Thread: VSD power tests

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

Originally Posted by Stustoys

Even if I could get comparative measurements, that might be a start.

Just keep it safe, we do not want to loose you. It is too easy to forget, that one is measuring on unforgiving power electronics.

Originally Posted by Stustoys

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

Hi Stuart,

You can increase the sensitivity of the CT by wrapping another turn through the toriod.

Ray

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

Originally Posted by Stustoys

So am I allowed to do a 180 around the coil? I cant see why not.........

Hi Chris,
I'm pretty sure the Teco only displays Hz(though I'm not game to try and measure the V on the 415V with that gauge, that might be pushing things). The cheap ones have A.

I'd been wondering what the PWM would do to the amp meter(and the V for that matter)
I have an anolog meter, would that average enough?
I have a scope but wouldnt the vsd or the scope need to be isolated? Cant imagine me being able to calculate area of signal.


Hi Bob,
I tested the gauge against a DMM on my variac.
Gauge mains% DMM

253 100% 249
192 75% 188
129 50% 125
106 40% 101
81 30% 76
68 25% 63
57 20% 50
52 15% 39
45 10% 26
39 7% 17 (just above the gauge turn off V)(didnt change range on the DMM)

So it seems pretty good down to 60V(of course it might let the smoke out after 5 minutes)


Stuart

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.

Originally Posted by cba_melbourne

Just keep it safe,

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.

Originally Posted by RayG

You can increase the sensitivity of the CT by wrapping another turn through the toriod.

Hi Ray,

Wont that double the amps displayed?(granted not a huge mathematical challenge)

Stuart

Originally Posted by Stustoys

Hi Ray,

Wont that double the amps displayed?(granted not a huge mathematical challenge)

Stuart

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

Originally Posted by RayG

You can increase the sensitivity of the CT by wrapping another turn through the toriod.

Do you think that would improve the accuracy of the current readings?

Originally Posted by Stustoys

Wont that double the amps displayed?(granted not a huge mathematical challenge)

Originally Posted by Theberylbloke

You can loop the primary through the coil as many times as you like. Naturally two loops doubles your reading in the secondary.

Thank you tbb, I'll take that as a yes. Damn I type slow when I'm trying to get three things done at once.

Stuart

Originally Posted by RayG

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

There is? I had better take a look. At least they will all be the same

So would a cable ties and a little hot melt glue to hold things in place be a good idea?

Stuart

Originally Posted by Stustoys

There is? I had better take a look. At least they will all be the same

So would a cable ties and a little hot melt glue to hold things in place be a good idea?

Stuart

Just cable ties would do.

The one I got, is a model DDH-303L and the pots are accessible through holes in the top PCB.. I'd use a plastic alignment tool, and be careful, there's 240V terminals not far away from the Voltage calibration pot.

Ray

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.

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

Originally Posted by Stustoys

Do you think that would improve the accuracy of the current readings?





Thank you tbb, I'll take that as a yes. Damn I type slow when I'm trying to get three things done at once.

Stuart

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

Originally Posted by Stustoys

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.

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.

Originally Posted by BobL

I see there are a lot of cheap Megger testing units on ebay these days - anyone have any experience with those?

I bought one when I got my mill - I figured I should test things before discovering the casting was live the hard way.
It seems to work. It said no shorts and there were not any but I've never had a fault condition with a real megger that I could compare with.

Michael