Why are projector/ spotlight bulbs 82 Volts?
Mark
a spotlight and the bulb was burned out. It took an 82V 326 Watt
bulb. The show must go on so in a pinch we found a 120V bulb that
would fit and the show went on, the spot was dimmer but at least
working.
I was curious about the 82 V bulb sp later I some Googling and found
that these projectors and lights operate with a diode in series off
the 120 V line and that does come out to about 82V RMS. OK so that
explains how it works..
But WHY?
Why design the light with a diode in series and use an 82 V bulb.
My guess.... that allows the use of a thicker heavier filament so it
should be more rugged for a given light output. Is that it? Don?
thanks
Mark
Clifford Heath
> Why design the light with a diode in series and use an 82 V bulb.
Probably because they can easily be controlled by an SCR phase-control circuit,
instead of the slightly more complicated and expensive TRIAC one.
Clifford Heath.
lang...@fonz.dk
guess that could get ugly if you don't balance the number of lamps
going each way
here in 240V land I've seen quiete a few that uses 120V lamps in
series, wonder if it is
because the thicker filament in a 120V lamp is more robust
-Lasse
Phil Allison
"Clifford Heath"
>> Why design the light with a diode in series and use an 82 V bulb.
>
> Probably because they can easily be controlled by an SCR phase-control
> circuit,
> instead of the slightly more complicated and expensive TRIAC one.
** Nonsense.
..... Phil
Phil Allison
"Mark"
>
>I had occasion this weekend to work on the crew on a semi pro show w/
> a spotlight and the bulb was burned out. It took an 82V 326 Watt
> bulb. The show must go on so in a pinch we found a 120V bulb that
> would fit and the show went on, the spot was dimmer but at least
> working.
>
> I was curious about the 82 V bulb sp later I some Googling and found
> that these projectors and lights operate with a diode in series off
> the 120 V line and that does come out to about 82V RMS.
** Where did you see that info ???
All the products I found incorporated a 120 to 82 volt step down transformer
(very likely an auto-transformer) to supply the lamp.
> Why design the light with a diode in series and use an 82 V bulb.
** That is not the intended use and there may be issues with visible flicker
and creating a DC offset on the AC supply.
> My guess.... that allows the use of a thicker heavier filament so it
> should be more rugged for a given light output.
** The lamp is of the QI type and has a rated life of only 75 hours - the
benefit being the colour temp is higher and the light output way higher than
for normal 1000 or 2000 hours lamps.
Pretty common for projector lamps and follow spots that do not get long
hours of continuous use.
..... Phil
Don Klipstein
Mark wrote:
Yes, that is correct. The lower design voltage results in a shorter
thicker filament. For a given life expectancy, a shorter thicker filament
can be operated at a higher temperature - inmcreasing percentage of its
radiation bgeing visible rather than infrared. Along with making the
color of the light slighter whiter, and the filament slightly more rugged
against vibration and mechanical shock.
Add to this - the shorter filament is a more compact light source whose
output is easier to concentrate, direct, etc. with optics than is the
case with a longer filament.
It appears to me that maximizing "overall luminous efficacy" of
incandescent lamps, when design voltage is the variable, favors design
voltages of:
~5-6 volts with vacuum fill when design power is near or under 1 watt
~6 volts with singly coiled filament and gas fill when design power is a
couple to a few watts
~12 volts with singly coiled filament and gas fill when design power is
~10-75 watts
Somewhere between near-28 and 82 volts with coiled-coil filament and gas
fill, some chance closer to 28 volts than to 82, when design power is in
the 100's of watts
Designing for lower voltage increases a heat conduction loss through the
ends of the filament.
-------------------------
--
- Don Klipstein (d...@misty.com)
Don Klipstein
How is the circuit more complicated with a triac than with an SCR?
Meanwhile, it appears to me that due to greater popularity and according
production volumes, triacs in sizes good for line voltage incandescent
lamp dimmers don't cost much more than comparable SCRs do.
Clifford Heath
> In <4d069915$0$8525$afc3...@news.optusnet.com.au>, Clifford Heath wrote:
>> Mark wrote:
>>> Why design the light with a diode in series and use an 82 V bulb.
>> Probably because they can easily be controlled by an SCR phase-control
>> circuit, instead of the slightly more complicated and expensive TRIAC
>> one.
>
> How is the circuit more complicated with a triac than with an SCR?
SCR is easier if you have a remote voltage control instead of a pot.
But as has been pointed out, that's probably not the reason.
Don Klipstein
>
>"Mark"
>>
>>I had occasion this weekend to work on the crew on a semi pro show w/
>> a spotlight and the bulb was burned out. It took an 82V 326 Watt
>> bulb. The show must go on so in a pinch we found a 120V bulb that
>> would fit and the show went on, the spot was dimmer but at least
>> working.
>>
>> I was curious about the 82 V bulb sp later I some Googling and found
>> that these projectors and lights operate with a diode in series off
>> the 120 V line and that does come out to about 82V RMS.
>
>
>** Where did you see that info ???
>
>All the products I found incorporated a 120 to 82 volt step down transformer
>(very likely an auto-transformer) to supply the lamp.
>
>> Why design the light with a diode in series and use an 82 V bulb.
>
>** That is not the intended use and there may be issues with visible flicker
>and creating a DC offset on the AC supply.
I have seen some 120V projectors with 82V-rated lamps, and too compact
and too lightweight to have a 400 or 600 VA transformer, even if such a
transformer is an autotransformer needing about 30% of that changed in
voltage.
Furthermore, the 82V rating is fairly obvious about unfiltered halfwave
rectification of "117"-120 VAC, in 60-Hz land. The lamp filaments
involved tend to be thicker heavier ones designed mostly for 300-plus
watts, often 600-plus watts.
Further improvement appears to me likely available by designing for a
voltage lower than 82 volts, due to considering performance of both 28V
and 82V design voltage lamps with coiled-coil filaments and design power
in the 100-400 watt range.
Accordingly, lack of incandescent lamps designed for voltages higher
than 28V and lower than 82V indicates to me that the 82V lamps were
originally designed with diodes rather than transformers "in mind".
It does appear to me that a diode used to accomodate an 82V lamp to
117-120 VAC is a lot less lossy, less expensive, smaller and lighter in
weight and easier to mount, than any "120-VAC 60-Hz primary" transformer
I ever saw, let alone ~90-100 VA sort of size" needed for a mere "buck
autotransformer" to power a 300 or 300's watt 82V lamp from 120V AC.
AllInTheChi
wrote:
Set your PC's clock correctly, ya dopey ditz.
Clifford Heath
> Set your PC's clock correctly, ya dopey ditz.
Thanks. This box has almost no networking, just NNTP via a proxy. That means no NTP.
Phil Allison
"Don Klipstein"
>
> I have seen some 120V projectors with 82V-rated lamps, and too compact
> and too lightweight to have a 400 or 600 VA transformer, even if such a
> transformer is an autotransformer needing about 30% of that changed in
> voltage.
** The step-down tranny only needs to be rated at no more than 100 VA.
Remember, it is fan cooled and drops 38 volts at 4.4 amps.
ALL the products I found on a search used such a tranny.
> Accordingly, lack of incandescent lamps designed for voltages higher
> than 28V and lower than 82V indicates to me that the 82V lamps were
> originally designed with diodes rather than transformers "in mind".
** A diode fed, 360 watt 120V lamp = an abomination.
> It does appear to me that a diode used to accomodate an 82V lamp to
> 117-120 VAC is a lot less lossy, less expensive, smaller and lighter in
> weight and easier to mount, than any "120-VAC 60-Hz primary" transformer
** Yadda, yadda, yadda.....
Oh how in love with out our opinions we are...
..... Phil
Rich Grise
1965-67), I did a stint in the booth at the 'little theater', and they had
a panel with MONGO rheostats.
Cheers!
Rich
Rich Grise
So, what _is_ the answer? It does no good to simply run everyone down
without providing an alternative.
IOW, If Clifford's answer is wrong, then what _IS_ the right answer, or
do you just get off on sitting spewing "NONSENSE" at everyone?
Thanks,
Rich
Phil Allison
"Rich Grise"
> Phil Allison wrote:
>> "Clifford Heath"
>>
>>>> Why design the light with a diode in series and use an 82 V bulb.
>>>
>>> Probably because they can easily be controlled by an SCR phase-control
>>> circuit,
>>> instead of the slightly more complicated and expensive TRIAC one.
>>
>> ** Nonsense.
>
> So, what _is_ the answer?
** Irrelevant.
One need have no idea at all what the *real answer* is to KNOW beyond any
doubt what is not.
Simple logic.
Way over your fuckwit, pointy head.
.... Phil
Sjouke Burry
> ** Irrelevant.
>
> One need have no idea at all what the *real answer* is to KNOW beyond any
> doubt what is not.
>
> Simple logic.
>
> Way over your fuckwit, pointy head.
>
> .... Phil
That answer sure is a beauty in the troll repertoire.
Thanks for proving you are trolling.
Mark
> In <819d1e66-8d61-4a19-9093-bee7f5d7f...@15g2000vbz.googlegroups.com>,
Don,
ok thanks I will try to determine if this particular follow spot has
a transformer or a diode. I got a glimpse inside the other day but
we were under duress.
I KNOW it has a fan and I suppose it is possible that the fan motor
has extra windings to double as a transformer. The cold turn on surge
current must be huge and that would be an issue for a series diode.
I'll try to get the model number and try to find a manual and will
report back here in a few days.
Mark
Mark
its a Chauvet 400 follow spot
http://www.chauvetlighting.com/products/manuals/TFX-FS360_Rev02b_UG.pdf
82V bulb, no transformer inside...
its does have electronic dimming so my guess is it is a standard triac
dimmer that is limited in the upper range
Mark