More about tires Tire sizes are expressed by the manufacturers with three sets of numbers: Tread width – Aspect Ratio – Wheel diameter (e.g. 215 55 R16) Automobile tires are described by an alphanumeric tire code (in American English) or tyre code (in British English, Australian English and others), which is generally molded into the [Read more]

Super capacitor discharge time calculator. This calculator determines timekeeping operation using a supercapacitor (ultracap) based upon starting and ending capacitor voltages, discharge current, and capacitor size. Formulas used: Bt(seconds) = [C(Vcapmax – Vcapmin)/Imax]  This formula is valid for constant current only. Bt(seconds) = -log(Vcapmin/Vcapmax)(RC) = t  This formula is valid for linear current only (simple [Read more]

The formula used in this calculation is from the famous Wheelers approximations which is accurate to <1% if the cross section is near square shaped. L (uH) =31.6*N^2* r1^2 / 6*r1+ 9*L + 10*(r2-r1) where… Please note that the diameter is measured from center of wire trough center of the coil and to center of [Read more]

Winding the wire in a single layer produces an inductor with minimal parasitic capacitance, and hence gives the highest possible self-resonant frequency (SRF). Striving to obtain a high SRF and low losses is the key to producing coils which have radio-frequency properties bearing some useful resemblance to pure inductance. The calculation is based on Wheeler’s [Read more]

This is an popular coil geometri used in todays wireless charger circuits. The formula used in this calculation is based on the Harold A. Wheeler approximations for air core flat spiral coil inductor. …where: 1 inch = 0,0254m=2,54cm = 25,4mm. This formula applies at ‘low’ frequencies (<30MHz) using enameled copper wire. Some people call it [Read more]

The first approximation is based on a modification of an expression developed by Wheeler; the second is derived from electromagnetic principles by approximating the sides of the spirals as current-sheets; and the third is a monomial expression derived from fitting to a large database of inductors (and the exact inductance values). All three expressions are [Read more]