- #1
tim9000
- 867
- 17
Hi,
Out of interest, today I was mucking around with a 160W LED, 240V, 50hz, outdoor light.
I looked at the Power Factor (it was 0.96) and the THD was 14.something %.
I then wondered what would happen if I put a capacitor in parallel with the light. It was a three phase 90uF cap, so since they were in Delta configuration I believe the effective capacitance was 135uF (90+45uF), which is something like -j23Ohms (if recollection serves).
Sooo, obviously this corrected the heck out of the PF, so it was almost zero (basically leading). And I think the THD went down to 11.5%.
'Good', I thought.
Not sure what the current did, but I expect it went up, a fair bit.
Then I thought, 'I wonder what would happen if I put an inductor in series with it'.
I think when I put the inductor alone, in addition to the light, it decreased the PF and decreased the THD slightly, possibly, I'll need to re-check.
So I put a 14.25mH in series with the active. Subsequently, the THD went up to 23+%!
I don't remember what the PF did.
'Interesting'; then I thought about it and my working hypothesis is that the LC resonant frequency for this is about 114 Hz. So perhaps 114 Hz is too close to the first and third harmonic?
But in conclusion, I'm not entirely sure why it decreased the performance so much when I had the inductor in series, and the capacitor in parallel, I initially thought it would be like an LC filter, but I have a suspicion that it was resonant on the third harmonic. Even then I'm not sure how that works. Thoughts?
Also, I was wondering, if you're filtering something like semiconductors, can your filter be too big? What would you do if you wanted to almost perfectly filter a non-linear load like an LED?
Thanks
Out of interest, today I was mucking around with a 160W LED, 240V, 50hz, outdoor light.
I looked at the Power Factor (it was 0.96) and the THD was 14.something %.
I then wondered what would happen if I put a capacitor in parallel with the light. It was a three phase 90uF cap, so since they were in Delta configuration I believe the effective capacitance was 135uF (90+45uF), which is something like -j23Ohms (if recollection serves).
Sooo, obviously this corrected the heck out of the PF, so it was almost zero (basically leading). And I think the THD went down to 11.5%.
'Good', I thought.
Not sure what the current did, but I expect it went up, a fair bit.
Then I thought, 'I wonder what would happen if I put an inductor in series with it'.
I think when I put the inductor alone, in addition to the light, it decreased the PF and decreased the THD slightly, possibly, I'll need to re-check.
So I put a 14.25mH in series with the active. Subsequently, the THD went up to 23+%!
I don't remember what the PF did.
'Interesting'; then I thought about it and my working hypothesis is that the LC resonant frequency for this is about 114 Hz. So perhaps 114 Hz is too close to the first and third harmonic?
But in conclusion, I'm not entirely sure why it decreased the performance so much when I had the inductor in series, and the capacitor in parallel, I initially thought it would be like an LC filter, but I have a suspicion that it was resonant on the third harmonic. Even then I'm not sure how that works. Thoughts?
Also, I was wondering, if you're filtering something like semiconductors, can your filter be too big? What would you do if you wanted to almost perfectly filter a non-linear load like an LED?
Thanks
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