X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 21 Oct 2012 09:56:38 -0400 Message-ID: X-Original-Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122] verified) by logan.com (CommuniGate Pro SMTP 6.0c2) with ESMTP id 5834613 for lml@lancaironline.net; Sat, 20 Oct 2012 12:29:02 -0400 Received-SPF: none receiver=logan.com; client-ip=71.74.56.122; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: X-Authority-Analysis: v=2.0 cv=IZ4FqBWa c=1 sm=0 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=3Zlka_XeuxsA:10 a=ttCsPuSJ-FAA:10 a=rTjvlri0AAAA:8 a=gO9SC9oaa5AA:10 a=Ia-xEzejAAAA:8 a=sJFQ5_iWvlX_tQUo2VoA:9 a=wPNLvfGTeEIA:10 a=EzXvWhQp4_cA:10 a=CjxXgO3LAAAA:8 a=rK1tjnaxhnuaefimSMwA:9 a=_W_S_7VecoQA:10 a=rC2wZJ5BpNYA:10 a=DIMIpXFZJF1ESFeR:21 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:1230] helo=lobo) by hrndva-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id F7/5A-01418-A21D2805; Sat, 20 Oct 2012 16:28:26 +0000 X-Original-Message-ID: <9BAC88A0A40B45E5A92958610E5C9BD2@lobo> From: "Wolfgang" X-Original-To: "Gary Casey" , References: Subject: Re: TCM 60A alternator--diodes X-Original-Date: Sat, 20 Oct 2012 12:28:20 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0062_01CDAEBE.6382D3F0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5512 This is a multi-part message in MIME format. ------=_NextPart_000_0062_01CDAEBE.6382D3F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Diodes are rated at average current. The peak that they can handle is = many times the average.=20 This is the result of the original usage of diodes, as in power = supplies, where rectifying current is a "part time" usage and they are = rated as such. The average current in any single leg of a 3-phase line is 1/sqr3 times = the average current in a single phase line, including rectified to DC. Taking the 50 amp diodes as a unit in a 6 diode 3-phase bridge = rectifier, the current through any pair of diodes is the DC bridge = output / sqr3.=20 The alternator windings are good for 60 amps DC output so the diodes = need to handle 60 / sqr3 =3D 34.6 amps. Wolfgang ----- Original Message -----=20 From: Gary Casey=20 To: lml@lancaironline.net=20 Sent: Friday, October 19, 2012 8:28 AM Subject: Re: TCM 60A alternator--diodes I wouldn't feel quite that confident in the replacement diodes. The = stator current flows in series through 2 diodes at any given time and = the current cycles between the diodes as the alternator rotates. So for = a portion of the time a given diode will be passing 100% of the current = - but not all the time since they "take turns." I don't know how the = diode package was rated, but I think the 50-amp rating is marginal for a = 60-amp alternator. Given that, the alternator will rarely, if ever, be = asked to deliver a full 60 amps, and there is certainly some margin = built into the diode rating. And the rating is a function of operating = temperature, so if the alternator stays cool, it's better. If you could = find a diode assembly rated at 60 amps or more it would be a good thing. = The 50 amp assembly will probably work okay, though. It's just not 50A = X 6 =3D 300A. And if you routinely fly IFR at night with everything = turned on and lit up....well, that's up to you. Gary Casey The diode assembly was sourced at my local shop with a spare set of = brushes for $20 total. These are 50A diodes (50A x 6 diodes) which is a = robust replacement satisfactory for even the 100A alternator. I had to = remove the B+ stud from the old diode assembly and press it into = replacement diode package. The re-assembly took about 20 minutes and it = fired up with 10A charge on low engine idle. This is much higher charge = at low idle than I can ever recall. Paul ------=_NextPart_000_0062_01CDAEBE.6382D3F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Diodes are rated at average current. = The peak that=20 they can handle is many times the average.
This is the result of the original = usage of diodes,=20 as in power supplies, where rectifying current is a "part time" usage = and they=20 are rated as such.
 
The average current in any single leg = of a 3-phase=20 line is 1/sqr3 times the average current in a single phase line, = including=20 rectified to DC.
 
Taking the 50 amp diodes as a unit = in a 6=20 diode 3-phase bridge rectifier, the current through any pair of diodes = is the DC=20 bridge output / sqr3.
The alternator windings are good for 60 = amps DC=20 output so the diodes need to handle 60 / sqr3 =3D 34.6 = amps.
 
Wolfgang
 
----- Original Message -----
From:=20 Gary=20 Casey
Sent: Friday, October 19, 2012 = 8:28=20 AM
Subject: Re: TCM 60A=20 alternator--diodes

I wouldn't feel quite that confident in the replacement diodes. =  The=20 stator current flows in series through 2 diodes at any given time and = the=20 current cycles between the diodes as the alternator rotates.  So = for a=20 portion of the time a given diode will be passing 100% of the current = - but=20 not all the time since they "take turns."  I don't know how the = diode=20 package was rated, but I think the 50-amp rating is marginal for a = 60-amp=20 alternator.  Given that, the alternator will rarely, if ever, be = asked to=20 deliver a full 60 amps, and there is certainly some margin built into = the=20 diode rating.  And the rating is a function of operating = temperature, so=20 if the alternator stays cool, it's better.  If you could find a = diode=20 assembly rated at 60 amps or more it would be a good thing.  The = 50 amp=20 assembly will probably work okay, though.  It's just not 50A X 6 = =3D 300A.=20  And if you routinely fly IFR at night with everything turned on = and lit=20 up....well, that's up to you.
Gary Casey


The diode assembly was sourced at my = local shop=20 with a spare set of brushes for $20 total.  These are 50A diodes = (50A x 6=20 diodes) which is a robust replacement satisfactory for even the 100A=20 alternator.  I had to remove the B+ stud from the old diode = assembly and=20 press it into replacement diode package.  The re-assembly took = about 20=20 minutes and it fired up with 10A charge on low engine idle.  This = is much=20 higher charge at low idle than I can ever recall.
Paul
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