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Old 08-01-2008, 04:03 PM   #1
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Fluorescent lamp flickering


I have a PL lamp like this one



This is a 13 W fluorescent which works on a magnetic choke ballast. They are connected in series to 240 V 50 Hz

Recently one end of the tube started getting black and the entire tube started to flicker very slightly at 50 Hz (it is somewhat similar to the flicker of some computer screens). In short lamp will soon burn out

I changed the lamp and the new lamp has similar flicker too. This never happened before

What can be the reason ?

Such flicker will be if the current is assymetric i.e. in one half cycle there is more current than the other. For this to happen there needs to be some 'semiconductor' in the circuit. But there is only the lamp and the choke (coil of wire). Choke can't do that for sure. Lamp is new and i'd expect it to be ok too

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Old 08-01-2008, 07:24 PM   #2
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Fluorescent lamp flickering


Two 120v lamps in series with 240v? I doubt they share the 240v equally.

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Old 08-01-2008, 07:25 PM   #3
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Fluorescent lamp flickering


Why are you connecting two flourescent bulbs in series on a 240 volt circuit? I assume you must be in the UK (or at least not in the US) since you mention 50hz. Though I thought the UK was all 250 volts 50hz. My first guess would be that those lights are usually intended to be used on a 120 volt 60hz not 50hz. This could be what is causing the issues...
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Old 08-01-2008, 11:12 PM   #4
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Fluorescent lamp flickering


I could be way off here, but I believe that the 'magnetic choke ballast' referred to is a simple 2 wire ballast that used to be popular in the USA many years ago. Usually found in fixtures of 24" (20 watts) or smaller.

These were a series connection, with the ballast, a starter, and both ends of the lamp involved. Realistically, this type of ballast was nothing more than a current limiting reactor. Once the arc was established in the lamp, it became basically a short circuit. The magnetic reactance of the ballast would limit current to a value that the lamp could handle. Alot like the reactance of a transformer with no load on the secondary results in very little primary current.

These ballasts must be matched to the lamps they drive, or undercurrent (flickering) or overcurrent (bright lamp that runs hot) will result.

Is the ballast in question specifically designed to operate the exact lamp it's connected to? A ballast of this type that is designed for a straight tube will not work with a U-shaped tube, or a PL lamp. The impedance of the arc inside the tube is higher in a non-straight tube, and a straight tube ballast will operate at less than optimal current (flickering).

Is the ballast designed to operate at 50HZ? Frequency is critical to a reactive circuit such as this. A 60HZ ballast operated at 50HZ likely won't work very well, but a 50HZ ballast operated on 60HZ might be OK.

Has this system ever worked properly? Occasionally, you get a bad ballast, or a bad lamp, or even a bunch of bad lamps in the same box.

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Old 08-02-2008, 04:10 AM   #5
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Fluorescent lamp flickering


This is a single lamp on 240 V 50 Hz (Israel). The ballast is built for this setup exactly and the watts are correct

The system worked OK since ~ 1995 and showed flickering only when lamps were about to fail (this time and once before in 2001)
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Old 08-02-2008, 10:24 AM   #6
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Fluorescent lamp flickering


Just a suggestion Ash, put your location in your profile, so you get more accurate answers and people can better understand your answers to questions.

PS Always replace both lamps together. Even if only one looks bad.
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Old 08-02-2008, 01:42 PM   #7
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Fluorescent lamp flickering


This is a single lamp
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Old 08-02-2008, 03:38 PM   #8
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Fluorescent lamp flickering


FLOURESCENT TROUBLESHOOTING
-blackening on ends, severe: filaments not heated, low ambient temp, poor contact
-blackening within 1 inch of end: normal mercury deposit, should disappear with use
-blinking, shimmering effect or dense blackening at one or both ends of tube extending 2 or 3 inches from base: normal end of lamp life
-blinking or dim: cold drafts hitting lamp
-dark lengthwise streaks: mercury, turn lamp over
-dim: dirty bulb
-EMI: ungrounded elex ballast for instant start
-ring, brown, at one end or both, 2 inches from base: normal
-short life: high ambient temperature or voltage surge for elex ballast instant start
-slow starting in high humidity: dirty lamps or low supply voltage
-swirling, spiralling, fluttering: cold temps, low input voltage, ballast/lamp compatibility, bad ballast, new lamp.
-short lamp or starter or ballast life, lamp won't start: miswired ballast (for a two lamp fixture, both ends of the same lamp must glow when you short the starter connections).
-blackening at one end, flickering, slimline or instart ballast will eventually fail (because filament is not heated). Electronic slimline ballasts are not affected by lamp failure.
-one lamp bright and the other dark on a two lamp rapid start means a pinched yellow lead.


GROUND THE BALLAST

I got most of these from Advance's website; they make ballasts.
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Old 08-02-2008, 09:34 PM   #9
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Fluorescent lamp flickering


Quote:
Originally Posted by Ash View Post
This is a single lamp
OK, sorry, this threw me off:

"They are connected in series to 240 V 50 Hz"
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Old 08-03-2008, 04:30 PM   #10
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Fluorescent lamp flickering


Checked all connections. No bad contacts found

The ballast is placed on the hot wire and is grounded
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Old 08-03-2008, 07:20 PM   #11
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Fluorescent lamp flickering


This might be reaching a bit but, consider trying another new lamp. I have seen more than one flickering florescent bulbs new out of the box.
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Old 08-03-2008, 07:35 PM   #12
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Quote:
Originally Posted by jrclen View Post
This might be reaching a bit but, consider trying another new lamp. I have seen more than one flickering florescent bulbs new out of the box.
. . .or else you might want to seek a good Exorcist. . .

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