REFLECTOR: [c-a] Re: COZY: 24 Volts VS 12 Volts

Sun Oct 6 08:48:19 CDT 2013

I can't help pointing out that Ohm's law is V = IR, not watts = VI.  Forgive me.......
  ----- Original Message ----- 
  From: Carl Hoffman 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Sunday, October 06, 2013 4:49 AM
  Subject: Re: REFLECTOR: [c-a] Re: COZY: 24 Volts VS 12 Volts

  On Oct 6, 2013, at 1:02 AM, Dave Philipsen <velocity at davebiz.com> wrote:

    But heat is measured in watts which is, basically, volts x amps (ohm's law).  So, essentially, you have the same amount of heat generated whether you are running 12v or 24v.  In theory, a 24v device may draw one amp which means it dissipates 24 watts.  The same type of device designed to run at 12v would draw two amps and dissipate the same 24 watts.  As long as you use the proper size wire I don't think there is greater danger of fire.

    Also, a 24v battery has essentially the same amount of reserve power as a similarly sized 12v battery.  The 24v battery would supply 1/2 the amps of a 12v battery but the same amount of watts (or watt-hours).  I'm guessing that a 24v battery would descend through its discharge curve at roughly the same rate as a similar sized 12v battery arriving at the point of 'full discharge' at about the same time if they were both delivering the same amount of power.

    While it is true that the voltage drop across wires in a 24v system may be a lower percentage of total voltage than with a 12v system, there is a point of diminishing returns somewhere.  Otherwise, why wouldn't we all just go ahead and run several thousand volts in our homes?  After all, it's available at the utility pole.  But, instead, we transform it down to a more manageable level.  

    Most of Europe might argue the need for 240v wiring in their homes but here in the US we, for the most part, are content with 120v and Japan, for the most part, is content with just 100v.

  Actually US homes have 240v for mayor appliances. Your 240v dryer has a 120v light bulb, and will draw more current on 208v. Also, your dryer has a 3 prong plug, and doesn't need a safety ground.

    In my opinion, 12v is sufficient for most experimental aircraft and, as was mentioned earlier, keeps you in the realm of inexpensive parts which are available for automobiles that, for the most part, are content to run at 12v.

Dave Philipsen
Velocity STD FG
N83DPOn 10/5/2013 7:48 PM, Izzy Briggs wrote:

      The biggest argument I read in favor of 24 volts was:

      Higher volts draws less amps (Ohms law) = less heat, less likely to have an electrical fire?

      Greater Reliability (Page 5 of Greg's document) - "A 24-volt system also has a LOT more reserve energy available for use than a 12- volt system. As in point #2, a failed alternator in a 12-volt system leaves you 2 volts from shutdown. It a 24-volt system you’ve got a lot more reserve before your avionics and FADEC drop offline. Look at the discharge curves, and you’ll see that a 12-volt battery at 11 volts is only partially discharged. A 24 volt battery at 11 volts is very close to dead."

      Izzy

--------------------------------------------------------------------------
      From: trcsmith <trcsmith at aol.com>
      To: INBRIGGS at YAHOO.COM; jerryskipschneider at gmail.com; n528dr at ca.rr.com 
      Cc: cozy_builders at googlegroups.com; canard-aviators at yahoogroups.com 
      Sent: Saturday, October 5, 2013 8:33 PM
      Subject: Re: [c-a] Re: COZY: 24 Volts VS 12 Volts

      24v in a small homebuilt today is just so wrong. You won't save that much weight in wire.  

      Tom Smith  A&P
      Long-EZ N12TS
      Cell-707-592-0869
      KVCB
      KJ6PZN

      -----Original Message-----
      From: Izzy Briggs <inbriggs at yahoo.com>
      To: Jerry/Skip Schneider <jerryskipschneider at gmail.com>; Dick Rohaly <n528dr at ca.rr.com>
      Cc: <cozy_builders at googlegroups.com> <cozy_builders at googlegroups.com>; <canard-aviators at yahoogroups.com> <canard-aviators at yahoogroups.com>
      Sent: Sat, Oct 5, 2013 3:09 pm
      Subject: [c-a] Re: COZY: 24 Volts VS 12 Volts

      The first few pages seem to suggest a 24 volt sytem is better. Is this what you meant Jerry?

      Izzy

--------------------------------------------------------------------------
      From: Jerry/Skip Schneider <jerryskipschneider at gmail.com>
      To: Dick Rohaly <n528dr at ca.rr.com> 
      Cc: Izzy Briggs <INBRIGGS at YAHOO.COM>; "<cozy_builders at googlegroups.com>" <cozy_builders at googlegroups.com>; "<canard-aviators at yahoogroups.com>" <canard-aviators at yahoogroups.com> 
      Sent: Saturday, October 5, 2013 5:16 PM
      Subject: Re: COZY: 24 Volts VS 12 Volts

      Have you read: http://www.eaa.org/experimenter/articles/0903_aircraft_wiring.pdf

      Greg makes a pretty good case for a 12vdc system.

      Jerry

      On Oct 5, 2013, at 5:10 PM, "Dick Rohaly" <n528dr at ca.rr.com> wrote:

      True and the wire size is smaller. Some Berkuts are running 24 volt systems with great success. 

      From: cozy_builders at googlegroups.com [mailto:cozy_builders at googlegroups.com] On Behalf Of Izzy Briggs
      Sent: Thursday, September 26, 2013 8:43 PM
      To: cozy_builders at googlegroups.com; canard-aviators at yahoogroups.com
      Subject: COZY: 24 Volts VS 12 Volts

      I spoke with an Avionics expert the other day about an electrical bus for my Cozy. He's trying to convince me that a 28 volt system for my Radios and other Avionics will be preferable to a 12 volt system because they perform better and the components are cheaper.

      Anyone ever try to do 24 volts in a Cozy? The last machine I ever drove with 24 volt system was my Grandfathers 1969 Volkswagen Squareback. It was nothing but trouble.

      Izzy

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