Ballast for drafting lamp.

[SteveSmit]

Very interesting board, I've spent a happy while browsing this place. Having found this particular thread, I wanted to see if someone could answer a query I have.

I've just acquired an old (I'm guessing around 1960s) fluorescent drafting lamp, it takes two 15W T8 tubes. I've just rewired it, because it was previously in a machine shop, and the wiring had become rather worn and dirty. In one place it had worn through the outer sheath and you could see the live and neutral wires, although fortunately, the sheath on those was still okay. Anyway, as I say I rewired it, bought a pair of new tubes and starters for it. The only part I'm a little unsure about is the ballast.

Now in the brief time I've been looking around the internet for it, I've not seen mentions of more than one tube being driven by a ballast. Usually the arrangement I see is either a ballast designed for two tubes (having two outputs), or two discrete ballasts.

Only this thing isn't arranged like that.

It has a single magnetic type ballast with a single live and neutral pair going in one end, and a single live and neutral pair coming out the other, going up to the starters and tubes.

My query (finally) is this: Would that ballast be rated at 30W (seeing as it's running two 15W tubes) or 15W? Just in case I ever needed to replace it.

I gather the basic purpose of the ballast is to limit the current through the tube, and also to provide an inductive kick to strike the tubes up, I just want to make sure I'm working things out right, and I've got the theory right in my head.

Thanks ever so much in advance if anyone can help me on this.

Steve.

Ah forgive me, one piece of information I probably should've added is the length. Each tube is 450mm

[Mr Moose]

Hello,

I presume the tubes are wired in series as in Fig 3 here http://www.metronomis.philips.com/in...allasts_tl.pdf which specifies a 30W ballast for two 15W tubes.

I think that you have to use different starters for series connected tubes, the ones I have seen used two 120v ones.

Yours Richard

[Lucien Nunes]

Yes, I expect the correct starters would be type FS2 for two 15W tubes in series, rather than an FSU that would be suitable for a single 30W tube.

Lucien

[SteveSmit]

Thanks very much for the replies Yeah, I came across the issue with the starters already. I just went to B&Q bought a pair of starters thinking they were all about the same, and nope, absolutely nothing when I switched on, totally dead.

By good fortune I have a chippy style bug-zapper in the kitchen that runs two UV tubes, and I had some spare starters that came with that sat on top. They were different, so I tried them, and it worked a treat.

Sure enough now I check, yeah, they're 110v Single, 230v Series rated.

I've ordered a 30W ballast. It's a square magnetic one, but if it doesn't fit, I'll just mount it in an enclosure on the mains lead somewhere, I'll just bridge the connections in the old ballast box.

Thanks for all your help.

Just for interest, I've attached an image of it to this post.

Thanks again.
Steve.

[BGmidsUK]

Series circuits are far more common than you might think, most shop/office lights which use four 18W or 20W 2ft tubes are configured as a pair of series circuits using one 40W choke per pair.

You are correct in that your lamp will use a 30W ballast (2 x 18" 15W tubes) and that FS2 (4-22W) starters are required (standard starters will take ages to strike if they work at all).

I have a lamp similar to this I rescued from a nearby student house several years ago but I haven't tested it yet!


You can also get electronic "pulsestarters" designed for series circuits.


P.S. I didn't compose this until after you had already replied ..


Brian

[Zelandeth]

People are right about the use of the series starters.

The one question which springs to mind though is why you're wanting to replace the ballast? Old magnetic ballasts will generally go on for just about forever, though they can get very noisy. Shorted turns aren't unknown, but generally they're quite reliable in my experience.

Series setups like this often have the lamps orientated so that they're arranged so that the lamps are the "opposite" way around so as to minimise the visual impact of mains frequency flicker from the ends of the tubes.

EDIT: Okay...now see that you were just asking *in case* you ever needed to replace the ballast. My bad...I need to read things more carefully!

[SteveSmit]

Oh yes, I don't plan on taking out the old one unless I have to, I just figured I might as well get myself a full complement of spares. Certainly when 30 watt magnetic ballasts are available on the net for around a fiver delivered anyway!

I'm all for rescuing old bits and bobs. When I heard that this thing was being binned at work, I couldn't resist. That and I needed a solid well built desk lamp. Modern stuff unfortunately doesn't often live up to these simple expectations.

Steve

[robin0577]

Just a general note to those of you working on old fluorescent lighting.

It may well be time to start hoarding magnetic ballasts and traditional switch starters, as the ever increasing demands of the EU efficiency regulations are staring to see the disappearance of mag. ballasts in favour of high frequency switch mode electronic tube drivers.

[julie_m]

Wirewound ballasts aren't necessarily any more wasteful than switched-mode ones, as long as they are made with decent gauge wire, so as to minimise resistive losses. And they can be kept below the losses of a badly-made switcher.

[ppppenguin]

I can happily live without the flickery start and flickery run of a magnetic ballast. Conventional fluorescents can be quite annoying when you see them flckering out of the corner of your eye. If you are using them to illuminate rotating machinery then the flicker is potentially dangerous too. In the past I have used dual tube lead-lag fittings to reduce this effect. In commercial installations using 3 phase on closely spaced groups of tubes is even better. HF ballasting completely solves the problem.

The first time I saw HF ballasted fluoros was back in 1986. It was a revelation, the first time I had ever found their light really pleasant. Mind you, it helped that I was also using D6500 tubes but modern triphosphor tubes would be fine too and a lot warmer colour than D6500.

[russell_w_b]

Originally Posted by ppppenguin

The first time I saw HF ballasted fluoros was back in 1986. It was a revelation, the first time I had ever found their light really pleasant.

Out of interest, I've just repaired a couple of Thorn electronic SMPSU ballasts (rectified mains smoothing cap failure, two-out-of-four 1N4007 mains rectifier diodes and the on-board PCB mounted fuse: two units identical fault, so spares ordered accordingly), and they run at about 43kHz.

[SteveSmit]

That's always an option, switching it to an electronic HF ballast when the time comes, but to be honest, I'm one of the fortunate types who doesn't notice the flickering like some do. I've got it powered up right by me here and honestly, I don't notice any flicker, or at least not enough to be an irritant.

[russell_w_b]

Don't know offhand whether tube life is extended or diminished with HF ballasts, but maybe worth finding out - especially if obtaining a replacement tube becomes a problem.

I forgot to mention that the ballasts I repaired had been in service and switched on for 99% of eight years: not bad! Perhaps this is better for the components than on-off-on-off-on-off, though...

[Brian R Pateman]

Originally Posted by russell_w_b

I forgot to mention that the ballasts I repaired had been in service and switched on for 99% of eight years: not bad! Perhaps this is better for the components than on-off-on-off-on-off, though...

In general, yes. Equipment left running tends to work quite happily. The problem is when spare units are bought and put into store for several years. People seem surprised when the 10 year old PSU they've just drawn from stores goes bang when they install it.

That's why critical systems (if they are well designed) use hot standby units.

[russell_w_b]

Originally Posted by Brian R Pateman

It's certainly my experience with SMPSUs: 'pop!' following a mains outage...

I had a bit look at the ripple ratings for the main C in this instance, and they were pretty damn close to the actual current drawn. I feel that, in the OPs case, tube availability is most important, and that the type of ballast that would prolong tube life is of most use here.

[matthewhouse]

For the most part, with a wound ballast the tube will last ages. A lot of newer 'energy saving' fittings which use PIRs to switch off the light or to dim the tube to save energy when no one is about, wreck the tubes at an astounding rate. You end up wasting money on tubes and damaging the environment by manufacturing new, and disposing of the old ones! Isn't it great to be living in 2011.

Most sensible manufacturers state that if PIRs are used with their fittings, the time should be set to maximum to reduce the amount of Ons and Offs - to ensure longer tube life. Repeated switching seems to be the main cause of short tube life, and could be more important than whether the ballast is wound or electronic. Stick with what you have got, put a pair of spare tubes and starters in the cupboard, and you will be set for years.