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

Mon Oct 7 09:53:54 CDT 2013

That is true and that's why I said 'for the most part'.  My HVAC systems 
and electric oven are the only things that use 240v in my house.  A 240v 
dryer, in general, will _not_ draw more current if run at 208v.  The 
only part that _might_ draw more current at the lower voltage is the 
motor that turns the dryer if it was designed to run specifically at 
240v only.  Any resistive only load will typically draw less current at 
lower voltages.  While it is true that the heating element of an 
electric dryer does draw more current when the voltage is first applied 
(inrush current because it is cold), I do not think that the relative 
'coolness' of the element running at 208v as compared to 240v is enough 
to cause it to draw more current at the lower voltage.

Dave Philipsen
Velocity STD FG
N83DP

On 10/6/2013 3:49 AM, Carl Hoffman wrote:
>
> On Oct 6, 2013, at 1:02 AM, Dave Philipsen <velocity at davebiz.com 
> <mailto: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
>> N83DP
>> On 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 
>>> <mailto:jerryskipschneider at gmail.com>>
>>> *To:* Dick Rohaly <n528dr at ca.rr.com <mailto:n528dr at ca.rr.com>>
>>> *Cc:* Izzy Briggs <INBRIGGS at YAHOO.COM <mailto:INBRIGGS at YAHOO.COM>>; 
>>> "<cozy_builders at googlegroups.com 
>>> <mailto:cozy_builders at googlegroups.com>>" 
>>> <cozy_builders at googlegroups.com 
>>> <mailto:cozy_builders at googlegroups.com>>; 
>>> "<canard-aviators at yahoogroups.com 
>>> <mailto:canard-aviators at yahoogroups.com>>" 
>>> <canard-aviators at yahoogroups.com 
>>> <mailto: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 
>>> <mailto: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> 
>>> [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 
>>> <mailto:cozy_builders at googlegroups.com>; 
>>> canard-aviators at yahoogroups.com <mailto: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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