Capacitor in Florescent Lamp

Discussion in 'General Electronics Chat' started by SEGAR, Jul 25, 2011.

  1. SEGAR

    SEGAR

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    What is the purpose of the capacitor in the florescent lamp. Do this capacitor is functioning as the power factor correlation. Could anybody help me on this.
    SEGAR, Jul 25, 2011
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  2. SEGAR

    shrtrnd VIP Member

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    I don't know your actual circuit configuration, if the cap is part of some control board or what.
    The purpose of capacitors in general, is to smooth out the ripple in an AC circuit, to
    help smooth-out the effective voltage supplied to the load during the negative cycle
    of an AC waveform.
    shrtrnd, Jul 25, 2011
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  3. SEGAR

    Resqueline Moderator

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    Capacitors (across the mains) in old fluorescent lamp fittings are for power factor correction. For 20W, 230V 50Hz for example it may be 4uF, correcting 290mA.

    shrtrnd; I think I see what you're trying to say in the last sentence but it's confusing and can be misunderstood.
    Resqueline, Jul 25, 2011
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  4. SEGAR

    duke37 VIP Member

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    The capacitors in fluorescent light are as Resqueline says primarily to correct the power factor. These are connected across the supply. They also help on switch off, reducing the arc in the switch due to the inductance.
    I had a fluorescent fitting which had the capacitor in series with the inductor and tube. The reactance of the capacitor was higher than that of the inductor so it controlled the current. This ate tubes at an enormous rate.
    duke37, Jul 25, 2011
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  5. SEGAR

    shrtrnd VIP Member

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    Not surprised Resqueline. All my ex-wives misunderstood me too.
    Glad you and duke37 were able to help SEGAR out.
    shrtrnd, Jul 25, 2011
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  6. SEGAR

    SEGAR

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    Thanks for the reply.
    SEGAR, Jul 26, 2011
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  7. SEGAR

    SEGAR

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    Power factor

    I have a situation, i need to correct power factor in T5 lighting circuit. My current circuit gives around 0.791 pf. Once i connected the capacitor (4uf) parallel with the AC and the power factor over compensated to 0.356. Could anyone can help me on this.

    1. What is the purpose of the power factor.
    2. With maintaining the capacitor of 4uf connected parallel with the AC as per can see in standard lighting circuit, how to reduce the power factor to 0.791 pf. If need any other additional info, i can provide. Please guide me on this.

    Thanks in advance.
    SEGAR
    SEGAR, Jul 27, 2011
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  8. SEGAR

    Resqueline Moderator

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    A bad power factor means that there is an inductive (lagging) or capacitive (leading) current flow that does no work but still loads the wiring.
    A big fluorescent light installation may for example draw 15A without correction but maybe only 9A with correction.

    If you got a worse power factor with a capacitor installed then the question is what kind of ballast do you have in that T5 lamp, iron-cored inductor or electronic?
    You probably have an electronic ballast, which is inherently capacitive already. The solution is then not to add more capacitance, but maybe/ rather an inductor.

    Oh, and don't use pf behind the number, it may be (mis)interpreted as pF (pico Farads). The power factor number is actually unit-less.
    Resqueline, Jul 27, 2011
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  9. SEGAR

    duke37 VIP Member

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    There is no purpose in the power factor. it just is. What is the purpose of the resistance of a wire?

    Why do you wish to reduce the power factor to 0.791? The ideal power factor is 1,

    By using different (smaller) capacitors, you should be able to plot power factor against capacitance to estimate the size of the best capacitor (if any).

    0.8 power factor does not seem to be too bad for a small load, do you have a very fussy supply?
    duke37, Jul 27, 2011
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