LEDs Pulsing when dimmed under Generator Power

[NSD09997]

Hi all!

I am facing an issue with dimming output, where I require an expert insight.


I have this project where Siemens Universal Dimmer (5WG1 527-1AB31) will be used. The dimmble LED in question is a chinese product. The facility is powered by a gas generator. I have been working with the same dimmer on other projects, but without this problem.

I have tested three different dimmable led samples on the facility (assuming chinese driver incompatibility), where the output of the LEDs were flashing/pulsing (constantly varying brightness between 400 to 500 lux level). The led samples worked fine when connected to grid or other generators (tested on other facilities). We have commissioned the Siemens universal Dimmers separately as Leading Edge and trailing edge to see the effects. The result is the same.


Can someone help me understand what is happening? I assume there must be some problem with the generator output. The issue appears only when dimmed.

Thanks in advance.

 

[romex jockey]

Are you seeing the lights mimic the generator rpm?

~RJ~

 

[NSD09997]

No, it doesn't flicker with the RPM.

It's more like varying brightness. Say, you set the dimming at 70%. The brightness of the light or the output actually varies between 60-70%.
It's more like wobbling at 5-10Hz. It doesn't go zero.

 

[kwired]

No, it doesn't flicker with the RPM.

It's more like varying brightness. Say, you set the dimming at 70%. The brightness of the light or the output actually varies between 60-70%.
It's more like wobbling at 5-10Hz. It doesn't go zero.

Did you check to see how stable source frequency is? It won't be as stable as utility frequency is, unless maybe it is going through an inverter.

 

[NSD09997]

Did you check to see how stable source frequency is? It won't be as stable as utility frequency is, unless maybe it is going through an inverter.

And, if the frequency/voltage is unstable, does the dimmer pass on the unstable frequency/voltage to the load? I understand that phase-cut dimmer only cuts a portion of the input waveform, rather than making changes (switching spikes aside).

 

[kwired]

And, if the frequency/voltage is unstable, does the dimmer pass on the unstable frequency/voltage to the load? I understand that phase-cut dimmer only cuts a portion of the input waveform, rather than making changes (switching spikes aside).

IDK, but you claim to not have the problem when same components are used on a utility supply. I think you need to compare voltage and frequency between this source and one that doesn't give you any problems and assume any differences probably are a contributing factor.

 

[nec_addicted]

LED's Pulsing

LED's Pulsing

Troubleshoot per OEM to prevent distructive testing. You might need a ground isolator like a Rochester Instrument Company Reference or PLC digital reference negative. Try to determine inside gen control panel where you could grab a test connection reference point. I have seen trouble with non linear loads in the same room but just thinking control reference negative or clean the connections maybe just grease.

Another possibility is there a GFI on the tool connection plug power inside the panel? Separate the min. interface clearance dimension.

 

[NSD09997]

IDK, but you claim to not have the problem when same components are used on a utility supply. I think you need to compare voltage and frequency between this source and one that doesn't give you any problems and assume any differences probably are a contributing factor.

Yes, it does not show any problem on the utility supply. I'll have to compare and record the differences. I'm not sure why the client is so skeptical on the dimmers when the problem is very evident.

 

[NSD09997]

Troubleshoot per OEM to prevent distructive testing. You might need a ground isolator like a Rochester Instrument Company Reference or PLC digital reference negative. Try to determine inside gen control panel where you could grab a test connection reference point. I have seen trouble with non linear loads in the same room but just thinking control reference negative or clean the connections maybe just grease.

Another possibility is there a GFI on the tool connection plug power inside the panel? Separate the min. interface clearance dimension.

I'm thinking of using a scope instead. That way I would be able to see input and output waveform. And see what happens with and without a dimmer in action.
I think you are an expert on generators? Can you tell me about the output of a generator running in island mode?

 

[nec_addicted]

Pulsing LED's

Pulsing LED's

Oh not really, I just had good experience with my electrical dept.leads. It does help to have full submittals manuals and start-up assist from OEM during check-out. The system common when separating ATS neutrals, number of poles in the line up , metering controls software release, factory reps helping and good maintenance team leaders or groups usually make successful start-up. That said where you are relative to end of line from the power company and harmonics, Mirus filter's on line voltage correct shielding on power conductors and good product delivery is always good tip have lots of project money and goof schedule can make or break your hard work effort.Admit when your wrong the general construction manager has lots of talent he can call in.

 

[steve66]

A generator is not as "stiff" as the utility supply. By that, I mean the voltage can be changed more easily by the loads connected. Add more load to the generator, and the voltage will drop more than the utility would.

It also means that loads that draw a lot of harmonics can distort the generators voltage waveform. If there are a lot of computers, or VFD's running off the generator (or even a lot of lights with electronic ballasts or drivers), it will distort the generators output voltage waveform. You should be able to see this with an oscilloscope.

It the waveform gets distorted too much, it will cause false triggering of the dimming circuits. It might cause a forward phase dimmer to shut off too early, and it might cause a reverse phase dimmer to trigger too early. If the harmonics are just enough that sometimes it causes false triggering, and sometimes not, I think that would explain the varying brightness.

Another possibility is that the generator frequency is just changing. It might not take much to notice a difference in light output. If setting the dimmer sets a time constant, the output will vary as the frequency varies. For example, just drawing numbers out of a hat, say the dimmer is set for 70%, and at 70% it triggers on at the start of the wave, and shuts off 5 ms later. It turns back on at the beginning of the next cycle. If the frequency goes up, it will turn on again faster, and the result will be more output power, and brighter light.

 

[NSD09997]

A generator is not as "stiff" as the utility supply. By that, I mean the voltage can be changed more easily by the loads connected. Add more load to the generator, and the voltage will drop more than the utility would.

It also means that loads that draw a lot of harmonics can distort the generators voltage waveform. If there are a lot of computers, or VFD's running off the generator (or even a lot of lights with electronic ballasts or drivers), it will distort the generators output voltage waveform. You should be able to see this with an oscilloscope.

It the waveform gets distorted too much, it will cause false triggering of the dimming circuits. It might cause a forward phase dimmer to shut off too early, and it might cause a reverse phase dimmer to trigger too early. If the harmonics are just enough that sometimes it causes false triggering, and sometimes not, I think that would explain the varying brightness.

Another possibility is that the generator frequency is just changing. It might not take much to notice a difference in light output. If setting the dimmer sets a time constant, the output will vary as the frequency varies. For example, just drawing numbers out of a hat, say the dimmer is set for 70%, and at 70% it triggers on at the start of the wave, and shuts off 5 ms later. It turns back on at the beginning of the next cycle. If the frequency goes up, it will turn on again faster, and the result will be more output power, and brighter light.

Thanks. That helped!

Apparently the design consultant failed to mention that the facility was powered by a Generator that is set to run in 'Island Mode'. This caused the voltage and frequency unstable at load end based on what you explained.

There are devices that are compatible with island bus power. But replacement of 380 dimmer devices is a lot. I hope there is an alternative solution to this.