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Calculator for resistors in parallel.

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the resistors

Enter resistance of original resistor
in Ohms (1) and Watts [2].

This calculator was made to calculate what resistor is needed to place in parallel with a higher value when you can not find a resistor the same value of one that is needed to be replaced.

  (1) Original   = Ohms.
Answer when (2) is 0 (zero) , Box (3) and (4) used.
[2]  Watt.

Enter resistance of first choice resistor in Ohms (3).

To find a value of two resistor in parrallel, enter the values in (3) and (4) (bottom) to get the combined value in (1) make sure box [2] is 0 (or zero in it).

(3) Your choice in Ohms.

What the power rating of first choice resistor should be.


The extra resistor needed.

(4)? Resistance = Ohms.
Answer when box 1, 2, 3 is used.

Lets say you have to fix something that needs a 15 Ohm 3 Watt resistor replaced, so you look in your parts stock and only find a 22 Ohm 2 Watts what resistor would you need to go in parallel with it, and would the 2 watt power rating be all right, by putting the three values 15 (in box 1), 3 (in box 2), 22 (in box 3) in the calculator above and pressing the [Answer] button, you will find the 2 Watts is just a fraction under the limit, this is all right (but check anyway) , a 47 Ohm (in box 4), 1 Watt will be good resistor to use in parallel.

 You could if you wish find the resistor values by the hard way.
1/Total Resistance = 1/first resistor in parallel + 1/second resistor in parallel + 1/third ..........
1/Total Resistance = 1/r1 + 1/r2 + 1/r3 ........
So without the calculator above you need,
1/unknown resistor = 1/original resistor - 1/first choice resistor

If you just need to find the value of two resistors in parallel try,
Total Resistance = (r1 * r2)/(r1+r2)

By leaving the "original resistor" power as "0" (box 2) then the calculator above can be use to find the total resistance (box 1) from two known resistors in parallel (box 3 & 4).

"NaN" on the calculator means that it is Not a Number, like infinity.

From Eric.
Have a happy day (Somebody has too).

Resistor/Capacitor TOLERANCE CODE:

 For the tolerance chart below,
 Use first 3 columns for capacitors.
 Use last 2 columns for resistors.

Tolerance   Capacitor   Resistors
A = ±0.05pF  ±0.05% Gray.
B = ±0.1pF  ±0.1% Voilet.
C = ±0.25pF  ±0.25% Blue.
D = ±0.5pF ±0.5%±0.5%Green.
E = ±1pF     
F = ±1pF ±1%±1% Brown.
G = ±2pF ±2%±2% Red.
H = ±2.5%   
J = ±5%±5% Gold.
K = ±10%±10%Silver.
L = ±15%   
M = ±20%±20%(No color)
N = ±30%   
P = +100 -0%   
R = +30 -20%   
S = +50 -20%   
Z = +80 -20%