Re: Parallel Resistance calculator


John T. Fitzer
 

You don’t need a specific calculator, Just keep in mind that for parallel values of resistors the equivalent resistance will always be lower than the lowest value of any one resistor in the parallel combination. The easiest way to calculate the needed value of a parallel resistor combination is to convert all values of resistance into conductance. The value of any resistance in mho is equal to 1/R where R is resistance in ohms. As an example let’s say you have an 81 ohm resistor and you want to parallel that with some value to get 50 ohms. 1/50=0.02 – 1/81=0.012345679=0.007654321 mho of additional conductance required =1/0.007654321 ohms =130.6451613 ohms. Nearest standard value = 130 ohm 5%. If you want to find the parallel resistance of 2 or more resistance, simply convert each resistance to conductance, add them all together then convert back to ohms by taking the reciprocal of the total conductance, i.e. R total = 1/ 1/R1+1/R2+1/R3 etc. Example the parallel combination of a 100 ohm, 150 ohm, & 180 ohm resistors in parallel = 1/100 = 0.01 + 1/150 =0.006666667 + 1/180 = 0.005555556 =0.022222222 mho = 1/0.022222222 = 45 ohm. I hope this helps

 

From: main@4SQRP.groups.io [mailto:main@4SQRP.groups.io] On Behalf Of Jeff Collins
Sent: Wednesday, June 20, 2018 3:11 PM
To: main@4SQRP.groups.io; 4sqrpio
Subject: Re: [4SQRP] Parallel Resistance calculator

 

Dear WA0ITP,

    Try this: https://gock.net/resistor/

    Or this: parallel resistor calculator reverse

Thank you,
 
Jeffrey R. Collins - W7GRV
FCC(SW) USN, Ret.
BS, EMT-P, FF I/II
Training Oficer -
Birch Tree Volunteer Fire and Rescue
Member of Missouri Region G HazMat Team

On 6/20/2018 2:45 PM, WA0ITP wrote:

A while back someone  posted, on some list, a link to a calculator that provided abt 15 or so parallel resistor combination which matched a desired value that was entered into the calculator.  Matching parallel values were tabulated as were error deviations in percent. Alas I lost the email with the link.

Google is not my friend on this.  Did anyone here see and save that email/link?  Thanks for checking, appreciate it.

-- 
72 WAØITP
I love this radio stuff.
www.wa0itp.com
www.4sqrp.com

 

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