X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 03 Jul 2006 00:26:37 -0400 Message-ID: X-Original-Return-Path: Received: from smtp113.sbc.mail.mud.yahoo.com ([68.142.198.212] verified) by logan.com (CommuniGate Pro SMTP 5.1c.2) with SMTP id 1221753 for lml@lancaironline.net; Mon, 03 Jul 2006 00:26:19 -0400 Received-SPF: none receiver=logan.com; client-ip=68.142.198.212; envelope-from=elippse@sbcglobal.net Received: (qmail 42974 invoked from network); 3 Jul 2006 04:25:33 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@75.15.128.186 with login) by smtp113.sbc.mail.mud.yahoo.com with SMTP; 3 Jul 2006 04:25:32 -0000 X-Original-Message-ID: <000c01c69e58$bf81bfe0$ba800f4b@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: Alternator no-load voltage X-Original-Date: Sun, 2 Jul 2006 21:25:41 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01C69E1E.121C9B70" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2869 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 This is a multi-part message in MIME format. ------=_NextPart_000_0009_01C69E1E.121C9B70 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable I did a test on a Nippondenso alternator the other day. Its no-load = voltage with 13.2V on the field and spun at 3000rpm was 40.2V. That's = average voltage; its 3-phase rectified peaks are higher. The = alternator's pulley OD is 2.75", and the pulley on the starter ring-gear = is about 9.5". This means that its output at 2700 rpm is about 125V. = Have any of you measured the time constant of your OV crowbar? I would = think that it would have a filter in the trigger circuit to prevent = false triggering on transients, so there is probably several = milliseconds from the appearance of an OV event until the crowbar = activates. There is probably a several millisecond L/R field time = constant for the decay of the field current. If one of you has the means = to test this total loop, it would be interesting to see just how long = this magnitude of OV would be present at the alternator output. Keep in = mind that there has to be an overvoltage existing on the main buss = before it can be detected. I have queried Exide about the L-R-C time = constants of a typical 25AH lead-acid battery, and its reaction to a = very brief high-voltage transient but have not yet received a reply. = Consider: a lead-acid battery generates voltage by an electrochemical = reaction, and is charged by the reverse reaction. Wouldn't an = electrochemical reaction of ion exchange on the cell walls take a finite = amount of time? I wouldn't think it would be on the order of the = light-speed of electricity flowing in a conductor. I would hazard a = guess that any sinking of a short-duration transient would be more due = to battery capacitance than to being through absorption by the chemical = reaction. The inductance in the leads from the battery to the buss would = also add an additional time delay. There is nothing instaneous in = electricity. Even the thought-to-be instantaneity of doppler radar = isn't. The processor counts cycles over a fixed gate period, which = yields the range change, so its apparent effective time, with constant = range-rate, is in the middle of the count period, and the range-rate is = range per count-period. So! How long would a 125 V transient from an = alternator exist on the buss? Long enough to damage some fine avionics? ------=_NextPart_000_0009_01C69E1E.121C9B70 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

I did a test on a Nippondenso = alternator the other day. Its no-load voltage with 13.2V on the field = and spun=20 at 3000rpm was 40.2V. That's average voltage; its 3-phase rectified = peaks=20 are higher. The alternator's pulley OD is 2.75", and the pulley on the = starter=20 ring-gear is about 9.5". This means that its output at 2700 rpm is=20 about 125V. Have any of you measured the time constant of your OV = crowbar?=20 I would think that it would have a filter in the trigger circuit to = prevent=20 false triggering on transients, so there is probably several = milliseconds from=20 the appearance of an OV event until the crowbar activates. There is = probably a=20 several millisecond L/R field time constant for the decay of the = field=20 current. If one of you has the means to test this total loop, it would = be=20 interesting to see just how long this magnitude of OV would be present = at the=20 alternator output. Keep in mind that there has to be an overvoltage = existing on=20 the main buss before it can be detected. I have queried Exide about = the=20 L-R-C time constants of a typical 25AH lead-acid battery, and its = reaction to a=20 very brief high-voltage transient but have not yet received a = reply.=20 Consider: a lead-acid battery generates voltage by an electrochemical = reaction,=20 and is charged by the reverse reaction. Wouldn't an electrochemical = reaction of ion exchange on the cell walls take a finite amount of = time? I=20 wouldn't think it would be on the order of the light-speed of = electricity=20 flowing in a conductor. I would hazard a guess that any sinking of a=20 short-duration transient would be more due to battery capacitance than = to being=20 through absorption by the chemical reaction. The inductance in the = leads=20 from the battery to the buss would also add an additional time delay. = There is=20 nothing instaneous in electricity. Even the thought-to-be instantaneity = of=20 doppler radar isn't. The processor counts cycles over a fixed gate = period, which=20 yields the range change, so its apparent effective time, with = constant=20 range-rate, is in the middle of the count period, and the range-rate is = range=20 per count-period. So! How long would a 125 V transient from an=20 alternator exist on the buss? Long enough to damage some fine=20 avionics?

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