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  1. #14
    Join Date
    Jun 2003
    Location
    Virginia
    Posts
    376
    Quote Originally Posted by JWB View Post
    ugly hackery. Takes the professionalism right out of what we do, surprised he didn't have a 7.5 (I have at least 4) but did have a 3mfd.....I may have 1 or 2......anyway, what is embarrassing is opening up a panel like that and the homeowner asks you if that mounting was 'correct'. My answer is no. I have strap and drill tips in my toolbag and will secure those even on a maintenance. I want them to know that I am there to make sure their system is ok. I work for them, ultimately. Nice picture.
    So, you have four 7.5's on your truck at the beginning of the work day. By 3:00 you used all 4 of them, and on your last call, you need another one. Do you travel 60 miles to get one and return to put it in? And the customer is ok with paying an additional $150 to $200 for the same result? And you're ok charging the additional $150 to $200 even though paralleling 2 is acceptable?

  2. #15
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Quote Originally Posted by jodybhvac View Post
    ok, now I know it is ok to wire caps like that. Would like to see the formula for series and parralel wiring.
    Wired in parallel, the value of the capacitors adds, so a 10f + 10f in parallel is 20f.
    This is how the Turbo capacitors from AmRad work.

    Wired in series, the a reciprocal formula is used.
    For 2 capacitors in series the easy formula is: Total f= (f1 x f2)/(f1 + f2)
    Two 10f capacitors in series would be 5f.
    (10x10)/(10+10)
    100/20 = 5

    For more than 2 capacitors in series, you would need a different formula.
    (1/f1)+(1/f2)+(1/f3)=1/fT
    f = 1/fT

    Three 10f capacitors in series would be 3.33f.
    (1/10)+(1/10)+(1/10)=1/fT
    .1 + .1 + .1 = 1/.3
    f = 3.33

    Typically there is not much, if any, use for capacitors in series in our industry.
    If more government is the answer, then it's a really stupid question.

  3. #16
    Join Date
    Mar 2011
    Location
    Jamestown,SC
    Posts
    45
    Thanks !

  4. #17
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,719
    One thing does concern me about the 2 single caps in parallel: Are they 370V or 440V?

    With a 120V blower motor, the working voltage (measure it while the motor is running) will not exceed 370... With a 240V fan motor, the working voltage may well exceed 370V, which means the caps may fail sooner.

    Now if those single caps are 440V, well disregard what I just said...
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  5. #18
    Join Date
    Apr 2007
    Location
    Saint Augustine, Florida, United States
    Posts
    1,168
    Quote Originally Posted by prorefco View Post
    So, you have four 7.5's on your truck at the beginning of the work day. By 3:00 you used all 4 of them, and on your last call, you need another one. Do you travel 60 miles to get one and return to put it in? And the customer is ok with paying an additional $150 to $200 for the same result? And you're ok charging the additional $150 to $200 even though paralleling 2 is acceptable?
    No, I would wire something together. My point was that the install is really unprofessional and just plain disappointing. I observe a lot of 5mf's on rheem/ruud/weatherking units in place of the manufacturer's recommended 3 mf. Which leads me to assume that guys would rather throw a 35+5 in cause they have it handy then wire together a 35 and a 3. Mostly I don't see a lot of 3's around so I assume they don't bother stocking them.

    And also, if my truck is out of stock, that is my problem, the customer at my company doesn't pay EXTRA for something I failed to stock. We eat the additional cost.

  6. #19
    Join Date
    Feb 2009
    Posts
    139
    If you have ever worked on old equipment manufacturers frequently used multiple capacitors. Of course they mounted them properly. As a refrigeration contractor I get the opportunity to replace capacitors frequently rarely are replacements the same physical size. Life is fun.

  7. #20
    Join Date
    Nov 2006
    Location
    SC
    Posts
    930
    Turbo 2000 basically does the same thing... multiple caps in a single shell. However, professional mounting is a must. I too have joined capacitors in a pinch, but always mount them securely to the metal wall.

  8. #21
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,838
    Quote Originally Posted by mark beiser View Post
    For more than 2 capacitors in series, you would need a different formula.
    (1/f1)+(1/f2)+(1/f3)=1/fT
    f = 1/fT

    Three 10f capacitors in series would be 3.33f.
    (1/10)+(1/10)+(1/10)=1/fT
    .1 + .1 + .1 = 1/.3
    f = 3.33

    Typically there is not much, if any, use for capacitors in series in our industry.
    Actually Mark, you can still use the (C1XC2)/(C1+C2) for more than 2 in series. (10X10)/(10+10)=100/20=5 5 is the combination of cap 1 and cap 2. Now use the value of C1 and C2 (5) times cap 3 and do it again. (5X10)/(5+10)=50/15=3.33 Just makes for one less mathematical problem to remember.

    As long as you continue using the calculated value for the next operation, you can keep going.
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  9. #22
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    21,719
    A supply house in my area closed last fall, bought a HUGE amount of parts for dimes on the $$$... lots of caps cheap. For this year and maybe next; just get more from stock in my shop.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  10. #23
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    the duct tape is hackery.

    wiring caps up to achieve what is needed.... been there, done that.

    ther've been times when on call, i've put two 20's together to make a ten and vice versa.
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  11. #24
    Join Date
    Jul 2002
    Location
    Centerville, Iowa
    Posts
    400
    Quote Originally Posted by doc havoc View Post
    Actually Mark, you can still use the (C1XC2)/(C1+C2) for more than 2 in series. (10X10)/(10+10)=100/20=5 5 is the combination of cap 1 and cap 2. Now use the value of C1 and C2 (5) times cap 3 and do it again. (5X10)/(5+10)=50/15=3.33 Just makes for one less mathematical problem to remember.

    As long as you continue using the calculated value for the next operation, you can keep going.
    Interesting, I too was taught the reciprocal method for adding capacitance in series/resistance in parallel in my electronics and house wiring course in high school. This is an alternative I hadn't heard of before. Thank you.
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  12. #25
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,915
    Quote Originally Posted by doc havoc View Post
    Actually Mark, you can still use the (C1XC2)/(C1+C2) for more than 2 in series. (10X10)/(10+10)=100/20=5 5 is the combination of cap 1 and cap 2. Now use the value of C1 and C2 (5) times cap 3 and do it again. (5X10)/(5+10)=50/15=3.33 Just makes for one less mathematical problem to remember.

    As long as you continue using the calculated value for the next operation, you can keep going.
    That works, but if/when I need to calculate something like that, I just use a scientific calculator and enter it all as one equation.
    If more government is the answer, then it's a really stupid question.

  13. #26
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    Apr 2004
    Location
    MN
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    1,838
    Quote Originally Posted by mark beiser View Post
    That works, but if/when I need to calculate something like that, I just use a scientific calculator and enter it all as one equation.
    I hear ya mark. I just like the idea of only having to remember 1 mathematic formula. Plus, it would take me a while to relearn a scientific calculator.
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
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