Electrical Formulae

Dionysus

Well-Known Member
I figured to further our "Codex" of technical information a listing of Electrical Formulae and relationships would be a handy reference for those newer to the wonderful math surrounding electricity.

This is only intended as a handy reference. Indeed the equations in this article are reference, and do not describe the underlying principles of electricity. For those of you interested in Electrical Engineering, a LOT of further instruction is required for proper understanding. Just because you know a formula, does not mean you know how to appropriately apply it in the real world. Please leave electrical work to the professionals.

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In the formulae I used "to the power of negative one" instead of the common notation to make it easier. The Equation above shows that they are indeed the same thing. It's just a lot easier to show the formulae on one line of text than two or more.

Letter meanings:

E = EMF or Voltage (In Volts (V))
I = Intensity of Current or Amperes (in Amps (A))
R = Resistance (In Ohms (Ω))
Z = Impedance (In Ohms (Ω)), for RCL circuits
X = Reactance (In Ohms (Ω)), for C and L circuits
P = Power (In Watts (W))
C = Capacitance (In Farads (F)), for capacitors
τ = Time for one Constant in Seconds (for calculating with Capacitance)
L = Inductance (In Henrys (H)), for Inductors
PF = Power Factor (%)
VA or S = Apparent Power
VARs or Q= Reactive Power
Q = Quality of an Inductor, The relationship between the Reactance and Resistance of an Inductor.
Q = Electric Charge in Coulombs (Yes Q is a commonly used letter to many people's annoyance)
f = Frequency (In Hertz (hz))

Electrical Formulae:
Basic:
E=IR
P=IE
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Capacitance: (I leads E by 90-degrees)
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Q = CV
pC = KA ÷ 4.45 D

Inductance:
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This is a work in progress, because just coding it was not going to work on these forums, so I am making a series of images to make the table readable with subscripts.

Calculations for Electronics:

Calculations for Motors:
K1 ... (Will complete later)
 
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Some comments:

What exactly is the "Quality of an Inductor"? Q is most commonly used as the letter for reactive power, like P is for real power. VAr's are the units for reactive power. VA's are the units for apparent power; S is the common letter for apparent power.

pC = KA ÷ 4.45 D -- What exactly is this?

The units for volts and real power should be capital V and W, not lowercase.

There should probably be some exclaimer about proper use of these formulae doth not an engineer one make.
 
Obviously I am nowhere near done. And welcome anyone to continue on...

The "Q" of an inductor is the relationship between the Inductive Reactance and the Resistance (which is XL over R). It's the letter I learned for such.

and Yes Q is also used for Reactive Power, however Commonly used VA and VAR for equations (instead of Q and S).


pC = KA ÷ 4.45 D is the formula to calculate the Capacitance of a capacitor.
Where K is the dielectric constant, A is the area, and D is the distance in inches. The p stands for Pico since this equation outputs picofarads instead of Farads.

1F is 1000000000000 pF.

humm, did I have the case wrong on W and V? *shrugs* typo.

you are more than welcome to continue contributing to this article indeed.
I've been making the equation graphics in Illustrator with the font Myriad Pro, Subscripts and superscripts in 9pt, normal 18pt. I certainly won't finish this article today on my own.
 
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