REFLECTOR: [c-a] Re: COZY: 24 Volts VS 12 Volts
Dave Philipsen
velocity at davebiz.com
Mon Oct 7 10:18:36 CDT 2013
Ok, you're forgiven. Technically, it's Watt's Law that calculates the
wattage and Ohm's Law that gets you there.
Dave Philipsen
Velocity STD FG
N83DP
On 10/6/2013 8:48 AM, Douglas Holub wrote:
> I can't help pointing out that Ohm's law is V = IR, not watts = VI.
> Forgive me.......
>
> ----- Original Message -----
> *From:* Carl Hoffman <mailto:hoffman3 at rcn.com>
> *To:* Velocity Aircraft Owners and Builders list
> <mailto:reflector at tvbf.org>
> *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
> <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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