Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Problem with CFL tube which is blackening

Status
Not open for further replies.
pranam77

pranam77

Advanced Member level 5
Joined
Apr 22, 2008
Messages
2,777
Helped
553
Reputation
1,104
Reaction score
369
Trophy points
1,363
Location
INDIA
Activity points
16,406
One of my friend gave me an emergency light with 11 watt CFL (AS shown in the photo) which operates with an Push pull inverter circuit powered with 6 volt 10 Ah battery. It has a peculiar problem which he coudnt solve. Initially the tube was blackened, and i replaced it. Within 10 minutes i lost the tube due to blackening at the ends. I tried with new tube of another make but with the same result.
Thus my questions are
1. What factors result in blackening of the Tubes?
2. Can rewinding the Ferrite transformer will help?
3. Should i measure the inductance of all the coils and wind with the same details?
4. Is the choke in series to the Positive supply reponsible for blackening?
5. Is the gaps between the 2 EE cores critical?
6. What factors are determined by the core gaps?
6. How can the distance between the cores determined?

Thanks in Advance
Pranam77
 

cfl emergency schematics

It doesn't make much sense to ask circuit details without providing the schematic and quantitative measurements of the circuit in operation. Generally an overload can be expected. The tube is either operated at an input power considerably above it's rating (11 W in this case) or the filament (if supplied separately in the circuit) is powered permanently. Less likely a current waveform with an unusual high crest (peak/rectified average) factor could be an issue.
 

cfl schematic

pranam77 said:
One of my friend gave me an emergency light with 11 watt CFL (AS shown in the photo) which operates with an Push pull inverter circuit powered with 6 volt 10 Ah battery. It has a peculiar problem which he coudnt solve. Initially the tube was blackened, and i replaced it. Within 10 minutes i lost the tube due to blackening at the ends. I tried with new tube of another make but with the same result.
Thus my questions are
1. What factors result in blackening of the Tubes?
2. Can rewinding the Ferrite transformer will help?
3. Should i measure the inductance of all the coils and wind with the same details?
4. Is the choke in series to the Positive supply reponsible for blackening?
5. Is the gaps between the 2 EE cores critical?
6. What factors are determined by the core gaps?
6. How can the distance between the cores determined?

Thanks in Advance
Pranam77
Click to expand...

most CFL tubes have a thermal starer for working at 50Hz on a copper choke.

It is a practice that those who adopt it to electronic adopter, remove the mechanical(thermal) stater at the plastic housing at the connector, with the R-C combination and re-pack it.
Once this is taken care, the blackening would not be there, as I gather.
Mstly, the issues arised when the tube is replaced, as this mod is not implemented.
 

resistors for 11 watt cfl ballast

Thanks Sarma ji and Frank for the replies.
Sarmaji, this circuit is powered by DC and the starter and capacitors are already removed as it was in the original. But still the tubes blacken. So i asked the list of questions i suspect. Here is the circuit for your reference.
 

cfl tubes in hyderabad

I understand, that the tube is ignited without powering the filaments, as in most inverter operated CFL tubes. Also the series resonant circuit provides a near to sine waveform. In this case, overload must be expected as most likely reason for early tube wear. You have to reduce the inverter output power, by reducing the winding ratio or de-tuning the resonant circuit.

You can monitor the tube current with a shunt resistor for test. You also may want to compare the luminance in operation with an existing ballast supply as simple input power check.

The said bimetal or electronic starter is external to the tube and thus must not be removed, normally.
 

cfl not working

the schematic shows a short across the inner pins of the tube. while we need to have a 100 K or above resistor there.
 

current shunt to measure cfl current

Hai Sarma ji
It looks like a short at the bottom, which is actually the box at tthe bottom which holds the starter and the capacitor in parellel. For this application, both of these components are removed to get a flicker free operation and the 2 wires of the inverter output are connected to only two pins of the tube while other 2 remain un connected inside the same box.
 

ballast resistor cfl

pranam77 said:
Hai Sarma ji
It looks like a short at the bottom, which is actually the box at tthe bottom which holds the starter and the capacitor in parellel. For this application, both of these components are removed to get a flicker free operation and the 2 wires of the inverter output are connected to only two pins of the tube while other 2 remain un connected inside the same box.
Click to expand...

here are my feelings to the 7 Qs Pranam jee

1. I feel, it is due to over crt in filament circuit
2. Unless there is a short in secondary winding(revealed by dimness of tube), there is no point in re winding.
3. once the turns ratio is known, it is sufficient. Ofcourse the secondary inductance can be measured for a working piece and recorded..
4. May not be.
5.Yes. This helps reducing core saturation while adjusting the inductance of secondary.
6.as at5

7.to much gap drastically reduces the inductance. no gap saturates the core (can be observed by increase of the battery current) drawn.


It may be better not to leave them open. like mains operated electronic ballast, you may try a 100K or so resistor for better illumination while the voltage at the secondary should not fall by more than say 10 to 15V.

you may see a sample application note of filament management, 12V application, though......
**broken link removed**
 

    pranam77

    pranam77

    Points: 2
    Helpful Answer Positive Rating
cfl schematic diagram

You can't exactly distinguish an overload of the filament circuit and the CFL as a whole. The lamp current is also heating (and possibly overloading)the filaments without explicitely supplying them. Even with cold filaments, the gas discharge is sputtering filament metal and causing a black coating inside the tube. You possibly know it from glow lamps.
 

cfl flickering overloaded circuit

In this case the filaments are not powered so it is most likely spluttering of the filament metal due to over voltage or under spec-ed tube. Try increasing the 120ohms bias resistor to 1K then decrease it downwards until you get the optimum brightness.
 

cfl blackening

Thanks Bongkk, Fvm and Sarmaji for the support. From all your replies, and one ore intresting thing i came to know from my friend who has given me this light. He has re wound the Transformor without measuring the inductance and too the gaps were set by trial and error. Hope the problem lies in these points. I have to find an original transformor and re wind it with original specs.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top