Thread: VSD power tests

Hi Stuart,

Your logic is correct, but it's unlikely that the A/D converter in the meter has 16 bit resolution, 8,10 or 12 bits would probably be more likely. But by adding extra turns on the primary you've increased the sensitivity of the amp measurement. Only potential downside is whether it's going to saturate the ferrite core... I'd say probably not, since it was good for at least 50A with just one wire through the core, and probably would go to 100A ( wild guess ) before saturating, now we have 5 times the field, so we now have full scale of 10A and saturation might be something over 20A.. but with no data on the ferrite to go on, I'm just making wild guesses.... go ahead and see how the calibration looks.

BTW I have a force meter, that you are welcome to borrow...

IMG_0651s.JPGIMG_0652.JPG

Came with some suspension testing gear from a Gray's auction ...

Ray

Hi Ray,

I've really got no idea of the wiring in the core.....but looking at it pretty simplistically as the secondary winding of a transformer designed to work with a primary winding of one turn at 300V max.... Now I have a 5 turn primary so the V in the secondary might be a little on the high side... I assume I've missed something

Nice meter.... you didn't happen to get two did you? 100g might be a little course though. I in the tests the back scale isn't doing much. Though the old scales you'd be hard pressed to read 100g steps. the new ones are said to be good to 5g.......... though they are cheap, something else to test lol

Stuart

Originally Posted by Stustoys

Hi Ray,

I've really got no idea of the wiring in the core.....but looking at it pretty simplistically as the secondary winding of a transformer designed to work with a primary winding of one turn at 300V max.... Now I have a 5 turn primary so the V in the secondary might be a little on the high side... I assume I've missed something

Nice meter.... you didn't happen to get two did you? 100g might be a little course though. I in the tests the back scale isn't doing much. Though the old scales you'd be hard pressed to read 100g steps. the new ones are said to be good to 5g.......... though they are cheap, something else to test lol

Stuart

Hi Stuart,

Doesn't work quite like that, it's a current transformer, and the key thing is the ratio of the current in the primary to that in the secondary, the secondary current is measured by terminating the secondary winding with a resistor, ( the terminating resistor stops the voltage from going crazy) and then to a circuit that measures AC volts... which you calibrate to read amps. The 300V maximum referred to is a seperate circuit that measures just the voltage.

I will be in town for a job tomorrow, I can drop the force gauge off at Phil's on the way out of town, if you want to borrow it.

Ray

Originally Posted by RayG

The 300V maximum referred to is a seperate circuit that measures just the voltage.

Originally Posted by RayG

I will be in town for a job tomorrow, I can drop the force gauge off at Phil's on the way out of town, if you want to borrow it.

Sounds like a plan. Shame I'm carless tomorrow. Thank you

Stuart

Originally Posted by BobL

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.

I am completely clueless as to whats going on in this thread but I'm loving it just the same.
My contribution would be a pic of the 'rope brake dynamometer' in Bobs book (Fig 2.5).
We have a real one if anyone is interested.
No, still, at least I feel I have contributed.
Great work Stuart.

Phil

Originally Posted by Steamwhisperer

I am completely clueless as to whats going on in this thread but I'm loving it just the same.
My contribution would be a pic of the 'rope brake dynamometer' in Bobs book (Fig 2.5).
We have a real one if anyone is interested.

Love to see a pic of it Phil

Yes please Phil

Originally Posted by BobL

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.

He sure did. Even got it extended if I recall correctly. He wasn't alone, I think he came up with the planet and sun gear for connection to the flywheel because someone else had managed to get a patent on the crank(strange even that spinning wheels had been around for ages).

Well I finished the amp gauge.
Tried testing it but without a lot of success. Turns out my DMM only do DC current, had to make my own bridge*. Power meter into variac, output through the amp gauge into a 32Vac transformer through bridge, DMM, into a headlight for load, with another DMM for V.

After all that the figures are "pretty rugged" at best. I'll try again tomorrow but I don't hold out much hope, while the amp gauge seems to be in the ballpark the same cant be said for my other power meters and at least one of the DMM amp scale is way out. Maybe I need to start looking for a real meter.

Stuart

A shed full of crap and not one 10amp+ bridge rectifier to be found lol.

Originally Posted by BobL

Love to see a pic of it Phil

No worries Bob.
Had to leave work early today so I will grab the pics on Friday.

Phil

Originally Posted by Stustoys

Well I finished the amp gauge.

It looks good!

Tried testing it but without a lot of success. Turns out my DMM only do DC current, had to make my own bridge*. Power meter into variac, output through the amp gauge into a 32Vac transformer through bridge, DMM, into a headlight for load, with another DMM for V.

Oh Poo!

After all that the figures are "pretty rugged" at best. I'll try again tomorrow but I don't hold out much hope, while the amp gauge seems to be in the ballpark the same cant be said for my other power meters and at least one of the DMM amp scale is way out. Maybe I need to start looking for a real meter. .

Somewhere in my midden I have a 30A AC analogue meter - I'll have to dig it out and see if it still works.

Hi Bob,

Thanks for that but don't go digging just yet. I think the amp gauge maybe the best of a bad bunch....... I just have to think of a way to prove it.
Also, would an analogue gauge handy PWM and variable Freq and better?
I'll test it more tomorrow and try it out on the VSD and see if it goes a little crazy.

Stuart

Originally Posted by Stustoys

Hi Bob,
Thanks for that but don't go digging just yet. I think the amp gauge maybe the best of a bad bunch....... I just have to think of a way to prove it.

Might go and see what they have at work Amp wise.

Also, would an analogue gauge handy PWM and variable Freq and better?

Dunno - just thought it would make an interesting comparison.

I'll test it more tomorrow and try it out on the VSD and see if it goes a little crazy.

Looking forward to it.

Hi Stuart,

There any number of ways of measuring AC current, but the simplest I think is to just get a good DVM with an AC amps range. Trying to rectify it and measure DC is fraught with errors..

If you are shopping for a general purpose DMM the Escort brand is excellent, I don't recommend Fluke, I've had endless troubles with bad switches and poor connectors over the years. If you want to add a clamp meter, the current favourite is the Kyoritsu KEW2300R, it's an open end and does non contact DC as well as true RMS AC

In the benchtop market Rigol are better value than most... I guess it depends how much you want to spend... I got a new chinese made Atten Digital Storage Oscilloscope not so long back and it leaves the Tektronix for dead.. times are changing fast.

Ray

Links... http://www.kew-ltd.co.jp/en/products...ers/2300R.html
Escort DMM's http://eshop.micronix.sk/data/sk/att/002/5058-3315.pdf

Check this video out for a cheap multimeter buyers guide.. http://www.youtube.com/watch?v=gh1n_ELmpFI

Hi Ray,

I was really just hopping for some repeatability, didnt even get that.

I've watched the video, time for a lay down and a bit of a think about what I need. lol

Thank you

My first thoughts are I can bin all the electrical measurements and just worry about the motor output, at the end of the day thats all that really matters. Input V output etc might be interesting but if I'm not going to get useful figures..............



Stuart

Originally Posted by Stustoys

My first thoughts are I can bin all the electrical measurements and just worry about the motor output, at the end of the day thats all that really matters. Input V output etc might be interesting but if I'm not going to get useful figures..............

Yep - its that motor output V frequency curve that interests me.

Well after a little postage stuff up my scales have turned up. I've tested the first one against Rays and it pretty damn good. Now assuming things go smoothly tomorrow I'm going to start running some tests. A the 240V VSD has a current display I figure I would start there.
The motor is rated 0.6kW at 1375rpm so thats an easy starting point. But what slip should I use for the other tests? the same rpm drop or the same % of max as the Hz, something else? I'm thinking same %.
5Hz steps?

Stuart