I bought a GE GELT60A12012LW (or one very similar to this). It is putting out a very odd waveform that may make it difficult to use in my application. I am wondering if this is normal or if I have a bad one.

The waveform is sort of a chopped sine wave which is only there for half of the 60 Hz, ac cycle. I apologize that I don't have the exact model number or a picture of the waveform -- I'm not in the lab right now.

Has anyone used one of these?

 

For the model number you give, there is a minimum load of 2.5W. When you were looking at the waveform did you have at least this load connected?

 

Thanks for your interest. I am adding more information...

I bought it at Home Depot. Their exact model number is GELT60A12012DIY. On the unit itself, it says "LET 60W" and "Series AGSLAT. 11.7V 5.0A" (Google thinks I have a typo and it should be AGSALT). Note that there are a bewildering number of GE products that are similar to this part number.

Yes, I had a 12 volt, 4 watt LED module connected. The waveform did not seem to be caused by a too-small load. But, what do I know? That is why I am asking.

Drat. I forgot to get a picture of the waveform. Unfortunately, it is too complex to describe in words. Let's just say it is a much more complex waveform than I expected. In fact it it has pulses that I think would create EMI.

 

I don't think this is a transformer like what you are imagining. This looks to me like a Solid State device. In fact, HD states it is an "electronic" transformer which means this unit takes the AC, rectifies and then synthesizes the output (most likely by using a small microcontroller with some power FETs).

This is why the output looks all weird. It is basically changing the waveform to supply an AC voltage of a given magnitude and as much current as required by the load. It wouldn't surprise me if it has some sort of PFC (Power Factor Correction) embedded into it, although I don't think you would need PFC for LED's???

I imagine they must have taken EMI under consideration. Although I don't think UL deals with this. It would need to pass FCC or CE for us to know for a fact that EMI is not an issue at all. However, I find it hard to believe a product you buy at Home Depot is not passing FCC or CE.

 

I don't think this is a transformer like what you are imagining.

Yes, I have seen these referred to as both solid state and "electronic" transformers.

This is why the output looks all weird. It is basically changing the waveform to supply an AC voltage of a given magnitude and as much current as required by the load. It wouldn't surprise me if it has some sort of PFC (Power Factor Correction) embedded into it, although I don't think you would need PFC for LED's???

This unit is mainly intended for halogen use so it is harder to say what may be inside.

I imagine they must have taken EMI under consideration. Although I don't think UL deals with this. It would need to pass FCC or CE for us to know for a fact that EMI is not an issue at all. However, I find it hard to believe a product you buy at Home Depot is not passing FCC or CE.

I agree but the waveform is real knarly.

I will be adding picture to this thread shortly...

 

For the model number you give, there is a minimum load of 2.5W. When you were looking at the waveform did you have at least this load connected?

Okay. Here are the promised pictures.



Some details about the pictures:
All were taken at a vertical setting of 5 volts/division.
The first picture is the output voltage with a 4 watt LED connected to the unit. It was taken at 1 ms/division.
The second picture is a detail of the output with a 14 ohm resistor connected to the unit. It was taken at 20 us/division.
The last picture is with the 14 ohm load and was taken at 2 ms/division.

Some conclusions:
The "round" waveforms are at power line frequency.

The unit seems to be reducing the power output for the low LED load by both cutting out one half of the "rounded" waveform and reducing the on-time of the remaining "rounded" part of the waveform.

The power is switched on and off at a 50 KHz rate.

The 50 KHz seems to have pretty fast transitions which might radiate from wiring.

These waveforms make it difficult to make quick voltage and current measurements.