capacitors in light fittings

[One_of_them]

guys,

as i understand it, light fittings with magnetic type ballast (fluro, SON) have capacitors to correct power factor. What I dont fully get is why?? (other than correct power factor LOL) as I have seen fittings without them and they work perfectly fine. I've asked a couple of people and the only decent thing mentioned was it may shorten the life of the ballast without the capacitor.

Is this the case?

 

[Knobhead]

The capacitor is for power factor correction.

 

[nickblake]

some capacators are also used for noise filtering ,stablisation , etc

 

[ian.settle1]

As Tony has said it is for power factor correction.

What is the ballast?

An inductor

 

[youngpadawan]

The light fittings produce an induction ( basically the fun stuff in any transformer) fairy which makes some magic happen, this magical reactive power is lost to the world making the true power output much higher than the power that it uses. The capacitor pixie does the same thing, however it has exactly the opposite effect of an inductor fairy. So even though the capacitor has no actual real use in the light fitting, just by sticking pixies in there helps scare off the nasty fairies, helping bring down the amount of power needed to run the light. Also some boring maths and trigonometry stuff happens, nobody likes that story though

 

[Darkwood]

If you have a poor power factor its wastes energy the nearer to 1 you can achieve the cheaper to run the fitting, clamp the current of the fitting with PF capacitor and then without, the light output the same but current use is different.

 

[Knobhead]

If you have a poor power factor its wastes energy the nearer to 1 you can achieve the cheaper to run the fitting, clamp the current of the fitting with PF capacitor and then without, the light output the same but current use is different.

This only applies if you pay for your power in KVAHr and not domestic KWHr. It can affect the CCC of the cables in use if there are a lot of fittings.

Just as an aside the latest scam to hit the US is power factor correction for domestic supplies. The vendors quote the current reduction, NOT the actual KW. Being Americans there's 50 born every minute :seeya:

 

[Darkwood]

As always you are correct i should have pointed that out but years of industrial and KVA calcs its easy to forget domestic isnt effected by the cost side of the PF difference although inductive loads that are found in domestic wont see massive savings even if you fitted these PF correction assuming you were billed in KVAhr.

 

[ayjay]

i remember back in the 70,s we fitted large capacitors in office block mains rooms