LED bulb flicker...

Redford · January 2010

I have a Cooper brand track light in my home that uses 3x 50w MR-16 Halogen bulbs. I purchased it with the intentions of getting new power LED mr-16's that only use a few watts of power. So I bought the bulbs and installed them, only to find that they flickered on and off, enough to really be a problem. I figured they were defective and I contacted the company, the next day they sent me 3 new bulbs and re-installed them with the same problem.

I figured it was the heat inside the metal housing....LED's don't like heat so I kind of attributed it to that. So, I took the fixture down and installed it outside on my porch were it was only Ten degrees (F). Same problem....

I called up a guy from Cooper lighting and (even though it took about 4 people to figure it out) we discovered that the electric transformer, housed inside the track light, would not run bulbs with a wattage of 5 watts. In order for the electronic transformers to operate properly, the output must be loaded to a minimum of 50% of the rated wattage of the transformer. Any output load below 50% may result in lamps flickering and premature burn out.

So I ended up taking out the transformer and re-wiring the lights to straight 12v
I ran a new dedicated 12v line to the 12v breaker box and they work like a charm and use only 15w DC as compared with 150w. With good light quality...almost as bright as the 50w halogen bulbs. The problem is, now the switch wire is 12g Romex, and the supply line is 10g stranded....that probably won't pass for code and could be a hazard, also considering there is a junction box in the ceiling where the old 120v supply line is spliced together...which would need an access panel if I were to leave it like that.

Anyhow, I was wondering if there were any other ways I could have fixed this problem? I was toying around with a magnetic transformer on the incoming line...but they are costly and there would still be losses in the transformer. The electrician also told me that magnetic transformers need to be run at 80% of their maximum output wattage....so they would need to be sized appropriately.

I tend to over-complicate things sometimes, and often overlook the simplest solution!

peterako · January 2010

Re: LED bulb flicker...

Hi Redford,

I am also using LED lights 12V and 230V (europe)
All the 12 V lights are running from elec. transformers whitout a problem. It is even so that after switching of the light stays on for 2-3 seconds.
I am using 2 and 3 Watt led bulbs.
You can also use the same transformer and installing more led lights on a different location:D.

Greetings from Greece8)

mike95490 · January 2010

Re: LED bulb flicker...

leave an old bulb in to keep the electronic transformer happy.

Also, it's BS about a magnetic transformer needs to be 80% loaded. What does your doorbell transformer do when it's not being rung? If anything, you don't want to load past 80%. And don't use one from radio shack, they run really hot, and then get hotter.

Redford · January 2010

Re: LED bulb flicker...

The guy told me that the 50% and 80% has to do with the output voltage of the transformer.

At a draw of 15 watts the transformer (intended for 100 to 200 watts) probably wasn't outputting a high enough voltage to operate the bulbs in their intended manner and they flickered....Of course that is theory! The doorbell example seems probable, except that the doorbell gets power from a momentary switch, but the LED lights are turned on for extended amounts of time.

But I ruled that it was the transformer because when I removed it from the equation the bulbs worked fine.

Adding more bulbs or leaving in a halogen bulb would detract from the wattage savings the led's offer. I may have to accommodate the NEC code somehow and leave it as it is.

westbranch · January 2010

Re: LED bulb flicker...

you could switch to GU 10 s as they are 110 v, have to change the receptacle in the light housing.

Eric

niel · January 2010

Re: LED bulb flicker...

now i'm not sure if i'm reading all of this rightly and i'm no lighting expert, but my comments in bold may hold merit.

Redford wrote: »

The guy told me that the 50% and 80% has to do with the output voltage of the transformer.

At a draw of 15 watts the transformer (intended for 100 to 200 watts) probably wasn't outputting a high enough voltage to operate the bulbs in their intended manner and they flickered....Of course that is theory! The doorbell example seems probable, except that the doorbell gets power from a momentary switch, but the LED lights are turned on for extended amounts of time.

in the simplest of power supplies there is a transformer and rectifier and most often a capacitor to smooth out ac ripple. when the load is less the voltage may appear higher rather than lower. voltages that are too high can cause troubles for leds and shorten their lifespan. too low just may not cause it to light, but i don't believe the voltage is low in your case. a regulated 12v output would allow proper operation.

But I ruled that it was the transformer because when I removed it from the equation the bulbs worked fine.

this does confuse me as i thought we were talking of bulbs and leds that all need a 12vdc source. did you replace the transformer with something or are the leds made to operate from 120vac?

Adding more bulbs or leaving in a halogen bulb would detract from the wattage savings the led's offer. I may have to accommodate the NEC code somehow and leave it as it is.

westbranch · January 2010

Re: LED bulb flicker...

reading the fine print on most good LED retailers sites, there is usually a statement regarding the need for an LED DRIVER as most transformers do not work well especially the small ones in track lighting units...

HTH
Eric

BB. · January 2010

Re: LED bulb flicker...

LED's are real nasty with respect to transformers. High peak current near sine wave peaks -- can cause heating in the transformers -- Basically very poor power factors (transformers running LED's probably need to be 2-4x larger to handle the current spikes).

Another suggestion would be to check electrical connections. We have some cheap1-2 watt LED reading lights and they tend to be real sensitive to bad electrical connections--check wiring connections and even for a bad switch (if in the DC side of the circuit). LED's are non-linear devices and any little change in voltage at the LED (poor electrical connections) can make for large changes in light output.

-Bill

n3qik · January 2010

Re: LED bulb flicker...

Redford wrote: »

The problem is, now the switch wire is 12g Romex, and the supply line is 10g stranded....that probably won't pass for code and could be a hazard, also considering there is a junction box in the ceiling where the old 120v supply line is spliced together...which would need an access panel if I were to leave it like that.

Wire- If it is UL listed and has an outer jacket. Then this will meet code.

Junction box- Just put a nice looking cover and move on.

Redford · January 2010

Re: LED bulb flicker...

niel wrote: »

this does confuse me as i thought we were talking of bulbs and leds that all need a 12vdc source. did you replace the transformer with something or are the leds made to operate from 120vac?

The fixture is wired to 120v then uses a transformer in each individual swivel type track mount.

I had three other track-lights that were the same kind (cooper) and removed the transformer from the housing, replaced it with two 10g wires and used a 3A inline fuse in each light on the negative lead.

I ran a new 10g stranded wire to the fixture from the 12v breaker box, making the fixture 12v.

The bulbs are 12v bulbs.

LED bulb flicker...

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