X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.3c3) with ESMTP id 3991861 for flyrotary@lancaironline.net; Thu, 26 Nov 2009 09:36:21 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Received: from computername ([75.191.186.236]) by cdptpa-omta01.mail.rr.com with ESMTP id <20091126143545755.DPUD2218@cdptpa-omta01.mail.rr.com> for ; Thu, 26 Nov 2009 14:35:45 +0000 From: "Ed Anderson" To: "'Rotary motors in aircraft'" Subject: Coil Current Draw Date: Thu, 26 Nov 2009 09:35:47 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0000_01CA6E7B.D5933E70" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 Thread-Index: Acpupb4h0XnE7qd3Quu+IuDwMFu4gg== X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Message-Id: <20091126143545755.DPUD2218@cdptpa-omta01.mail.rr.com> This is a multi-part message in MIME format. ------=_NextPart_000_0000_01CA6E7B.D5933E70 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hi Jeff, It appears the primary coil resistance can typically range from 0.8 - 1.4 ohms for an ignition coil. So picking 1 ohm as a nominal value. The stabilized current flow for one coil would be 13.8 /1 = 13.8 amps - not too surprising for what is almost a dead short. But, we know the coils are not on continuously - fortunately. IF all four coils were on continuously they would draw 4 * 13.8 = 55.2 amps. Steve Bose provide me some ignition data from the EC2 which indicated that at approx 3000 rpm the period between firings is 20 msec with a dwell (on) time of approx 3.7 Msec. So that gives a duty cycle of approx 3.7 / 20 = 0.185 or 18.5 %. That indicates for a single coil a DC current flow of approx 0.185 * 13.8 = 2.55 amps. Taking that 0.185 * 55 = 10.175 amps as the outside limit on the total current for all four coils. Now this is a DC resistive analysis approach. The time it takes for the current to build in an inductor, building and collapsing magnetic fields and their effects would indicate somewhat less current flow than this purely DC resistive type analysis. I found some information at the MSD (ignition) forum where the company replied to a question stating their "Blaster Coils" drew approx 1/2 amp average per 1000 rpm when used on a 4 cylinder engine. So if we applied that to the Renesis coils at 3000 rpm, we would have 1.5 amps each or a total of 4*1.5 = 6 amps at 3000 rpm. Now, not certain if that relationship holds linearly for the higher rpm or not. Probably drops off a bit due to less dwell time to charge the coils - but that is speculation on my part. So I would say that Al's 6 - 8 amps sounds right to me. Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm ------=_NextPart_000_0000_01CA6E7B.D5933E70 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

Hi Jeff,

 

It appears the primary coil resistance can typically = range from 0.8 – 1.4 ohms for an ignition coil.  So picking 1 ohm = as a nominal value.  The stabilized current flow for one coil  = would be 13.8 /1 =3D 13.8 amps – not too surprising for what is almost a = dead short.  But, we know the coils are not on continuously - = fortunately.  IF all four coils were on continuously they  would draw 4 * 13.8 = =3D 55.2 amps. 

 

Steve Bose provide me some ignition data from the EC2 = which indicated that at approx 3000 rpm the period between firings is 20 msec = with a dwell (on) time of approx 3.7 Msec.  So that gives a duty cycle of = approx 3.7 / 20 =3D 0.185 or 18.5 %.  That indicates for a single coil a = DC current flow of approx 0.185 * 13.8 =3D  2.55 = amps.

 

Taking that 0.185 * 55 =3D  10.175 amps as the outside limit on the total = current for all four coils.  Now this is a DC resistive analysis approach.  The time it takes for the current to build in an = inductor, building and collapsing magnetic fields and their effects would indicate somewhat less current flow than this purely DC resistive type = analysis.

 

I found some information at the MSD (ignition) forum = where the company replied to a question stating their “Blaster = Coils” drew approx 1/2 amp average per 1000 rpm when used on a 4 cylinder engine.  So if we applied that to the Renesis coils at 3000 rpm, we = would have 1.5 amps each or a total of 4*1.5  =3D 6  amps at 3000 rpm.  Now, not certain if = that relationship holds linearly for the higher rpm or not.  Probably = drops off a bit due to less dwell time to charge the coils – but that is speculation on my part.

 

So I would say that Al’s 6 = -  8 amps sounds right to me.

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/i= ndex.html

http://www.flyrotary.com/

http://members.cox.net/roger= sda/rotary/configs.htm#N494BW

http://www.rotaryaviation.co= m/Rotorhead%20Truth.htm

 



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