Thread: Some VSD questions

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.

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

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

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

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.

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

Originally Posted by RayG

Hi Stuart,
I'm not sure where you are going with the donkey motor idea? can you draw a circuit..

I think he means running the 3.5 kW and 1 HP (0.75 kW) motor simultaneously off the one 2.2 kW VSD. I have no idea why.

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

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

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

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.

Originally Posted by RayG

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

Ray,
I just read the article. I'll definitely be making one for my pool pump. If that works I reckon the drill press will get one too.
Chris

Originally Posted by jack620

Ray,
I just read the article. I'll definitely be making one for my pool pump. If that works I reckon the drill press will get one too.
Chris

I've never really taken any notice but does a drill motor have a centrifugal switch? The DIY drive is not suitable for motors with a C/Switch.
Nice looking project though. I'm not subscribed so I can't read the rest.

My drill motor has a centrifugal switch. I will replace it with a 3 phase motor as it's underpowered anyway.