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Thread: VSD power tests

  1. #31
    BobL is offline Member: Blue and white apron brigade
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    Thanks Michael, I might get one and compare it to the one at work.

  2. #32
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    Hi Stuart,

    saw this thread last night at work but for some reason the internet was slow so couldn't watch the video!

    Just watched it now. I understand that power = force x velocity or = Newtons x Metres/time (keeping with SI units) but I'm struggling to picture how the differential force between the two springs equates to the total force reading. It's obviously correct and a very practical and simple way to measure a quantity that would otherwise be beyond the scope of the average backyard shed operation. I like it. Thanks for taking the time to set this up. It's obviously captured the interest of many here because I blinked and now there are already 2 pages!

    The guy in the video needs to be a little more realistic with his significant figures he quotes though!

    Glad to see you getting use out of that motor. I knew you would get good use out of it! Is there a reason why you have chosen an induction type current sensor instead of the usual inline shunt type ammeter? This may have been explained previously if so I'm sorry.

    Can't wait to see some of your figures!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #33
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by simonl View Post
    Hi Stuart,

    saw this thread last night at work but for some reason the internet was slow so couldn't watch the video!

    Just watched it now. I understand that power = force x velocity or = Newtons x Metres/time (keeping with SI units) but I'm struggling to picture how the differential force between the two springs equates to the total force reading.
    It may help to think of the two forces as being in opposite directions with one force opposing the motion of the rotating shaft while the other is in the same direction as the shaft motion.

    CHapt 2 in this book has some diagrams of version of the de Prony Dyno that may help the old grey matter
    http://books.google.com.au/books?id=...ometer&f=false

    There's also a brief history of the dyno and lots of other examples. Very easy to read.

  4. #34
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    Hi Bob,

    I just went for a walk and had a think. I understand what you are saying and I came up with the same reasoning. By having two forces and the rotation, one force cancels out the upward force and so the net or resultant is the force in the direction of rotation (or in opposite direction to rotation) and is what the motor "sees" or "feels".

    I'll have a read. Thanks Bob.

    I can sleep now!

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  5. #35
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    Hi tbb,
    Yes digital. If I can find my plastic screw driver I'll see how much adjustment it has, maybe I can skip the maths. Only one way for me to find out, at least I have the cheap VSD's A to check it against. I though toroid's werent effected by freq so much.......but that doesnt mean it will work correctly.



    Hi Bob,
    I only have the plugs from when I first setup the 415V VSD which lets me switch it between two machines but also unplug so I can use it on other machines(this was all done before vsds got so cheap). I now have plugs from here and there over the years plus a box full of 3 phase stuff I bought off ebay for $20, so I've added a 10amp and 25amp(?) socket to one of my cheap VSD's(simply because I have plenty of 10 and 25amp plugs)

    A megger tester is on my list of things but is yet to make it to the top. In hindsight maybe I should have though a little more before I put that motor on my 415V VSD, I knew it had been on a 240V VSD and not let the smoke out. I'm not sure a megger tester is going to do much for safety on the wiring side of things(though it might save a vsd). If I wired it up with bare copper wire, as long as I kept the wires apart it would pass a megger test right?

    Quote Originally Posted by simonl View Post
    but I'm struggling to picture how the differential force between the two springs equates to the total force reading.
    Hi Simon,

    It took me a bit of thought to twig also. The good thing is the materials don't matter at all. If Bob's post didnt do it for you try this. Think of it set up with the motor off and the brake wound on until both scales read 10kgs. Now think about the same setup with the motor running, the total of the scales will still be 20kgs, the difference between the scales is the power. (did I just make things worse? lol)

    Quote Originally Posted by simonl View Post
    Is there a reason why you have chosen an induction type current sensor instead of the usual inline shunt type ammeter?
    Does "coz I had one" count?
    The only shunt gauges I have are in DMM. I've not been inside the "kill-a-watt" plug packs listed above, I'd WAG they have a toroid transformer, I did think about pulling one of those to pieces as they read W directly. But given what is likely to happen to the reading with freq changes and pwm I decided to stay with the simpler one, which is also cheaper to replace


    Quote Originally Posted by BobL View Post
    CHapt 2 in this book has some diagrams of version of the de Prony Dyno that may help the old grey matter
    http://books.google.com.au/books?id=...ometer&f=false
    "by James Watt (1736-1819), the inventor of the steam engine." He so was NOT! he invented the external condenser. Looks like a good read though.

    Stuart

  6. #36
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    Thanks Stuart,

    I like that analogy. That does it for me totally! I like the setup, it's simply genius and relies on easily measurable quantities. I don't need such a setup but I still want one! I love measuring stuff.

    Now, get back out in the shed and make things happen. I want to see some graphs before the end of the day!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  7. #37
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    Quote Originally Posted by simonl View Post
    Now, get back out in the shed and make things happen. I want to see some graphs before the end of the day!
    I see where you've gone wrong now. You've confused me with Ewan..... Total work today so far(apart from typing of course), solder and heatsink the 6 wires to the switch.

    Have to go out and pick up an ebay bargin(fingers crossed)

    Stuart

  8. #38
    BobL is offline Member: Blue and white apron brigade
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    A megger tester is on my list of things but is yet to make it to the top. In hindsight maybe I should have though a little more before I put that motor on my 415V VSD, I knew it had been on a 240V VSD and not let the smoke out. I'm not sure a megger tester is going to do much for safety on the wiring side of things(though it might save a vsd). If I wired it up with bare copper wire, as long as I kept the wires apart it would pass a megger test right?
    I'm dabbling with a few old motors so I thought I should test them before applying AC. I was given an old 1HP motor that had been outside and got some water in it - I dried it out but was still worried about it. I took it into work and it was sort of borderline on the megger. The senior techo suggested I take it apart and leave it in the sun for a while and it indeed came good.

    It took me a bit of thought to twig also. The good thing is the materials don't matter at all. If Bob's post didnt do it for you try this. Think of it set up with the motor off and the brake wound on until both scales read 10kgs. Now think about the same setup with the motor running, the total of the scales will still be 20kgs, the difference between the scales is the power. (did I just make things worse? lol).
    I like it.

    "by James Watt (1736-1819), the inventor of the steam engine." He so was NOT! he invented the external condenser. Looks like a good read though.
    The other thing it was said he perfected was manipulation of the patent system to keep every possible competitor out of the field for as long as possible" - he would have fitted in well in today's business world.

  9. #39
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    Quote Originally Posted by Stustoys View Post
    Hi tbb,
    Yes digital. If I can find my plastic screw driver I'll see how much adjustment it has, maybe I can skip the maths. Only one way for me to find out, at least I have the cheap VSD's A to check it against. I though toroid's werent effected by freq so much.......but that doesnt mean it will work correctly.

    Stuart
    Hi Stu,

    Not sure I made myself clear, perhaps it's my understanding of how digital meters work...

    If your meter scales from 0 to 25 amps and has a 16 bit range then I thought each bit was "equal" to about 1.5 amps...

    So if your motor draws 5 amps you have only three or four bits that describe the magnitude of the current...

    If you loop the primary 5 times through the toroid then you will get all 16 bits describing the magnitude of the current because the meter will read 25 amps...

    Thus you divide the reading by 5 (being the number of loops) and each bit would now be equal to 0.3 amps??

    Perhaps I am mistaken in how these things work?

    Cheers

    The Beryl Bloke
    Equipment er.... Projects I own

    Lathes - Sherline 4410 CNC
    Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.

  10. #40
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    Didnt get much done today. Couldnt find my plastic screwdriver so I figured 5 turns where as good as 2, maybe a little better as I'm less likely to forget. I havent just wound a primary winding have I?

    Stuart

    p.s. typing again! lol
    Hi tbb, I really wouldn't know one way or the other.
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    Quote Originally Posted by Stustoys View Post
    Didnt get much done today. Couldnt find my plastic screwdriver so I figured 5 turns where as good as 2, maybe a little better as I'm less likely to forget. I havent just wound a primary winding have I?

    Stuart
    I can only see 4 windings on your pic...

  12. #42
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    It looks like you have wound the 3 core flex through the coil, if so, it will not work.

    Lex.

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    Quote Originally Posted by cba_melbourne View Post
    I can only see 4 windings on your pic...
    I'm pretty sure its five. (I've checked it 20 times now lol. Sort of 4.5 but the wire goes through the center of coil 5 times and that's what matters right?)

    Quote Originally Posted by Techo1 View Post
    It looks like you have wound the 3 core flex through the coil, if so, it will not work.
    Nope single core flex.

    Stuart

  14. #44
    BobL is offline Member: Blue and white apron brigade
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    for cba
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    Quote Originally Posted by Theberylbloke View Post
    Hi Stu,

    Not sure I made myself clear, perhaps it's my understanding of how digital meters work...

    If your meter scales from 0 to 25 amps and has a 16 bit range then I thought each bit was "equal" to about 1.5 amps...

    So if your motor draws 5 amps you have only three or four bits that describe the magnitude of the current...

    If you loop the primary 5 times through the toroid then you will get all 16 bits describing the magnitude of the current because the meter will read 25 amps...

    Thus you divide the reading by 5 (being the number of loops) and each bit would now be equal to 0.3 amps??

    Perhaps I am mistaken in how these things work?

    Cheers

    The Beryl Bloke
    Hi TBB,

    i Kinda understand what you mean but if it's a digital meter with 16 bit resolution then I would have thought that it would have a current measurement resolution of 25/65536 A (16 bits gives you 2^16 resolution) or a resolution of approx 0.4mA, which even if you only used a single turn on the toroid would produce sufficient resolution for such purposes. Using 5 turns and and then dividing the figure by five would give you the "equivalent" of 0.08mA resolution which would not really be necessary nor would a display that read 5 amps as 5.0000A be realistic.


    Just my thoughts. Could be totally barking up the wrong tree!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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