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Series capacitor on fluorescent 125w T12 light fitting

EvanA

Jan 23, 2018
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Jan 23, 2018
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I need some advice regarding using a series capacitor on some 8 foot T12 fittings I have been given. The ballast is marked 100/125w but there weren't any capacitors in the fitting. I believe there should at least be a 7.2uF power correction capacitor in parallel but I read that these fittings used to use an 8.4uF series capacitor. I have a selection of 100w and 125w tubes but have not tried any yet. Can anyone shed any light on what I should use? Thanks, Evan.
 

Minder

Apr 24, 2015
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Apr 24, 2015
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I don't recall any capacitors on all my T12 fixtures?
M.
 

dave9

Mar 5, 2017
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Mar 5, 2017
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Can you find documentation for the ballast? Or a label on it specifying the requirement?

Are 8' T12 common in the UK still? In the US most people aren't doing new installations with them, instead phasing them out for 4' T8 (tubes easier to install, transport, cheaper) or conversion to LED.

However here in the states you can get a high PF electronic ballast for T12 96" that doesn't need a capacitor for not much money which is the route I'd go before installing an old ballast for a new deployment and still needing to buy capacitors for them.
 
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duke37

Jan 9, 2011
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Most fluorescent lights use a series inductance with a value sufficient to control to the design current. A capacitor across the input may be added to correct for power factor and reduce interference.

My aunt had a light with inductance and capacitance in series with the tube. The current was controlled by the reactance of the capacitor and the inductor was there for high voltage starting. It was a terrible system with poor starting and it gobbled tubes. They blackened at one end and then would not start.

I still use T12 tubes which are replenished from replacements where houses are rewired. I prefer the T12 tubes to the T8 which do not start so well.
 
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