ANTIQUE-RADIO-LAB
Welcome, please log-in to participate in this (your) forum, by logging in you agree to abide by the rules of this forum. Until you make your FIRST Login and post, you cannot PM a Member.
ANTIQUE-RADIO-LAB

Antique Radio Forum for Collectors antique-radio-lab.forumotion.com
 
HomeHome  RegisterRegister  Log inLog in  FAQFAQ  PublicationsPublications  SearchSearch  
Can't Log In?: 1st. thing is to clean out your cookies. if that doesn't work , click on Contact field.
(registration and/or Login Help ONLY) For other questions go to our FAQs link above.

Share | 
 

 Needing an unkown resistor calculation

Go down 
AuthorMessage
Cliff Jones
Site Administrator
Site Administrator
avatar

Join date : 2010-11-22

PostSubject: Needing an unkown resistor calculation   March 23rd 2018, 3:19 pm

I have a burned resistor but I don't have that value, so I have to improvise by making a parallel resistance circuit for replacement of the bad resistor.

I have had to scrounge my resistor stash to find a specific value, but ALAS no such luck!

So what do I do?

Get the next closest Higher Value and do this calculation.
If this doesn't work then I would go to the next higher value that I do have. This will be my starting point.

So I now designate a reference ID in brackets = () to numbers of each value.

Original Total Resistance for the circuit.

  = 150ohms (Rt)

The available closest higher resistor that I found in my parts bin.
 
= 200ohms (Ra)

Now I need to use that found value, to find what Unknown resistor value do I need to wire in parallel to come up with the original resistance value.
 =       ?   (Ru)

Calculate with this Transposed ALGEBRAIC formula: Note that the order in the original formula has changed by transposition.


From:    1     
         Rt +  Ra

 Plus to Minus


       1         
1/Rt -  1/Ra      = Ru? or 1/found or needed replacement.




               1               
 (1 / 150) - ( 1 /200 ) = Answer of 600ohms

Now let's prove my calculation formula by the reciprocal of the reciprocals for parallel resistor's method. study

          1       
1/Ra + 1/Ru? = 


   1    
200 = .0050   = Ra 


   1    
600 = 0.001667 = Ru


.0050 + 0.001667 = .006667
        
       1       
 .006667  =  150 total ohms for circuit  cheers

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
Back to top Go down
 
Needing an unkown resistor calculation
Back to top 
Page 1 of 1
 Similar topics
-
» The ups and downs of "needing" others
» AGE CALCULATION FROM LIFE LINE
» Feeling sad and needing some TLC from the people who understand
» Unknown man in my dream
» pregnant needing c section

Permissions in this forum:You cannot reply to topics in this forum
ANTIQUE-RADIO-LAB :: General Chatting Forum-
Jump to: