lightinggalleryuser33450
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| What do SBMV lamps do when the incandescent filament fails? is the arc tube connected to mains voltage? does it just not work at all? or something else?
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dor123
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| The lamp simply stop working, as the circuit inside the lamp going open. The ballasting filament acts also as an oxygen fuse, so when its burns out, the arctube being disconnected.
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
I lives in Israel, which is a 220-240V, 50hz country.
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joseph_125
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| Yeah it just stops working as the filament is connected in series with the arctube so if the filament is broken there's no power going to the arctube.
There were some SBMV that used a halogen lamp in series with the arctube, those will still go out if the filament breaks, but the filament in those won't break if the outer is broken like on a standard SBMV though.
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RRK
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| I believe another popular failure mode of SBMV is to go into cycling. Have seen a string of SBMV in cobraheads all go cycling. Can be explained as - 1. Thermal mode of SBMV is more problematic than a regular MV because filament generates additional heat especially when lamp run horizontal. 2. Resistive ballast does not generate voltage spikes at reignition, so discharge reestablishment on AC is trickier and even new lamps run with current pause - see an oscillogram.
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dor123
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@RRK: Cycling isn't a failure mechanism of SBMV lamps. It happens in low wattage SBMV lamps, when they are burning horizontally. Because of this, SBMV lamps shouldn't be burned horizontally but only vertically. There were some SBMV that used a halogen lamp in series with the arctube, those will still go out if the filament breaks, but the filament in those won't break if the outer is broken like on a standard SBMV though.
SBMV lamps with halogen lamps, will also fail when the filament in the halogen lamp break, but not if the outerbulb breaks, as the filament is protected from oxidization by the halogen capsule. |
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« Last Edit: May 07, 2023, 05:56:34 AM by dor123 »
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
I lives in Israel, which is a 220-240V, 50hz country.
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RRK
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| You are right here that you should not run SBMW lamp horizontally. In fact, they are usually specified 'vertical +-30 degrees' to 'vertical +-45 degrees' (for Osram HWL250). In the cobrahead lamp runs probably tilted more than 45 degrees from vertical, so that might be a reason they cycle. That was many years ago, those were neither Philips or Osram, probably early Electrofar Romanian ones. Good luck finding a datasheet for them.
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dor123
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| In the cobraheads, the lamp runs horizontally.
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« Last Edit: May 07, 2023, 09:09:10 AM by dor123 »
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Logged
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
I lives in Israel, which is a 220-240V, 50hz country.
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