friend in my bedroom there is a CFL bulb which shows a typical behaviour as below
daily evening i switch it on, and as normal routine it remains on for 2-3hours and then i switch it off but after switching it off, about 3-4 minutes latter the cfl bulb again glow by itself without any source . this glow remains hardly for 2sec and then it goes off and then again blink after certain interval and this keeps repeating for many hours now what is causing this?
There appears to be a leakage in your switch. Thus, even though the switch is "off", there is a very small current flowing through it, which charges up the filter capacitor after the input rectifier of the CFL ballast electronic circuit. There is a diac trigger circuit to ignite the lamp after the capacitor voltage reaches a certain voltage. That is why you see an attempt to ignite the lamp after the long charging interval (due to low leakage current). The capacitor discharges quickly as there is no steady input voltage supply. Again after some time, the cycle repeats due to the leakage current.
Try replacing the switch.
Dear Shaikh, yes it will. This is a feature often discussed around the thermal radiation after power down, see for example
http://physics.stackexchange.com/questions/999/why-do-lightbulbs-continue-to-glow-after-the-light-is-turned-off
Regards, Gerro
sir thanx for answer but my problem is this
that my bulb is getting off properly but then after 3min it blinks again for couple of sec again it go off and again blinks after couple of min and this keeps repeating
sir is it due to electronic blast system in my cfl bulb might be some issue there
There appears to be a leakage in your switch. Thus, even though the switch is "off", there is a very small current flowing through it, which charges up the filter capacitor after the input rectifier of the CFL ballast electronic circuit. There is a diac trigger circuit to ignite the lamp after the capacitor voltage reaches a certain voltage. That is why you see an attempt to ignite the lamp after the long charging interval (due to low leakage current). The capacitor discharges quickly as there is no steady input voltage supply. Again after some time, the cycle repeats due to the leakage current.
Try replacing the switch.
sir i partially agrees with you since i myself is of same conclusion but it is not happening with other cfl at same source
Hi Mr. Shaikh,
But the other CFL is not powered through the same switch, is it?
If the sequence and periods of what you described are constant i. e. systematic.. the reason is most probably what Dr. Sujit said. Check the switch and try change it. Also chech whether the line is going through the switch as the proper wiring should be, or is the line directly going to the lamp.
salah sir other cfl is also being powered by the same switch. and rest thing which you have asked me to check i will surely check it
OK Mr. Shaikh.. Change the bulbs. I mean replace them each other .. If the one which was doing what you have described is still doing so, then the problem is in the lamp it self (internal problem) ..
Tell us what has happened as well, Best regards.
Shaikh, assuming that all the CFL's are in parallel, please clarify if they are of the same make and same power rating. This will help diagonise the problem better, even though it is sure that leakage current is the cause of momentary glow after turn off. What I am speculating is that amongst paralleled CFL's, the CFL with the inherent earliest trigger characteristic only will blink first. Salah's suggestion of interchanging CFL's will be useful in finding the answer.
Salah also has a point in that the leakage current may not be through the switch but through the direct live supply (wrong wiring) with a leakage return through earth (via wall) even when the switch is off.
sir not a parallel connection but a single holder i replaced the said cfl with another cfl of less power rating and of another maker and that blink issue is not visible in the replaced cfl
The 1-phase power supply system comes with a live line and another (neutral line) which is at earth (or ground) potential. When we connect a lamp between these two lines, the current flows through the live and neutral lines. A lamp can also be connected between the live and the earth in our house and the lamp will glow, with the current now flowing through the live line and earth back to the point of connection of the neutral with earth (the distribution transformer), without flowing through the neutral line. Now in case the live line has reached the lamp directly (the switch being wrongly connected to the neutral) and the neutral line coming from the lamp to switch has a leakage to earth because or poor insulation at some point with respect to the earth (causing a relatively moderate impedance conducting path), the lamp can carry a leakage current from the live through the earth as above even if the switch is off.
In your case, there is definitely some leakage path. However, the loading on the ballast DC capacitor is somehow more on the other CFL, therefore their capacitor voltages dont rise up much, compared to the specific sample that glows. Maybe the others have self-discharging high resistances (bleeders) across the capacitors and your specific sample does not have one.
thanx every one for contributing in helping me understand few concepts better than before..special thanx to sujit sir....
Another possibility regarding the source of the leakage: are you using a switch that has a neon (orange) light inside which glows when the switch is OFF? In this type of switch, there is a neon bulb in series with a resistor across the switch contacts. When the switch is ON the bulb and resistor are "shorted" and the neon bulb does not glow. When the switch is OFF the neon bulb and resistor are still in-circuit across the (open) switch contacts. The bulb and resistor can provide a path for leakage current.
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