[pure-silver] Re: ELC bulbs failing in D2 Dichro Head
- From: "Nicholas O. Lindan" <nolindan@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 16 Jan 2008 11:57:12 -0500
From: "J Stewart" <jrstewart8@xxxxxxxxxxx>
Folks, can anyone help me troubleshoot reasons why my lamps are blowing
out
within a few seconds of turning on my Dichro II color head (on a D2).
The power supply is busted. Most likely the triac regulator. I am
guessing how the supply works by extrapolation from other vendor's
supplies, so take this with a grain of salt as it may be quite wrong.
ELCs are 250W 24V bulbs, running at about 10A. The voltage is
converted to 24V by a transformer in the power supply.
If the power supply is regulated then odds are it uses a triac (a
sort of transistor-like thingy) to do the regulation with the transformer
producing 28 volts or so. The system is sort of an inside-out lamp dimmer:
it keeps the lamp from dimming by always keeping it slightly dim. It
adjusts itself if the AC power fluctuates so the dimness/light output
stays the same and the lamp always sees the 24V it wants.
When a lamp fails naturally it produces an arc for a fraction of a second -
the bright flash and pop when a bulb goes. The arc is pretty much a dead
short-circuit and the current spike from the short circuit destroys the
triac, leaving the fuse that is supposed to protect the triac intact.
This is the common failure mode of household lamp dimmers.
Triacs short-out when they fail. For a lamp dimmer this means the lamp
is always at full brightness. For your power supply this means the
lamp is not dimmed and is driven with 28V instead of 24V. The higher
makes the lamp burn brighter for a short period and then fail.
If it is only the triac that has failed then it is fixable and replacement
triacs are generally available - Radio Shack even.
==
Nicholas O. Lindan
Cleveland Engineering Design, LLC
Cleveland, Ohio 44121
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