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Thread: Some VSD questions
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3rd April 2012, 09:45 PM #1GOLD MEMBER
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Some VSD questions
Couple of questions for the VSD gurus.
Lets say I have 3.5kW 415V star motor would it be ok to run it on the 2.2kW 240V VSD?
Ok now assuming that the last idea isnt going to let the smoke out of anything, could I then use the above as a sort of donkey motor and switch say a 1hp star motor on and off without letting the smoke of the the VSD(or anything else)?
No plans to use either idea at the minute, just some ideas I've been wondering about.
Stuart
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3rd April 2012 09:45 PM # ADSGoogle Adsense Advertisement
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3rd April 2012, 09:52 PM #2.
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It sounds like you have this the wrong way around. Anyway, I wouldn't run a larger HP motor on a VSD than the VSD was rated for. The other way around is OK but ideally they should be matched.
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3rd April 2012, 10:07 PM #3GOLD MEMBER
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hi stuart . I think i can hear alarm bells ringing regarding this. You did ask for vsd gurus which i am clearly not.
It would be interesting to see if a motor run below its rating can be run by a lower rated vsd.
one thing i do know is with some vsd's a severely miss matched drive to motor wont spin the motor.
ive tried it.
aaron
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3rd April 2012, 10:10 PM #4SENIOR MEMBER
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Bob it depends on the VFD manufacturer, as some will allow to run a frame size over the nominal value. I run one of my VFD in such a configuration.
Stuart maybe I've misunderstood what you want to do, but you would need to convert the motor to delta to run on that VFD. Are you sure the motor is 3.5 and not 3 kW?
The last part I'm afraid you completely lost me on.
Pete
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3rd April 2012, 10:30 PM #5
I think I understand your logic, Stuart. In fact I may test it tomorrow.
Running a 415V motor on 240V does require less power (as the current draw at the lower voltage through the 415V coils will be less) - and obviously produce less power/torque.
The maximum being the capacity of the VSD/VFD.
I have a 4kW motor and a 3kW VFD that I wanted to try this with one day anyway.
Since you can set the max current delivered by the VFD, it should come to no harm at all.
By the way, I have run 415V star wired motors smaller than the VFD capacity for hours on end under load several times with several motors to test if the motors were OK and usable. I just haven't tried it with a larger motor than the VFD capacity.
I'll let you know how I go.
However, I wouldn't try switching ANYTHING on the dowstream side of a VFD! I think the starting current would be quite unpredictable and well fry the VFD.
Joe
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3rd April 2012, 11:52 PM #6
Hi Stuart,
For V/F drives...
Short answer is yes, no problem running a 3.5kw 415 star motor on a 2.2kw vfd, you won't get full power of course. But you won't damage anything. The vfd will trip at whatever you've set the current limit to.
I'm still running the 2.2kw motor on the shaper off a 1.5kw vfd, still wired for star, I haven't changed it to delta.
For vector drives, you couldn't run them in vector mode, but in simple V/F mode no problem .. the above applies.
I'm not sure where you are going with the donkey motor idea? can you draw a circuit..
Regards
Ray
EDIT: On a related topic I've heard of people running a rpc into a 3phase vfd and the vfd does the phase balancing, I don't quite see the point since I think you would be better off with a transformer.
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4th April 2012, 12:02 AM #7
There you go, I'd forgotten that Ray was running his 415V shaper motor on 240V - perfectly well.
I still want to know if my 4kW motor is actually functional...
Joe
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4th April 2012, 12:26 AM #8.
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4th April 2012, 12:36 AM #9
Hi Bob,
I thought he might be thinking of using it as a generator and getting perpetual motion...
Since we are on the subject in general, has anyone noticed that Silicon Chip magazine is running a construction article on a DIY VFD, pic32 based, It would be a good electronics project as an alternative to the Huanyang VFD's.
Regards
Ray
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4th April 2012, 12:53 AM #10GOLD MEMBER
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Hi Guys,
Where to start?
They are just some ideas I've had kicking around in my head for awhile.
Part A would be for example if you were looking at buying a machine that had a motor bigger than you needed(or could run on your current shed wiring). So the answer seems to be yes. (I also run lower hp grinders and my drill in 415 star(or for all I know they are 415 delta I havent been inside them, but being they are 2hp or less I am guessing they aren't))
Part B was along the lines if you had say a 4 speed 0.9hp motor so couldnt rewire it. The theory being that the 3.5kW motor would have more "spinning reserve" than a 2.2kW motor. maybe adding a flywheel would help?
Stuart
lol Ray
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4th April 2012, 01:12 AM #11
Hi Stuart,
PartB.. The 4 speed motor is switching the number of poles, 2 4 6 8 I guess?
So long as you don't switch poles while the vfd is running, it should be ok.
However I'm guessing you really want to switch while it's running...
If that's the case, chances are the high voltage transients would kill the vfd, maybe you could clamp the transients with big varistors on the vfd output.
A big LC harmonic filter might be worth investigating, along with dv/dt filtering.
I'm sure it could be done.
Regards
Ray
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4th April 2012, 01:28 AM #12GOLD MEMBER
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Hi Ray,
Yes
Yes (I have done that and it works as far as it went but the braking and reversing had to be done on the vsd, which only sort of worked as the speed difference meant different ramp times, external resistor would likely have helped)
Yes
Ok I'll take that as a "No" or at least certainly not a cheap/easy way to go.
I was hoping it could be a easy way to make up something that did the same job as a RPC, allowing you so switch things on and off as you pleased, without having to worry about loading and caps.
Thanks
Stuart
edit oops I forgot, the kW numbers used were just made up. 3.5Kw being about the biggest motor I "think" you could run on a 2.2kW VSD.Last edited by Stustoys; 4th April 2012 at 01:33 AM. Reason: edit
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5th April 2012, 06:14 PM #13GOLD MEMBER
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5th April 2012, 06:52 PM #14
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5th April 2012, 07:38 PM #15GOLD MEMBER
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My drill motor has a centrifugal switch. I will replace it with a 3 phase motor as it's underpowered anyway.
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