Electrical Question

drunkenbeagle said:
In most places, at least you are being charged for power, not current. They aren't the same thing.
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True, but unless they've changed something they're directly proportional (P=IE) or is that different with AC? I've brain dumped all that since 99.5% of the time if I'm chasing electrons they're going in a straight line not bouncing back and forth.
 
Flying Saluki said:
The main thing to remember is that while generators can produce either AC or DC power, the only way to STORE DC power is in a battery. Without a battery, the only way to get AC power is to generate it by engine rotation.
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You can't "store" current, period. Whether it is DC or AC, current means the rate of movement of electricity, 1 Ampere = 1 Coulomb per second. Coulombs are electric charge, equal to about 6X10^18 electrons (a lot). You can store electric charge, which both a battery and a capacitor can do. There are also, in fact, devices that store energy from a change in current (AC), these are called Inductors (the change in current creates a magnetic field as current changes, and will produce a charge as the field collapses.

Of course, all of that is irrelevant to storing power for aircraft electrical systems. Honestly, expecting pilots to know this is like expecting them to know how to refine West Texas Intermediate into JetA.
 
Roger Roger said:
True, but unless they've changed something they're directly proportional (P=IE) or is that different with AC? I've brain dumped all that since 99.5% of the time if I'm chasing electrons they're going in a straight line not bouncing back and forth.
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Depends if they care about power factor, which does often matter for commercial customers. Simplified, if you take an amp in, and send .5 amps back out, they don't like that. So you get charged for the whole kilowatt, instead of the half kilowatt you actually used. (The math is a bit more involved with AC, but you get the idea).

If you are curious: https://en.wikipedia.org/wiki/Power_factor
 
drunkenbeagle said:
Depends if they care about power factor, which does often matter for commercial customers. Simplified, if you take an amp in, and send .5 amps back out, they don't like that. So you get charged for the whole kilowatt, instead of the half kilowatt you actually used. (The math is a bit more involved with AC, but you get the idea).

If you are curious: https://en.wikipedia.org/wiki/Power_factor
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Yeah, see, witchcraft.
 
drunkenbeagle said:
AC can allow for thinner gauge wiring, which is lighter and costs less. This is mostly because AC is typically a much higher voltage as compared to DC. In GA aircraft, the currents involved don't justify the added weight and complexity of transformers and separate electrical buses. Larger aircraft - it can shave off enough weight to be substantial. While DC could technically be more efficient at higher voltages, there are lots of practical reasons that you don't want a 400vDC electrical system: It arcs, promotes corrosion, difficult to step down, no batteries available at those voltages...

It is also much easier to get "clean" AC power without too much noise in it. DC tends to have a lot of ripple, so needs to have voltage regulators which add to the losses.
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I intendegauge required between AC vs DC, instead will add giant capacitors store enough DC power to start diesel truck engines and can be recharged
drunkenbeagle said:
AC can allow for thinner gauge wiring, which is lighter and costs less. This is mostly because AC is typically a much higher voltage as compared to DC. In GA aircraft, the currents involved don't justify the added weight and complexity of transformers and separate electrical buses. Larger aircraft - it can shave off enough weight to be substantial. While DC could technically be more efficient at higher voltages, there are lots of practical reasons that you don't want a 400vDC electrical system: It arcs, promotes corrosion, difficult to step down, no batteries available at those voltages...

It is also much easier to get "clean" AC power without too much noise in it. DC tends to have a lot of ripple, so needs to have voltage regulators which add to the losses.
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AC allows lighter gauge wiring I s true, but capacitors store DC voltage .
 
Bandit_Driver said:
Just fly a Saab it has a little bit of everything to make everyone happy.

2 Alternators
2 28 DC Generators
2 115v AC Generators with Wild Freq's
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The Dash-8 had a similar setup. Two DC starter/generators. Three inverters to go from DC to 400hz AC for avionics. 2 AC variable frequency generators for the hot stuff, but could also power TRUs to convert the AC back into DC. There were about a jillion buses and bus ties to go with it.

Those crazy Canuks...with all that juice, they couldn't figure out how to pipe cold air into the cockpit. Hell, they could have hung a window AC unit on the cockpit door with all that wattage.

Richman
 
hook_dupin said:
This is an important lesson. It clearly demonstrates that DC has red electrons while AC has green electrons. Note the variable grey. Eventually, that breaks and releases the electrons in the form of grey smoke. The circuits don't work if you let the smoke out of them...

EE major here.
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I wasted my entire youth on model rockets, airplanes, computers and yes, electronics. Had everything that RadioShack sold and had an account at Digikey. Rocked the breadboards and had some cool stuff.

Thought I was the man. Then I took "EE for Non-Majors" at school...read some of what I was supposed to know, and was basically "derp" for the whole semester. The lab looked like it had been donated by Dr. Frankenstein (pronounced Fraan-ken-schteen). As much as we thought the CivEs were arts and crafts, the EEs were, phew, smart guys. We were just the "Doesn't fit? Hit it with a hammer. Still doesn't fit? Get a bigger hammer, and some moly grease" MechEs.

When I did my Extra Ham ticket, the study book was chock-full-of-stuff that brought back all sorts of unpleasant EE memories, like a toilet backing up after a visit to Del's Taco Truck Emporium and Smoothie Stand. Ugh.

Richman
 
Richman said:
The Dash-8 had a similar setup. Two DC starter/generators. Three inverters to go from DC to 400hz AC for avionics. 2 AC variable frequency generators for the hot stuff, but could also power TRUs to convert the AC back into DC. There were about a jillion buses and bus ties to go with it.

Those crazy Canuks...with all that juice, they couldn't figure out how to pipe cold air into the cockpit. Hell, they could have hung a window AC unit on the cockpit door with all that wattage.

Richman
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Well, the Q400 is mostly a DC aircraft, has two DC starter/generators, two AC generators and two TRUs. NOW, the problem is that the cockpit is freezing cold while the back is hot. They can't seem to find a happy medium, as now it will freeze you out!
 
Richman said:
The Dash-8 had a similar setup. Two DC starter/generators. Three inverters to go from DC to 400hz AC for avionics. 2 AC variable frequency generators for the hot stuff, but could also power TRUs to convert the AC back into DC. There were about a jillion buses and bus ties to go with it.

Those crazy Canuks...with all that juice, they couldn't figure out how to pipe cold air into the cockpit. Hell, they could have hung a window AC unit on the cockpit door with all that wattage.

Richman
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The SAAB isnt much better. It gets so freaking hot in there during the summer. Lately its been over 100 in Redding and we have been burning up. It just takes forever to cool down.
 
It's also the story of competing entrepreneurs: Thomas Edison (liked DC) and George Westinghouse (liked AC). As the science evolved (1880s - 1910 and on), the prize: an electrical system to power both homes and factories. Apart from the other advantages of each, the major issues involved transmission over distance, and generating the damn stuff in the first place (advantage: AC) and safety & storage (advantage: DC). In this area of endeavor (Iong term), Edison lost and Westinghouse won.

The Wright Brothers didn't care much. Today, they just might.
 
FloridaLarry said:
It's also the story of competing entrepreneurs: Thomas Edison (liked DC) and George Westinghouse (liked AC). As the science evolved (1880s - 1910 and on), the prize: an electrical system to power both homes and factories. Apart from the other advantages of each, the major issues involved transmission over distance, and generating the damn stuff in the first place (advantage: AC) and safety & storage (advantage: DC). In this area of endeavor (Iong term), Edison lost and Westinghouse won. The Wright Brothers didn't care much. Today, they just might.
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someone forgot Tesla ... 8(
 
Richman said:
Thought I was the man. Then I took "EE for Non-Majors" at school...read some of what I was supposed to know, and was basically "derp" for the whole semester. The lab looked like it had been donated by Dr. Frankenstein (pronounced Fraan-ken-schteen). As much as we thought the CivEs were arts and crafts, the EEs were, phew, smart guys.
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Even as an EE major, I think I really understood about 5% of what I was supposed to be learning at the time. Lies and magic - that's how most of it apparently worked. As sharp as the EE folks were, I think the Physics majors had it harder.
 
drunkenbeagle said:
Even as an EE major, I think I really understood about 5% of what I was supposed to be learning at the time. Lies and magic - that's how most of it apparently worked. As sharp as the EE folks were, I think the Physics majors had it harder.
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People don't realize how broad EE is. My wife is also an EE, but she loved power systems. Load balancing, lag shifts, etc ...I just didn't get it. I loved embedded systems... the idea that you could create code to etch individual gates was amazing to me. My wife hated that stuff, and we never studied together.
 
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