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Thread: VSD power tests
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18th February 2014, 10:03 PM #16GOLD MEMBER
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Hi Chris,
Thanks for that, at least some of that makes sense.
I guess the first thing to check is if the A on the VSD and the meter are even close. Which it sounds like there is a good chance they wont be.
Even if I could get comparative measurements, that might be a start.
Stuart
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18th February 2014 10:03 PM # ADSGoogle Adsense Advertisement
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18th February 2014, 10:17 PM #17Cba
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18th February 2014, 10:21 PM #18
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18th February 2014, 10:49 PM #19
ring around the rosie, er I mean coil
Hi Stu,
You can loop the primary through the coil as many times as you like. Naturally two loops doubles your reading in the secondary.
It may not be obvious to everyone that you only loop the active through the coil and not say the active and neutral together as the induction in that case will cancel out and give you nothing.
Cheers
The BerylBloke
Equipmenter.... Projects I own
Lathes - Sherline 4410 CNC
Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.
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18th February 2014, 11:02 PM #20.
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Thanks for the info on the meters.
I might go out to the Uni and see if I can borrow a up market meter to cross check my DMM and the little V/I panel meter.
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18th February 2014, 11:04 PM #21GOLD MEMBER
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Yes, as this will be running for much more time than any normal bench test I'm double insulating everything like its a permanent installation. I might end up letting the smoke out of something but as long as it isnt me or the Teco I'll be happy.
Though I was more worried about the drum coming apart. Even though I was "pretty sure" it would be ok I was standing 10ft away behind my mill... just in case. I make it about 250kph at 2800rpm........though the loads and temps arent the same.
Hi Ray,
Wont that double the amps displayed?(granted not a huge mathematical challenge)
Stuart
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18th February 2014, 11:13 PM #22
There's a pot for calibrating the amps, and another for calibrating the volts. Just wind it back to match the NIST certified DVM
The data sheet I looked at says that the amp range is 0-50A, since I figure that you'll be down below 10A for most of the measurements, you'd get better results by changing the range to 0-25A..
The mechanical stability of the CT is important and wrapping a turn around the toroid makes it more stable mechanically as well.
Ray
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18th February 2014, 11:15 PM #23GOLD MEMBER
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18th February 2014, 11:23 PM #24GOLD MEMBER
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18th February 2014, 11:30 PM #25
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18th February 2014, 11:31 PM #26.
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For ease of connectivity and safety I made up a pair of 3 phase leads, one to connect the VFD to a high current terminal strip inside a transparent plastic box, and then the other lead connects the motor to the terminal strip.
The connections to the VFD and the motor are via soldered ring terminal crimp connectors, while the terminal box has with proper cable glands in the sides, so everything is robust and secure.
Using a break out box has a number of advantages such as, I'm not constantly connecting and disconnecting wires inside the VFD, I can also test V/A at the terminal box without needing to poke probes into the VFD or at the motor end so I can leave these safely covered and the only thing exposed is the terminal box - for testing over time, I can also screw the cover over the terminal box.
When I finish I leave the terminal box connected to the VFD for testing other motors, and pack the whole lot away in a plastic tool case.
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19th February 2014, 12:05 AM #27
Ammeter Accuracy
Hi Stu,
If this is a digital meter then I'd put as many turns on the primary as required to get the reading towards the top of the ammeter's range. That way, after taking your multiplier into account, each bit will equate to less primary current and should give you greater "accuracy". I use the term loosely as I'm not sure of the toroid's behaviour at other than design frequencies, likely 50 hz? Also what is the the toroid's original use as that will affect it's accuracy? It's been many years since I played with metering transformers, for some reason the term "saturation" comes to mind??
Cheers
The Beryl Bloke
Equipmenter.... Projects I own
Lathes - Sherline 4410 CNC
Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.
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19th February 2014, 12:10 AM #28GOLD MEMBER
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These VSD's are setup with 3 phase plugs and sockets. I was planning on making the connections inside the plug, but I spare plugs, sockets and boxes, maybe that would be a better way to go. I'll have a look tomorrow.
Stuart
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19th February 2014, 01:44 AM #29.
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I also originally used 16A 3Phase plugs and sockets but given that the 3HP or less motor currents (while quite lethal!) are not that high I decide to go with a chunky break out box. I use soldered ring terminal crimp connectors where I can and solder the ends of all bare wires, triple check the connectors are snug and tight. I am sometimes able to borrow a Megger testing unit from work but now that everyone is back at work I have to take stuff out there for testing.
I see there are a lot of cheap Megger testing units on ebay these days - anyone have any experience with those?
Yep I do know that a megger shouldn't be used with a VFD in the circuit but at least it can be used to check out the wiring and motor etc before the VFD is connected.
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19th February 2014, 06:46 AM #30Philomath in training
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