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  1. Tha fios agaibh

    Ground and neutral wires

    Not enough information given, but probably no. Firstly you need to be qualified by the authority having jurisdiction in your area to alter your electrical system. Contrary to popular belief, grounding is the most important part of an electrical system. Getting it wrong could be fatal. Even...
  2. Tha fios agaibh

    Troubleshooting: LED lamp

    Yes, I'd shunt the two contacts of the light from the 120v (hot) side to the common (white wire?) don't go to ground. I'd put the high value resistor right across the back of the light. You probably want to make sure whomever has authority over the ship is ok with these modifications. It's...
  3. Tha fios agaibh

    2 transistor circuit input output question.

    Yes, I got it. I was hung up on the current direction. I know, but it flows into the 5k and out of the 20k. So yes your right, but I was thinking of the configuration like the bottom of my sketch. Another words I was focusing on current direction instead of just calculating Rth. Even with...
  4. Tha fios agaibh

    2 transistor circuit input output question.

    Thank you dorke, I think I get it. Even though current through the 20k doesn't flow up into the base, the resistance of both resistors still needs to be considered, even if current is flowing in opposite directions. That's why when using thevenin equivalent, the voltage source treated as a...
  5. Tha fios agaibh

    2 transistor circuit input output question.

    Thanks for you patients in explaining this to me. The above qote by Dorke is what I'm having trouble with. Why is the thevenin resistance of 4k used in determining ib. What I'm trying to understand is why 4k is used in the formula. I understand how the thevenin resistance is calculated, but...
  6. Tha fios agaibh

    2 transistor circuit input output question.

  7. Tha fios agaibh

    2 transistor circuit input output question.

    Right two paths, but only one into ib via the 5k. The other path in flowing down through the 20k so I don't see the 20k as part of the equation. Or, to put it another way; Current is not flowing the other way from ground up through to 20k and into the base. I would expect base current to be...
  8. Tha fios agaibh

    2 transistor circuit input output question.

    Thanks for the explanation but it doesn't answer my question. I understand the Thevenin resistance calculation, but not necessarily why its used in this case. I also get that the biasing resistors forum a voltage divider. What I don't understand is why the 20k resistor is considered, (paralled...
  9. Tha fios agaibh

    2 transistor circuit input output question.

    Ok, I think I get it. But I can't completely get my head wrapped around why you would parallel the 5k and 20k resistors (using thevenin eq) when calculating ib. I want to think of the base current traveling primarily down thru the 5k into the base, then out the emitter and thru the 10k...
  10. Tha fios agaibh

    garage door opener

    Ah soo! (I'm going scram now because Dave is about to close this thread.)
  11. Tha fios agaibh

    2 transistor circuit input output question.

    Dorke: Pardon my ignorance, but how did you arrive at the 4k series equivalence? John
  12. Tha fios agaibh

    Why I prefer electronics to plumbing

    I'm sure on the plumbing forum their are similar posts as to why they prefer plumbing. Good story Bob. Btw, Put your primer and glue cans into a good quality zip-lock bag. It will keep it from drying out.
  13. Tha fios agaibh

    garage door opener

    You call #4 minimum size? I would think you'd recommend #28 for maximum smoke. Disclaimer; Kids, don't try this at home.
  14. Tha fios agaibh

    garage door opener

    30HP might be a bit much for this.:rolleyes: Good explanation about the motor Hop. It goes well with that motor sketch in post 11.
  15. Tha fios agaibh

    Troubleshooting: LED lamp

    If it is rated 120v and 1.4w then that is what I would base it on. 1.4/120=.012A is pilot light current. Better yet measure it with an ammeter. I was proposing a pull down resistor to mitigate leakage current form your controller. That would be wired in parallel with the light. You are...
  16. Tha fios agaibh

    Troubleshooting: LED lamp

    I asked about voltage and current to help you size the resistor. (If you need help)
  17. Tha fios agaibh

    Varistor

    When in doubt replace it, especially if it's more than 10 years old.
  18. Tha fios agaibh

    garage door opener

    The main take away here is that it is not a continuous duty motor and will quickly overheat and die for what the op wants to use it for.
  19. Tha fios agaibh

    garage door opener

    Thanks for leaving out "punk" Hop. Lol Seriously though, it's critical that you add an inline fuse for overload protection. I don't see one in the picture.
  20. Tha fios agaibh

    garage door opener

    Oops, I first thought you were trying to repair the opener. Boring trumps the excitement of the paramedics trying to save you, and the firemen trying to save your house. (Squinting my eyes) "A mans got to know his limitations" Clint Eastwood as Dirty Harry.
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