VFD current

[ptonsparky]

Is the amperage displayed on a ASD/VFD the input current or the output?
Does the drive use the input current for its determination of overload?
If yes, how do I determine what the trip current level should be for a drive operating on 1ph?

I used a small drive to run a 3 hp three phase fan from a single phase source today. I had the drive & customer had 3ph fan. At peak rpm the unit would trip on overload of 4.3 amp nameplate setting. I had to increase the current setting to above 7 amps to keep it operating. Drive is rated 27 amps input single phase with 10 amp 3phase output. I know the drive has to use more current while operating on 1ph. Dark, cold & motor sounded right so no amp reading on load side of drive tonight. Bearings are good.

 

[kspifldorf]

You generally set current limits on the drive to your FLA of the motor nameplate, and set a time limit on that just for motor protection. If you've set that limit for 7 amp and your motor only good for 4, you're asking for trouble.

 

[Ranch]

Is the amperage displayed on a ASD/VFD the input current or the output?

Output

Does the drive use the input current for its determination of overload?

No

I used a small drive to run a 3 hp ..... 4.3 amp nameplate setting.

What's the voltage? Your numbers indicate 460

had to increase the current setting to above 7 amps

your need to increase the OL setting are more in line with 208-230

Drive is rated 27 amps input single phase with 10 amp 3phase output.

If 10A flow through each of three output legs than 17.3A must flow through two input legs when voltage in and out is the same (square root 3 multiplier). But since you have higher ripple in the VFD (rectifying two legs) you must compensate for added burden on the DC bus capacitors (you are using a VSI inverter) which is why you may come across the “double” the VFD size rule of thumb - your VFD is generously sized - good thing

Also note the VFD by default should reduce the OL trip proportionate to reduction in frequency output since the motor cooling fan slows down.

So – what is your voltage and what frequency output is the VFD operating at when you see the OL trip?

We can definitely help you out, you might get a second opinion also by measuring each of the three output legs for balance with a clamp on (preferably true RMS)

Make sense?

 

[ptonsparky]

Is the amperage displayed on a ASD/VFD the input current or the output?

Output

Does the drive use the input current for its determination of overload?

No

I used a small drive to run a 3 hp ..... 4.3 amp nameplate setting.

What's the voltage? Your numbers indicate 460

had to increase the current setting to above 7 amps

your need to increase the OL setting are more in line with 208-230

Drive is rated 27 amps input single phase with 10 amp 3phase output.

If 10A flow through each of three output legs than 17.3A must flow through two input legs when voltage in and out is the same (square root 3 multiplier). But since you have higher ripple in the VFD (rectifying two legs) you must compensate for added burden on the DC bus capacitors (you are using a VSI inverter) which is why you may come across the ?double? the VFD size rule of thumb - your VFD is generously sized - good thing

Also note the VFD by default should reduce the OL trip proportionate to reduction in frequency output since the motor cooling fan slows down.

So ? what is your voltage and what frequency output is the VFD operating at when you see the OL trip?

We can definitely help you out, you might get a second opinion also by measuring each of the three output legs for balance with a clamp on (preferably true RMS)

Make sense?

By golly I think you won!! Check is in the mail.

 

[Ranch]

so is it 208 or 230?

 

[ptonsparky]

230. I had the farmer read the label for me while I was punching wholes in a box. Can't blame him though because I have a simlar fan in my shop that we use as a test stand for various scenarios. It trips to, but we seldom run it on high. I will have to clean off my bifocals and look at the labels again. Quite probably another "Duh" moment.

 

[Ranch]

I have a veritable museum of small VFDS in my office, mostly to evaluate the firmware (we call them paper weights). Some models made it to market, some did not. Needless to say, all of my buddies and my house have our homes filled with these prototypes in our workshops. Nothing like a VFD on a drill press, router and I love the VFD I put on my table saw. I made a sanding wheel for it and run that thing up to 240Hz plus. Yup - the days of Roto phase and "fake a phase" are done. VFDS rule.

It’s like Joe the farmer taught me something. C’est la vie, back to military power quality issues ………ho hum