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Electrical Experts

Not true, all circuits are essentially the same, the equipment for medical equipment is just more sensitive to the capacitance and inductance that is inherent in the circuit. Even semiconductors have resistance, capacitance and inductance.

Also, where you were talking about Ohm's law above is somewhat correct, the added resistance of the wire will drop the current draw. However, 12 volts is not constant. The wire is in series with the lamp, this causes a voltage drop across the wire, therefore, at the lamp the voltage is not 12 volts, this is why the lights are dimmer. The lower voltage at the light causes the current through the light to be less, which generates less light.
 
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Wires do not have any capacitance

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I suppose you can't say that wire has ZERO capacitance

[/ QUOTE ] you stand corrected,,,,,
 
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Ohm's law is just that--electrical law. It is established as proven fact in the sense of the way current flows in a circuit. It is impossible to defy electrical law just like it is impossible to defy gravity or any other scientific law.

If one day you can figure out how to prove it wrong, it will no longer be accepted as mathematical fact. Until then, Ohm's law is just as valid the fact that my 140 lbs can't jump off a cliff and fly. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif

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Lightning strikes and the current generated during a lightning strike will not always obey Ohm's Law.
 
I'm not going to read the whole thread since it looks like a bunch of people arguing over weewee size.

I'll assume we're talking about DC because confusing people with reactive power, power factor, et cetera would be far too much fun. Therefore, we'll assume we're at a power factor of 1. And we'll keep it simple and not pay attention to any curves and use my best friend Mr. Watt to explain power.

Volt-Amps and Watts are not the same. Watts include the power factor. Therefore, Watts only include the amount of power available for work. VAs include all power.

It's all about the Volt-Amps (VA) rating of the battery. More often than not they're rated using amp-hours. So, at say 12 volts it'll run at 10 amps for 20 hours.

12 volts * 10 amps = 120 watts
and it'll do it for 20 hours
so that would be .120 * 20 kilowatt-hours. or 2.4kwh.

Almost all batteries are rated based on 20 hour discharge time.

There is no way by merely looking at a battery to get a good idea of how many VAs it has. It is all relative to plate surface area, volume of chemical inside, and the temperature it is at.




As for the goons arguing about capacitance and inductance... go sit in the corner. There is no noteworthy capacitance, reactance, admittance, reluctance, or inductance in a DC circuit that isn't being switched on and off in the millisecond or more frequent range. You can get rid of the capacitance by twisting the effing wires.

While you're sitting in the corner with the paper cone on your head... think about why once a 60 hertz wire gets half an inch thick they start filling it with a hollow core.
 
What are you talking about a 60 Hz wire? Are you talking about 600V building wire? High voltage conductors? I'm just curious what the hollow core wire is used for?
 
A wire in the middle of outer space with nothing near it has basically zero capacitance. It is the interaction between conductors that leads to wire capacitance. Since the wire for the lights runs near the chassis or other wires, there is some. Since this is a steady state circuit, the amount of capacitance doesn't matter. The battery is kind of a huge capacitor anyway, several orders of magnitude greater than the wiring capacitance.

The wire also has inductance, probably 1uH for every 4 feet or so. This matters for transient equipment like amplifiers, but not for this lighting example.

The only property we care about in this example is the wire's resistance.


Capacitors block current flow? Not a good definition. One simple application is to block DC current. Fundamentally, a capacitor stores electrical energy proportional to it's voltage. It can be used to store energy for transients, work as a high-pass or low pass filter, etc.
But we digress.....
 
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You can get rid of the capacitance by twisting the effing wires.

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Oh man, I thought you were an MTU student? Twisting the wire reduces the mutual inductance between them. It increases the capacitive coupling.
 
Wanna Bet. Follows the path of least resistance to ground (Earth). Also makes a hell of alot of RF. But that's a whole bunch of other formulas.
 
[ QUOTE ]
[ QUOTE ]

Ohm's law is just that--electrical law. It is established as proven fact in the sense of the way current flows in a circuit. It is impossible to defy electrical law just like it is impossible to defy gravity or any other scientific law.

If one day you can figure out how to prove it wrong, it will no longer be accepted as mathematical fact. Until then, Ohm's law is just as valid the fact that my 140 lbs can't jump off a cliff and fly. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif

[/ QUOTE ]

Lightning strikes and the current generated during a lightning strike will not always obey Ohm's Law.

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Sorry, forgot the quote.
 
I never said it wouldn't follow the path of least resistance. It will do some funky stuff as far as voltage and current though. If you really want me to, I can find some of the studies I have seen where it was not exactly following Ohm's law.
 
I would be interested in them if you can get them. I read some years ago, some pretty wild (jeep) happens before, after and during a strike. I wouldn't want to be around. /forums/images/graemlins/eek.gif
 
We're going to play word games, eh? It'd be nice if we could get rid of capacitance that way.

Last I knew were were talking about DC systems... but yes, twisting a pair of wires does trade "mutual inductance" for capacitance.

In our special case I don't think we have to worry about capacitance... since it's a DC system and chances are the voltages being used are small, the insulator thick, the wire pretty small, and the proximity of the wires probably aren't very close.

I suspect that inductance is a larger concern than capacitance.
 
60Hz... what's in your house.

After two depths of penetration you're flowing around 99% of the current. Making the wire thicker won't gain you much current carrying capacity. So once the wire gets to half an inch thick (roughly two depths of penetration) they start putting a core in the middle.
 
So have we established who has the biggest dick yet?

/forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif

Rene
 
So what you are saying is any wiring used on a 60 Hz system that is over a 1/2 inch in diameter has a hollow core?

That is not true, I have a piece of 500kcmil copper conductor that is 7/8" in diameter. It is stranded, but there is no hollow core. The stranding gives it more surface area for the current to "travel" on.

And just for the record, they do not rate a wire on frequency. The insulation is rated based on voltage and temperature, and the conductor is sized per ampacity.
 
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So have we established who has the biggest dick yet?

[/ QUOTE ] yeah,,,ME /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif /forums/images/graemlins/woot.gif
 
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So what you are saying is any wiring used on a 60 Hz system that is over a 1/2 inch in diameter has a hollow core?

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No, I'm saying that there is no need for the wire to continue to not be hollow. The depth of penetration is around 8mm at 60Hz if I remember correctly. 16mm is roughly half an inch. Many manufacturers will choose to make the wire hollow after just one depth of penetration if they can get away with it (makes it a bitch to terminate). By the time they get to two depths (32mm or so, roughly 1.25") almost all manufacturers will start to use some kind of core because you're at 99%.

Saying ALL wiring over 1/2" in diameter has a hollow core is like saying all Justins in the world have common sense.

I gave you the reasoning for it, what you do with the information is up to you.

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That is not true, I have a piece of 500kcmil copper conductor that is 7/8" in diameter. It is stranded, but there is no hollow core. The stranding gives it more surface area for the current to "travel" on.

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Would you like a cookie or a "I have a big penis" badge for your efforts? There's a lot more to why they stand wire than eddie currents.

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And just for the record, they do not rate a wire on frequency. The insulation is rated based on voltage and temperature, and the conductor is sized per ampacity.

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Oh, really? I'd have never thunk it. /forums/images/graemlins/rolleyes.gif However, many wires have specifications on frequency. The dome light wire to your mom's Civic isn't going to function too well when I hook it up to my oscilloscope.
 
First of all, I now realize and fully admit that I am, in fact, a geek. I must be because this is one of the most interesting threads I've read in a while.
Having said that... Now I know why I went with Civil Engineering instead of EE. This stuff (AC/DC circuits) can get extremely complicated in a hurry!!! /forums/images/graemlins/eek.gif
 
Okay, the cocky attitude doesn't really do much. Since you said it's for 60Hz and that's what's in my house, I want you to show me a manufacturer currently selling a hollow core THHN/THWN or similar conductor. /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif

I would like to see this, since I have never heard or seen of a manufacturer supplying it.
 
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