Author Topic: Installing a VFD  (Read 1665 times)

eskoilola

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Installing a VFD
« on: January 01, 2018, 05:22:59 AM »
This is a walkthrough to install a VFD aka Inverter.

A chinese VFD is easy to install and operates quite reliably provided that You take some precautions, install it carefully and do not try to save money in wrong places. I write this posting in hopes it casts light on the very confusing material available in the internet. Nine out of ten articles are only telling how bad the chinese VFD's are - it is really rare to find out an article describing what to do to make it work. This posting is based on my own experience which was not that bad. The VFD this posting is talking about is a chinese Huanyang HY03D023B.

Step #1: Evaluate Your motor



Power inverters are capable to fry Your motor in milliseconds. It is very important to make it sure that the motor can withstand the stresses the VFD is putting on it. In addition to certain electrical properties there are motor types that are not suitable to be used with a frequency converter. The following is a list of some things You should look into:

  • Insulation of the windings. Older motors with Schellack as insulating media are not suitable. This material was used in older motors before epoxy was invented. Even if the motor is rated at voltages that seem to fit, the VFD will introduce voltages that, due to resonences, may pierce through weak insulating material. Further more, this type of insulation becomes soft when it heats up which brings in additional risk of windings shorting. If the motor seems to be unsuitable it is better to get a modern motor rated for VFD use. Another option is to let a professional to make new windings for the motor. The picture above is the motor of my chinese lathe. Although the copper wire is most certainly of the correct type the way the winding is done makes this motor unsuitable for WFD use. My estimation of the lifetime of this motor is under one second when connected to VFD.
  • Type of the motor. The motor should be a genuine 3-phase motor. Further more, if the VFD is going to be run as a converter from single phase to 3-phases then the motor needs to be connected in delta to get the full power out of it. Some single phase motors appear to be able to fill this criteria by just removing a capacitor. Unfortunately this is not always the case although it looks that way. My chinese lathe motor had 2 capacitors and a centrifugal switch. This would have ruined the VFD. In addition the 3rd winding was different from the other 2 to save on the size of the capacitors. I have a friend who does motor windings - this one will visit his workbench.
  • Cooling of the motor. If the motor has an inbuilt fan it is most probably designed to create sufficient air flow at the rated speed. If the motor is ran on slower speed the cooling may not be enough to keep the motor in it's specified temperature range. The blower fins may also be designed in a way that they are not working correctly if the motor is running backwards. If the motor is running hot without the VFD it will certainly not run any cooler with it. My chinese motor runs quite hot although it has proper cooling.


Step #2: Select the VFD



The internet is full of horror stories about chinese VFD's. The usual case is a fried VFD or a VFD that is not performing up to the specifications. This is mostly because of the misunderstanding of the specification. Chinese seem to talk about limiting values, not the values for normal use. Therefore:
  • Choose a VFD that has at least twice the power rating of Your motor
  • If the VFD is used as single phase -> 3-phase converter then use a triple rating. This is because the internal rectifier and capacitors are rated with 3-phase supply. They work with single phase input but the stresses for those components are much harder with single phase application. I ended up with a 3kW VFD for my 0.75kW motor for those reasons.
  • Make sure that the VFD can utilize a braking resistor. Some chinese VFD's claim to do this but in reality this feature is actually not supported because of missing components. Consult the seller and make sure that a braking resistor can be used. The VFD can start and run the motor without the resistor but stopping a large rotating mass can be difficult and usually ends up with the VFD tripping. One of the advantages of the VFD is that it can stop the rotation really quicly when it has somewhere to dump the energy from the motor. This is what the braking resistor is used for. In my case the resistor is a 100ohm 100W resistor and the test motor stops from 3600 RPM in 2.5 seconds. I think this can be made even faster but that would be pushing it.
  • Some VFD's come without a speed adjustment potentiometer. This is not needed but it makes installation and testing lot easier. The buttons on the front panel are not exactly the best way to adjust the speed. They will wear quickly out and are not tolerant on workshop chemicals. The panel is intended for setting up the VFD - not operating it.


Step #3: Connect the dots

There are four connections needed for the VFD installation:
  • The power input cable from Your wall outlet. This cable is feeding the juice for the VFD. In a 3-phase application the cable is connected to (R), (S) and (T). In a single phase application any 2 of these will do. The protective ground is mandatory. This is because the VFD's usually have some sort of filter in the power input and this will put the frame in mid potential in single phase applications. The current is large enough to kill You. I recommend to have a mains power switch to switch off the VFD when not used. My VFD has a rather loud fan which makes a very irritating, high pitch sound. Another recommendation is to use a large ferrite bead located near the VFD. This keeps the EMI inside the VFD.
  • The motor cable. The motor cable is special. It feeds the power from the VFD to the motor. The juice in this cable will contain stuff that is not the every-day AC. There are high frequency and high voltage components which will get even worse if this cable is long. Choose some heavy duty cable and keep this cable as short as possible. The protective earth should be running along the cable or better yet, over the cable. It is not a bad idea to put this cable inside a metal (copper) tube or have a braided shielding on top of it. Again, a large ferrite bead near the VFD is a recommended thing to do. The cable connects to (U), (W) and (V) terminals inside the VFD. The motor should NEVER be disconnected from the VFD when running. This will instantly fry the VFD.
  • The braking resistor cable. This cable needs to be medium duty. There will not be very high currents but the voltage will be high nevertheless. Also, be aware that the braking resistor may get hot if the stopping involves a high rotating mass with high RPM. I was lucky enough to find a ceramic resistor with suitable rating and value along with ceramic mounting components in my stash. If You are not that lucky, I recommend to buy one. The breaking resistor is not just a nice thing to have - it helps stopping the motor quickly. Breaking resistor is connected to (P) and (Pr) terminals inside the VFD.
  • The control cable. This is optional if the VFD is not used to adjust the frequency but rather just convert the 2 phases into 3 phases. The control cable does not need to be heavy duty but it needs to be well shielded. I used a 8 x 0.22 communications cable inside a flexible hand-shower metal tube from the nearby hardware store. This is not just a good shield, it protects the cable from all the stuff that is flying around near the lathe. I connected the cable to the following terminals inside the VFD: (FOR)=Forward, (REV)=Reverse, (RST)=Stop, (SPH)=Reset, (DCM)=Ground(D), (+10)=10 Volts, (VI)=Speed and (ACM)=Ground(A). Please note that the (DCM) and (ACM) are two separate cables. Analog ground should be kept separate from digital ground. The buttons are reconfigured to this particular application. The Stop button is different from all other buttons - it must be normally closed. To stop, the connection needs to open. In addition to this there is a separate cable from the spindle cover switch to terminals (DCM) and (SPM)=Emergency. This will stop the lathe and does not allow it to be started if the spindle cover is open.


Step #4: Mount the VFD

I decided to mount the VFD in such a way that it is easy to replace the unit if it fails. Although I am quite confident with this VFD I am still a little bit suspicious. Now, if it fails it is very easy to replace it. The VFD can get warm. It should NOT get hot. It needs free air flow around it. The VFD can be put inside a cabinet but then care must be taken to ensure that there is enough room around it. As all electronic equipment, the VFD is allergic to dust. This is because the dust creates an excellent heat insulation blanket on top of heat sinks causing them to heat up. In a shop environment it is probably impossible to get rid of the dust. This was another reason for my "open air" installation. Now it is very easy to give this unit a gentle blow from the air gun annually.


Step #5: Configure the VFD

Here are the preliminary values for configuration parameters for my application. These may be different depending on the motor power and button setup.

ParameterValueRemarks
PD01308Reset parameters to factory defaults. Do this first.
PD0011Uses external terminal
PD0021Uses analog voltage for speed control
PD00350.00Main frequency.
PD00450.00Base frequency.
PD005100.00Maximum operating frequency.
PD0062.50Intermediate frequency. Used for torque compensation.
PD0070.50Minimum frequency. Used for torque compensation.
PD008220Maximum voltage. This is suitable for delta connected motor.
PD00924.00Intermediate voltage. Maximum torque boost at low RPM.
PD0108.00Minimum voltage. Maximum torque boost at low RPM.
PD01110.00Minimum operating frequency.
PD0142.50Acceleration time.
PD0152.50Deceleration time.
PD072100.00Maximum frequency the potentiometer can set.
PD07310.00Minimum frequency the potentiometer can set.
PD04402(FOR) terminal is forward. Exchange values with PD045 if motor runs the wrong way.
PD004503(REV) terminal is reverse. Exchange values with PD044 if motor runs the wrong way.
PD04604(RST) terminal is stop. Note that this terminal works the other way around. Contact is opened to stop.
PD04714(SPH) terminal is reset. Used to recover a tripped VFD.
PD04913(SPL) terminal is emergency stop. Used to keep the motor from starting if spindle cover is open.

Last some pictures. Click on them to see a larger version.


« Last Edit: January 01, 2018, 05:26:39 PM by eskoilola »

Offline Pete.

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Re: Installing a VFD
« Reply #1 on: January 01, 2018, 08:48:16 AM »
It's a good write-up but I have never seen a centrifugal switch on a 3 phase motor (or a capacitor for that matter, unless it was fitted deliberately to run it off single phase). There's not much point warning about something that you are never going to come across.

Other than that - good job.

Offline John Rudd

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Re: Installing a VFD
« Reply #2 on: January 01, 2018, 09:54:06 AM »
Ditto, a decent write up.....however, the motor needs to be connected in Delta if it is to work with a 220-240 v input vfd.....most modern motors suited to vfd use are dual voltage, the windings can be connected in Star for true 3 phase or in Delta for a 0-240 v 3 phase supply from a vfd....
It may be necessary to locate the Star point on a 3 ph motor and bring out leads connecting to the phase winding ends to do so......
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Offline vintageandclassicrepairs

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Re: Installing a VFD
« Reply #3 on: January 01, 2018, 03:37:38 PM »
Hi All
I would not mount the VFD near the workings of the lathe as in the photos,
metal chips and swarf flying around can easily enter the  ventilated unit in the position shown
 :zap: :zap: :zap:
+1 on the comments on single vs 3 phase motors  :doh:

John

eskoilola

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Re: Installing a VFD
« Reply #4 on: January 01, 2018, 05:30:56 PM »
Thanks for everyone who bothered to read and comment the walkthroungh. Did some corrections:

  • removed the useless babble about 3-phase motors with centrifugal switches and capacitors. These exist but are really rare and very application specific.
  • corrected the term 2-phase motor to single phase motor
  • corrected a handful of typos ... and hopefully did not introduce too many new ones.

Offline PekkaNF

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Re: Installing a VFD
« Reply #5 on: January 02, 2018, 02:49:54 AM »
Very good! I had no problem with the original test.

Now the interesting part: How would you connect chuck guards or other interlocking guard? How about E-stop.

I know what EU regulation says about real production machines, but it get's complicated. Principle would be that E-stop tells VFD to brake and a safety timer will turn out the VFD feed after a propriate delay time from the E-stop signal. In real life it gets a bit more complicated.

Best compromise I now is to put interlocking guards in series with enable/inhibit or stop signal (if it is active LOW) of the VFD.

E-stop I would like to kill all...I.E. cut voltage off from the spindle VFD, but it is not the fastest way to stop the spindle. This needs a little consideration and probably varies a lot depending of the application. Normal E-stop buttons don't handle full current of the bigger equipment, they need to be connected to a contactor.

Pekka

Offline mexican jon

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Re: Installing a VFD
« Reply #6 on: January 02, 2018, 03:18:16 AM »
Guard interlock is relatively easy as this can be tied into the stop or drive enable circuit, setting the deceleration time to suit  :thumbup: E-stops are an interesting thing  :scratch: In reality an E-stop shouldn't take into consideration the effect it may have on the machine (provided it doesn't make the machine dangerous) by that I mean when an E-stop is used in it's correct function it is to safe guard people and therefore doesn't worry about any damage or detrimental effect on the machine. As per their name Emergency Stop compared to a controlled stop which is the normal.
People say you only live once ! I say thank F@*K can't afford to do it twice.

Offline Pete.

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Re: Installing a VFD
« Reply #7 on: January 02, 2018, 07:05:45 AM »
I wire the estop in series with the door/guard interlocks. Also in line with the stop button. That way if you hit stop, estop or open a cover the spindle is braked to a stop.


Online awemawson

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Re: Installing a VFD
« Reply #8 on: January 02, 2018, 08:11:37 AM »
ESTOP should drop power to the servos / steppers & motors so you are not relying on electronics to stop things. On my CNC Plasma table for instance there are two poles on the ESTOP switch. One tells the electronics to stop everything, but the other drops out a relay in series with the stepper power supply
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Offline mexican jon

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Re: Installing a VFD
« Reply #9 on: January 02, 2018, 03:56:32 PM »
Here's an Emergency stop system in its true meaning.


People say you only live once ! I say thank F@*K can't afford to do it twice.

Offline PK

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Re: Installing a VFD
« Reply #10 on: January 02, 2018, 04:27:57 PM »
ESTOP should drop power to the servos / steppers & motors so you are not relying on electronics to stop things. On my CNC Plasma table for instance there are two poles on the ESTOP switch. One tells the electronics to stop everything, but the other drops out a relay in series with the stepper power supply
Agree. On small machines, just turning the power off is probably OK.  But on something with some moving mass (like a spindle, or servo driven mill table) you generally get a faster stop by telling the drives to put the brakes on (and then turning the power off).   The decelerating spindle/axis etc.. will generate enough power to keep the drive running while it dumps energy into it's braking resistor or injects DC to trigger eddy current braking.