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Thread: VFD's 101?

  1. #1
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    VFD's 101?

    I'm trying to get into a shop that does a lot of VFD's and they want me to do a bit of homework on the topic. Don't like studying systems I don't have my hands in just yet, but I'm up to the task and really wanna get into that shop (lots of interesting work). Now, most of the material I've come across falls into 2 categories:

    1) Promo material for beancounters who know nothing about HVAC but they wanna save $$$ - oooh your energy savings will be 60% and it will pay for itself in a few months

    2) Techs who already have plenty of VFD experience, so it's more along the lines of why "our" product is better than "their" product - oooh, you can commission one of our units in 36 seconds

    I'm stuck in the middle as both categories leave out a lot of information that I could use in understanding the technology and implementation. Is there anything out there for a tech who understands mechanical systems and refrigeration but never worked with VFD's? Thanks in advance

  2. #2
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    Check Fluke on line which has had some articles on VFD's. There is also a basic's book which they also have available.

    But there is much more to them as they are application specific, whether controlling a process of handling product on a conveyor line, paper mill, fan speed control, pumps etc.

    I never seen any VFD which can be programed and commissioned properly in less than 2 hours.

    If you have the basic down it's no problem. But if not you will need to understand in-puts and out-puts such as speed in put or reference which is usually a 4 to 20 Milli amp signal or 0-10 VDC signal.

    really there are no basics but specific functions and you will need to know this before you start with any VFD.

    You will definitely need to read ALL the literature with each specific VFD. If you miss just one setting which has been imputed wrong it probably wont work correctly.

    Hope this helps.


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  3. #3
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    Thanks for the tips heads up on Fluke. I'll definitely check them out as well as the PDF you attached. Got some reading to do over the weekend. Since I'm technically not even an apprentice yet, I'm sure they are testing me and just wanna figure out how much I'm willing to learn to get that job. Haven't touched any of the equipment and they indicated that I'd receive proper training before I do.

  4. #4
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    Magnatek engineer told me years ago what you HVAC guys are doing with the VFDs is the lowest end of the applications on them...keep that in mind...it's alot of nothing.read up on static pressure and VAV systems ...then go into VFDs which replaced Inlet Guide Vanes on air delivery from rooftops...
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

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  6. #6
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    I am replacing a ABB 150 Sunday, whole lot of data entry.

  7. #7
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    Quote Originally Posted by jimp View Post
    I am replacing a ABB 150 Sunday, whole lot of data entry.

    Not understanding this...With the new macros programmable drives it made data entry pretty much a thing of the past...

    I installed, programmed and started 6 ABB VFD's in one day last week...only 3 of them were change outs.
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  8. #8
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    programming time/options really dpeends on manufacturers, some are simple, others a pain. As far as hvac drives, they are simple in comparison to some used in industry. A certain pharma uses a drive intended to be used for conveying systems. Each time you change a parameter, something else changes. We had a bucnh to do and I had to pay my guy ot sit home and read for a day prior to even attempting it, and he does drives all of the time.

  9. #9
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    Is a VFD the answer for commercial ECM? or do i have it all wrong?

  10. #10
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    VFD's have been around for quite a while. At least 15 that I know of. I believe the ECM motors are fairly new.

  11. #11
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    Here is some great information on the fundamentals of Variable Frequency Drives. This stuff only begins to scratch the surface of what really goes on inside of a VFD. If you can understand the basic components and theory of operation, you'll be a god amongst the garden variety techs. They are not complicated, but many people look at them as if there's some kind of magical wizardry that takes place inside the box.

    vfd facts worth knowing.pdf
    vfd 101 lesson 1.pdf
    vfd 101 lesson 2.pdf
    vfd 101 lesson 3.pdf
    vfd 101 lesson 4.pdf
    vfd 101 lesson 5.pdf

    Both VFDs and ECMs have been around in HVAC for a long time. They are similar in that they both use rectifiers and capacitors, but an ECM is a synchronous motor with a permanent magnet rotor. It's operation is similar to that of a stepper motor. The voltage output is mostly constant, but the rate at which the magnetic field in the motor winding rotates is what dictates the speed. Because the rotor is a permanent magnet, it's essentially locked onto the magnetic field as it rotates through the 3 or 4 windings in the stator. This is where the term synchronous comes from; there is no slip like in normal induction motors.

    Most modern VFDs are what is known as a vector drive, which modulates the output voltage in proportion to the frequency to keep from distorting the sine wave as the frequency drops and the motor slows down. While they're called Variable Frequency Drives, they really should be called Variable Voltage & Frequency Drives. Some manufacturers like to refer to them as Adjustable Speed Drives, Adaptive Frequency Drives, Variable Speed Drives, but it's just semantics, really.
    The key to happiness is lower expectations.

  12. #12
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    Quote Originally Posted by GT Jets View Post
    Not understanding this...With the new macros programmable drives it made data entry pretty much a thing of the past...

    I installed, programmed and started 6 ABB VFD's in one day last week...only 3 of them were change outs.
    I have three sheets of changes to make from the chiller manufacturer. Apparently it has some communication problems with the PCO remote.

  13. #13
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    Hey Tech Rob, thanks for the info. That's some good reading material which you sent.

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