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  1. #27
    Join Date
    Dec 2007
    Location
    Frognot TX
    Posts
    836
    Quote Originally Posted by coronado2412 View Post
    I am prety sure that the voltage that is read on the capacitor is the rated "apparent voltage"..... this is the applied vlotage from the power company along with (but not aditive) the back electro motive force generated in the field windings of the compressor at start up.... If I am wrong about this.... then please educate me.................. thanx
    That's the way I was taught, but maybe someone can explain why do alot of 480 volt PSC motors use a 370 cap?

  2. #28
    Join Date
    Jul 2008
    Posts
    26
    Quote Originally Posted by RoBoTeq View Post
    Shouldn't do any harm other then not starting under certain conditions, but you do need to replace it.

    When you restock your truck, only stock with 440v capacitors. You can go up on voltage, but not down. A 440v capacitor will be a little better on a compressor designed to be able to start with a 370v capacitor.
    This may not be true. It certainly used not to be true with electrolytic capacitors, as they were dependent on being operated at an optimal voltage level in order to properly maintain their dielectric film and to a insure long life. Electrolytics operated at levels significantly below their rated working voltage failed well before those operated at or near their rated working voltage.

    Electrolytic capacitor technology may have progessed to a point where is does not matter as much any more, or it may not have. I haven't kept up with it. But I would make sure it was the proper thing to do before I replaced an electrolytic with one with a different working voltage.

    If the manufacturer doesn't say it's OK, it's not OK.

  3. #29
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The capacitor used has nothing to do with the voltage supply to the equipment, it is simply the voltage present at the terminals of the capacitor.
    The run and start windings go back to the same side of the line voltage, the capacitor is never connected to both sides of the line.
    A bit of a simplification, but the voltage the run capacitor sees is an induced voltage potential between the run and start windings.
    The induced voltage is usually higher than the voltage supply to the equipment, but can also be lower, which is why it is not uncommon to find 370v run capacitors for condenser fan motors in 460v equipment.

    To keep it simple, if you can get the motor running, measure the voltage between start and run.
    If it is under 370v, a 370v capacitor is fine, but a 440v capacitor will do the job, and likely have a longer life.
    If it is over 370v, always use a 440v run cap. A 370v run cap could be used temporarily, but may not last very long, or it could last for years.
    If more government is the answer, then it's a really stupid question.

  4. #30
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by Frog_Pond View Post
    This may not be true. It certainly used not to be true with electrolytic capacitors, as they were dependent on being operated at an optimal voltage level in order to properly maintain their dielectric film and to a insure long life. Electrolytics operated at levels significantly below their rated working voltage failed well before those operated at or near their rated working voltage.

    Electrolytic capacitor technology may have progessed to a point where is does not matter as much any more, or it may not have. I haven't kept up with it. But I would make sure it was the proper thing to do before I replaced an electrolytic with one with a different working voltage.

    If the manufacturer doesn't say it's OK, it's not OK.
    Well, since we typically see a very wide range of voltages across the terminals of run capacitors in HVAC, and we only get a choice of 2 voltage ratings of capacitors, I don't think it is true for run capacitors for induction motors.
    If more government is the answer, then it's a really stupid question.

  5. #31
    Join Date
    Jul 2008
    Location
    RTP North Carolina
    Posts
    81
    Well this thread has moved on a bit from the OP's topic, but I wanted to drop in and say that you should carry a few of these on your van:

    http://www.americanradionic.com/content/view/30/60/

    Never get stuck without the right capacitor for the job again! Keep in mind they are about 3X the cost of a regular 440v dual cap, so they won't be replacing your normal cap stock.

  6. #32
    Join Date
    Jul 2008
    Location
    Orange Park Florida
    Posts
    224
    The good ole multi value capacitor has saved me a few times. Never had to leave it there for more than a day though.

  7. #33
    Join Date
    Jun 2004
    Location
    Howell, Michigan
    Posts
    16,176
    Quote Originally Posted by JohnnyValvecore View Post
    Well this thread has moved on a bit from the OP's topic, but I wanted to drop in and say that you should carry a few of these on your van:

    http://www.americanradionic.com/content/view/30/60/

    Never get stuck without the right capacitor for the job again! Keep in mind they are about 3X the cost of a regular 440v dual cap, so they won't be replacing your normal cap stock.

    I question the quality of those caps. Seems like everyone we installed has gone bad and had to be replaced. I have banned them at our shop!

  8. #34
    Join Date
    Aug 2008
    Location
    Rockport, Texas
    Posts
    6
    Hi folks, my first post. My multi-value capacitors say they are permanent replacements although I never leave them for very long either. Why would you not leave for more than a day?

  9. #35
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    For the cost of 2 or 3 of them. You can buy a good supply of caps that will cover you.
    And you can alwyas put 2 standard ones together to make the right one, for less then one of those.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #36
    Join Date
    Aug 2008
    Location
    Rockport, Texas
    Posts
    6
    Guess I never left one long enough to fail but I have used one over and over for short periods. I seem to always run into an oddball capacitor and we don't have a local supply house handy.

  11. #37
    Join Date
    Aug 2008
    Location
    Rockport, Texas
    Posts
    6
    I do use 2 or more standard ones wired together but sometimes space is an issue and it just seems easier to grab the multi. And again, I've never left one for more than a day or so.

  12. #38
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    Space is tight for 2 sometimes. But you can leave them in and save a trip.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #39
    Join Date
    Jun 2008
    Location
    NW Florida
    Posts
    707

    true

    Quote Originally Posted by beenthere View Post
    Space is tight for 2 sometimes. But you can leave them in and save a trip.
    That is true but with enough wire you can always put the second capacitor just about anywhere just have to make sure that is insulated well (I do not like leaving them in there boxes I have seen them short out in a heavy rain) also make sure that they cannot vibrate against anything. That will lead to loss of freon or that old sticky electrolyte everywhere. BY THE WAY I HEARD THAT STUFF IS EXTREMELY CANCEROUS.

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