X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from elasmtp-dupuy.atl.sa.earthlink.net ([209.86.89.62] verified) by logan.com (CommuniGate Pro SMTP 6.0.7) with ESMTP id 6619625 for lml@lancaironline.net; Fri, 29 Nov 2013 21:47:16 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.62; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=OSd0dm7U6D8KxTXuZ4pspLzDmU18ZPrOnZTqDsVfI/g6sVJMdTgg/we8V8FIPdDM; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [72.92.128.101] (helo=[192.168.1.24]) by elasmtp-dupuy.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1VmaZu-0007aT-U1 for lml@lancaironline.net; Fri, 29 Nov 2013 21:46:43 -0500 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: multipart/alternative; boundary=Apple-Mail-44--549491044 Subject: Re: [LML] Motor locked current Date: Fri, 29 Nov 2013 21:46:41 -0500 In-Reply-To: To: "Lancair Mailing List" References: Message-Id: X-Mailer: Apple Mail (2.1085) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da9401a03d44e2ee7b0f3fe1a1f4c66660aa4350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 72.92.128.101 --Apple-Mail-44--549491044 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Jack, I was with you until you got to "The solenoid Lancair recommends". See the reply to Giff I just posted where Bob Nuckolls argues to the = contrary. On Nov 29, 2013, at 6:53 PM, Jack Morgan wrote: Hi John, A good rule of thumb on dc motors is 4 to 1 so your measurement seems = good. Your readings are also consistent with the 35 amp breaker which I = understand is typical for the pump. Inductive loads like the motor are easiest to turn on for relays since = the contacts are made before the current reaches the locked value. = Incandescent lamps are the worst case turn on load..... 10 to 1 is the = rule of thumb (no kidding) for the inrush into a cold lamp. With only = the inductance of the connecting wires the relay really sees an inrush = while it is making contact in lamp circuits. If a normally sized relay were to break with the pump rotor locked it = would be highly stressed, maybe even fail. Most designers rely on the = breaker to trip to protect the wiring, motor, and relay and ignore the = unlikely possibility of the relay being turned off during the short time = it takes the breaker to trip with a locked motor. The solenoid Lancair = recommends is capable of surviving turning off the starter for awhile so = won't be damaged in any case. Nothing like belt and suspenders. Jack Morgan On Nov 29, 2013, at 6:00 AM, Lancair Mailing List wrote: > From: John Cooper > Subject: [LNC2] Oildyne Hydraulic Pump Inrush > Date: November 28, 2013 4:56:30 PM EST > To: lml@lancaironline.net >=20 >=20 > Today I inserted a 75A / 50mV shunt in the power lead to my hydraulic = pump in order to measure the current draw. I connected my Fluke 87-V = digital voltmeter on the 600mV range across the sense terminals of the = shunt . With the pump running in the "gear down" direction and the = equalization valve open, the motor was drawing a steady 29 Amps. I then = shut off the pump, closed the equalization valve, and with the Fluke in = the "250 uS peak" mode, measured the inrush when the pump started up = again briefly. Would you believe 135 Amps! (Disclaimer: I purchased the = shunt on eBay and can't vouch for its calibration.) >=20 > Next time the plane is up on jacks, I'll re-do this test in both gear = up and gear down directions. Also, I intend to temporarily remove the = ZNRs across the hydraulic relay contacts and measure the voltage spikes = with no protection. --Apple-Mail-44--549491044 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii Jack, = I was with you until you got to "The solenoid Lancair = recommends".
See the reply to Giff I just posted where Bob Nuckolls = argues to the contrary.

On Nov 29, 2013, at 6:53 = PM, Jack Morgan wrote:

Hi John,

A = good rule of thumb on dc motors is 4 to 1 so your measurement seems = good. Your readings are also consistent with the 35 amp breaker which I = understand is typical for the pump.

Inductive = loads like the motor are easiest to turn on for relays since the = contacts are made before the current reaches the locked value. = Incandescent lamps are the worst case turn on load..... 10 to 1 is the = rule of thumb (no kidding) for the inrush into a cold lamp. With only = the inductance of the connecting wires the relay really sees an inrush = while it is making contact in lamp circuits.

If = a normally sized relay were to break with the pump rotor locked it would = be highly stressed, maybe even fail. Most designers rely on the breaker = to trip to protect the wiring, motor, and relay and ignore the unlikely = possibility of the relay being turned off during the short time it takes = the breaker to trip with a locked motor. The solenoid Lancair recommends = is capable of surviving turning off the starter for awhile so won't be = damaged in any case. Nothing like belt and = suspenders.

Jack = Morgan


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