Return-Path: Received: from fed1rmmtao02.cox.net ([68.230.241.37] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 145983 for flyrotary@lancaironline.net; Wed, 09 Jun 2004 12:10:48 -0400 Received: from BigAl ([68.107.116.221]) by fed1rmmtao02.cox.net (InterMail vM.6.01.03.02 201-2131-111-104-20040324) with ESMTP id <20040609161015.BMGA21686.fed1rmmtao02.cox.net@BigAl> for ; Wed, 9 Jun 2004 12:10:15 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: LS1 Coils - amp draw? Date: Wed, 9 Jun 2004 09:10:24 -0700 Message-ID: <000001c44e3c$45c725a0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C44E01.99684DA0" 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_01C44E01.99684DA0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Al=20 =20 Don't think it is a worry. All can be on for a short time (possibly = long enough to blow a fast acting fuse) but not long enough to heat a 16 ga = wire significantly.=20 Tracy =20 Tracy; =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 Oh darn, I knew this would happen.=20 =20 The momentary 9A load on each coil only lasts in the range of 50 - 100 milliseconds under worst case conditions during start sequence. There = is no way to avoid it but FWIW, it just isn't a problem. The 16ga wire would = not have time to get even warm. The specs you are discussing relate only = to long term events and do not address short term transients. =20 =20 Tracy =20 Tracy; =20 I am in full agreement that the short spike is of no concern to the = wire, even though I checked and find that I used #18 for the 3 coils; not #16. = It is a factor, not a problem, only in regard to circuit protection. As = I've said in another post, the wire needs to be protected against overload = for reasons other than the spike. And even in a broader sense, the spike is = not an issue - IF you know it's there and design the circuit and select components accordingly. I designed based on the info that I had that = the coils (all of them) drew 6-8 amps in normal operation. So a #18 wire = and 10-15 A circuit protection is fine. =20 If the spike really is only 50-100 ms then it still isn't much of an = issue, particularly for only 2 coils on the power lead. But John's 15A fuse = blew with 2 coils; which raised this issue. The average automotive 15A fuse = will blow at 20A steady, 30A for 1 second, 70-80 A for 100 milliseconds. = (The typical Time-Current Curve can be seen at http://www.bussman.com/library/bifs/2009.) There is, of course, a = tolerance on the current at which they melt; but John's fuse was either faulty, = there was some other reason that it blew, or the spike was higher and longer duration than we think. =20 I checked the Schottky bus isolation diodes that I installed, and they = are rated for 60A and should withstand up to about 400A for 100 ms, so = that's no problem. I need to consider what change, if any, to make on the fuse selection; so I'd appreciate whatever info you have, if any more than = you've already posted, on the startup spike; especially it's possible duration. = I assume the 9A max is pretty firm based on the coil circuit design. And = I'm curious when it happens - when the EC2 power is on and coils are on, or after you start cranking? =20 BTW; in the argument (sorry, discussion) of fuses vs CBs, this is a case where a CB has the advantage. They are slow acting, and will allow 10 = times there rating for up to a second. (See http://tycoelectronics.com/product/circuitbreaker/w2331_DS.pdf ). This = is more like a slo-blo fuse. I find that you can't get a slo-blo in a = blade type except in the "maxi" version, and then the lowest rating is 20A. = You can get them in the glass tube type. =20 Al =20 ------=_NextPart_000_0001_01C44E01.99684DA0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
=
=

Al =

 

Don't think it is a worry.   All can be on for a short time = (possibly long enough to blow a fast acting fuse) but not long enough to heat a 16 ga = wire significantly.=  

Tracy

 

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?

 

Thanks,<= /font>

 

Al

 

Oh darn, I knew this would = happen. 

 

 The momentary 9A load on each = coil only lasts in the range of 50 - 100 milliseconds under worst case = conditions during start sequence.  There is no way to avoid it but FWIW, it = just isn't a problem.   The 16ga wire would not have time to get = even warm.   The specs you are discussing relate only to long = term events and do not address short term = transients.  

 

Tracy

 

Tracy;

 

I am in full agreement that the = short spike is of no concern to the wire, even though I checked and find that = I used #18 for the 3 coils; not #16.  It is a factor, not a problem, only = in regard to circuit protection.  As I’ve said in another post, = the wire needs to be protected against overload for reasons other than the spike.  And even in a broader sense, the spike is not an issue = – IF you know it’s there and design the circuit and select components = accordingly.  I designed based on the info that I had that the coils (all of them) = drew 6-8 amps in normal operation.  So a #18 wire and 10-15 A circuit = protection is fine.

 

If the spike really is only = 50-100 ms then it still isn’t much of an issue, particularly for only 2 = coils on the power lead.  But John’s 15A fuse blew with 2 coils; which = raised this issue.  The average automotive 15A fuse will blow at 20A = steady, 30A for 1 second, 70-80 A for 100 milliseconds.   (The typical Time-Current Curve can be seen at http://www.bussman.com/library/bifs/2009.)  There is, of = course, a tolerance on the current at which they melt; but John’s fuse was = either faulty, there was some other reason that it blew, or the spike was higher and = longer duration than we think.

 

I checked the Schottky bus = isolation diodes that I installed, and they are rated for 60A and should withstand = up to about 400A for 100 ms, so that’s no problem.  I need to = consider what change, if any, to make on the fuse selection; so I’d appreciate = whatever info you have, if any more than you’ve already posted, on the = startup spike; especially it’s possible duration.  I assume the 9A = max is pretty firm based on the coil circuit design.  And I’m curious when = it happens – when the EC2 power is on and coils are on, or after you = start cranking?

 

BTW; in the argument (sorry, = discussion) of fuses vs CBs, this is a case where a CB has the advantage.  They = are slow acting, and will allow 10 times there rating for up to a second. = (See <= font color=3Dblack>http://tycoelectronics.com/product/circuitbreaker/w= 2331_DS.pdf ).  This is more like a slo-blo fuse.  I find = that you can’t get a slo-blo in a blade type except in the = ”maxi” version, and then the lowest rating is 20A.  You can get them in the glass = tube type.

 

Al

 

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