Author Topic: Is the filament of SBMV lamps is single coiled?  (Read 2515 times)
dor123
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Is the filament of SBMV lamps is single coiled? « on: November 21, 2010, 07:52:25 AM » Author: dor123
The shape of the filament of SBMV lamps is similar to incandescent lamps that have a coiled filament (See a shape of a coiled filament here http://www.lamptech.co.uk/Documents/IN%20Coiling.htm).
Is SBMV lamps have also coiled filaments? Or they have the regular Coiled-coil filament?
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Re: Is the filament of SBMV lamps is single coiled? « Reply #1 on: November 22, 2010, 12:58:09 AM » Author: Medved
I would guess CC, mainly as it lead to thicker, so stronger wire for the same wattage...
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Re: Is the filament of SBMV lamps is single coiled? « Reply #2 on: November 29, 2010, 03:24:49 PM » Author: James
It is standard practice to use a single coil filament as the ballast.  The main reason for this is that SC filaments are better from the point of view of vibration resistance.  A CC filament in streetlighting service with wind vibrations would not be expected to last very long.

Also since only about 1/3 of the light of a mercury blended lamp is made by the filament, the relative advantage of using a CC filament is small.

The third reason is because of arcing.  The filament in a typical 230V 160W SBMV lamp is rated about 160 Volts, but immediately after switch-on when the arc tube voltage is low, about 210V is applied across the filament, severely over-loading it.  Due to the shorter length of a CC filament and the higher voltage gradient, when they are over-run to this extent, arcing can occurr, which would destroy the filament.  SC filaments are somewhat longer and are less prone to failure by arcing.

As a consequence of these factors, I am not aware of any lampmakers (except some Chinese) who are using CC filaments in mercury blended lamps.
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