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Thread: major confusion on variable speed thingys

  1. #1
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    major confusion on variable speed thingys

    I've stated before, when it comes to stuff electrical, I'm practically a zero knowledge guy. But, with the help of an instruction book and two Boy Scouts, I can (usually) successfully change flashlight batteries.
    Enneyhow, I have seen posts here, and elsewhere, using electro-lingo and acronymns that leave me in the dust talking when about speed controllers, DC and more. I only learned enough to know that this was something I wasn't going to experiment with.
    But, then, today, while perusing catalogs (MLCS in particular) I come across speed controllers that seem to be something even I can deal with.
    These items are under $30.00 and promise no loss of torque. They are essentially 'plug and play' items.
    Now, the confusion: When y'all talk about variable speed here, it requires special motors and controllers that cost way up into the hundreds of dollars.
    I guess the bottom line question is: Wassup?
    "Folks is funny critters."

    Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire

  2. #2
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    Without getting too deep - the expense is directly related to the nature of the motor. I think this is the product you're talking about:

    http://www.mlcswoodworking.com/shops.../speedcon.html

    Sure enough, they claim no loss of torque. That's interesting to me because, as I understand these devices, they vary speed by reducing amperage. On a universal motor (which is the ONLY motor these work on) when you reduce amperage you're going to lose torque, as far as I undestand it. Personally, I'm chalking up their claim to marketing hype, unless someone credible can make me see the light. I may just know enough to be dangerous, though, so my ways may certainly not be the right way.

    The other controllers that are expensive are for induction type motors. These are the kinds of motors you'll find on contractor and cabinet table saws, 14"+ bandsaws and most bigger machines. The electricity to your house runs at a certain frequency - 60hz in the US. That frequency is what determines the speed of an induction motor. In order to control the speed of these types of motors, you have to vary the frequency of the electricity coming into it. This is where the expensive comes in - it's not a cheap task, as far as I know.

    As for "DC", when we're talking about electricity DC means "Direct Current" - Like what comes out of a battery. The stuff that comes out your wall at home is AC - meaning Alternating Current - what this means is that it switches from positive to negative so many times per second - in the US, that's 60 times per second (or 60hz).

    I don't fully understand the reason behind 3-phase motors being cheaper nor do I understand why it's easier to control the speed of a 3-phase motor. 3-phase motors are still kinda foreign to me. Hopefully someone who actually knows what they're talking about (unlike me) will clarify things a bit
    Jason Beam
    Sacramento, CA

  3. #3
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    Frank,

    Interesting... Do you have a link to one of these inexpensive controllers?

    Thanks

    Opps, Thanks Jason... We were typing at the same time...almost...
    Last edited by Greg Cook; 06-15-2007 at 06:21 PM.

  4. #4
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    Frank, I don't know a lot more about things electric than you do, but the $30 variable speed controllers from places like MLCS or Rockler are for "universal" motors like you'd find on a router. These will slow down the motor, but they also lower the torque, so a low speeds, the tool is pretty gutless. Still, for some tools they work out great. I've got one I built from a kit back in high school, and I still use it on my Dremel. Works like a champ in that application.

    The bigger motors like you'd find on a tablesaw or lathe (dunno what the opposite of "universal" is called) operate differently, so changing the speed on them becomes trickier and more expensive. I don't really know much about the nuts and bolts of those speed controllers, so I'll let someone who does know chime in.

    Wow, I type slow...two people already did chime in.
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  5. #5
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    Frank,
    They work on universal motors only (router, biscuit jointer, etc.)
    They will not work on an induction motor like on most table saws, drill presses, etc.
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  6. #6
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    If you motor has a capacitor on it, forget about variable speed except by mechanical means.

    In a nut shell there are two good ways to do variable speed.
    And yes I know there are others, these are IMHO the best/simplest/most practical ones.

    DC motor with a controller. Not very common but they do work very well.

    3 phase motor with a VFD for speed control. My personal favorite.


    Jeff
    Waiting to be corrected.... oh wait. This isn't woodnet is it??
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  7. #7
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    Yes, that link Jason showed is what I saw in the MLCS catalog. And, thanks guys (I think ) for the explanation. This means I can't turn my Grizzly lathe into a Power Monster for $30.00. Oh, well.
    "Folks is funny critters."

    Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire

  8. #8
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    Quote Originally Posted by Frank Fusco View Post
    Yes, that link Jason showed is what I saw in the MLCS catalog. And, thanks guys (I think ) for the explanation. This means I can't turn my Grizzly lathe into a Power Monster for $30.00. Oh, well.
    Bill Lantry was having a similar thought in this thread:

    http://familywoodworking.org/forums/...ead.php?t=4174
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

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  9. #9
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    Thanks, Vaughn. I forgot that thread. I guess when I saw the price and claims it struck me as being too good to be true. And it was.
    "Folks is funny critters."

    Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire

  10. #10
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    I think the person(s) who wrote that ad claiming no lose in torque are the same ones that sell the "free energy" kits on the net.

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