Why Do Lights Start Flickering Suddenly?

The initial startup load of the lights is higher than the load when they are running steady state.

That is an old myth. The load of the coils is on the order of 2 Watts and the initial impedance of the lamp is in the mega ohm range. Striking an arc with a high voltage open circuit presented to the lamp does not necessarily increase the overall load by more than a few Watts. So, where is the higher load?

In truth, the lamp current ramps up as the impedance drops and the high voltage presented to the lamp drops rapidly during the initial ionization of the gas.

I would say that the flickering is coming from brief dropouts that the UPS is making as it switches in and out of line power. Sometimes a simple change of ballast will solve the problem. Look for one with a Universal Input (90V to 377V) and see if that has flickering issues.

The starting (inrush) current of a typical fluorescent lamp is in the neighborhood of 50% more than its normal operating current.

The "old myth" is that it is more economical to leave florescent lamps on then to turn them off. This is not true because the inrush current lasts no more than a second, which in the grand scheme of things is not enough to cause concern when it comes to electrical economy.

However, a 50% higher inrush current is cause for concern when the UPS is not sized to handle that extra load. Actually, the peak load is worse! It is the same problem with electric motors. The current to start a motor is momentarily higher than the normal operating current by a significant margin.

So, I still stand by claim that the inrush is the problem.

You can see from a graph I pulled from Lutron's website why inrush is a problem and that electrical installers must take that inrush into consideration when designing a lighting system for a client. Not good for a UPS.

This documentation puzzles me and makes me wonder if it is relevant to the question of the OP. Power distribution in the US is at 60 Hz which has a period of about 16.7 msec. Half a cycle then is about 8.33 msec. This documentation shows a surge current happening for less than 12% of a half cycle of the power distribution voltage. We cannot see lights flickering at 60Hz or at the even faster 120Hz of each half cycle. The OP does perceive the lights flickering so this flicker is a much slower process than either of these surge currents.

Note that the original post claims they dim drastically, then get brighter

I think the observed "flickering" is due to the UPS power fluctuating or fluttering because the inrush current causes either the UPS voltage to sag or a protection circuit is momentarily engaged.

After the initial start and sag the voltage and power ramp back up, the florescent lamps kick back into their startup mode again, causing another sag event.

The other issue with many UPS systems is that they do not all deliver a clean sine wave. If the ballasts have a transformer, then a non-sinewave voltage may not deliver full power to the lamps, aggravating the problem.

I simply have to take issue with the graph you borrowed from Lutron. The inrush current as depicted is simply the power necessary to bring the ballast up to a "ready" state and has nothing to do with lamp starting.

Other devices that convert AC to DC also have a large current inrush when initially energized. Basically what you are seeing in this graph is that the Lutron uses a circuit that only stores a few Joules of energy as opposed to the competition that uses bigger capacitors. It is all propaganda!

The other thing is that these graphs are altered so that they look impressive. The vertical and horizontal axis are not on the same scale. And they represent a situation where there is plenty of excess electromagnetic energy available in the power supply. Of course, a UPS won't have that kind of delivery capability, but neither will a fairly loaded power distribution network.

Frequently, the manufacturers of devices or equipment will publish testing of their devices under ideal conditions. They rarely publish or even discuss what happens when you have real world conditions so you end up testing that yourself.

Lastly, even if there was a condition that would allow a spike of current as shown in the graph (before or after the lamp was started) you would not be able to see it. The human eye is simply too slow to register an event this brief event.

The moral of this story is that sometimes you have to do certain investigations yourself to get to the facts. And it is fairly easy to be fooled by "graph manipulation". It is similar to taking facts out of context.

So, are you claiming that when you throw the switch on your florescent lights that the inrush current at startup is equal to or less than the steady state current? Actually, you did in your first post.

Please post your proof of that.

While you are nit-picking the sales brochure, the point of the argument is that inrush current can cause a UPS system to disfunction if that current exceeds the overload trip point of the UPS.

He said no such thing!

Your erroneous reading filter has been turned ON again.

NUOJ differentiated between the lamp impedance, the gas impedance and the lamp fixture impedance as they change in time during start up.

The first problem I still see with your earlier posting of ballast (fixture) current draw is time. The time interval is much too short to be seen by the naked eye. The OP sees these lights flickering. Additionally the OP says nothing about this happening during the start up of any lamps. You added this stipulation of lamp start up "out of whole cloth". By implication the OP states that most of the time these lamps do not flicker for this started about a month ago. If the power distribution and/or UPS for the lights was grossly under sized for the fluorescent light surge current then they would flicker every time.

Post # 3 clearly states my claim is a myth.

My rebuttal followed with a graph, which he disputes as marketing speak.

The graph may not be exactly accurate, but the principle is! Inrush current > Steady State current. It is a well established fact.

That's my claim.

As to the time factor, who knows how long the definition for flicker is. The original post also mentioned dimming drastically.

My guess was and is that the initial inrush current either trips a circuit safety in the UPS or causes a voltage sag. The resultant recovery is what takes the time and is visible as the lights "flickering".

I buy the idea that they would have flickered from the point of installation, but "what's changed?" The original poster did not say. So either the UPS system has changed (i.e., battery decay or component variation) or something else may have been added to the circuit or something else is switching on/malfunctioning in the circuit to cause this.

This is India, by the way, and they do have their unique way of wiring things up!

I would be happy to provide graphs if I had access to my thousands of measurements. Unfortunately, the fluorescent lighting manufacturer and I didn't see eye to eye after 17 years. But the loss was really theirs because I was one of the few with patients and trade secrets covering my walls.

Having spent 10+ years in R&D I can describe the lamp/ballast measurements quite accurately. Just about every ballast I examined was wired to be disconnected from the power source until someone came along and threw the switch. At that point, the ballast would have to power up first, and then the lamp could be started. The newer electronic ballasts use a variable Q type oscillator which has a very low Q for starting. When the lamp changes impedance from megaohms to a few hundred ohms, it changes the Q of the circuit. I believe it to be a very clever solution for lamp starting.

To make a long story short, the measurements tend to look like the following:

In this case, the lamp current is in blue. NEMA has a well defined set of instructions as to how to measure starting conditions. In general, the starting time is defined as the time it takes for the lamp to go from 10 to 90 percent of full load current. Ballast initialization spikes do not come into play. As you can see, there is no "inrush" current shown here because that is not what normally happens at startup.

Without the ballast to limit things, the current would continue to climb higher and higher until a component failed. So, the ballast is designed specifically to limit the lamp current. But there are no rules about limiting the "inrush" current required to bring the ballast up to an operating condition. There only marketing people who know how to manipulate the information so as to create a concern where there is none.

Lastly, if you check your graph, all of this "inrush" current occurs in less than 1 millisecond. It takes 16.67 mSec for a full cycle (at 60Hz). Most devices connected to an AC distribution system are designed to filter out or ignore any noise that fast. So, I don't buy the claims or concerns about inrush currents.

And I can further state that taking the kind of measurements shown in the graphs are more difficult than it looks. Actually, if you look carefully, it shows the current returning effectively to zero which would not make much sense. But that could be due to scaling and so on. In any case, I object to claims meant to trigger decisions based on fear or mis-information which I believe your brochure is guilty of making. There is a lot they are not telling you about the effects, and so on.

I stand corrected.

Is that chart using an electronic ballast or a transformer ballast or what? My understanding is that there are three different types. It really depends on the type, I would think.

On further reading from manufactures of UPS systems the reason they do not recommend fluorescents has more to do with the noise and back EMF generated, which can interfere with the UPS and causes it to trigger its protection circuitry or worse. Depends on what grade the UPS is and what it is connected to.

So, it isn't the inrush current unless you consider back EMF inrush (for those ballast types that have that), but then again, that is the same way motors work, too.

...or moving the lighting onto IPSs and keeping emergency lighting only on the UPS.

Better solution.

I don't have a solution for your problem but I do wonder why your lighting is even on a UPS? typically a UPS is for computer areas or critical pumps or equipment that never goes offline during usual operating hours. lighting almost always runs off of "house power,and is part of a total energy managment system. are you working in a secure area? what is your application?Why would your lighting be so important that it's being covered by a UPS system?...this might be interesting

In India its a noramal practice to connect the emergency lighting through UPS. So that during power failure there woun't be interruption in the lighting of the area.

I don't really agree with you. Normally inverters with battery are used for emergency lighting. In case of power failure there will be auto changeover from grid power to inverter power with momentary interruption which does not cause any problem so far as illumination is concerned.

The UPS power supply is normally used for computer or other electronic appliances where even momentary interruption of power is not acceptable.

I think that it's a mind control, reprogramming attempt.

You didn't see anything.

You didn't see anything.

You didn't see anything.

You like your boss.

You didn't see anything.

Oh, hang on. Is this the same indoor farm as in this thread?

The problem be that whoever specified/bought the UPS did not account for the type of load it was going to serve. Depending upon their design, age, price, etc., discharge fixtures can have very poor power factor and/or very high harmonic content, either/both of which can be very hard for a UPS, not designed for such duty, to handle.

Has the Load Changed???

If the UPS is working properly, it is probable that a device attached to the UPS load side is either Faulty or your load has grown and is now approaching the UPSs capacity.

If the UPS is approaching capacity, a large enough device will cause a voltage drop at the output or in some cases cycle between UPS and Bypass.

Based on the information provided I would be looking for new or extended circuits on the UPS output first.

Regards,
Sapper

How fast is the flickering -- near 30 or 60 Hz?

Does the flickering problem exist only when the UPS is on during longer power failures or after a short "upset"? If the problem happens only during long failures, then I would see if you have a capacity problem (either bad batteries or higher than configured loads for whatever reason). Try this: leave only some of the lights turned on on the UPS supported circuit and now artificially turn off outside power, do you have the same symptom? If yes, then my guess is either a UPS switching or UPS waveform problem. If no AND you haven't overloaded the UPS (due to the startup issue mentioned above), then have the batteries checked. If the batteries are OK, then you might have a faulty load in your circuit.

There is a possible alternative explanation to the flickering lights. The batteries in the UPS might have failed (depending on the type of battery used the life of a UPS battery can be as low as 2 years, particularly sealed lead acid batteries). This is possible unless the person who checked the UPS switched off the input power with the load switched on, thus confirming that the UPS can maintain the output with the input power off.

If the batteries have failed then when the input power fluctuates there is no stored energy with which to maintain the output voltage at the desired level.

Thanks you all for your replies.. it learned me out a lot..

Hi, The UPS connected with genset right.. There is posibility the UVR faulty. Its make momentary signal for auto changeover to switch. Then your UPS also do internally switch btween batteries and incoming source. Better get the UVR replace. I have same experience before.

...And of cause, UPS should meet the purpose for not intterrupt the load. But,you may consider to check the battery and get the UPS history log print to find out for any abnormality.

I'm mildly surprised that nobody has mentioned these possibilities.

This might have nothing to do with the UPS. This would be consistent with your UPS service person measuring nothing being wrong at the UPS output. You might have a loose electrical connection some where, a bad wire, a bad circuit breaker, a bad batch of fluorescent light ballasts or tubes. Do all of the UPS lights operating at this facility flicker or just the ones in your office? You might find that some one is playing a joke on you.

"On the other hand" the root of the problem could be your UPS service person. Did you press them why they believe nothing is wrong with your UPS? Did they measure only the output voltage during this switch from mains power to UPS power? Did they measure your lighting current draw and compare that to the UPS rating? Did they measure the drop out time during this transition? Did they measure the electrolyte levels in the batteries? When is the warranty on the batteries due to expire?

In my world, a group of lights flickering slow enough to be noticed by the human eye is always associated with some measurable changes in voltage and current. I cannot attach a single test instrument to your circuit. You need some methodical testing on these circuits to find the real root of this problem.

Probably, there is a poltergeist... ...

as far as i know the UPS-es make a Backup-Battery test when they are turned on

now if and only if your model makes that dummy test in regular during it's operation it likely shows you have serious overload in the grid your lights are or your battery is getting old /!\ in last case it is vital to replace it with one supported by (listed in) the UPS manufacturers documents - i've F-d 1 of my APC units with wrong battery /!\ although the battery maker claimed that their product is suitable for replacement

in first case (consuming side overload) you have to track the problem monitoring the amps travelling at each time of the operation (? there might be a faulty lighting unit - - doesnot start/keep operating -- lowwers the Vtg 4 rest ...?)

The incoming source might be fluctuate for a short time depending on peak hour. It may go up or down. On weekend sometime the incoming voltage may raised a bit due to surrounding premises or in your premises not connected with a large load / load has been switch off. This also can happen during weekdays. During this time, the UVR may sense the voltage as not in usual tolerance that its usually operate. Then due to the UVR internal electronic wcircuit faulty it can cause the NO/NC to momentary open and close. This condition will affected your ups to memontary switch between battery and normal source, and if this happened to often your battery also can flat. Get the print out of history log of ups can help to diagnose the cause. For a system source from stepdown transformer that use auto tap changer, its also can cause the lighting to flickering if the auto tap changer faulty. Our member comments above also can be use as guide to find what is the cause is. Please let us know and share when you found the cause and how you resolve it.

Alright, now this is the post that came close to the issue I am facing now. I have a 1450 VA UPS-Inverter from one of the reputed brands in India with two batteries to power up my entire house. I discovered in the event of a power failure when the UPS goes into battery backup mode, all my tube lights (flueroscent ones) as well as CFLs start to flicker really bad. No impact on the LED lights around house.

The issue was bugging me so much, I deicided to take multiple readings of voltage/current/duty cycle and tried to isolate the issue. The voltage drop is generally from 230/240 V to 220/219 V. Duty cycle drop is from 49.95 to 49.85 or so. The UPS manages to keep those levels consistent.

In the process, I started taking out equipments out of the circuitary to isolate the problem. To my surprise when I took out my HP laptop charger the flickering immediately stopped. The same happened when I took out my 55 inch Sony TV from the backup. As of now these are the two culprits which cause the lights to flicker. I can live without the HP charger, but not without the TV.

Any suggestion here folks?