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8 ft. Switch start fluorescent batten fitting.

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I came across one of these yesterday. It has failed. I suspected the series capacitor had gone open circuit. The choke winding was continuous and the tube looked o.k. The fitting was removed and a new one fitted.

So, having forgotten the theory, how does the circuit work with an 8 ft. tube and a choke and series capacitor? What is the principle of operation?

 

Z.

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    You can put the cap direct across the mains and measure the current that flows.

    If the current is 230*2*pi*F C all is well

    (so if mains is 50Hz that is  about 3200 j.ohms per microfarad) 

    1uF, 75mA

    2uF about 150mA,

    4uF about 300mA etc

    If the fuse in the test plug blows, the cap was short circuit, and you should have checked for that first ! Yes, we have all been there…

    If the current is a lot less than this figure, the cap is either totally or partly disconnected inside.

    If the tube filaments measure a few ohms each between the pins, and the tube ends are not black then the chances are the tube is a goer.

    The starter can be removed and the brief application of a short circuit should glow the filaments at the end, and a sharp removal of the short should strike the tube. (the nervous could be with gloved hands and expect a bit of flash and pop as the circuit is opened…)

    It is fair to say that the 8 foot tube is a historical curiosity, and is probably better on the way out.

    Mike.

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  • 0

    You can put the cap direct across the mains and measure the current that flows.

    If the current is 230*2*pi*F C all is well

    (so if mains is 50Hz that is  about 3200 j.ohms per microfarad) 

    1uF, 75mA

    2uF about 150mA,

    4uF about 300mA etc

    If the fuse in the test plug blows, the cap was short circuit, and you should have checked for that first ! Yes, we have all been there…

    If the current is a lot less than this figure, the cap is either totally or partly disconnected inside.

    If the tube filaments measure a few ohms each between the pins, and the tube ends are not black then the chances are the tube is a goer.

    The starter can be removed and the brief application of a short circuit should glow the filaments at the end, and a sharp removal of the short should strike the tube. (the nervous could be with gloved hands and expect a bit of flash and pop as the circuit is opened…)

    It is fair to say that the 8 foot tube is a historical curiosity, and is probably better on the way out.

    Mike.

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