(12C) Resistors in Parallel - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Software Libraries (/forum-10.html) +--- Forum: General Software Library (/forum-13.html) +--- Thread: (12C) Resistors in Parallel (/thread-11657.html) (12C) Resistors in Parallel - Gamo - 10-25-2018 10:18 AM Program that solve up to "Four Pair" of unequal value of "Resistors in Parallel" and little add-on program that solve for one unknown out of two parallel resistors from your desire Total. Procedure: 1st Program: All resistors must be "unequal" in value. Store each value from R0 to R7 [R/S] 2nd Program Store R0 for known Total Store R1 for one of the two known resistor. To run first goto line 40 [R/S] ---------------------------------------------------- Example: Program 1: FIX 4 What is the total with 4 resistors in parallel? 50, 65, 120 and 250 50 [STO] 0 65 [STO] 1 120 [STO] 2 250 [STO] 3 [R/S] 20.9565 ------------------------------------------------------ Program 2: FIX 4 1st resistor is 50 and my desire total is 28.2608 What is the 2nd resistor value? 28.2608 [STO] 0 50 [STO] 1 [GTO] 40 [R/S] 64.9996 = 65 Program: Code:  01 RCL 0 02 1/x 03 RCL 1 04 1/x 05  + 06 RCL 2 07 X=0 08 GTO 37 09 1/x 10  + 11 RCL 3 12 X=0 13 GTO 37 14 1/x 15  + 16 RCL 4 17 X=0 18 GTO 37 19 1/x 20  + 21 RCL 5 22 X=0 23 GTO 37 24 1/x 25  + 26 RCL 6 27 X=0 28 GTO 37 29 1/x 30  + 31 RCL 7 32 X=0 33 GTO 37 34 1/x 35  + 36 GTO 38 37 X<>Y 38 1/x 39 GTO 00 -------------------------------------- 40 RCL 0 41 RCL 1 42  x 43 RCL 1 44 RCL 0 45  - 46  ÷ Gamo RE: (12C) Resistors in Parallel - Albert Chan - 10-25-2018 12:50 PM Hi Gamo Dieter had a better program, with more accuracy by doing R = R1 R2 / (R1 + R2) Quote:What is the total with 4 resistors in parallel? 50, 65, 120 and 250 There is no need for more code. Just keep running each pair in parallel. Parallel of 50, 65, R = 50*65/(50+65) = 28.261 "Add" 120, R = 120*28.261/(120+28.261) = 22.874 "Add" 250, R = 250*22.874/(250+22.874) = 20.957 (total of 4 resister in parallel) Quote:1st resistor is 50 and my desire total is 28.2608 What is the 2nd resistor value? Again, no need for more code. Remove a resister from total R, just negate the resister. R1 = -50*28.2608/(-50+28.2608) = 65.000 RE: (12C) Resistors in Parallel - Thomas Klemm - 10-25-2018 02:57 PM Or then we can use the method described by Sam Levy in his article EE calculations, some not obvious: Quote:Resistive Dividers When calculating from known resistors, enter the lower resistor repeatedly. Key in the top resistor, and add, the result is the total resistance, then divide, the result is the fractional output voltage of the divider. Then multiply and subtract to see the output resistance from the divider tap. This leaves us with a program that consists of just the 4 arithmetic operators: Code: + ÷ × - Example: 50 ENTER ENTER ENTER 65 R/S 28.2609 Kind regards Thomas This method uses: $$R_1 - \frac{R_1^2}{R_1 + R_2} = \frac{R_1 R_2}{R_1 + R_2}$$ RE: (12C) Resistors in Parallel - Gamo - 10-26-2018 05:01 AM Thanks to Albert and Thomas Many good varieties of ways to solve this type of problem. Gamo RE: (12C) Resistors in Parallel - Dieter - 10-28-2018 09:23 AM (10-25-2018 12:50 PM)Albert Chan Wrote:  Dieter had a better program, with more accuracy by doing R = R1 R2 / (R1 + R2) Here is how you can do it on the 12C: Code: 01 ENTER 02 ENTER 03 R↓ 04 R↓ 05 X<>Y 06 x 07 X<>Y 08 LstX 09 + 10 ÷ As already pointed out, this is all you need for both calculations: Add up parallel resistors: enter resistor values, one ofter another, and press [R/S] Simply think of [R/S] as an "add resistor" key. Find the required resistor for a given total: enter resistors as before, finally enter the desired total and press [CHS] [R/S] [CHS] Example 1: Two, three, four or more resistors in parallel. 50 [ENTER] 65 [R/S] => 28,26 120 [R/S] => 22,87 250 [R/S] => 20,96 Example 2: Find the missing resistor. Assume you have 100 and 220 Ω, and a total of 50 Ω is required. 100 [ENTER] 220 [R/S] => 68,75 50 [CHS] [R/S] [CHS] => 183,33 Or for Gamo's example: 50 [ENTER] 28,2608 [CHS] [R/S] [CHS] => 65 Dieter