Capacitor value in Fluoresent fixture?

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Some information here on cap values.

BUT, and here is the biggest BUT.... at least one of those beasts in there is not a choke, but a "primary autotranformer" to make the different voltages required.

As to replacing the fixture/ballast vs. a couple of caps.

Home Depot/Dollar Store/Lowes will sell you a "shop-light" complete with tubes for about $12. You will spend several $$ for the caps, they will need to be AC rated at 200V or better, and you will need either to order them on-line and pay shipping or find an electrical supply- house and pay 'retail'. I betcha that purchasing a new ballast outright (and save the sheet-metal, sockets and lamps) will be your cheapest option,

Capacity does matter.

Be careful. you could be seeing the most expensive savings ever. And if you do decide to repair the unit without proper testing of the choke and transformer, you will wind up still having to replace the fixture at the end, notwithstanding the possibly spectacular method whereby the unit tells you to try something else.

Peter Wieck Wyncote, PA

These are resonant circuits on both sides, and cap value is critical.

As for how to determine the value, either measure a working one, find a similar type of ballast and see what value it uses, or maybe ask at the expert sites such as sci.engr.lighting, or ask folk like Don etc at their expert sites.

Tinkerers usually use salvaged parts that cost nothing.

As for the claim that reliability of old fittings is bad, the opposite is in fact the case, with old fl fittings enjoying greater average life expectancy than new.

What isnt worth salvaging is old halophosphate T12 tubes. Theyre free, but new lower powered T8s will pay their cost back in use plus a bit more.

NT

T8 lamps will require a different ballast... Not a bad idea ultimately if the first-cost for new lamps and ballasts can be carried. Of course, for ~$17, Home Depot will sell you a new 2-tube T8 shop-light, complete. Our local one had a stack of them out front @ $16.99 + tax.

Peter Wieck Wyncote, PA

On Wed, 20 Jun 2007 22:50:51 -0400, Meat Plow put finger to keyboard and composed:

That doesn't look right. For one thing, there doesn't seem to be anything to limit the lamp current.

- Franc Zabkar

One of the "chokes" is an auto-transformer.

Peter Wieck Wyncote, PA

Over here in the UK, T8's and T12's are sold interchangeably as merely "standard" or "slimline" - no different ballast or fitting required. I have many 15 or more year-old fixtures here, that came with T12 tubes originally, that now have T8's in them.

Arfa

Just don't go the other way - and - if you are still using magnetic ballasts, you are not realizing any savings... OK, the difference between a nominal 40W (really about 38), and a nominal 34W (really about 32), with the ballast taking nearly 30W in its own right. vs. less than 10W for the typical electronic ballast and 5W for a high efficiency ballast.

And, if you are running a T8 on a T12 ballast the T8 will run dimmer. But, I would have thought you would be running mostly T5 by now?

Peter Wieck Wyncote, PA

This sort of thing often happens in these discussions. UK and US standards are different, we dont even have the same type of 4' tubes you have.

Here (UK) there are 2 types of 4' tube: T12 40w T8 36w Both are designed to run on the same ballast, IOW the T8s are retrofit tubes rather than requiring a new standard of ballast.

Thus there are 2 ways to save a very little energy:

1. replace T12 with T8
2. Replace mag ballast fitting with electronic.

NT

The UK T8 lamps are different than the US lamps. My friend and I have discussed this quite a bit and came to the conclusion that the true 40W T12 lamps over here in the US are the same as in the UK, though the old standard phosphor types are all limited to 34W now which never happened there because the lower lamp voltage when used with a choke just increases the current to compensate and no power is saved.

US T8 lamps are 32W for the 4' size. The ballasts they use are all high frequency electronic, if you put one in a standard rapid start T12 fixture they will light up, but not very bright and lamp life will be decreased.

The savings you can get with an electronic ballast are significantly less than what we see when replacing an autotransformer ballast. A standard 4' twin tube rapid start ballast burns up something like 18W just in the ballast itself. A choke ballast for 240V mains and the same tubes burns half that or less.