Dimmable ballast failure.

[powerplay]

A client is wondering why their dimmable ballasts for cfls are failing... power quality? ... poor quality ballasts? Originally the installation wasn't done correctly and I found broken bulbs where they made contact with the trim that wasn't secured properly...if the bulbs were touching the metal trim I assume they would arc at the contact point and cause premature wear?

 

[gar]

110903-1555 EDT

What is a "dimmable ballast for a CFL" ?

Are you referring to the ballast inside a dimmable CFL or something else?

Any dimmable CFLs with which I have played do not dim very much (obviously using phase shift dimming), not at all comparable with an incandescent or LED, but are very good at producing a more nearly constant light output from a sine wave input from 100 V to 130 V. They quit at about 100 V with sine wave excitation. But this means they minimize flicker when air conditioners turn on.

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[RCinFL]

I have tried several manf. dimmable CFL without much luck. They don't last. Most get 6-18 months life. Dimming flourescent bulbs requires tight control on bulb current. Just dropping the voltage in front of the ballast does not keep good control on current as bulb ages.

 

[gar]

110906-1144 EDT

RCinFL:

Dimmable CFLs sense phase angle of the phase shifted start point from a phase shift dimmer. The internal electronics of the bulb adjusts the bulb current based on the phase angle where conduction starts in a cycle. A phase shift dimmer, one that uses a Triac or similar device, controls the point in the cycle where conduction starts by the when the Triac is triggered. This adjusts the average voltage or current to a resistive load by varying the on time in the cycle.

If instead of adjusting average voltage by the conduction angle within a cycle you use a Variac to adjust the magnitude of a sine wave, then the electronics in the dimmable CFL simply works as an approximate constant current source to the bulb.

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[steve66]

110903-1555 EDT

What is a "dimmable ballast for a CFL" ?

Are you referring to the ballast inside a dimmable CFL or something else?

Any dimmable CFLs with which I have played do not dim very much (obviously using phase shift dimming), not at all comparable with an incandescent or LED, but are very good at producing a more nearly constant light output from a sine wave input from 100 V to 130 V. They quit at about 100 V with sine wave excitation. But this means they minimize flicker when air conditioners turn on.

.

I assume we are talking about a lamp similar to these:

http://www.blocklighting.com/c-506-triple-twin-tube-4-pin.aspx

They do make dimming ballasts for these types of lamps. For example, I think the Advance Mark X works on CF lamps.