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  1. #1
    Join Date
    Jan 2012
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    Fraser Valley
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    HELP understanding inductive and capacative loads

    Hey guys,

    I recently got a position with a pretty awesome company. Ill be able to finally start putting all of the stuff I learned in school into place in the real world because I'll be working with a crew of refrigeration mechanics on refrigeration equipment instead of just being an air cundishnin guy- LOL

    No offense intended to anyone out there, HVAC has been good to me so far throughout my apprenticeship and I have learned a lot, but let's face it; most guys who work on roof tops for a living don't even know what a subcooling valve is or the difference between a current relay or a potential relay- I know this because that was me except for the few weeks in school when I tried to absorb as much as possible.

    All that being said, I guess I should get to to the point of this thread- understanding inductive and capacative loads. So, I can understand pretty well on a graph or chart that the voltage leads by 90* in a purely inductive circuit, the current leads by 90* in a purely capacative, and that in a purely resistive circuit they're in phase..........but what the hell does this mean in the real world? Maybe a better way to ask this question would be, "What kind of resources can ANYONE recommend for helping a guy to understand vectors and impedance and capacitance outside of black and white friggin charts in a text book. I can run the calculations and size my caps and figure out power factors etc, etc..........but I have always seemed to have a disconnect between seeing it on paper, which I think i can grasp relatively easily, and seeing it in a mechanical room or with the motor in front of me.

    I think most of you senior techs can understand now why I felt the need to post my recent career change details at the beginning of this thread now: you basically need not even care about this stuff if you're just changing out oem parts on rooftops all day long between flipping filters.

    Again, anyone who knows of some good resources via a good electrical website or even a good RSES book or publication (Im a proud and participating member).......please feel free to hook a young dumb apprentice up!

    Thanks for all the help guys.......stay tuned for more questions from a hopeful young fridgie.

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    68,171
    No offense intended to anyone out there, HVAC has been good to me so far throughout my apprenticeship and I have learned a lot, but let's face it; most guys who work on roof tops for a living don't even know what a subcooling valve is or the difference between a current relay or a potential relay-
    Not a good way to get help. Comparing many of our members here, to your limited knowledge and time in the trade.
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  3. #3
    Join Date
    Nov 2006
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    Southeastern Pa
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    18,618
    Apparently, you have not worked with the right HVAC guys.

    And probably, not with the right HVAC company.

    "Changing OEM parts all day."
    You were fortunate if you had an expereinced tech to identify and order the OEM parts. I have seen SO many hacked systems where someone was forced into using a non-OEM motor, where the factory part had non-NEMA dimensions, like the Carrier blower motor with the extended length shaft. I say "forced into" because many commercial accounts will dictate what parts will be used, and/or what they are willing to pay for those parts.

    "Flipping filters."
    This reminds me of the service brokerage in-house techs that get sent out to do PMs. Anything beyond a filter is beyond their abilities. And often, those little arrows showing the direction of airflow are overlooked. The upside is that these guys get in over their heads quickly, and give guys like me an opportunity to look like heroes.

    I like refrigeration. In may ways, the vapor cycle is more of your focus, and interpreting values is more critical because losses like food are involved. However, commercial HVAC is often just as complicated and vexing as refrigeration.

    You just were not there long enough or in the right situation to appreciate the challenges of the comfort side.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  4. #4
    Join Date
    Dec 2002
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    SouthEast NC ICW & Piedmont Foothills
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    Quote Originally Posted by beenthere View Post
    Not a good way to get help. Comparing many of our members here, to your limited knowledge and time in the trade.
    how to win friends & influence people
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  5. #5
    Join Date
    Nov 2006
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    Quote Originally Posted by dandyme View Post
    how to win friends & influence people
    Yep.

    He needs two things:

    1) The Dale course, (http://www.westegg.com/unmaintained/carnegie/dcc.html)
    and

    2) the Forrest Mims book.
    http://www.amazon.com/Getting-Starte.../dp/0945053282
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  6. #6
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    Dec 2003
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    Citrus County, Florida
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    1,578
    He also needs a spell checker for his title. Capacative???
    Doug

  7. #7
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    Quote Originally Posted by timebuilder View Post
    Yep.

    He needs two things:

    1) The Dale course, (http://www.westegg.com/unmaintained/carnegie/dcc.html)
    and

    2) the Forrest Mims book.
    http://www.amazon.com/Getting-Starte.../dp/0945053282
    The Dale Carnegie book How to Win Friends and Influence People has the potential to change your life. I would venture to say that it will make you more successful in HVAC/R than knowing how the magnetic lines of flux in a motor winding affect something you'll rarely ever measure anyway.

    That is not to say that you should not seek out an answer to your question. Just realize one is wisdom the other is knowledge.
    Good luck.
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  8. #8
    inductance=creation of voltage through changes of magnetic flux

    reasearch electromagnetism.

    inductance and capacitance work against each other in an ac circuit. when current lags voltage it is being restricted. For example, a very crude example: a motor creates back electromotive force that pushes current in the opposite direction of the way it is supposed to go. The capacitor stores energy to counter act this. This is just one example.

    visit this site.

    http://www.daviddarling.info/encyclo..._and_lead.html

  9. #9
    Join Date
    Jan 2012
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    Fraser Valley
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    Quote Originally Posted by HVAC/R-Wizard View Post
    inductance=creation of voltage through changes of magnetic flux

    reasearch electromagnetism.

    inductance and capacitance work against each other in an ac circuit. when current lags voltage it is being restricted. For example, a very crude example: a motor creates back electromotive force that pushes current in the opposite direction of the way it is supposed to go. The capacitor stores energy to counter act this. This is just one example.

    visit this site.

    http://www.daviddarling.info/encyclo..._and_lead.html
    hey awesome example- believe it or not, that 'crude' little example of yours actualy put a few critical pieces of the puzzle together for me-LOL

  10. #10
    It goes so much more in depth than that though. A lot of electrical engineers (I didn't say all) would not be able to remember the physics behind all of this unless they use it every single day. I know I had a better understanding of it a few years ago. Use it or lose it...

  11. #11
    Join Date
    Jun 2004
    Posts
    863
    I can already see..
    The more you know
    The bigger your head will be.
    Looking down at every technician.

    Be humble my friend

  12. #12
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    Jan 2008
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    Quote Originally Posted by shaka View Post
    I can already see..
    The more you know
    The bigger your head will be.
    Looking down at every technician.

    Be humble my friend
    Occupation
    Refrigeration mechanic Apprentice, recently left HVAC to be a real refrigeration mechanic

    Yep he's just a know it all kid.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  13. #13
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    Dec 2002
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    the difference between refrigeration & air conditioning = 10 degrees
    It`s better to be silent and thought the fool; than speak and remove all doubt.

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