Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Fri, 09 Jul 2004 03:12:45 -0400 Message-ID: X-Original-Return-Path: Received: from [206.246.194.60] (HELO visi.net) by logan.com (CommuniGate Pro SMTP 4.2b6) with ESMTP id 300108 for lml@lancaironline.net; Fri, 09 Jul 2004 00:58:23 -0400 X-Virus-Scanner: ClamAV Received: from [69.143.133.93] (account rpastusek@htii.com HELO cp172883-b.arlngt01.va.comcast.net) by visi.net (CommuniGate Pro SMTP 4.1.5) with ESMTP id 12143114 for lml@lancaironline.net; Fri, 09 Jul 2004 00:55:31 -0400 Reply-To: From: "Bob Pastusek" X-Original-To: "Lancair Mailing List" Subject: RE: [LML] 14V vs 28V X-Original-Date: Fri, 9 Jul 2004 00:56:46 -0400 X-Original-Message-ID: <041701c46571$232d55e0$6601a8c0@cp172883-b.arlngt01.va.comcast.net> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0418_01C4654F.9C1BB5E0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook 8.5, Build 4.71.2173.0 In-Reply-To: Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 This is a multi-part message in MIME format. ------=_NextPart_000_0418_01C4654F.9C1BB5E0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Dennis, In simple terms, folks use 28 volt systems because you get twice as much power to operate electrical goodies at the same system current (Power = Volts x Amps). Since the current is lower for a given power requirement, you can use smaller wires and the other components tend to be smaller and lighter in general. As a practical matter, 28 volt systems are not quite that efficient, but do offer significant weight savings for high electrical loads. The "down" side is that 28 volt components tend to be harder to find, more expensive, and much more limited in choice/variety of components. Between cars, boats, and the model world there is an almost endless variety of 12 volt components to tickle your every fancy. Except for the high end avionics typically used in business jets and commercial aircraft, avionics and other electrical components for GA and experimental aircraft are also available in 12 volt versions. When electrical components each drew the power of a small toaster (and radiated an equivalent amount of heat), GA and experimental airplane builders went to 28 volts just to cover the electrical power demand--and run the cooling fans... Today, only the hydraulic pump, landing/taxi lights and pitot heat draw any significant power--and some of the new LEDs and gas-discharge lights use less than 30% of their incandescent counterparts. Avionics have truly gone on a power diet, and some draw less than 10% of the power that equivalent equipment of 20 years ago used. You can still overload any system, so I'd strongly recommend you make a list of the electrical components you intend to put in your new plane, and total their power. Considering that you're unlikely to ever use all of them at the same time, estimate your maximum and "steady state" power requirements under various flight conditions (night, IMC, etc) against your respective battery and alternator capacities. Bob Knuckols' "Aeroelectic Connection" is a very good reference for this and other electrical considerations. Jim White and I installed 28 volt systems in our two Lancair IV-P's. It was a decision we made in 1998, and we've "paid" for it several times over. We built "all electric" airplanes with EFIS panels, significant redundancy and back up. Given the actual loads, we're well over powered for everything except electric anti-ice, and probably well short of the power needed for that--assuming it's ever perfected. If I had it to do over, I'd go with a 12 volt system-it's one of the very few things I'd do differently if starting to build an IV-P today. I considered changing, but the mile or so of wiring in my plane was sized for 28 volt and corresponding current; changing to 12 volts would require replacing much of it...not worth it. The moral of this: once you start building/installing electrical components, you probably need to stick with whatever you decide. Hope this helps. Bob Pastusek ... I am an electrical neophyte .....anybody want to explain the Pro's or Con's of these too me ....its decision time ... Dennis Shy ------=_NextPart_000_0418_01C4654F.9C1BB5E0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Dennis,
 
In=20 simple terms, folks use 28 volt systems because you get twice as much = power to=20 operate electrical goodies at the same system current (Power =3D Volts x = Amps).=20 Since the current is lower for a given power requirement, you can use = smaller=20 wires and the other components tend to be smaller and lighter in = general. As a=20 practical matter, 28 volt systems are not quite that efficient, but do = offer=20 significant weight savings for high electrical loads. =
 
The=20 "down" side is that 28 volt components tend to be harder to find, more=20 expensive, and much more limited in choice/variety of components. = Between cars,=20 boats, and the model world there is an almost endless variety of 12 = volt=20 components to tickle your every fancy. Except for the high end = avionics=20 typically used in business jets and commercial aircraft, avionics = and other=20 electrical components for GA and experimental aircraft are also = available in 12=20 volt versions. When electrical components each drew the power of a small = toaster=20 (and radiated an equivalent amount of heat), GA and experimental = airplane=20 builders went to 28 volts just to cover the electrical power demand--and = run the=20 cooling fans... Today, only the hydraulic pump, landing/taxi lights and = pitot=20 heat draw any significant power--and some of the new LEDs and = gas-discharge=20 lights use less than 30% of their incandescent counterparts. Avionics = have truly=20 gone on a power diet, and some draw less than 10% of the power that = equivalent=20 equipment of 20 years ago used. You can still overload any = system, so=20 I'd strongly recommend you make a list of the electrical components you = intend=20 to put in your new plane, and total their power. Considering that you're = unlikely to ever use all of them at the same time, estimate your maximum = and=20 "steady state" power requirements under various flight conditions = (night, IMC,=20 etc) against your respective battery and alternator capacities. Bob = Knuckols' "Aeroelectic Connection" is a very good reference for this and = other=20 electrical considerations.
 
Jim=20 White and I installed 28 volt systems in our two Lancair IV-P's. It was = a=20 decision we made in 1998, and we've "paid" for it several times over. We = built=20 "all electric" airplanes with EFIS panels, significant redundancy and = back up.=20 Given the actual loads, we're well over powered for everything = except=20 electric anti-ice, and probably well short of the power needed for=20 that--assuming it's ever perfected.  If I had it to do over, = I'd go=20 with a 12 volt system-it's one of the very few things I'd do = differently if=20 starting to build an IV-P today. I considered changing, but the mile or = so of=20 wiring in my plane was sized for 28 volt and corresponding current; = changing to=20 12 volts would require replacing much of it...not worth it. The = moral of=20 this: once you start building/installing electrical components, you = probably=20 need to stick with whatever you decide.
 
Hope=20 this helps.
 
Bob=20 Pastusek
 ... I am=20 an electrical neophyte .....anybody want to explain the Pro's or Con's = of=20 these too me ....its decision time ...
 
Dennis Shy
 
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