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VFD as a LED light dimmer
4

VFD as a LED light dimmer

VFD as a LED light dimmer

(OP)
Hello All,

Does anyone has any experience using a VFD as a light dimmer? I am a recent graduate and I have just started working at this company not too long ago, my boss wants me to take a ATV12H018M2 (240V Single Phase) and use it as a dimmer. I know there are triac, sine and IGBT dimmers out there in the market but they seem to be either incompatible or expensive.
Anyhow, I have read the manual and since it is meant to be for a motor I don't understand what configuration menu to use for my purpose. I have so many questions. Firstly, I would like to know about the drive outputs u,v,w and GND. How do I connect a 3 wire lamp to these outputs? U-Hot, V or W-Neutral and GND - Ground wire?
Secondly, if I connect drive output to a oscilloscope would I be able to see a PWM signal? I have so many more but I want to start with these two first. I think what he would like me to do is control when it fires or crosses zero. I'm so clueless and the manual seems to be not so helpful either. I would really appreciate if someone could guide me through this. Attached please find the user manual for the VFD I have been using.

Thanks,
GoldenEagle

RE: VFD as a LED light dimmer

I was assigned a similar task on my first "real" job. At that time, there were no such things as VFDs. I remember starting out with the assumption that I should find a good solution but I soon realized that this was a test to see how independent and analytical I was. Or just clueless.

I think this is a similar situation. One thing you shall NEVER try is to connect GND to the VFD output. N is OK, but not the GND.

Make sure you understand the specs for the LED first. Is it one single led? Or a string of LEDs? Is there any driver involved? Or series resistors?

Then read up on VFDs. They are all PWM these days. Connect between U and V (or W) you will probably fry something when doing so. Then find out why it didn't work. After adding a full bridge rectifier, some resistors and capacitors, you may have something that blinks - or burns.

You should chose scalar control, aka U/f.

Varying the frequency and thus the output RMS voltage, you will notice that the LED's output varies between dark and bright at double the set frequency. If that is what your boss wants, then show him that result. If it isn't (which I think) then tell him that it will not work. And explain why.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

Neutral here in North America is always Ground potential, so if you are here, do NOT connect the output of the VFD to anything that needs the Neutral to work. Instant VFD death.

So here's what you are left with. You CAN use it, but only if the lighting is Line-to-Line powered. I would also be VERY hesitant to connect it to anything other than incandescent lighting, or rather nothing that has a ballast. Unlike a PWM UPS, the output of a VFD is not at all filtered (for the most part) so it may damage another SMPS or magnetic ballast by over heating it with the harmonic rich output. By the time you got done buying the appropriate filters, you would likely have spent less using a device designed for this purpose.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies

RE: VFD as a LED light dimmer

(OP)
Thank you guys for your response.
Skogsgurra, I thought I would give it a try and tell him that it won't work too. But, when I talked to my colleagues(30+ years experience) they said they did this last spring and were able to control the brightness of the lamp using the same VFD I have with me now. They did by using the controls and codes from the user manual but they have not recorded the procedure anywhere. So, I have no choice but to say him that I don't understand how to use the terms, codes and configurations on the manual for our setup. We do use full bridge rectifier and current sink (transistors and resistors) as the lamp driver.

jraef, yes I live in NA and I'll keep that in mind. Thank you. As in the harmonic output, I was under impression that there is stage (DC bus/link) just for filtering in a VFD.


RE: VFD as a LED light dimmer

oldeneagle272, the DC is filtered, but the output of the VFD is a PWM waveform - without any filtering. Lots and lots of harmonics in the waveform, as jraef has stated.

RE: VFD as a LED light dimmer

By the way, we used to test VFDs (and soft starters) by hooking them up to incandescent heat lamps on the test bench. You just have to be cognizant of the voltage ratings. I can attest to the fact that a 120V rated lamp glows brilliantly at 480V, albeit very briefly.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies

RE: VFD as a LED light dimmer

In North America the neutral is grounded at the source. You should take a look at the circuit, but I would expect you can put power on the neutral without any issues. The incandescent base (E26 base?) lights use the outside screw shell as the neutral to reduce shock hazard.

Now, it sounds like this lamp is 120VAC, so you could use a 240:120 transformer and this would filter most of the PWM signal out of the waveform on the secondary side. You can also ground one of the transformer secondary terminals and call it the new neutral.

If you factory reset the drive it would likely work as programmed. Set the motor voltage to 120V if you direct connect the lamp. Give a start command and see what happens. Wear the proper PPE.

RE: VFD as a LED light dimmer

For some reason, up until now I had not noticed the "LED" reference in the title. Not going to be feasible. Here in the US anything you install (that will be subject to National Electric Code authority inspection) must be NRTL listed, by someone like UL. UL has a rule on dimmers that a dimmer MUST be tested and listed SPECIFICALLY with any non-incandescent bulb. When you buy a wall dimmer, it will come with a list of specific bulbs it has been tested with, technically you cannot use it with untested bulbs. So in effect, by doing this YOU are taking on that responibility and unless you have an extra $50k floating around for UL listing of that VFD as a dimmer for non-incandescent lamps, you will be in code violation. Maybe that's OK for your boss because he is not planning on pulling a permit and getting inspected, but he should also check with his insurance carrier. The underwriters often throw in clauses which stipulate that any damage caused by a fire determined to have been started in equipment that is not used and listed for the intended purpose, will not be covered by insurance. That's usually an idea killer on things like this.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies

RE: VFD as a LED light dimmer

Jeff - The big question - Is this for an installation or just to experiment?

RE: VFD as a LED light dimmer

Quote (GoldenEagle )

I am a recent graduate and I have just started working at this company not too long ago, my boss wants me to take a ATV12H018M2 (240V Single Phase) and use it as a dimmer.

Quote (LionelHutz)

Jeff - The big question - Is this for an installation or just to experiment?

Given tha above statement, I see your point. His boss may just be giving him a "what if" sceanrio.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies

RE: VFD as a LED light dimmer

(OP)
Jeff and LionelHutz, It is just an experiment for now but we might potentially use them with our lamps if we can get them to work like we want.

RE: VFD as a LED light dimmer

Good luck with that...
Let us know how it turns out, preferably with pictures of the fireworks.

Take precautions... knight

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies

RE: VFD as a LED light dimmer

(OP)
So far this is what I have got.

Around 200V AC i/p was applied to a VFD to get 120V o/p(across a L and GND).
The moment I apply voltage to a non-running VFD it generates a surge output and this surge is enough to a flick a lamp.
When the lamp was powered through a VFD, I have tried changing the frequency using a jog dial on a VFD. I was able to see change in pulse width on oscilloscope but I have not seen any change in the brightness of the lamp. And the last but most annoying part was when the VFD was running, a buzz sound was heard from a lamp, the buzzing sound changes with the change in frequency and stops when I stop the VFD. I think the buzzing has to do with the 8KHz output of a VFD.

Sorry Jeff, no fireworks hence no pictures.smile

RE: VFD as a LED light dimmer

You don't get much variation on voltage between output and GND. You need to connect between two output lines.

Told you so.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

Which may mean you need two bulbs in series to meet the voltage.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFD as a LED light dimmer

...or produce Jeff's fireworks...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

Or if you're planning on using an 'off the shelf' LED lamp assembly, be cognizant of the the fact that the input leads are rated for a specific range of input voltages. Internally, the fixture's power supply rectifies and regulates the actual output to the LED array.

I strongly suspect that if you vary the input voltage, specifically lowering it to dim the array, the poor power supply will do its very best to maintain the nominal output of the LED's until it either shuts down or dies trying.

It might be interesting to try. I'd think I want to get a lot of instrumentation around to see what happens to voltages and currents and input and output waveforms.

old field guy

RE: VFD as a LED light dimmer

(OP)
Skogsgurra, I think the voltage across lines (U, V and W) within themselves was same to what I saw between a line and GND. I'll double check on that tomorrow.
I don't get why changing the frequency is not changing the RMS output am I doing something wrong?
May I know what is a scalar control U/f you have mentioned above? Is it a kind of VFD with that control?

Thanks

RE: VFD as a LED light dimmer

Why would it change the RMS anything? The VFD is going to deliver the same RMS at all frequencies because that is what determines the delivered hp. Just because the user selects a different frequency doesn't me they want only a 1/4hp instead of 1/2hp.

If you want to effect the RMS you need to adjust the programmed power/hp that the drive is set for.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFD as a LED light dimmer

Not quite so. Voltage and frequency are proportional to each other up to base speed (in scalar mode). It is more about grid voltage and PWM voltage being superimposed when you connect between output line and ground. I shall measure on a VFD on my bench. Stand by!

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

(OP)
Is there a relationship between i/p and o/p voltage of a VFD? With the one I have got, for 230V input (single phase), the o/p voltage (three phase) across a line(any) to GND is around 160Vrms where as the voltage between lines is only 20-30Vrms. Is this how it is suppose work (I guess not from Gunnar's post above) so do you guys think my VFD acting up? I have used multimeter for testing.

Thanks

RE: VFD as a LED light dimmer

Sorry. Didn't get the time. Turbine explosion nearby got in my way. Will be back later with some measurements.

In the meantime, make sure you understand the difference between RMS voltage, fundamental component and total voltage (including all harmonics). With a good multimeter, you will read all components in the output voltage while the voltage you set via the input setpoint is RMS of fundamental voltage.

And don't forget that it is between lines on the output of the VFD that you shall measure. Not fom line to GND. That was described in an earlier post.

Finally, not so sure that your LED reacts to RMS. Could just as well be AVG. Also, if your LED "ballast" is anything else than a resistor, you may be in for some surprises.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

Gunnar. The RMS should definitely change with (speed)frequency adjust. I was under the impression goldeneagle272 was talking about the modulation frequency. The "8KHz" mentioned above. Re-reading I could go either way. :)

goldeneagle272 What exactly are you using for "lights"? Got a link?

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFD as a LED light dimmer

If I am not mistaken the VFD will rectify the line Voltage and charge the DC link capacitor to the peak value.
As soon as it starts it will turn on a pair of transistors to apply the full capacitor directly across the load.
For the brief instant in time while the transistors are on I would expect the LED to be very bright.

One way of making LEDs more appear brighter to the human eye is to pulse them at high power/high frequency, the eye is fooled into seeing it as though it was on all the time just as the image on a TV appears to be there when in fact its flickering off and on.
Another example is a movie screen for the split second while one picture is changed for the next the screen is blacked right out by the rotating shutter, your eye can't see that but will notice wheels that appear to rotate backwards.
I thing the numbers in a calculator (I'm talking about the old LED or discharge tube displays) are also flashed in sequence too fast for your eye to see.


RE: VFD as a LED light dimmer

Details on this LED ligtht would help. If you're applying the VFD output to a rectifier inside this LED light then the DC after the rectifier will be the peak of the PWM modulated output of the VFD. The VFD may be PWM modulating an equivalent 0-60Hz RMS output voltage, but the peak voltage of the VFD output PWM waveform never changes.

RE: VFD as a LED light dimmer

(OP)
Here is the Link

I cannot share more about it since this technology is patent pending, all we use is a current sink (MOSFET and sense resistor) to control each LED stage. LED stage consists of number of LEDs depending up on our requirement, voltage drop and i/p voltage.

As in the frequency control I mentioned above it was just by using the jog dial, with the set output frequency 2kHz - 8kHz.

I was able to control the brightness a little, flickering at low frequency (again jog dial) to constant brightness at high frequency. But, with the restricted range (jog dial)I wasn't able to fully turn up the brightness, I used both 120V and 230V lamps.

RE: VFD as a LED light dimmer

It looks to me like the frequency you were adjusting was the carrier frequency, not the equivalent line frequency. That would be why you were not getting any change in the output. It is the carrier frequency that also causes the hum you were hearing. Either you have to filter out the carrier frequency or get it above hearing (over 20KHz if I remember right.)

RE: VFD as a LED light dimmer

(OP)
That might be it but I'm not so sure since the manual is not very clear about it. The carrier (switching) frequency range is 2kHz - 8kHz where as for line (or motor frequency) I have to choose either 50 or 60 Hz. So, When I setup the VFD, I have been entering the motor frequency as 60Hz(my lamp is compatible at this frequency).

This is an excerpt from the manual about the jog dial, "the jog dial on the HMI acts as a potentiometer to change the reference value up and down within the limits preset by other parameters (LSP or HSP)." LSP being low speed set at 0Hz and HSP high speed set at 400Hz(max). The adjustment range for a jog dial is 0-100%.

RE: VFD as a LED light dimmer

Are you kidding? The switching (carrier) frequency does not have much (next to nothing) to do with the output frequency. Forget about the kHz. You will need to filter the carrier out anyway.
The VFD output is a variable frequency and voltage going from zero Hz up to a few hundred Hz. Just as your excerpt says.

It is fine that your lamp is "compatible" with 60 Hz. Good, good. Sarcasm.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

Thanks for the link
I'm still puzzled why you would want to use a VFD to
control LED brightness though.

RE: VFD as a LED light dimmer

I have not seen a VFD for motor control where you can set the VFD so a pot controls the carrier frequency so I highly doubt that's what the pot was doing.

If you set the VFD for a motor rated frequency of 60Hz with a motor voltage of 240V then the pot should vary the PWM generated V/Hz output from 0V/0Hz to 240V/60Hz.

RE: VFD as a LED light dimmer

I got somewhat tired of seeing clueless guys trying to discuss simple matters on EngTips. We have a policy, after all, and that is to avoid hobbyists and hobbyist discussions. Unless there are good reasons not to. This is a compilation of measurements that I made recently. With comments.
http://www.gke.org/pub/files/VFD%20as%20a%20LED%20...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFD as a LED light dimmer

At this point, you should likely do more reading and learning to understand exactly what's going on. I expect your boss wants you to show that you understand exactly why it won't work, not that you blindly tried some things and failed and then read on the internet that it doesn't work so you gave up.

What do they teach in engineering schools these days? You're doing it all backwards. The first step of this experiment is to investigate the LED SMPS to determine how it will you can dim the lamp. If you can dim the lamp, ou then have to determine if the VFD output will give the SMPS what it wants to be able to dim the lamp. If it's not compatible then determine if there is a way to make it compatible.


You have to learn to read too. The first 2 posts told you to connect between phases on the output of the VFD and that connecting to a SMPS was a dumb thing to do.

RE: VFD as a LED light dimmer

Actually, I believe that circuitry goldeneagle272 is testing is linear, not SMPS. But I do agree, he has to learn to read... And Gunnar, thanks for for your insights.

RE: VFD as a LED light dimmer

Thanks Gunnar. I liked that. lps

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: VFD as a LED light dimmer

SciZee - it's described as a rectifier feeding some type of circuit which appears to be active. It might be some type of linear current regulator too though. At any rate, it's still described as having a rectifier first, which means the peak voltage from the PWM output gets to the circuit regardless of what lower frequency output the PWM is simulating.

I already posted what should work as the solution.

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