Milling machine - video

[tonyfoale]

I used my mill for couple days and there is a problem with motor-filter-vfd setup.

My vfd throws overcurrent error when I'm pushing hard on the motor (big drill for example) or when I set carrier frequency below 8 khz - during acceleration/deceleration. It never happened before installing the filter.

Do you have any ideas what can be wrong? .

When I made my dV/dt filter I had a similar problem when I had capacitors as well as inductors. Inductors alone work fine for reducing motor noise and increasing general smoothness.

[SteelCraft]

I went to my workshop and checked current during work. Peak is 3.1A when motor is about to stop completely. Normally it drags around 2.1 Amps.

Inductors alone work fine for reducing motor noise and increasing general smoothness.

So I should try unsolder capacitors from my filter?

[tonyfoale]

I went to my workshop and checked current during work. Peak is 3.1A when motor is about to stop completely. Normally it drags around 2.1 Amps.



So I should try unsolder capacitors from my filter?

Try it. You can always put them back if necessary.

[SteelCraft]

I tried. Without capacitors it just not filtering at all :P

[mwmkravchenko]

When I made my dV/dt filter I had a similar problem when I had capacitors as well as inductors. Inductors alone work fine for reducing motor noise and increasing general smoothness.

The capacitors need to be sized correctly. They are called snubber capacitors.

https://www.eng-tips.com/threads/snu...697/post-82332

https://fscdn.rohm.com/en/products/d...esign_an-e.pdf

https://www.aosmd.com/res/applicatio..._Reduction.pdf

https://ietresearch.onlinelibrary.wi...-cds.2014.0329

There's plenty of information here to design what you need. Make sure you look for the sections that are for the L-C subbing circuit. The last one at section 3.3 calculates it out, and in the following section calculates against power usage. A little thought of source for higher power inductors is audio, iron laminated cored inductors.

Mark

[nova_robotics]

I used my mill for couple days and there is a problem with motor-filter-vfd setup.

My vfd throws overcurrent error when I'm pushing hard on the motor (big drill for example) or when I set carrier frequency below 8 khz - during acceleration/deceleration. It never happened before installing the filter.

Motor is 3 phase 1,5kW, 380V, 1420 rpm, 3,4Amps (parameters from motor nameplate). VFD is for 1,5kw motor, and it can take 3,8 Amps. Filter is rated for 5 Amps.

Attachment 49068

I connected wires from VFD to UVW input on filter, ABC output goes as phase wires to motor and N is connected to this plate (marked in red circle)
Attachment 49069

Do you have any ideas what can be wrong?

I think too small VFD would throw overcurrent errors even without filter.

Filter on the motor side of the VFD? Generally you shouldn't have filters on the motor side of the VFD. Most VFD manuals (industrial or home gamer) say explicitly to not put a filter between the VFD and motor. If you want to install a filter you have to put it on the mains side.

Sorry I should clarify. If you add a boat load of inductance it can overshoot voltage and really do a number on that waveform. Generally VFDs are designed to have absolutely nothing between the VFD and the motor, and it's generally frowned upon to put any filtering between the motor and VFD. If you're getting weird noise and transients filter the mains side of the VFD. Install teck cable on the motor and ground the shield if you're getting interference.

[tonyfoale]

Filter on the motor side of the VFD? Can't have filters on the motor side of the VFD. If you want to install a filter you have to put it on the mains side.

Filters on the motor side are common on bigger motors fed from a VFD. You are only looking at half of the picture. LC filters on the mains side are to reduce feeding VFD noise back into the mains.
The filter on the other side of the VFD is there for another reason. It is called a dV/dt filter, which is the time rate of the voltage build up. This can be noisy and damaging to the motor.
An inductive filter is used to reduce dV/dt, the switching in VFD control causes high values. It is best to keep dV/dt to below 800 to 1200 V/us.
I use both a mains filter on the input and a dV/dt filter on the motor side. The mains filter makes no noticeable difference to anything but I like it there. The dV/dt filter makes a huge difference. See Stuff about VFDs and motors

Long cables to the motor make the problem worse. In severe cases or where a damaged motor would be hard or expensive to replace there are sine wave converters available, these take the PWM signal and turn it into a sinewave with a fraction of the dV/dt values.

Generally VFDs are designed to have absolutely nothing between the VFD and the motor, and it's generally frowned upon to put any filtering between the motor and VFD.

This is just not true. VFD makers and suppliers sell and recommend using dV/dt filters and they are strongly suggested for larger motors to avoid shortening motor life.

[nova_robotics]

This is just not true. VFD makers and suppliers sell and recommend using dV/dt filters and they are strongly suggested for larger motors to avoid shortening motor life.

Fair enough. I stand corrected.

[Carnel]

Hi SteelCraft, Can you please post the selfinduction value (L) of the filter coils and the capacity value (C) of the capacitors? And whether each capacitor is connected between two phases or between phase and N?

[SteelCraft]

L for filter coil is 2mH, Capacity value of the capacitor is 4,7uF.



Looks like capacitors are connected between phase and N