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 Electronic Theory and Principle Discussion of electrical theory, law, etc.

#11
08-03-2012
 dish_moose micro ATX User Join Date: Apr 2012 Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts

^+1 If things were too easy people without iron rings on their fingers could do it too. ;-)
-Bruce
#12
12-22-2017
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

Quote:
 Originally Posted by jonnyGURU Thanks smart ass. I got an A in algebra, perfect score on the exam and was a programmer for some years. That's not the point of my question. I was just wondering if I could apply it to the electrical equations because the paper I was looking at was clearly trying to differentiate P = I^2 * R and V = I * R and I can't for the life of me understand why.
P = I * V is always true, V = I * R (Ohm's law) is not always; they are independent equations.

One can use Ohm's law to get variations

P = V^2/R
P = I^2 * R

but these depend on Ohm's law, and so are not always true; as such it is best to see the last 2 as derived, and not fundamental.
 The Following User Says Thank You to ashiekh For This Useful Post: jonnyGURU (12-22-2017)
#13
07-04-2018
 gdjacobs micro ATX User Join Date: Jul 2018 Location: Manitoba, Canada Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post

Quote:
 Originally Posted by jonnyGURU Right... because Ohm's Law is I = V / R which is the same as V = I * R. Damn... Why bother with the P = I^2 * R. Sheesh!
Usually because R is an end product of actually measuring voltage and current (and phase) through a circuit branch.. More often than not, components will be dynamic with different operating conditions and Requiv is not an invariable number.
#14
07-05-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

Quote:
 Originally Posted by gdjacobs Usually because R is an end product of actually measuring voltage and current (and phase) through a circuit branch.. More often than not, components will be dynamic with different operating conditions and Requiv is not an invariable number.
True, a capacitor and inductor have a frequency dependent imaginary impedance, and together with resistance in a circuit they form a complex impedance; one needs to know about complex numbers, which have a real and imaginary part. Imaginary is a rather unfortunate name, as they are as real as real numbers.

Practical Electronics for Inventors, 4th Ed, by Scherz and Monk is a good place to start as well as being very affordable; but be forewarned about the many typos and errors in this text.
Attached Images
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Last edited by ashiekh; 07-05-2018 at 01:40 PM.
#15
07-05-2018
 gdjacobs micro ATX User Join Date: Jul 2018 Location: Manitoba, Canada Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post

Quote:
 Originally Posted by ashiekh True, a capacitor and inductor have a frequency dependent imaginary impedance, and together with resistance in a circuit they form a complex impedance; one needs to know about complex numbers, which have a real and imaginary part. Imaginary is a rather unfortunate name, as they are as real as real numbers. Practical Electronics for Inventors, 4th Ed, by Scherz and Monk is a good place to start as well as being very affordable; but be forewarned about the many typos and errors in this text.
Yes, in a general sense, you have to account for complexes of reactive components. Even for pure DC, though, components often have complex behavior that can't be modeled as pure resistance (although they usually have a resistive component). For instance, a DC motor will include resistances from the rotor coils, brushes, and field coils (although those are separately measurable) as well as back EMF generated on the rotor coil.

I prefer Electronics Principles by Malvino. His approach using successive approximations of components is brilliant and clear, I think.
#16
07-05-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

Quote:
 Originally Posted by gdjacobs I prefer Electronics Principles by Malvino.

\$136 is out of my budget, so I ordered the 6th edition to save money; thanks for the suggestion.

Electronics for Inventors is \$21 new for the latest edition
#17
07-11-2018
 gdjacobs micro ATX User Join Date: Jul 2018 Location: Manitoba, Canada Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post

I believe my copy is the 6th Ed as well. I hope you enjoy reading it.
#18
07-11-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

Came in yesterday, but I haven't really started it yet.
#19
07-14-2018
 Batboy88 1kW User Join Date: Jul 2018 Location: OH Posts: 100 Thanks: 0 Thanked 2 Times in 2 Posts

That's where some got into trouble changing stuff and think that really matters...they designed it all for a reason and matching PWM, Impedances frequency dependent etc, as well stated it's not just resistance.
#20
07-14-2018
 jonnyGURU Site Founder Join Date: Oct 2006 Location: jonnyGURU forums, of course! Posts: 15,301 Thanks: 489 Thanked 1,995 Times in 1,236 Posts

LOL! Why does this 10+ year old thread continue to thrive!!!!????
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