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Date: Tue, 14 Mar 2006 15:43:49 -0500
From: Chad Robinson <crj@lucubration.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Electrical requirements
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Ernest Christley wrote:
> EM/2 0.6A
> EC/2  0.3A
> Injectors/Coils 10A (@6000RPM)
> Fuel Pump-1 6.5A
> Fuel Pump-2 6.5A
> EWP-1 5A
> EWP-2 5A
> Landing Lights 10A
> LED Position Lights 3A
> LED Cockpit Lighting 1A
> Cockpit Circulation Fan 2A
> Transponder 0.5A
> Radio 1A
> CD Player 0.3A

Well, yeah, but those EWPs are doing real work in return for saving you that 
engine HP. So you have a 10A draw there. You're also counting two fuel pumps 
running  - are you actually going to cruise with both going? You'd probably 
have higher reliability if you switched back and forth, only running both for 
TO/landing and other critical times. That's another 5A.

I don't know about the injectors/coils but that number looks a bit high to me. 
You probably need to fuse it for at least that, but it's a pulsed load, so its 
average power draw is not going to be 10A*12v, the usual formula. It's going 
to be some smaller percentage of that. I don't have my formula books with me - 
maybe some geek (heh) can Google it, but the point is that it's probably less 
than that. (Unless 10A is what somebody measured?) Maybe knock another 2-3A 
out of that.

Right there that knocks out 17-18A of the load calculation. Not in YOUR case, 
since you're using an EWP and it'll draw what it draws, for instance. But 
that's a sacrifice you're making. =)

Regards,
Chad