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Thread: VSD power tests
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19th February 2014, 10:13 AM #31.
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Thanks Michael, I might get one and compare it to the one at work.
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19th February 2014, 10:18 AM #32GOLD MEMBER
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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!
SimonGirl, 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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19th February 2014, 10:59 AM #33.
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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.
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19th February 2014, 12:15 PM #34GOLD MEMBER
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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,
SimonGirl, 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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19th February 2014, 12:24 PM #35GOLD MEMBER
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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?
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)
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
"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
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19th February 2014, 12:41 PM #36GOLD MEMBER
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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!
SimonGirl, 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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19th February 2014, 04:52 PM #37GOLD MEMBER
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19th February 2014, 06:24 PM #38.
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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?
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).
"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.
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19th February 2014, 09:07 PM #39
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 BlokeEquipmenter.... Projects I own
Lathes - Sherline 4410 CNC
Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.
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19th February 2014, 09:21 PM #40GOLD MEMBER
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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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19th February 2014, 09:26 PM #41Cba
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19th February 2014, 09:27 PM #42Senior Member
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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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19th February 2014, 10:01 PM #43GOLD MEMBER
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19th February 2014, 10:28 PM #44.
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for cba
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19th February 2014, 10:28 PM #45GOLD MEMBER
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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!
SimonGirl, 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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