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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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6th Jun 2020, 3:58 pm | #21 |
Octode
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,465
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Re: Parallel Resistor Chart
One little wheeze that I found out some time ago when considering parallel combinations of resistors was that the final resistance is always smaller than the smallest resistor in the combination. If you are doing the calculation in your head, this is a useful sanity check.
Colin. |
6th Jun 2020, 5:39 pm | #22 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,191
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Re: Parallel Resistor Chart
Another trick is to remember that if you have n identical resistors in parallel, the resistance is 1/n of the resistance of one of them. So 2 off 100 ohm in parallel gives 50 ohms.
You can sometimes extend this. For example, what is the resistance of a 50 ohm and a 100 ohm resistor in parallel? Well, think of the 50 ohm as being 2 off 100 ohm in parallel. So you can consider the overall circuit as 3 off 100 ohm in parallel, giving 33+1/3 ohms. |
6th Jun 2020, 7:08 pm | #23 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
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Re: Parallel Resistor Chart
The four level stack reproduces from the top when dropped, so you can take say the 96th root of 10, jack the result up to the top, then just keep pressing x and the display will step through the E96 resistor values for 1% components. 24th root of 10 will generate the E24 series stepped with a single button press. Set the display to round to your preferred resolution.
David
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12th Jun 2020, 11:59 pm | #24 |
Nonode
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
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Re: Parallel Resistor Chart
I still use the old method I was taught in college almost 50 years ago. (X= either R or C)
1) Resistors in series act like capacitors in parallel and 2)resistors in parallel act like capacitors in series. 1) XT= X1+X2 2) XT= (X1*X2)/(X1+X2). However it's only a simple maths process to transpose values to find the resistor (parallel mode)/capacitor (sere is mode) needed to get a value. Perhaps the most simple method using a program is using Sinclair Basic, with something like Basin. ,where one could use a resistor series and a data string to find which pair /or more got within the needed tolerance of the value. |