8 ft. Switch start fluorescent batten fitting.

Its a semi-resonant circuit.

The inductance of the choke & capacitance act together to effectively increase the mains voltage when the starter opens. This gives the necessary kick to start the discharge in the tube.

8 foot fluorescent lamps were largely a UK thing, and never popular in most other countries. They are very sensitive to supply voltage and need a full 240 volts to operate reliably. They don't work well on 220 volt circuits and  are marginal on a nominal 240 volt supply if at the bottom end of the permitted range.

The voltage across the lamp is about 160 volts, much higher than other types.

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.

Thanks all.

Z.

It used to confuse some as it could be had in either 100W or 125W versions too.

Every xmas it was not uncommon to purchase fairy lights and wire in series with a flu starter, it gave a happy twinkle xmas effect and just about lasted over xmas. Cheap man`s version. Not that I ever did it of course!!!

We had an 8 foot flu lamp in part of my old works twas my first job. I remember sometimes the tube would be reluctant to strike especially in winter. I also know that we suffered from low mains there we had a transformer as part if the test set up  supposed to give us 500 volts for 240 in sometimes could only manage about 495 ish even on the 220 tap on the primary. Any how one day this light wasn't going to come on it had been about 10 minutes already so I stood under it and said come on tube today would be nice then flash flash it lit my boss laughed his head off after that 5hey called me flu lamp girl Lol

If a lamp fails to strike, you can always get everybody in the room to wave their hands in the air.

If anyone wishes to keep an 8 foot fluorescent light fitting working, then it is worth fitting an electronic starter in lace of the more commonly used glow starter. 

Only a short term measure as AFAIK the lamps are no longer manufactured, and remaining stocks are becoming hugely expensive.

Kelly Marie Angel: 
 

We had an 8 foot flu lamp in part of my old works twas my first job. I remember sometimes the tube would be reluctant to strike especially in winter. I also know that we suffered from low mains there we had a transformer as part if the test set up  supposed to give us 500 volts for 240 in sometimes could only manage about 495 ish even on the 220 tap on the primary. Any how one day this light wasn't going to come on it had been about 10 minutes already so I stood under it and said come on tube today would be nice then flash flash it lit my boss laughed his head off after that 5hey called me flu lamp girl Lol

My recent experience with a faulty 8 ft. flu revealed that the beast had not been earthed at all. Perhaps that affected its performance as well as it being ancient.

Z.

Just for general information really - not necessarily for Zoomup- its mostly for those too young to have ever needed to understand this - 

A basic switch start circuit is the most basic florescent circuit and has a starter, a ballast and a lamp)

The ballast is a wire wound coil. (Modern ballasts are electronic though) It is firstly used to generate a voltage large enough to strike across the tube (and when you consider the distance this spark has to jump it is a significant voltage generated) and then to control the flow of current across what has now become a very very low resistance current flow across the tube. If it was not for the ballast once the electricity strikes across the tube the amperage would go through the roof (The lower the resistance - the higher the current: I=V/R). Hence the name choke as it chokes the flow of current allowed to flow through the circuit.

For those saying it is the starter that causes the strike across the tube this is almost incorrect. The starter is used to stop the flow of current in the circuit - this causing the magnetic field created by the ballasts wound wires to collapse causing a much greater current than the one that created it which is the spark that is big enough to jump across the lamp end to end. Whey! Lenz law I think…………