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Big load on BAT BUS

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Apr 23, 2010 10:31 pm Post subject: Big load on BAT BUS

In an attempt to keep redundant critical items from the same bus, I have placed the fuse (10-15 amp) for my EFI injectors on the Bat Bus. 

However, this violates BoB N's limit of <7a on that bus. How does one deal with this? I would like to keep it on the Bat Bus so if both alts go down, my plane doesn't. I know it's unlikely, but if I'm on the back up alt, I'd still like to know that the Bat is in reserve. 



The sister fuse is on the E-bus.



Also, the feed from the bat to the bat bus is about 20". It will come through the FW with a bundle of wires in firesleeve via a "towel bar" pass through. I am contemplating sheathing it in SS braid for crash protection. Good or bad idea? Effective or no?



John

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Apr 23, 2010 10:38 pm Post subject: Re: Big load on BAT BUS

Never mind about the SS sleeve question. It will only be a 10 gauge wire and I will 18 ga fuselink it at the battery.



J

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 24, 2010 6:08 am Post subject: Big load on BAT BUS

At 01:31 AM 4/24/2010, you wrote:

 	  Quote: 	
		  



In an attempt to keep redundant critical items from the same bus, I 

have placed the fuse (10-15 amp) for my EFI injectors on the Bat Bus.

However, this violates BoB N's limit of


	


   Then you need a "mini-contactor" at the battery

   bus as illustrated in Z-32, except that the

   feeder is for the EFI instead of the E-bus.



   It would be nice if it were a solid state

   relay. I believe Eric Jones still offers

   on.



   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 24, 2010 7:08 am Post subject: Big load on BAT BUS

At 01:38 AM 4/24/2010, you wrote:

 	  Quote: 	
		  



Never mind about the SS sleeve question. It will only be a 10 gauge 

wire and I will 18 ga fuselink it at the battery.


	


    This sounds like another "loose cannon"

    implementation of fusible links. Fusible

    links are ROBUST circuit protection and should

    never be used in an always-hot feeder from

    a battery.  If you've attached a wire to

    a battery that calls for this kind of circuit

    protection, it should enjoy upstream, crew-

    controlled management of power.



    As a general rule, please do not add fusible

    links to any application not already illustrated

    in the Z-figures without discussing it here

    on the List . . . and I can tell you in advance

    there's a 90+ percent chance that the proposed

    application is not recommended.



    Always-hot feeders should be breakered at

    5A or less, fused at 7A or less. Anything

    larger should still take a fuse or breaker

    but CONTROLLED IMMEDIATELY ADJACENT to

    the bus with a relay like that shown in Z-32.



    Bob . . .

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klehman(at)albedo.net
Guest

Posted: Sat Apr 24, 2010 7:23 am Post subject: Big load on BAT BUS

There are details that aren't mentioned but I would be cautious with 

this. I'd only recommend an additional mini contactor if it is truly 

redundant and can't fail the engine. Risk from engine stoppage is likely 

far higher than the risk from electrical fire. Other considerations 

might be whether the EFI system already has a relay to supply injector 

power - many do have an ecu controlled relay that might be easily placed 

near the battery. Or is there a mechanical switch in the injector 

circuit - there is in my system and it is close to the battery which is 

under the instrument panel. The 10 amp fuse is at the battery.

Ideally a redundant engine control system would be powered by its own 

power source with no shared wiring.

To understand where I am coming from, understand that the so called 

"redundant" electronic engine systems that I've examined do not come 

close to true redundancy. Most do not have dual injectors and most share 

a single feed to the injectors.

Ken

Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)aeroelectric.com>

 At 01:31 AM 4/24/2010, you wrote:

> 

> <jonlaury(at)impulse.net>

>

> In an attempt to keep redundant critical items from the same bus, I 

> have placed the fuse (10-15 amp) for my EFI injectors on the Bat Bus.

> However, this violates BoB N's limit of

   Then you need a "mini-contactor" at the battery

   bus as illustrated in Z-32, except that the

   feeder is for the EFI instead of the E-bus.

   It would be nice if it were a solid state

   relay. I believe Eric Jones still offers

   on.

   Bob . . .

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Sat Apr 24, 2010 8:03 am Post subject: Re: Big load on BAT BUS

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 01:38 AM 4/24/2010, you wrote:

 	  Quote: 	
		  



Never mind about the SS sleeve question. It will only be a 10 gauge 

wire and I will 18 ga fuselink it at the battery.



	


    This sounds like another "loose cannon"

    implementation of fusible links. 

    Bob . . . 	




Admittedly, it is. And that is why I "disclosed" what I was going to do. It seemed like a good idea. The feedback here is invaluable as is an occasional slap upside the head

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 24, 2010 6:36 pm Post subject: Big load on BAT BUS

 	  Quote: 	
		   >     This sounds like another "loose cannon"

 >     implementation of fusible links.

 >     Bob . . .

Admittedly, it is. And that is why I "disclosed" what I was going to 

do. It seemed like a good idea. The feedback here is invaluable as 

is an occasional slap upside the head 


	


   Naw, just a short "time out" in "now you

   know better corner".  Folks on this List

   strive to be gentle but clear teachers. This

   should be an experience of discovery not

   of discomfort. Thanks for sharing.



   Bob . . .

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Wed Apr 28, 2010 8:19 am Post subject: Re: Big load on BAT BUS

 	  klehman(at)albedo.net wrote: 	
		  There are details that aren't mentioned but I would be cautious with 

this. ..snip...



To understand where I am coming from, understand that the so called 

"redundant" electronic engine systems that I've examined do not come 

close to true redundancy. Most do not have dual injectors and most share 

a single feed to the injectors.



Ken



	




Ken,



Thanks for your observations and I'm sorry for the delayed response. My ISP has been down for awhile. It's not often that we have rain and low temps in April in Central Calif and the wireless system antenna on a 6500' peak took a load of ice and collapsed.



My EFI system is the quasi-redundant type that you referred to. A single ECU, injectors, TPS, etc. I inquired about "dualing" up the system but they said that they had tried that and that the result, because of the additional complexities, was a far less reliable system than the single system. SDS has accumulated 15,000+ flight hours, over 12,000,000 ground ops hours and bench top set up that has been firing away, 24/7, for years, all without a single equipment failure that was not caused by customer wiring/installation errors. MTBF far exceeds that of any reciprocating engine. I decided that the track record that Simple Digital Systems has accumulated gave me sufficient confidence to run the single system.

BUT... as long as I had multiple sources of power (2 alts, 1 bat), I wanted to hedge my bets by connecting my single EFI to all 3, via  Z-13. The Z-32 contactor add-on will be the third power source after losing two alternators.



John

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