From: Dale Rogers <rogersda@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: LS1 Coils - amp draw?
Date: Mon, 7 Jun 2004 21:32:56 -0400
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---------------- original message:

> From: "Al Gietzen" <ALVentures@cox.net>
> Date: 2004/06/07 Mon AM 11:52:28 EDT
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: LS1 Coils - amp draw?
> 
> Tracy;
> 
> Well; the worry is this.  Safe wiring practice requires being able to
> protect the wire, especially if it is in a bundle or close proximity with
> other wires, against any failure which would overload the wire.  Running the
> numbers says that the maximum safe current for a 16 awg wire is 15 amps.  If
> I interpret you correctly; it is possible for my coil power lead to have to
> carry 27 amps (for 3 coils) for a short time, which would trip a breaker, or
> blow a fuse.  Under these conditions one can not properly protect the wire
> against a potential short - unless a much larger wire is used.  My wires run
> in a wiring duct, which isn't exactly a bundle, but the analysis says for 27
> amps in a bundle you need about a #10 wire.
> 
> Further; I went to great lengths to maintain the redundancy that you also
> strived for in the ECU with the dual controllers and the isolation switches.
> I have the engine critical bus connected to the dual battery system, and
> isolated by 40 amp diodes.  I think you're suggesting that it's possible for
> the coils to momentarily draw 54 amps (6 x 9), plus pump and injectors;
> maybe up to nearly 70 amps.  Ain't gonna work.
> 
> So what am I misunderstanding here, or how do we get around this?  Under
> what temporary condition can this high current exist?  Is there an
> operational sequence to avoid this possible condition?
 
Al,

   I'm not Tracy, but I do have some experience with wire 
and current draw.

   How about running a 10g wire from your source (essential 
bus?) to a fuse block with six stations.  Then connect one 
16g wire from each coil - supply side - to each of the six 
fuses.  Wires are protected, and the current draw is well 
within the limits for each wire used.  Plus, if you get a 
coil fault that blows the fuse, you only lose 1/6 of your 
fire.  This assumes, of course, that the ECM is controlling 
the injectors at the "ground" side.

Dale R.
COZY MkIV-R #1254