# Calculation of Inductance from referred website.

Discussion in 'General Electronics Chat' started by Spark Plug, Jan 17, 2009.

1. ### Spark Plug Thread Starter New Member

Jan 16, 2009
3
0
Sarg...

This is a very beginner question. I went to the website you posted for resistance in parallel calculations and inside it I clicked on Inductance calculator: http://www.qsl.net/in3otd/indcalc.html

Can you please clarify the 'd' in the formula and picture.

I thought it was the diameter of the coil. But in the picture it looks like a cross sectional picture of the wire size windings making up the coil? Can you please clarify which it which?

Another puzzle is, if the L is proportion to the square of the "d", then how is it inversely proportional to the length of the windings plus .45 x the coil's 'd'?

I am trying to picture how and which the square of the d adds to the L while the length of the coil plus .45d would diminish it?

signed, Spark Plug

2. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
Moderator's Note: Posts 1 and 2 have been copied here from the "Tips and Tricks" thread. Post #3 was moved here. Please enjoy this current thread's discussion on inductance calculations!
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It has occurred to me that a thread where posters could pass on useful tips, tricks, rules-of-thumb, and conventions that may be of use for when you need a 'how to answer' not an in depth understanding. Please don't use this thread for asking questions.

I will kick off with a very simple but useful formula for making a non standard resistor by adding a parallel resistor to a standard one.

$R_{1} = \frac{R_{2}R_{d}}{R_{2} - R_{d}}$

$R_{1}$ is the required shunt resistor

$R_{d}$ is the desired non preferred value

$R_{2}$ is the (next) higher preferred value

Last edited by a moderator: Jan 18, 2009
3. ### SgtWookie Expert

Jul 17, 2007
22,183
1,732
In retaliation for StudioT's post...

Attached files:
1) Series_ParallelResistanceCalculator.zip - contains an Excel spreadsheet that has StudioT's formula in it, and also does series of lookups on standard E6 thru E192 series resistance tables to ensure use of only the standard values in the results. Just put in the resistance you want where indicated, and resistor combinations for all E-series are displayed.
2) E24PLL.ZIP - contains E24PLL.TXT, a rather large (224kb) text file that you can scroll through to find pairs of resistors to use in parallel to obtain a particular resistance.

Here's a handy web page that does both series and parallel calculations for you, for E12 and E24 series resistors:
http://www.qsl.net/in3otd/parallr.html
Note that you must select E12 or E24 each time you enter a new value, or you will receive an error message.

[eta]
3) CapSMTMarkings is an excerpt from a KEMET Packaging and Marking document, for identification of SMT capacitor values.
If there are two letters and a number, the manufacturer is the first letter. If just a letter and a number, only the value and multiplier is specified.

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