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OT - A/C Electrical systems - 5/6/2012 4:43:32 PM   
vettim89


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While perusing various WWII aircraft and their upgrade paths, I have noticed that it was common to see the electrical systems upgrade from 12v to 24v to sometimes even 48v. For those in the know, what advantages did the higher voltage systems over the lower voltage ones. Just a dumb question from an uniformed historophile

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RE: OT - A/C Electrical systems - 5/6/2012 4:55:38 PM   
pws1225

 

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The higher the voltage, the lower the amperage (and associated wire size) to deliver the same amount of power. It probably helped reduce an AC's weight, but that's just my guess as to why.

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RE: OT - A/C Electrical systems - 5/6/2012 6:16:33 PM   
JWE

 

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If I remember right from E&M , V = IxR. For the same resistance (R) a higher voltage gives more current. Power = IxV = I^2xR. For the same resistance (R) a higher voltage gives lots more power to lots more systems (i.e., you can have more goodies that consume electrons). You might want to thicken up the wires a bit to minimize power loss through resistive heating.

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RE: OT - A/C Electrical systems - 5/6/2012 6:55:15 PM   
JocMeister

 

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I´m not familiar with the American abbrivations but I think JWE got it right: The higher the voltage the more amount of power from the sampe Amps. Amp is controlled by battery size. So basically you don´t need bigger batteries for the same amount of power. You can´t really cut down on the wire size since that is dependend on the maximum amp not the voltage. I doubt they wanted to lower the amp since I guess they crammed more and more stuff into newer models.

You really don´t need to thicken the wires though. The lenght of the cables would be to short to make a difference. It would loss negligeble.

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RE: OT - A/C Electrical systems - 5/6/2012 7:10:35 PM   
Panther Bait


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Regarding wire size, higher voltages and lower amperages do allow you to use thinner wires for the same amount of power. Now if you're increasing voltage to get more power for the same amperage, than the wire size will not get smaller.

My guess for the reasoning of increasing the voltages was a combination of electrical equipment (generators, batteries, transformers, etc.) getting smaller/lighter as the tech base improved during building which allowed more powerful systems, a need to add more and more sophisticated equipment to aircraft (all of which takes power), and maybe a desire to save copper in wiring by upping the voltage.

Mike


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RE: OT - A/C Electrical systems - 5/6/2012 9:35:27 PM   
JWE

 

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Well, I don’t remember that all from E&M. But you all are much smarter than me, so I asked my friend Elmo, the Free Electron.




Elmo says that for a given length of a given material, resistance (R) is inversely proportional to the cross sectional area. A thinner wire has a higher specific resistance and a greater drop along its length and a higher power loss through resistive heating. That’s why you have mongo copper connected to your 220V (30-40 Amp) mains, for your washer dryer, in your garage. Also why your regular mains are 110V, 20 Amp, because code won’t allow 25 Amps to run through nominal 20 Amp wire in most places. Keeps your wires from heating up, melting, and your house from burning down.


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RE: OT - A/C Electrical systems - 5/6/2012 10:12:17 PM   
pws1225

 

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Who could argue with Elmo?

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RE: OT - A/C Electrical systems - 5/6/2012 10:28:58 PM   
HMSWarspite

 

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quote:

ORIGINAL: JWE

Well, I don’t remember that all from E&M. But you all are much smarter than me, so I asked my friend Elmo, the Free Electron.




Elmo says that for a given length of a given material, resistance (R) is inversely proportional to the cross sectional area. A thinner wire has a higher specific resistance and a greater drop along its length and a higher power loss through resistive heating. That’s why you have mongo copper connected to your 220V (30-40 Amp) mains, for your washer dryer, in your garage. Also why your regular mains are 110V, 20 Amp, because code won’t allow 25 Amps to run through nominal 20 Amp wire in most places. Keeps your wires from heating up, melting, and your house from burning down.



Unless you live in an uprated society, with 240V 13 amp mains

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RE: OT - A/C Electrical systems - 5/6/2012 10:34:03 PM   
pompack


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quote:

ORIGINAL: HMSWarspite


quote:

ORIGINAL: JWE

Well, I don’t remember that all from E&M. But you all are much smarter than me, so I asked my friend Elmo, the Free Electron.




Elmo says that for a given length of a given material, resistance (R) is inversely proportional to the cross sectional area. A thinner wire has a higher specific resistance and a greater drop along its length and a higher power loss through resistive heating. That’s why you have mongo copper connected to your 220V (30-40 Amp) mains, for your washer dryer, in your garage. Also why your regular mains are 110V, 20 Amp, because code won’t allow 25 Amps to run through nominal 20 Amp wire in most places. Keeps your wires from heating up, melting, and your house from burning down.



Unless you live in an uprated society, with 240V 13 amp mains


And really, really efficient hair dryers

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RE: OT - A/C Electrical systems - 5/6/2012 10:47:02 PM   
JWE

 

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quote:

ORIGINAL: HMSWarspite
Unless you live in an uprated society, with 240V 13 amp mains

Yeah, yeah, 240V stuff and 50 cycle AC. Every stinking time I get to London and plug in my Norelco it starts to smoke and I have to buy a package of BICs. I think you guys and Marcel Bic have a thing going. Woof !!

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RE: OT - A/C Electrical systems - 5/6/2012 11:58:24 PM   
mullk

 

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As others have stated When you increase voltage you decrease current flow for the same amount of power. As others have stated it allows for smaller wires and tighter wire bundles. Their is a trade off of resistance and wire size that is affected by temperature of the wire. But depending on how much the wire size is cut down the change in resistance is minimal. Their are a lot of reasons why voltages could have been increased. One item might be it's easy to down convert voltages and something of a pain to up convert them for a multi voltage system. A higher voltage also means more items in a row if the items are set in series. Another advantage of a high supply voltage and low unit voltage is if for some reason their is a draw down of the supply voltage the voltage regulator of the unit power supply would have an easier time keeping voltage. An interesting question would be what was the voltage powering? Lights both inside and outside, starting on some aircraft, electrical equipment like radars and transmitters and receivers (with their vacuum tubes) perhaps the gun sight.

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RE: OT - A/C Electrical systems - 5/7/2012 12:01:44 AM   
wdolson

 

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Stepping up the voltage to overcome transmission line losses is why long distance power lines run at thousands of volts. Higher voltage and lower current means lower IR loss in transmission. When the power is consumed, there is virtually no advantages to higher voltages and a lot of dangers, so it's stepped down to 240V for neighborhood distribution (even in the US). There are also a medium voltage level for distribution from the high voltage sub-stations to local neighborhoods. The power pole transformers in neighborhoods that can explode when hit by lightning step the medium voltage down to 240V.

In the US houses further break out the 240V by splitting it into two rails. Some appliances like electric dryers and ovens run on 240V, but the rest run on 120V.

Aircraft of that era ran on DC not the AC of the terrestrial grid, but the IR loss principle through the plane's wiring still applied. Aircraft of that era saw an explosion in devices needing electrical power and the plane's electrical system needed to provide it. The IR loss from running power all over the plane probably started to mount up and that drove the push to raise the voltage of the electrical systems.

Bill

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RE: OT - A/C Electrical systems - 5/7/2012 12:30:21 AM   
pws1225

 

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quote:

ORIGINAL: wdolson

Aircraft of that era ran on DC not the AC of the terrestrial grid, but the IR loss principle through the plane's wiring still applied. Aircraft of that era saw an explosion in devices needing electrical power and the plane's electrical system needed to provide it. The IR loss from running power all over the plane probably started to mount up and that drove the push to raise the voltage of the electrical systems.Bill


I think you're right Bill. And I imagine Elmo would agree.

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RE: OT - A/C Electrical systems - 5/7/2012 4:14:15 AM   
vettim89


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Thanks everyone for your insightful replies. You learn somethign new every day here on the AE Forum

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RE: OT - A/C Electrical systems - 5/7/2012 2:56:28 PM   
dr.hal


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Who's this Elmo dude???

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RE: OT - A/C Electrical systems - 5/7/2012 3:50:48 PM   
JocMeister

 

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Im not really with you guys. Might be a language thing. When you say IR what do you mean by that?

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RE: OT - A/C Electrical systems - 5/7/2012 4:12:13 PM   
pws1225

 

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quote:

ORIGINAL: dr.hal

Who's this Elmo dude???


Elmo is a free electron. He is rumored to have started the Free Love movement back in the sixties,

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RE: OT - A/C Electrical systems - 5/7/2012 4:19:26 PM   
witpqs

 

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quote:

ORIGINAL: JocMeister

Im not really with you guys. Might be a language thing. When you say IR what do you mean by that?


E=IR (voltage = current times resistance)

http://en.wikipedia.org/wiki/Ohm's_law

Note that many of us were taught it in school with the older abbreviations of "E" rather than "V" for voltage; and "I" is used for current rather than "A" meaning Amperage.

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RE: OT - A/C Electrical systems - 5/7/2012 4:31:24 PM   
Erkki


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And I thought its U=RI Where [U]=V, [R]=capital omega and [I]=A?

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RE: OT - A/C Electrical systems - 5/7/2012 4:35:49 PM   
witpqs

 

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quote:

ORIGINAL: Erkki

And I thought its U=RI Where [U]=V, [R]=capital omega and [I]=A?


No Omega on keyboards helped to change that usage I guess, but yes I remember that. I don't recall "U" for voltage, though.

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RE: OT - A/C Electrical systems - 5/7/2012 4:36:49 PM   
JocMeister

 

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I´m with Erkki on this one! I know Ohm law pretty good since I´m an electrician. Why I´m asking is that the losses from resistance should be negligeble over the short distances. That being said I don´t know how long the total lenght of all cabales where in and Aircraft thoses days? It guess it can add up!

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RE: OT - A/C Electrical systems - 5/7/2012 4:50:14 PM   
steamboateng


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I think wdolson was right on; radar & navigation systems increased power demand.
Did WWii aircraft carry IFF equipment?

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RE: OT - A/C Electrical systems - 5/7/2012 5:00:26 PM   
Erkki


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quote:

ORIGINAL: steamboateng

I think wdolson was right on; radar & navigation systems increased power demand.
Did WWii aircraft carry IFF equipment?


At least in Europe, many did. But I could imagine them not having being used quite often.

< Message edited by Erkki -- 5/7/2012 5:02:19 PM >

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RE: OT - A/C Electrical systems - 5/7/2012 6:23:57 PM   
pompack


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quote:

ORIGINAL: steamboateng

I think wdolson was right on; radar & navigation systems increased power demand.
Did WWii aircraft carry IFF equipment?



Very definitely. A lot of the fighter direction problems at both Santa Cruz and Eastern Solamons were due to a lack of (or malfunctioning) IFF gear. The carrier radars kept picking up inbound a/c without an IFF squawk and vectoring CAP to intercept what turned out to be returning a/c. When the real raids came in the CAP was dispersed from all that mistaken activity. The problem was completely solved by 44 and the Phillipines Sea and thus the Turkey Shoot.

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RE: OT - A/C Electrical systems - 5/7/2012 6:53:15 PM   
Erkki


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Also....

http://en.wikipedia.org/wiki/Battle_of_Barking_Creek

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RE: OT - A/C Electrical systems - 5/7/2012 7:16:10 PM   
JWE

 

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quote:

ORIGINAL: pws1225
quote:

ORIGINAL: dr.hal
Who's this Elmo dude???

Elmo is a free electron. He is rumored to have started the Free Love movement back in the sixties,

Yep, freed by Gauss, Coulomb, and especially Millikan. I really enjoy my new found Mobility.


And it's not a rumour, either. Shockley knew I was a coupled cluster and needed to find Hermione the unfettered Hole in order to be satisfied back to my ground state. Woof !! Being a free electron, in search of a hole is a worthy task and I can do much work as a consequence. But then I rented a billboard on the 101, just past Palo Alto (just looking for some help in my quest, you understand), and things just went from there and got out of hand. And then this Garcia fellow grabs me and promises holes galore if I would put more power into his amps, and then Jim Marshall came along, and the rest is history.

Quicksilver Messenger Service and the Summer of Love, brought to you by Elmo, your friendly Free Electron.



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RE: OT - A/C Electrical systems - 5/7/2012 7:38:12 PM   
pws1225

 

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Well done!

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RE: OT - A/C Electrical systems - 5/7/2012 9:43:50 PM   
steamboateng


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+1 JWE. But from you it may be another one of your silly cons!

< Message edited by steamboateng -- 5/7/2012 9:45:37 PM >

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RE: OT - A/C Electrical systems - 5/8/2012 12:24:39 AM   
wdolson

 

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quote:

ORIGINAL: Erkki

And I thought its U=RI Where [U]=V, [R]=capital omega and [I]=A?


quote:

ORIGINAL: witpqs
No Omega on keyboards helped to change that usage I guess, but yes I remember that. I don't recall "U" for voltage, though.



Maybe it's different customs in different countries/languages? In the US, I've always seen the equation as V = IR and the power equation as P = VI. I should have said I^2R losses in my earlier post. Not enough tea that day...

If you substitute IR for V in the power equation, you get another way to calculate power which is (IR)*I, which is I^2R. What it means is that if you have high current, your transmission losses are going to be the square of the current. Even if the resistance is low, the power lost in transmission can be big. By raising the voltage and lowering the current, the transmission losses are reduced.

There is a difference between the unit designation and the letter used in calculations. In calculations, V=Voltage, I=Current, and R=resistance. When showing a value, Volts=V, Amps=A, and Ohms=Ω (omega).

And IFF was used extensively in the Pacific. In the Aleutians ground controlled approach was also used to allow landing in zero visibility conditions. This required the plane to have extra equipment on board. My father was a photographer attached to different units at different times. He flew with B-29s at Saipan, B-25s in New Guinea and the Philippines. At the end of the war he was flying in B-25s out of Attu. He said the Aleutian B-25s were loaded down with a lot of extra electronics that wasn't on the 5th AF B-25s. The planes were very cramped inside.

Sometimes aircraft also had more than one radio and radios were large power hungry beasts back then.

Bill

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RE: OT - A/C Electrical systems - 5/8/2012 12:38:56 AM   
witpqs

 

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quote:

ORIGINAL: wdolson

quote:

ORIGINAL: Erkki

And I thought its U=RI Where [U]=V, [R]=capital omega and [I]=A?


quote:

ORIGINAL: witpqs
No Omega on keyboards helped to change that usage I guess, but yes I remember that. I don't recall "U" for voltage, though.



Maybe it's different customs in different countries/languages? In the US, I've always seen the equation as V = IR and the power equation as P = VI. I should have said I^2R losses in my earlier post. Not enough tea that day...

If you substitute IR for V in the power equation, you get another way to calculate power which is (IR)*I, which is I^2R. What it means is that if you have high current, your transmission losses are going to be the square of the current. Even if the resistance is low, the power lost in transmission can be big. By raising the voltage and lowering the current, the transmission losses are reduced.

There is a difference between the unit designation and the letter used in calculations. In calculations, V=Voltage, I=Current, and R=resistance. When showing a value, Volts=V, Amps=A, and Ohms=Ω (omega).

And IFF was used extensively in the Pacific. In the Aleutians ground controlled approach was also used to allow landing in zero visibility conditions. This required the plane to have extra equipment on board. My father was a photographer attached to different units at different times. He flew with B-29s at Saipan, B-25s in New Guinea and the Philippines. At the end of the war he was flying in B-25s out of Attu. He said the Aleutian B-25s were loaded down with a lot of extra electronics that wasn't on the 5th AF B-25s. The planes were very cramped inside.

Sometimes aircraft also had more than one radio and radios were large power hungry beasts back then.

Bill

"E" for voltage is what you might find in older books in the US. I remembered it from high school. Never made sense using E, so it's good they changed it to V. You will still find E in plenty of places, just call up this Google search (I hope this link works, it's from the results page):

https://www.google.com/webhp?source=search_app#hl=en&sclient=psy-ab&q=E%3DIR+ohms+law&oq=E%3DIR+ohms+law&aq=f&aqi=g-q1&aql=&gs_l=hp.3..0i22.24752.26525.1.30685.9.9.0.0.0.0.229.1542.0j8j1.9.0...0.0.mfP-m9Q9IEI&pbx=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&fp=ecb6a798695883bc&biw=1566&bih=907

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