X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 05 Jul 2006 11:03:11 -0400 Message-ID: X-Original-Return-Path: Received: from mta10.adelphia.net ([68.168.78.202] verified) by logan.com (CommuniGate Pro SMTP 5.1c.2) with ESMTP id 1224478 for lml@lancaironline.net; Wed, 05 Jul 2006 09:49:12 -0400 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.202; envelope-from=glcasey@adelphia.net Received: from [70.34.70.106] by mta10.adelphia.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20060705134826.WACJ10784.mta10.adelphia.net@[70.34.70.106]> for ; Wed, 5 Jul 2006 09:48:26 -0400 Mime-Version: 1.0 (Apple Message framework v749.3) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-3--146073092 X-Original-Message-Id: <0DF7E02E-A8EF-4E1B-B30B-9DEB5D3E4CF4@adelphia.net> From: Gary Casey Subject: Re: Visibility, transient voltage X-Original-Date: Wed, 5 Jul 2006 06:48:22 -0700 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.749.3) --Apple-Mail-3--146073092 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed The "current-limiting" of the alternator is due to the inductance of the stator winding. If the alternator is connected to any constant- voltage device (a battery or even a dead short to ground) and given full exitation of the field the current will rise as the rpm goes up, but eventually the inductance of the stator windings will generate enough back-emf to limit the current. A further increase of the rpm will not produce any more current. It's not because there is a loss from internal resistance or anything. Even overdriving the stator windings won't do anything as the iron saturates at a stator current that is not far from the max normal current. The point is that as long as the output is connected to a constant-voltage load the output current will be limited to a value close to the current rating of the alternator. So what happens if the battery becomes disconnected? As long as all of your expensive electronics are on the battery side of the fault there is no problem, even though the alternator itself is subjected to a very high voltage. What happens when it is reconnected? Good question, but I don't think the system will be exposed to the full voltage because as soon as there is current in the system the voltage will drop, but I haven't looked at this particular scenario. If for any reason the alternator stator becomes disconnected from the system it might be best to leave it disconnected. That's one reason I used a fuse in this line. Gary On Jul 5, 2006, at 3:08 AM, Lancair Mailing List wrote: > Garey-very interesting scenario; another one is worn slip-ring > brushes in the alternator making intermittent contact as in the LML > posting that started all this conjecture. I'm not sure what is > meant by the alternator being a "current-limited" device; is that > due to some internal circuitry or just the stator winding > resistance? If the latter, then what you are saying is that with > maximum field current at high rpm, there is all but 14V of its > output being dropped across the internal resistance, or 125V-14V. > Is that the case? The open battery condition you postulate is a > real zinger! 'looks like that could let the smoke out of a lot of > electronic equipment! --Apple-Mail-3--146073092 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1 The "current-limiting" of the = alternator is due to the inductance of the stator winding.=A0 If the = alternator is connected to any constant-voltage device (a battery or = even a dead short to ground) and given full exitation of the field the = current will rise as the rpm goes up, but eventually the inductance of = the stator windings will generate enough back-emf to limit the current.=A0= A further increase of the rpm will not produce any more current.=A0 = It's not because there is a loss from internal resistance or anything.=A0 = Even overdriving the stator windings won't do anything as the iron = saturates at a stator current that is not far from the max normal = current.=A0 The point is that as long as the output is connected to a = constant-voltage load the output current will be limited to a value = close to the current rating of the alternator.=A0 So what happens if the = battery becomes disconnected?=A0 As long as all of your expensive = electronics are on the battery side of the fault there is no problem, = even though the alternator itself is subjected to a very high voltage.=A0 = What happens when it is reconnected?=A0 Good question, but I don't think = the system will be exposed to the full voltage because as soon as there = is current in the system the voltage will drop, but I haven't looked at = this particular scenario.=A0 If for any reason the alternator stator = becomes disconnected from the system it might be best to leave it = disconnected.=A0 That's one reason I used a fuse in this line.

Gary

On Jul 5, = 2006, at 3:08 AM, Lancair Mailing List wrote:

Garey-very interesting scenario; another one is worn slip-ring = brushes in the alternator making intermittent contact as in the LML = posting that started all this conjecture. I'm not sure what is meant by = the alternator being a "current-limited" device; is that due to some = internal circuitry or just the stator winding resistance? If the latter, = then what you are saying is that with maximum field current at high rpm, = there is all but 14V of its output=A0being dropped across the internal = resistance, or 125V-14V. Is that the case? The open battery condition = you postulate is a real zinger! 'looks like that could let the smoke out = of a lot of electronic = equipment!

= --Apple-Mail-3--146073092--