Electronics > Beginners
Calculating value of resistors in parallel
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ArthurDent:
Here.

paf:

Well, if you are not good at algebra, cheat a little with some short circuits. 

Calling the conductance G1=1/R1 and so on, you can do the following:

1)  Shorting 1 with 4 and 3 with 2, between those two terminals   Gx=G1+G3
2)  Shorting 1 with 3 and 4 with 2, between those two terminals   Gy=G2+G4
3)  Shorting 1 with 2 and with 3, between those  terminals and 4  Gz=G3+G4
4)  Shorting 1 with 2 and with 4, between those  terminals and 3  Gt=G2+G1


Measure Rx, Ry, Rz and Rt. Invert those and you got  Gx, Gy, Gz and Gt.

Solve the equations, and invert the found values to have the resistors.


 
 
soldar:

--- Quote from: ArthurDent on January 02, 2019, 10:51:24 pm --- Here.
--- End quote ---
Thanks! That fits the data pretty nicely. It makes the value of one resistor infinitely large and it makes sense that there are only three resistor elements.  I am really curious as to how you did it.
soldar:

--- Quote from: paf on January 02, 2019, 11:02:07 pm --- Solve the equations, and invert the found values to have the resistors.
--- End quote ---
Easy to say isn't it? The problem is that several people come in and suggest a way but they don't do it. And I have thought of those ways and I always get stuck. So I would like anyone who thinks they can solve it to actually do the work of solving it and showing us how it is done. Because I just get stuck along the way.
ArthurDent:
I first assumed no real hotplate would have a diamond shaped resistor configuration because it would probably make the switching too complex. Next I rounded the values so they were more common and easier to visualize. I then noticed that 60+90+180=330 so I guessed there might be just 3 resistors, not 4. Then I tried different series combinations to see if I could get a combination that fit the data given and found one. On the first go around I copied the last equation wrong and that slowed me down until I realized that it was 3*4-1*2 which would put the 3 resistors in parallel to give 30 ohms where I originally got 90 because I had 3*4-1 so I was missing one jumper.

It actually took a while to see what to do and there were a few dead ends before I got it right. No higher math was used, only the parallel resistor equation. It is simple once you see how it's done.
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