I rigged up a basic flouro system at home, and something is wrong.
I have 2 x 8W fluoro tubes and 2 x 13W fluoro, with the correct ballasts. The 8W light work fine, but the 13W lights try to start, but fail. I put the 8W tubes into the 13W set up and they work fine, so I know my wiring configuration is fine.
Is there something wrong with the 13W ballast? Or can I safely run 8W tubes with a 13W ballast which is the path of least hassle?
Do not try to run 8 watt lamps with a 13 watt ballast. If the striking voltages and burning voltages are equal, the 13 watt ballast will allow to much current to flow and the 8 what bulbs will have a bright, glorious life, but a short one.
Poster didn't give control gear type or supply voltage, which is rather important for answering the question.
However, the current consumption of 4/6/8/13W T5 lamps are all similar, and since the control gear is mainly concerned with current limiting, they are often all run from the same control gear. Actually, the 13W lamp was designed to run from exactly the same switch-start series ballast inductance as the others on a 240V supply. This might not work as well on 120V supplies or other types of control gear.
If the voltages are the same, how can the current be the same. As you say the ballast limits current (and provides a positive resistance to the source) The current for each lamp would be different.
By the way I have designed a few ballasts and hold a patent on a dimmable ballast.
Why do you think the voltages are the same? The voltage, as with the power, is roughly proportional to the tube length of these old T5 lamps, and the currents are all roughly the same.
Then I would have expected you to know this already.
Because he said they were the same. I have worked with lamps with many different currents. Thank you but I do not remember the voltages and currents for all the lamps.
It has been a while, but I believe that while the striking voltages may be different, most of the lamp voltages were the same, at least on the lamps I worked on for the most part.
Current depended on many things. I was able to make some lamps light with as little as 10 microamp flowing in them with my ballast and that was with out styrating. I could bring them on with 10 or less microamps and bring them up to full current or drop them down from full current to less than 10 microamps.
I saw some capacitive ballasts in the market. Is it better? I think it can start much faster.
Does capacitive ballast work well in fluorescent lamp? It will start the lamp much faster than magnetic inductive ballast. Why don't few people use it in the market?
There are some problems with capacitive ballast which make them difficult to use with dimmable lights. At least with my design. There are other designs that vary the frequency to dim the light. They can probly be used there. But the operation frequency has to be sort of high for those types of ballast and they give off a tremendous amount of RFI which my design doesn't
The cap is to big for 60 cycles and they make a lot of noise. You have to use a converter to get the frequency to the lamp to about 4000 hertz min. to be really practical.
| There are some problems with capacitive ballast which make them difficult to | use with dimmable lights. | At least with my design. | There are other designs that vary the frequency to dim the light. | They can probly be used there. | But the operation frequency has to be sort of high for those types of | ballast and they give off a tremendous amount of RFI which my design doesn't
Can you give a patent number?
Any chance your design could work with direct DC?
The voltage must be stepped up from 110 to light the lamps. The unit lights two lamps in series.
DC is not good to put on florescent bulbs, it considerable reduces the life.
But if you came in with the proper dc voltages it would work, the whole control circuit works on dc. I effectively uses an infinite inductor.
They work fine for high frequency operation, but they are a disaster for low frequency (50~60Hz). As the voltage waveform rises from zero V each half cycle, when it reaches the voltage necessary to start conduction in the arc tube, you get a sharp inrush current to change the charge in the capacitor, limited only by the supply impedance and the arc tube. This quickly wears out the lamp. You can get ballasts which are mainly capacitive but contain something to limit this per-halfcyle inrush current -- typically an inductor but significantly smaller than the inductor which would have been required by itself without the capacitor.
Thorn Lighting in the UK had a patent many years ago for using fluorescent lamps in mixed leading/lagging power factor. IIRC, twin lamp fittings were supplied with one conventional lagging ballast for one lamp and a leading mainly capacitive ballast for the other lamp, resulting in a near unity power factor for the fitting. I think single lamp fittings were also available boxed with a 50% mixture of leading and lagging power factor ballasts.
On 2 Jun 2004 08:02:31 GMT Andrew Gabriel wrote: | In article , | "Gong" writes: |> I saw some capacitive ballasts in the market. Is it better? I think it can |> start much faster. | | They work fine for high frequency operation, but they are a | disaster for low frequency (50~60Hz). As the voltage waveform | rises from zero V each half cycle, when it reaches the voltage | necessary to start conduction in the arc tube, you get a sharp | inrush current to change the charge in the capacitor, limited | only by the supply impedance and the arc tube. This quickly | wears out the lamp. You can get ballasts which are mainly | capacitive but contain something to limit this per-halfcyle | inrush current -- typically an inductor but significantly | smaller than the inductor which would have been required by | itself without the capacitor. | | Thorn Lighting in the UK had a patent many years ago for | using fluorescent lamps in mixed leading/lagging power factor. | IIRC, twin lamp fittings were supplied with one conventional | lagging ballast for one lamp and a leading mainly capacitive | ballast for the other lamp, resulting in a near unity power | factor for the fitting. I think single lamp fittings were also | available boxed with a 50% mixture of leading and lagging power | factor ballasts.
What about an inductive ballast on one end and a capacitive ballast on the other end?
Interesting The Ballast I designed can be set for a leading or laging power factor by the gap in the transformer.
I use a capacitive ballast in my design. This is followed by a fet which is normally in saturation but comes out of saturation to limit the current. The current through the lamp can be set any wheres from a few microamps (Or zero current) to full on. The current is determined by a pot that the flight stewardess sets to determine the lamp level. At full on or full off there is no dissipation. At half brightness, the least efficient point, the dissipation is about 25% or the power rating of the two lamps put together
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