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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
    Location
    PA
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    68,758
    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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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    19,497
    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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    7,635
    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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    Southeastern Pa
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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
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
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    1,625
    He also needs a spell checker for his title. Capacative???
    Doug

  7. #7
    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

  8. #8
    Join Date
    Jun 2004
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    896
    I can already see..
    The more you know
    The bigger your head will be.
    Looking down at every technician.

    Be humble my friend

  9. #9
    Join Date
    Jan 2008
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    Dallas ,Texas
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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.

  10. #10
    Join Date
    Dec 2002
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    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    the difference between refrigeration & air conditioning = 10 degrees
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  11. #11
    Join Date
    May 2011
    Location
    Oklahoma
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    362
    Electromagnetic and inductance theory is not for the faint of heart. Unless you want your brain to explode just learn the basics for the trade. Capacitors resist a change in voltage, inductors resist a change in current.

    Luckily someone much smarter has figured out that motor made of a number of coils wrapped in a certain diameter circle pushing a piece of steel made of more coils of wire needs a 7uF capacitor.

  12. #12
    Join Date
    Jan 2012
    Location
    Fraser Valley
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    55
    honestly guys- No offense intended whatsoever and if coming across as arrogant or as having what we refer to here in BC as "the refrigeration walk" then I most sincerely and humbly apologize to all.

    As timebuilder said, I should have been more specific and said the RIGHT HVAC company. I've had several peers from other companies as well as mentors who have spent their careers in HVAC and have a very impressive understanding and well rounded perspective to many things not found in the more 'purely-refrigerative' areas of the trade (for lack of a better term).

    Apologies to all and many thanks for the great links as well

  13. #13
    Join Date
    Jan 2012
    Location
    Fraser Valley
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    55
    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

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