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Aux Battery Idea Was: Speaking of Aux Batteries

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Dave Saylor

Joined: 11 Jan 2015
Posts: 210
Location: GILROY, CA

Posted: Sun Sep 08, 2019 9:01 pm Post subject: Aux Battery Idea Was: Speaking of Aux Batteries

We're going to remodel our panel soon.  Some of the things I want to do better than the existing setup are to simplify operation, provide anti-sag for starting, and provide some backup power.



Most of the components I plan to install have main power and aux power inputs.  Aux power inputs (also called aircraft power 2, etc) would be powered from the aux (anti-sag) bus.  Almost everything on the aux bus would also be primarily powered from the main bus, and only be pulling from the aux when the main voltage is low.  That's all built in to the components.

I don't mind an extra battery, especially if I can convince myself that a small EarthX is something I can live with.  It does a few nice things, including limiting is charge rate.  But that's not what I'd like to discuss now.  I would like comments on this anti-sag idea.

I think separating the starter contactor coil from the main bus would eliminate the timeliness issue that Bob described:

  The 'trick' is all in the timing. Boost

  has to initiate before the starter

  contactor closes and needs to sustain

  past (1) rise in battery voltage due

  to expiration of inrush current or (2)

  contactor opening, which ever happens

  first. I'm fiddling with some ways to

  get that to happen.



Here's a work in progress.  Obviously not complete, no alternator shown, lot's of detail omitted, etc, but the starter contactor power is shown.  That's the key, unless I'm missing something.

Please ignore the current ratings.  They're not complete yet.  



--Dave

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--Dave
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user9253

Joined: 28 Mar 2008
Posts: 1928
Location: Riley TWP Michigan

Posted: Mon Sep 09, 2019 3:43 am Post subject: Re: Aux Battery Idea Was: Speaking of Aux Batteries

The starter contactor is normally energized by switching the positive wire.

It is dangerous to switch the negative wire.  If that wire ever gets shorted

to ground, the starter motor will spin the prop, causing damage or injury.

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Joe Gores

Dave Saylor

Joined: 11 Jan 2015
Posts: 210
Location: GILROY, CA

Posted: Mon Sep 09, 2019 11:00 am Post subject: Aux Battery Idea Was: Speaking of Aux Batteries

Good point, and easy enough.  Thanks!



On Mon, Sep 9, 2019 at 4:48 AM 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)>

 

 The starter contactor is normally energized by switching the positive wire.

 It is dangerous to switch the negative wire.  If that wire ever gets shorted

 to ground, the starter motor will spin the prop, causing damage or injury.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=491247#491247

 

 

 

 

 

 

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Dave Saylor

Joined: 11 Jan 2015
Posts: 210
Location: GILROY, CA

Posted: Mon Sep 09, 2019 12:03 pm Post subject: Aux Battery Idea Was: Speaking of Aux Batteries

Thanks Bob,



What is the cost of accidently leaving the aux battery on during start?  Is it just a sag, or does starter-sized current try to run through the small relay and associated wiring?  If the main is weak, will the aux battery work that much harder?  I'm concerned that a relatively simple mistake like leaving the aux batt on during start will do some damage.



(I've put switches in the wrong position before...)

--Dave



On Mon, Sep 9, 2019 at 10:13 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		     	  Quote: 	
		  

 Here's a work in progress.Â  Obviously not complete, no alternator shown, lot's of detail omitted, etc, but the starter contactor power is shown.Â  That's the key, unless I'm missing something. 	


   There are no 'timing' issues with using

   a second battery for brownout protection.

   Consider Z-35 for second battery and

   simply leaving the aux battery relay

   open until after the engine is running.



 

 

   Bob . . .

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