Return-Path: Received: from fed1rmmtao01.cox.net ([68.230.241.38] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 143167 for flyrotary@lancaironline.net; Mon, 07 Jun 2004 14:59:09 -0400 Received: from BigAl ([68.107.116.221]) by fed1rmmtao01.cox.net (InterMail vM.6.01.03.02 201-2131-111-104-20040324) with ESMTP id <20040607185838.FFOY29317.fed1rmmtao01.cox.net@BigAl> for ; Mon, 7 Jun 2004 14:58:38 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Average vs Instanteous Power was Re: LS1 Coils - amp draw? Date: Mon, 7 Jun 2004 11:58:40 -0700 Message-ID: <000001c44cc1$72c46850$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C44C86.C6659050" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C44C86.C6659050 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 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. =20 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. =20 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? =20 Thanks, =20 Al =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 =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. =20 Ed=20 =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 =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. =20 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. =20 Al =20 ------=_NextPart_000_0001_01C44C86.C6659050 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
=
=

 

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?

 

Thanks,<= /font>

 

Al

 

 

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??). 

 

 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 =

 

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. 

 

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

 

------=_NextPart_000_0001_01C44C86.C6659050--