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Thread: Bleeder Resistors

  1. #61
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    Quote Originally Posted by Steve Rowe View Post
    Ahh, but the Heisenberg uncertainty principle would most certainly apply in this thread.
    "Heisenberg was here, but I can't prove it..."
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  2. #62
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    The lack of agreement among people who actually know something about electricity makes me feel much better about my own complete ignorance on the subject.

  3. #63
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    Quote Originally Posted by Frank Drew View Post
    The lack of agreement among people who actually know something about electricity makes me feel much better about my own complete ignorance on the subject.
    I would be inclined to agree with one person or another if I was more comfortable with how motors are designed and wound. Since I'm not, I have to make educated guesses within my comfort zone, or bow out when it gets beyond those boundaries... other sparkies here are probably the same.
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  4. #64
    I think this comment should of been in the tool section but since this thread got the most attention I'll post it here. As I mentioned I will not get involved in the augment about a bleeder resistor and I won't. I need to make a comment however about different types of motors that are on our big power tools and what to watch out for. The motor on my very expensive Euro Bandsaw burnt out as I mentioned. I assumed, and that is an awful word, that because of its reputation ,price and Euro make that this was a quality item. I didn't do my home work and paid dearly. My fault entirely. So now a brief message about motor design and what to look for.

    1. the cheapest- PSC type. That stands for permanent split capacitor. The cap is permanently installed in series parallel to the major winding. Advantages to elcheapo- there is no starting switch and some other stuff to cut cost, low temperature rise and low start up current. Disadvantages- Low starting torque and should not be used on heavy loads like cast iron bandsaw wheels and compressors. That stinker is what was in my band saw. How can you tell you ask? Read the capacitor value. If it is around 60-80 mfg and is the only cap on the motor that's what is is. Not for good power tools!

    2- Start Capacito types- middle range, Good starting torque. Adds 200-400% more torque during the first 75% of its RPM when starting. Fast start reduces heat build up and allows motor to be cycled on/off rapidly.( Especially if cap voltage is bled off. ) I just made that up you know. Single Cap is in the 300mfd range or even higher.

    3- Start/run capacitor types. Top end.Best for hard loads like air compressors , heavy band saw wheels and impellers on Cyclones. It has both a start cap with switch circuit and a run cap that increases efficiency. Two caps on side of motor. One about 300 mfd the other about 70MFD. Costs more to make.

    There are a low of other things like class of insulation and weight of motor. I don't have room for all of this. As a side note Tesla who invented the induction motor was told by Professor Poeschel that it would not work. Yes I too have a MSEE but found that I didn't learn much in School. Big deal a EE means nothing except in your speciality. Talk to the Electricians . They have the answers. The smart ones that is. I had my share of the Professors like Poeschel in my life.
    Last edited by Aaron Rowland; 03-08-2011 at 4:21 PM.

  5. #65
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    But does the motor need a "plastic thingy" on the power cord? You know, the bump that contains a ferrite core noise suppressor, toroid choke thingy, or . . . . an RFID tag?

  6. #66
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    Just a small nit... it's µF, not mF. 1,000 times the difference in capacitance (and often size!).
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  7. #67
    Quote Originally Posted by Aaron Rowland View Post
    ... installed in series parallel to the major winding. ...
    What is "series parallel"?

    Quote Originally Posted by Aaron Rowland View Post
    It has both a start cap with switch circuit and a run cap that increases efficiency.
    Not true. It increases power factor, not efficiency.



    Aaron, PSC motors are commonly found on things like ceiling fans and other consumer-electronics. I've never seen one >0.5HP. Although I'm sure they exist, suggesting that people need to check to make sure they aren't getting one on, say, a bandsaw, is just silly. I doubt you could find a single commercially-available band saw that uses one.

    Also, capacitor value is just a silly way to ascertain what type of induction motor you have. A PSC will not have a centrifugal switch.

    There is nothing wrong with motors without run capacitors ("start capacitor type", as you call them). They are actually likely more reliable than start/run types.

    Your information on this (and the original topic) is quite factually inaccurate. Perhaps you should spend more time reading the material (it is well-understood), and less trying to explain it.

  8. #68
    Quote Originally Posted by Dan Hintz View Post
    Just a small nit... it's µF, not mF. 1,000 times the difference in capacitance (and often size!).
    This has got to be one of the more confusing things in EE - many larger caps are marked "MFD", but they mean microfarad. Probably a hold-over from the days when typeset labels couldn't easily produce a "mu", so they just used an "M".

  9. #69
    The US system and Euro system are sometimes a bit apart for naming things electronic.
    The name for the capacity of a capacitor is Farard. This is a huge amount like using the distance between the sun and earth as a unit instead of a Mile , or meter or what every we use.

    For capacitors a common US term is MFD, pronounced MicroFarad. The amount is 1000-2 Farads.. The Euro symbol is mu but most keyboards including this one does not have that letter which is still pronounced Micro. Don't ask for a cap by saying 300 mu from the parts store. In fact don't write that either. If you look at the cap on a motor in the US you will usually see" MFD" not the symbol for mu.

    The term Nano is rarely used in the US but is used in Euro. Symbol is n. Amount is 1000-3 Farads.

    The term pico is used in the US and Euro. Symbol is p. 1000-4.

    If you have a large air compressor in your shop check it out. You will see that the motor probably has two caps mounted on it if it is a good one. This motor really works hard with many ,many starts per hour. My 5 HP unit when I'm spray painting or using an air tools may start every 2-3 minutes. Probably the best and most reliable motor in the shop bar none. That type is going to replace the Euro motor on my band saw.

    So my method of determining what kind of motor is used when literature is not available works. This is only a hobby and I'm sure most wood workers reading this electric stuff could care less. As I said "Never argue with a fool,the onlookers may not be able to tell the difference."
    Last edited by Aaron Rowland; 03-08-2011 at 10:38 PM.

  10. #70
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    Folks,

    I am really close to closing this thread and moving it to the Moderators Forum where it's out of public viewing. I will remind everyone that civility will prevail at SMC.
    Ken

    So much to learn, so little time.....

  11. #71
    Quote Originally Posted by Aaron Rowland View Post
    For capacitors a common US term is MFD, pronounced MicroFarad.
    This is only true on some capacitors. Most will actually use the symbol "mu". The letter "m" is for milli (10^-3). Any use of mF is millifarad, not microfarad. Just in the very strange world of some specific types of capacitors do they use MFD and trust that you have some intuition for how much capacitance can be packed in a given space, allowing you to discern between microfards and millifarads.

    Quote Originally Posted by Aaron Rowland View Post
    The term Nano is rarely used in the US but is used in Euro. Symbol is n. Amount is 1000-3 Farads.
    This is factually incorrect. Nanofarad is an extremely common unit in the US. Also, I don't know what "1000-3" means, but a nano is 10^-9.

    Quote Originally Posted by Aaron Rowland View Post
    The term pico is used in the US and Euro. Symbol is p. 1000-4.
    This is factually incorrect. A pico is 3 orders of magnitude smaller than a nano, making it 10^-12 (not whatever "1000-4" means)

  12. #72
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    Aaron,

    Sidenote... nano is quite common in low-voltage electronics (e.g., microprocessor stuff) and is quite often sprinkled in amongst the µ/micro stuff. Pico is also very common, and the more experienced sparkies pronounce it "puff", as in "Go get me a thirty puff cap" when they want 30pF. It becomes second nature to say puff instead of pico. No idea where it came from, but there it is...
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  13. #73
    Ken. I'm new here and can't believe the vitriol. My posts were intended for non electric type wood workers who have or will have some motor problems. The non electric people here will not be able to get much from this exchange and are by now totally confused imho.

    Please remove my entire thread. One would think I was recommending washing down a shop with acetone with a heater running.

    Too bad, Some might of benefited.

  14. #74
    Well I think I benefited from this thread as I went out to my ts3650 tablesaw and put a 7,000 ohm 3 watt resister across the terminals of the start cap and noticed a difference right away. Before when I turned the saw off the whole tablesaw would shudder just as the centrifical switch for the start cap would close and now with the resistor when that same switch closes after I turn the saw off it smoothly comes to a stop. No more shudder or vibration. The 7,000 ohm resistor is all I could find in my electronics parts at the time but I'm going to try a 15 k just to see if there is any difference.

    There has to be a reason for this little add on to smooth out the motor on shut down so instead of saying it has no use why not take another look at this and maybe post something useful as to why it works like this.

  15. #75
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    Quote Originally Posted by Steve Rowe View Post
    Popcorn please. Has anyone mentioned the advantages of 3 phase power yet?
    Yes, but only on a Sawstop. :-)

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