anyone know how to diagnose a faulty Choke / Ballast in fluorescent light circuit

[nick]

Hi all

I'm hoping somebody knows more about this than I do.

We have a standard fluorescent light that has stopped working. I have replaced the tube and starter with known working ones and still light doesnt work.

With the light switch on, I measured 240 volts going into the Choke, but zero volts coming out of the choke.

From this I assumed the Choke was faulty (is this a correct assumption) Also I took out the Choke and no current passes through it using an Ohmmeter/ Multimeter connected across the 2 terminals. Again I figured the Choke must be faulty / open circuit from this (is this correct?)

I then replaced the 40W Choke with a similar thing from an old fitting called a Ballast hoping this would fix the light. It didnt - although for some unknown reason the light did come on for about 5 minutes then died after putting the outer light casing back on for the night???? Now when I switch on, there is a very dim light just at both ends of the tube.

By the way the ballast I put in is 65W (is this important when the old unit was a 40W choke. The light tubes are 40W.)

I am still left wondering if the Choke is faulty, and if it is then why isnt the replacement ballast not working. (Yes I did connect it up the same way)

Thanks for any help and advice (Im surprised this isnt more of a common problem - I couldnt find anyone experiencing this same problem)

Regards Nick

[Frisket]

Very likely.

Same thing, different name

I think the old choke has probably bitten the dust. Someone else is doubtless an expert on these things but I always try to replace like for like when swapping components - 65w is considerably more than 40w - maybe the 1st firing killed your starter.

[BigWallop]

Stop there. If you've replaced both the tube and starter lamp and it still ain't working, then the fitting itself is at fault and needs replaced. You don't have to go any further with more tests and the like. You need a new fitting.

[impvan]

Yes, the choke's knackered.

You haven't come across anyone else with the problem as chokes don't often fail like this. They normally develop shorted turns and melt, then go bang.

[Chris Oates]

and stink like hell

[Terry]

Not sure if this would apply to your 230 volt versions but I have usually found that a faulty "ballast/transformer" (as we call our

115 volt and various other voltage versions) will have an open primary/mains input winding. However ours, unless they are very old like 40 to 50 years, do not use 'starters'. ballasts for the last 40 or so years have incorporated a thermal cut out in case the ballasts overheats and AFIK it does not reset thus protecting against shorts and potential fires. And yes, some of them do ooze black 'goo'. Which these days is said to be not of the 'cancer causing' variety. i.e. PCBs! Some appliances do use just a series choke in a very simple inductive circuit to fire the fluorescent tube/s. Idea anyway.

[Chris Oates]

series choke here, no thermal protection not suitable as raceway even though they are used that way.

[BigWallop]

You better believe it.

[The Natural Philosopher]

No, it doesn't. We have enough strike voltage without needing a step-up transformer.

but I have

[Dave Plowman]

Hmm. It might be one of several, and or no longer available. What's wrong with fixing it?

I've put electronic ballasts in old fittings before now to retain the appearance.

[nick]

Thanks for the advice

Seems that it is the choke then (still not sure why the replacement 65W ballast didnt work though - unless thats busted aswell)

I will find out how much a replacement choke costs before probably buying a complete new fitting.

Much Obliged Nick

[Dave Plowman]

A 40w choke costs 3.85 + vat from TLC.

[Dave Plowman]

Not really. A ballast refers to an 'all in one' control unit. A choke is simply an inductor.

[N. Thornton]

Why not turn the fitting into a 65w arc light? :)

Regards, NT

[Andrew]

Sounds from discussion that it's a simple non-electronic fitting in which case the wiring is sooo simple.

To fault find try wiring an ordinary light switch across the starter connections (remove the starter) - but only if you can do it safely. Ensure the temporary switch is open, switch on the main light switch, close the temporary switch for a couple of seconds and open it again. If the tube doesn't strike (light) after a few attempts then there's another fault beside the starter.

Andrew