Thread: VSD power tests

Interesting stuff !

I don't understand why you would be measuring at voltages other than 240/440?

BTW I'm using the same V/A units in my gear.
I have one of these attached to an extension cord so I can move it around between machines.
It's very useful and interesting to see what is going on, with start up currents etc.

Hi Bob,

As I understand it the lower the Hz the lower the V. So if you want to know power input you need V as well.

I've been thinking about running two wires through the core, one from an extension cord and other wire for phase to phase or voltages "other than 240"

Stuart

Originally Posted by Stustoys

Hi Bob,

As I understand it the lower the Hz the lower the V. So if you want to know power input you need V as well.

I've been thinking about running two wires through the core, one from an extension cord and other wire for phase to phase or voltages "other than 240"

Stuart

This will be interesting to see what power you get.. hp = torque * RPM / 5252 ... or in Metric kW = torque * RPM / 9.5488 ( torque in newton-meters )

So if you measure the kW at the motor shaft as well as the input kVA, you should be able to calculate motor efficiency vs Hz.. Need a means of measuring the phase relationship between current and voltage to calculate power factor... I'll do some research on that to see if there's a simple solution.

Ray

Stuart,
RS Components have a full range of wire labels.

P/N 554-620 is Qty: 250 of Size C labelled "0" rated to fit OD 2.5 to 5.0 mm, about $8.50.
Unfortunately, the P/N sequence is not contiguous, and the letters are different again.
John

Originally Posted by Stustoys

Hi Bob, As I understand it the lower the Hz the lower the V. So if you want to know power input you need V as well.

Good point.
I had assumed one could just measure VFD input power and the VFD would be about 95% efficient but a bit of reading suggests that is not the case especially at low frequencies

I've been thinking about running two wires through the core, one from an extension cord and other wire for phase to phase or voltages "other than 240"

I'm still trying to think through how that would work?
Given they are not that expensive, wouldn't it be easier just to use two meters?
Then you could also measure the VFD efficiency - some might be better than others?

Hi Ray,

I might start with the 415V test..... might be able to get some useful numbers from that, even it I have to repeat them later on when the new scales arrive.

Thanks John,
I'll have a look, shame they dont sell them in 20offs. Now I'll have to put some thought into just how to number these windings

Hi Bob,
As I understand it the "coil" just measures the magnetic field produced by the current following through the wire....... I cant see it being a problem that there are two wires..........been wrong before though.

I have a couple of these

http://www.ebay.com.au/itm/Electrici...baeff9c&_uhb=1

Which give V, A and W. I'd only need the other one above 10A. so maybe its not really needed.


One other thing, VSDs can have higher output (to a certain point) based on input V right? The V around here spends most of its time at or above 250V. I guess its 4%. (its enough that when all the contactors on the lathe are open the secondary V on the control transformer goes high enough that the LED work light goes off until you mover the lever to OFF so one of the contactors closes and drops the V enough for it to come back on.....better change my V drop resistor one of these days, but it worked fine for 6 months.... ok I'll stop waffling now)

Stuart

For wire labels you can use clear heatshrink with either a paper or dymo label inside.

Originally Posted by racer123

For wire labels you can use clear heatshrink with either a paper or dymo label inside.

The tight### in my likes this idea . Not sure if I have any clear I'll have to check.

Stuart

I'm also interested to see results on this.... Particularly at high frequencies.

I think the most useful info would be input to the vfd vs mechanical output of the motor as it will give the total picture of returns from input power (and potentially seems a bit easier to measure). Measuring current and voltage between the vfd and motor only lets you quantify vfd losses, which while interesting is ultimately less important than the total input.

Not sure why you want to measure current, Stu. Most VFD drives can display this directly.

If you must measure it, it may not be that easy. The output of a VFD is the outline of a sine wave made up of many pulses at the chopper frequency. Your clamp type meter may be slow enough to average it out, but maybe not. You may have a better chance using a more expensive true RMS meter, but even this may not like the RF noise in the signal. A better way would be to look at the signal with the scope and "manually" calculate the area of the signal.

That said, I am really interested to see what you find out.

Originally Posted by Stustoys

Measuring gear. Laser taco, a watt meter for the 240V input(not really sure why but I've got one) and I'm currently putting one of these V/A gauges in a box.
http://www.ebay.com.au/itm/161026024...84.m1497.l2649 .

Those things are suppose to only work correctly between 100 and 300V.
I just tried out what freq 100V represents with a 2.2kW VFD /1.5kW motor combo and it was 10Hz.

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

Hi Stu,

I am NOT selling meters, and I do NOT suggest that you go and buy this meter. But I am sure you will find it instructive to have a read at this Fluke application note, aimed exactly at VFD measurements:

http://www.testequipmentdepot.com/ap...289-dmm_an.pdf

Another excellent application note regarding measurements on VFD drives:
http://assets.fluke.com/AppNotes/Ele...r/GO416b_u.pdf