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Resistor Question

Discussion in 'Home Brew' started by Low_Boy, Apr 14, 2018.

  1. Low_Boy

    Low_Boy Well-Known Member

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    I am doing a experiment and need a 47K ohm 1 watt resistor. Something I do not have. Why when I put 4, 47K 1/4 watt resistors side by side and wrap them together I end up with 11K? Shouldn't I end up with a 47K 1 watt? I am hoping this does not make me sound like too much of a idiot.


     

  2. sp5it

    sp5it Master of puppets

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    11k, right.
    Mike
     
  3. OldTech03

    OldTech03 Well-Known Member

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    BECAUSE YOU NEED TO PUT 2 47 Ohm'ers IN SERIES AND THE OTHER 2 IN SERIES AND THEN PUT THEM IN PARALLEL. 47+47 WILL BE 94 AND THEN IN PARALLEL, IT WILL HALF THAT. THAT SHOULD RESULT IN A 47 Ohm 1 watt+ reistor
     
    #3 OldTech03, Apr 14, 2018
    Last edited: Apr 14, 2018
    Captain Kilowatt and Robb like this.
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Resistors in series add. Resistors in parallel divide. OldTech03 has the correct answer.
     
    Robb likes this.
  5. Low_Boy

    Low_Boy Well-Known Member

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    OK that is why I was getting 11.7K Roughly 1/4 of what I wanted with the 5% tolerance.
     
  6. Low_Boy

    Low_Boy Well-Known Member

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    I screwed up
     
  7. sunbulls

    sunbulls Well-Known Member

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  8. Low_Boy

    Low_Boy Well-Known Member

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    Thanks, that page has a lot of good info.
    I think I am, and did order what I need. That one will be hard to come up with. LOL.
     
  9. Onelasttime

    Onelasttime Well-Known Member

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    You need to be thinking "series and parallel" no different than batteries or caps or speakers. They all function in much the same way when looking at combining them to get whatever value you need. You will seldom run into a situation when you need all "series" or all " parallel" outside of some fairly narrow situations. In real life more often than not you will need to mix and match!

    You need to comitt Ohms Law to memory and now how to solve for X. Just like batteries you have to know if you are after more volts or more current etc....Depending on which you are after you can have very very different configuration!

    So this is just a simple issue of you asking the wrong question! Ask the wrong question and no matter how perfect the answer is it will still be the wrong answer because you asked the wrong quest! Make sense! So problem-solving is just like math even when you are given all the information to solve a problem if you ask the wrong question nothing else matters! This is fundamentally true in almost everything!

    When you do something and get a different outcome than what you think you should get you should always do two things. First, take a break if you can go get a beer or coffee or tea etc....Sit down and look closely at what you think you are asking! That and you check the parts to make sure that each part matches what is on the part.

    The second time I went back to college I was the old man sometimes I was older than the Prof.! I was 36 years old. When my fellow students got stuck and me and my partner had figure out the answer often they would want to answer. Normally I would instead tell them that they already had all the skills and info to solve the problem they were just asking the wrong questions. I would then proceed to ask them the question they needed to ask instead of the question they did ask. In 100% of the cases, I would walk them through problem-solving not giving them a single answer only asking them the right questions in the right order and they always got the right answer. In about 85% of the cases, these 18-20-year-old students had better math skills than I had but they did not understand how to problem solve.

    Over the course of 13-16 weeks, I taught them how to think and how to regroup after a failure! I gave them the skills to tackle any problem instead of giving them the answer. By the end of my time with them instead of asking me for the answer, they would ask me what question they should ask or what question they failed to ask or if they had asked the questions in the wrong order. They did not want the answer instead they wanted to learn how I do what I do. No one in their public schools or at University ever took the time to teach them how to think critically both vertically and horizontal. These kids where hungry to learn though and saw the value in learning how to think instead of just getting the right answer!

    It is the classic "Give a man a fish he eats for a day teach a man to fish and he eats for a life time!" situation. They thought I was some genius but I told them that unlike them I just had really good teacher's that wanted me to be able to solve any problem life tossed at me for a life time and that that sort of thing comes from learning how to think in general not just learning specific knowledge.

    In fact one of the biggest differences between someone that is just book smart versus someone that can apply what they have learned to real life is the ability to think for your self critically so that you can apply what yo have learned. That and you have to take action and be willing to make mistake and adapt when you fail to get the outcome you wanted!

    Good luck and God Bless! Give what I have said some serious that!
     
    #9 Onelasttime, Apr 30, 2018
    Last edited: Apr 30, 2018
    Shadetree Mechanic likes this.
  10. Low_Boy

    Low_Boy Well-Known Member

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    Also in batteries if you do something wrong you can get hurt pretty bad.
     
  11. 543_Dallas

    543_Dallas Sr. Member

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    If you have a smart phone there are some decent apps out there. I use electrodroid occasionally.
     
  12. Low_Boy

    Low_Boy Well-Known Member

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    I like graphic resistance calculator
     
  13. loosecannon

    loosecannon Sr. Member

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    four 180K 1/4watt resistors would get you 45K @ 1 watt.
    four 200K resistors would be 50K.

    both of those values are within about 5% of the 47K resistor you need.
    LC
     
  14. Low_Boy

    Low_Boy Well-Known Member

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    I ended up just buying some. It looks much nicer with one instead of 4 twisted together. The 4 were only temporary until the others showed up.
     

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