DIY Doctor

Fluorescent Tube Lamps in Shed won't Switch on?

Postby Nick56789 » Mon Nov 16, 2015 10:48 am

I have a problem with the two fluorescent tube lamps in my shed – they won’t come on. Here are the symptoms and course of events:

Since we bought the house 4 years ago, Lamp A has always just flickered dimly at the ends, presumably due to the starter motor having worn and needing replacing. Until last weekend, Lamp B worked fine, though as of last Sunday it did not light at all – no flickering, just dead. At the same time, Lamp A did continue to be very dimly lit at the ends. I think I left the light switch on overnight – it was dark and so I did not remember to turn the switch off when I left the shed – and by Monday neither lamp showed any signs of life.

I replaced the tubes - old 40w T12 tubes - with 36 w T8 tubes. No light. I replaced the starter motors (I installed 4w-to-65w starter motors, like those that they replaced). No light. This weekend, I also replaced the ballasts/chokes (36w choke). Still no light. I have retained the old parts for comparison.

The consumer unit to which the circuit is attached shows no damage, and the sockets in the shed (which run off a different circuit from the same consumer unit) work without issue. I have eyeballed the wires between the consumer unit and the light fittings and can see no issues.

What could be the problem?
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Postby ericmark » Tue Nov 17, 2015 12:23 am

Can only guess now the fuse has blown. Many lamps have fuses in the fitting. However without some readings it's all guess work.

Original fault likely the tube. As the tube ages it gets harder and harder to strike. In the end the starter is doing so much work that also fails. So I always replace tube and starter together.

I had a problem with a 65W five foot unit, the 65W tubes are no longer made. The 58W tube will fit and it will work. However the ballast does two jobs. One it gives a strike voltage and two it limits the run current so instead of 5 years for a tube the tube only lasted 5 months.

I was left with two options, renew the ballast or use a LED tube. In my case I used an LED tube because the lamp was above a load of rubbish (wife calls it craft supplies) so hard to remove and refit the fitting.

In a shed cold will effect the fluorescent and is less likely to effect the LED tube, but the LED tube is a much smaller output. In my case 5100 lumen down to 2400 lumen don't make the mistake thinking a LED tube is more efficient they are not. They are just lower output devices.

Using a HF ballast the lights will strike faster, give out more light, work better in the cold, and last longer and work better when there is a voltage dip. A HF ballast plus tube is far cheaper than LED.

However the LED tube will work in colder conditions than fluorescent and likely even more of a volt drop to HF ballast. However there is a major safety problem. The starter needs replacing for a fuse and this will blow if a fluorescent tube is ever put back in. To get full value from LED tubes the ballast should be removed or shorted out. Again a problem if ever some one tries to change back.
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Postby Nick56789 » Tue Nov 17, 2015 4:53 pm

Thank you for the advice - I will search for a fuse within the fitting tonight.
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