------

 Dan





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 73392#273392

jay(at)horriblehyde.com
Guest

Posted: Tue Nov 17, 2009 10:36 pm Post subject: EFIS backup battery switch wiring

There is one quite important thing to note, no matter how one wires the

switches (I used two DPST switches in the Sling - one for the power to the

Enigmas and one to the backup batteries)- that is that the backups will not

charge unless the voltage to them is sufficiently high.  Obvious of course,

but where this becomes a problem is if you have a diode between your main

bus and the e-bus.  You get a 0.7v drop across it and then there are some

voltage drops inside the Enigma and the backup batt gets a voltage of

between 12.5 -13v.  



To solve this we now run the aircraft with the e-bus alt feed permanently

on, which boosts the e-bus voltage back up sufficiently to charge the backup

battery.



Jay



--

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 18, 2009 7:04 am Post subject: EFIS backup battery switch wiring

When crafting your project's electrical system architecture

it would be helpful to be aware of the marketplace for

to which avionics suppliers deliver most of their products.

99.9% of all light aircraft built feature an architecture

that has not changed materially in 40+ years when the

avionics bus and master switch was added to protect

transistors from will-o'-the-wisp spikes.



Those same aircraft are largely owned and operated

by individuals who know little if any more about their

airplanes than they do about their cars. Further, even

if they knew and understood a great deal about them,

they would not be permitted by regulation to make

any meaningful improvements upon them. Phrases

like "failure tolerance", "meeting design goals",

and "artful preventative maintenance for maintenance

of system reliability" might just as well be spoken

in Swahili.



Now we have the starry-eyed entrepreneur who

tailors a product for best-fit into spam-can/

FAA-trained aviation. Not only is the product marketed

and sold as the greatest accessory since sliced bread,

it may include a suite of "back up" features designed

to ward of a host of failures uncomfortable to contemplate.



Internal back up batteries are popular. Keep in

mind that internal batteries MIGHT make sense in

the spam-can/FAA-trained world of flight . . . but

we're OBAM aviation. We can craft power sources that

are exceedingly robust. In fact so robust that

flight-critical systems are more likely to become

unavailable due to internal failure than for lack of

ship's power.



Staying true to our design goals for failure tolerance:

If your are PLANNING for any accessory to be critical

to comfortable completion of flight, then your plan-B

for failure of that device needs to go BEYOND any

need for ship's power. If you have a system like Z-13/8

(and assuming further that you exercise due diligence for

battery maintenance) then the probability of the E-bus

ever becoming un-powered in flight is on the same

order as prop bolt failure.



At the same time, probability of some flight critical

system going down for for reasons OTHER than power

failure is decidedly higher.



With that reasoning in mind I'll suggest that fussing

over the optimum back-up battery installation for any

accessory is a distraction from the real task of

crafting a failure tolerant system.



If it were my airplane, I'd go for Z-13/8, ditch the

internal back-up batteries and figure out how I'm

going to comfortably deal with a failure of the LEDs

that light up the screen or a rate sensor that goes

south, etc. etc.

        Bob . . .



         ---------------------------------------

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

         ---------------------------------------

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