Capacitor to remove AC distortion in dimmer

Thread Starter

Willen

Joined Nov 13, 2015
328
Hi,
I just heared, when we use powerful dimmer (Maybe PWM) like in mega structures to control light intensity etc, it causes distortion in AC and distortions can produce unexpected heat in cables and sometime fires. I saw a video and found that to remove the distortion, they used a bigger capacitor like 6 inch in diameter. Where they use the capacitor? I searched some equivalent circuit but found nothing exactly.
 

tcmtech

Joined Nov 4, 2013
2,867
More than likely it was a common, but large, power factor correction capacitor connected across the main power lines.

Besides adjusting the power factor up those types of capacitors typically have very low ESR ratings which make them very effective as harmonics traps and HF snubber devices too.

I use several smaller ones, ~ 2 uF 600 VAC ,around my home and shop electrical system just for that purpose of knocking out HF noise on the AC line sides which in some of the things I experiment with probably gets pretty wild. :D
 

Thread Starter

Willen

Joined Nov 13, 2015
328
Just curious, can you link in the video?
Hi
I cannot see videos in the internet. I saw a engineering program in National Geography channel where they were describing many basic engineering techniques behind a Burj Al Arab, mega structures. And they were talking about light dimmer technology and a big capacitor. I have posted a YouTube link thinking that I found that video by guessing just from its thumbnail picture.
 
Last edited:

Thread Starter

Willen

Joined Nov 13, 2015
328
More than likely it was a common, but large, power factor correction capacitor connected across the main power lines.

Besides adjusting the power factor up those types of capacitors typically have very low ESR ratings which make them very effective as harmonics traps and HF snubber devices too.

I use several smaller ones, ~ 2 uF 600 VAC ,around my home and shop electrical system just for that purpose of knocking out HF noise on the AC line sides which in some of the things I experiment with probably gets pretty wild. :D
Hi,
Small 2uF 600V capacitors like used in single phase AC motors? How you connect them in mains, any circuitry?
 

#12

Joined Nov 30, 2010
18,223
I think connecting a capacitor to 220V 50Hz cause short circuit, instead of any improvements.
I think you have a lot to learn. I have posted several times that the best test of an oil filled run capacitor is to connect it directly to 240 VAC and measure the current.

Look at the power poles as you go by and see the capacitors up there.
They do power factor correction.
 

Thread Starter

Willen

Joined Nov 13, 2015
328
I think you have a lot to learn.
Yes. I am engaged in totally different profession from electronics but I am a kind of addicted to electronics.
I have posted several times that the best test of an oil filled run capacitor is to connect it directly to 240 VAC and measure the current.

Look at the power poles as you go by and see the capacitors up there.
They do power factor correction.
I just heard and seen the oil filled capacitor. I guess electrolytic capacitor are poor choice and oil filled big capacitors are good choice for the purpose.

Can I say 2uF in 50Hz have almost 1.5k capacitive reactance. So it will consume 0.14A when connected directly to 220V mains?
 

#12

Joined Nov 30, 2010
18,223
You did the math right but capacitors do not consume current. They allow current.
If they consumed current, they would get hot. They do not get hot.
 

bertus

Joined Apr 5, 2008
22,093
Hello,

Most noise from a triac circuit will come from the fast switching flange of the triac.
The switching flange can be influenced by an snubbing circuit.
The attached PDF will tell you more about this.

Bertus
 

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ian field

Joined Oct 27, 2012
6,536
Hi,
I just heared, when we use powerful dimmer (Maybe PWM) like in mega structures to control light intensity etc, it causes distortion in AC and distortions can produce unexpected heat in cables and sometime fires. I saw a video and found that to remove the distortion, they used a bigger capacitor like 6 inch in diameter. Where they use the capacitor? I searched some equivalent circuit but found nothing exactly.
You'll need to find out whether its PWM, or something else.

PWM usually implies the standard rectifier/reservoir like in a typical SMPSU. The most common PFC front end is a flyback boost converter interposed between the rectifier and reservoir. It works at a much higher frequency than mains and takes pulses of current from the rough DC waveform that are proportional to its amplitude. On some ATX PSUs they just stick a dirty great iron-cored choke in series with the mains input.

On a triac dimmer - a PFC capacitor will do little more than take the edges off the switched current waveform.
 
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