Re: HID Lamp dimming
- From: don@xxxxxxxxxxxxxx (Don Klipstein)
- Date: Wed, 22 Mar 2006 01:02:42 +0000 (UTC)
In article <1142955216.266787.147770@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Zink
wrote:
I posed a question a few days ago that I believe is indirectly related
to your problem. Unfortunately, I got no response to my posting.
As far as I know, the current method for dimming or changing lighting
levels for an HID is by switching in/out an auxiliary capacitor. This
does not require a special ballast, but does call for a relay in the
housing to toggle the extra capacitor in or out. Some of the ballasts
and associated capacitor information is included in the current Advance
HID Ballast catalogue. I found it in the
2002-2003_Advance_Atlas_Section_4_High_Intensity_Discharge_Ballasts.pdf
on page 4-48 under the section labeled "Recommended Capacitors for
Bi-level Ballast Operation". They list the capacitance values for
lowering the light output, and the associated drop in wattage consumed
by the ballast.
There are many companies that have systems based on this feature, some
which use programmable addressable relays to control individual
ballasts, or banks of fixtures. One such system I found as an example
is described in: http://www.wide-lite.com/Literature/cntrls.pdf. From
your description, I believe this technique may be what you are looking
for.
What I wonder is what is the effect of slightly increasing, or
decreasing the capacitance in a CWA ballast - a 400w Metal Halide in
particular. I was offered an inexpensive high-bay fixture with a
277v-only ballast that I considered using on a 240v feed. I assume that
if this is a proper way to alter an HID output, then that may be a
method to correct for the lower input voltage (240v) I would have to
use.
I see a possible problem: Capacitors that do what you want on one
ballast may not do exactly the same thing on another of the same basic
type and ratings. What happens could vary with brand, model and
production run of the ballast.
Keep in mind that capacitors have tolerances and temperature
coefficients. Also, the ballast's regulation characteristics (degree of
overpowering/underpowering the lamp due to varying line voltage or lamp
voltage drop) can change with use of a capacitor other than what the
ballast manufacturer intended for that particular ballast.
Keep in mind that if current through any ballast winding is above
intended warmed-up value (as opposed to higher values allowable only
during warmup), the ballast could overheat, and not necessarily quickly.
Also watch voltages across capacitors, especially in early warmup - they
could exceed the ballast open circuit output voltage, and vary with line
voltage and capacitor tolerance and capacitor temperature.
I have even seen in some experiments with HPS lamps and experimental
capacitive-inductive ballasts the lamp having conductivity increase as a
half-cycle of AC voltage progresses, making the lamp have some simulation
of an inductor. This effect could vary from one lamp to another and vary
with the lamp's age and condition.
One thing to be wary of with an experimental or modified ballast with
capacitance in series with the lamp is the lamp being overpowered or
merely being run when the lamp voltage is highly excessive due to age/wear
- while with a proper ballast used as directed the lamp may instead cycle
or refuse to run. I have gotten HPS lamps to even have lamp voltage above
the ballast's open circuit output voltage by using series capacitance in
experimental setups - and the arc tube temperature and internal pressure
in that case I expect to be outside the ranges that the arc tube was
intended to withstand! Such experiments I did in my more reckless younger
days, and I had explode an oil filled capacitor about the size of a beer
can in the process!
If you do anything not specifically recommended by the ballast
manufacturer for your particular ballast, then your system is
experimental. That is somethinmg I would run in my basement, and only
while I am around to use the fire extinguisher if necessary - and keep the
lamp in a suitable enclosure in case the lamp explodes, even if the lamp
is a "protected" type. Or wear safety goggles and be willing to endure
burns from hot lamp fragments, and don't have much of anything burnable
around.
If you are going to use an HID lamp for lighting rather than for some
experiment, you may as well get a proper ballast with a lamp it is rated
for and use them as recommended by their manufacturers. If you burn down
a building doing other than this, you could have extra liability - even if
no voltage, current, or other ratings of anything were exceeded.
If the tooth fairy's evil aunt not liking you is the only reason your
ballast or lamp starts a fire, the fire insurance company will give a lot
less grief if the ballast was being "used as directed".
- Don Klipstein (don@xxxxxxxxx)
.
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- Re: HID Lamp dimming
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