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 Forum for Collectors
HomeHome  RegisterRegister  Log inLog in  FAQFAQ  PublicationsPublications  SearchSearch  
CAUTION!!! When New Members post and leave a link to click on It may be Malicious so DONT, until they have posted a lot of times.


 Needing an unkown resistor calculation

Go down 
Cliff Jones
Site Administrator
Site Administrator
Cliff Jones

Join date : 2010-11-22

Needing an unkown resistor calculation Empty
PostSubject: Needing an unkown resistor calculation   Needing an unkown resistor calculation Icon_minitimeMarch 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/Rt -  1/Ra      = Ru? or 1/found or needed replacement.

 (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/Ra + 1/Ru? = 

200 = .0050   = Ra 

600 = 0.001667 = Ru

.0050 + 0.001667 = .006667
 .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
» pregnant needing c section
» Calculation methods for FTFM problems

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