Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 143256 for flyrotary@lancaironline.net; Mon, 07 Jun 2004 16:17:05 -0400 Received: from EDWARD (clt25-78-058.carolina.rr.com [24.25.78.58]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i57KG2fP020818 for ; Mon, 7 Jun 2004 16:16:03 -0400 (EDT) Message-ID: <004f01c44ccc$45335d50$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Average vs Instanteous Power was Re: LS1 Coils - amp draw? Date: Mon, 7 Jun 2004 16:16:08 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_004C_01C44CAA.BDED3FD0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_004C_01C44CAA.BDED3FD0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message-----=20 =20 =20 Al, not Tracy, but I think what Tracy is saying that in the = milliseconds or so it takes the EC2 to calculate the proper coil dwell = time it is possible for a coil(s) to draw up to 9 amps (or perhaps even = 27 amps in your case). The instantaneous power in that case would be = 27*12 =3D 324 watts IF that current drain remained for as much as 1 = second (actually probably less because when cranking you probably would = not have more than 10 volts). However, I believe the duration of that = surge is much shorter duration. IF I am correct then I suspect your 16 = gauge wire is more than adequate because of the very short time interval = in which this happens (I'm guessing that situation does not last for = even 100 milliseconds, Tracy??).=20 If that is the case then the power (which is what we are really = concerned about) per second would be 1/10*27*12 =3D 32.4 watts average = power consumed during that time. The very conservative Power = transmission (bundled) for 16 gauge is 3.7 amps x 12 volts =3D 44.4 = watts. Therefore, IF the surge is l00 milliseconds duration or less then = it would appear you wiring is more than adquate. Now if the surge = condition can actually last for as long a second then its a different = story. Ed=20 Ed; You've got that right, but I guess I wasn't really clear on what = my concern is. I'm not necessarily worried about the #16 wire being = seriously overheated by the draws of the coils. I'm worried about being = able to safely protect that circuit against a different failure - like a = short - and not have a condition that will continue to blow the = appropriately sized fuse, or trip a breaker. =20 On the broader view, I think a potential spike of close to 70 amps = on my engine critical bus is not acceptable; so I think we need to hear = from Tracy before carrying this any further, and see that we are not off = the track here. And I don't want to be redesigning my electrical system = at this point. In my particular case; the engine critical leads are protected by = fuses; for the reasons John paraphrased from Bob Nuchols; but also for = maximum reliability. The power to my breaker buses goes through the = master switch solenoid. Go directly from the battery(ies) to the engine = critical bus and eliminate a couple of single point failure modes. My = search for data led me to conclude that MTBF for properly sized fuses is = greater than for CBs. I wouldn't try to convince anyone that one way is = better than another; just that my logic lead me to this approach. I = would assert; however, that there should not be a circuit in my = airplane; unless it is one wire all by itself that could not damage = anything else if it melted, that is not suitably protected against a = possible short circuit. Not having protection in the engine critical = circuits, or having one breaker for all the circuits doesn't might that = criteria. So there is a fuse for each circuit; pump, leading ign, = trailing ign, primary injectors and secondary injectors. Al I agree, Al. Always better to make decision like this based on = real information rather than spectulation or back-of-the-envelope = scratchings. Ed ------=_NextPart_000_004C_01C44CAA.BDED3FD0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
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Al, = not Tracy,=20 but I think what Tracy is saying that in the milliseconds=20 or so it takes the EC2 to calculate the = proper coil=20 dwell time it is possible for a coil(s) to draw up to 9 amps (or = perhaps=20 even 27 amps in your case).   The=20 instantaneous=20 power in that case  would be 27*12 =3D 324 watts = IF=20 that current drain remained for as much = as 1=20 second (actually probably less because when cranking you probably = would=20 not have more than 10 volts).  However, I believe the = duration=20 of that surge is much shorter duration.  IF I am correct = then I=20 suspect your 16 gauge wire is more than adequate because of the = very short=20 time interval in which this happens (I'm guessing that situation = does not=20 last for even 100 milliseconds, Tracy??). 

 

 If that=20 is the case then the power (which is what we are really concerned=20 about) per second would be 1/10*27*12 =3D 32.4 watts average = power=20 consumed during that time.  The very conservative Power = transmission=20 (bundled) for 16 gauge is 3.7 amps x 12 volts =3D 44.4 watts. = Therefore, IF=20 the surge is l00 milliseconds duration or less then it would = appear you=20 wiring is more than adquate. Now if the surge = condition can=20 actually last for as long a second then its a different=20 story.

 

Ed=20

 

Ed;

You=92ve got that=20 right, but I guess I wasn=92t really clear on what my concern = is.  I=92m=20 not necessarily worried about the #16 wire being seriously = overheated by=20 the draws of the coils.  I=92m worried about being able to = safely=20 protect that circuit against a different failure =96 like a short = =96 and not=20 have a condition that will continue to blow the appropriately = sized fuse,=20 or trip a breaker. 

 

On = the broader=20 view, I think a potential spike of close to 70 amps on my engine = critical=20 bus is not acceptable; so I think we need to hear from = Tracy = before=20 carrying this any further, and see that we are not off the track=20 here.  And I don=92t want to be redesigning my electrical = system at=20 this point.

 

In my = particular case; the engine critical leads are protected by fuses; = for the=20 reasons John paraphrased from Bob Nuchols; but also for maximum=20 reliability.  The power to my breaker buses goes through the = master=20 switch solenoid.  Go directly from the battery(ies) to the = engine=20 critical bus and eliminate a couple of single point failure = modes. =20 My search for data led me to conclude that MTBF for properly sized = fuses=20 is greater than for CBs.  I wouldn=92t try to convince anyone = that one=20 way is better than another; just that my logic lead me to this=20 approach.  I would assert; however, that there should not be = a=20 circuit in my airplane; unless it is one wire all by itself that = could not=20 damage anything else if it melted, that is not suitably protected = against=20 a possible short circuit.  Not having protection in the = engine=20 critical circuits, or having one breaker for all the circuits = doesn=92t=20 might that criteria.  So there is a fuse for each circuit; = pump,=20 leading ign, trailing ign, primary injectors and secondary=20 injectors.

 

Al

 

 

I = agree,=20 Al.  Always better to make decision like this based on = real=20 information rather than spectulation or back-of-the-envelope=20 scratchings.

 

 

Ed

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