Film-Tech Forum ARCHIVE: Help with lamp starting problems

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Posted by Brad Allen (Member # 470) on 08-18-2003, 02:55 PM:

I have 3 Kniesley Kni-Tron Xenex L2000 lamphouse's w/Rectifier Model M85Rax2x1 Kniesley.
Osram 2000 watt bulbs.
When a show starts 15 minutes or less after the runout of the previous show, the lamp does not want to ignite reliably, sometimes won't ignite at all until it cools down some more. This usually starts occuring more frequently when the lamp gets over 1000 hrs on it. If we always allow 30 minutes for lamp to cool between shows, usually no problem.
First showing of the day. Lamp usually fires right off with no problem.
It seems to me that these lamp house's by design do NOT have nearly the air flow over the bulb that I have seem on other lamphouse's. I had another theater owner suggest cutting a hole in the side of the lamp house and mounting a small squirel cage fan with it's air flow directed at the center of the bulb.
The only fan currently is at the back of the lamphouse with the air flow directed at the telsa coil.
Then someone else said it was a problem with the Kneisley rectifiers not having the proper ignition voltage and I needed to get a boaster kit from Kneisley to cure it.
All 3 lamphouse's are ducted to an external exhaust system.
I used a temp probe to take the temp of the inside of the lamphouse, it was 110F after 20 minutes of running.
What's the thoughts of this group on this?
Thanks!

Posted by Jeff Taylor (Member # 443) on 08-18-2003, 04:16 PM:

First, it is common for xenons to become harder to strike as they age, and you should also be aware that striking takes a disproportionate amount of overall life from a lamp. I've heard estimates ranging from 20 minutes of running time to an hour for each strike, so turning a lamp on and off isn't a good idea. Lots of operators strike the lamp at the beginning of each day and just leave it on--certainly running changeovers you should leave the lamps on for the entire show or if there's only 15 minutes between shows. In terms of things to check, before you get into any kind of booster check to make sure all of your connections are tight on both the high and low voltage sides, and look for discolored or pitted connectors which are a sign of overheating or arcing. Finally, the ventilation idea may be worth looking at, but remember that a xenon doesn't want a blast of air on it--the idea is to cool the anode and cathode ends of the lamp by exhausting air through the lamphouse rather than blowing on the lamp. Good luck.

Posted by Brad Allen (Member # 470) on 08-18-2003, 04:26 PM:

Thanks Jeff,
Reason I thought maybe the air flow was the problem, I had looked at some Christie consoles that have a hefty squirrel fan mounted on a box at the back of the bulb mount. This puts a very high air flow at the back of the bulb, and then the air is forced out the hole in the mirror along and towards the front of the bulb.
Certainly creates much much more air flow around the bulb than the Kneisley setup does.
That was the basis for my thinking maybe it was lack of air flow.

Posted by Richard Fowler (Member # 893) on 08-18-2003, 04:47 PM:

The Kneisley L2000 with the glass dichroic reflector, if the rear blower ( Grainger 4C012 ) is in good shape and the deflector is on to cool the rear bulb seal and ignitor, this meets Osram's specification. The bottom vent grills in the lamphouse should be clean and unobstructed and an exhaust fan of 350 - 500 cfm should be all you need to ventilate the lamp. Look into the spark gap, connections to the tesla coil on the ignitor, condition of the coil, corroded lamp fittings, dryed out or cracked insulator on the front support....or could be one of those tempermental bulbs [Wink]

Posted by Brad Allen (Member # 470) on 08-18-2003, 05:23 PM:

Thanks Richard,
How do I check the spark gap?
I can see the voltage jump across the bulb gap when pressing the manual ignition button.
How does one measure the CFM's being pulled by an exhaust system?
How do I check the condition of the coil?

Posted by Ken McFall (Member # 845) on 08-18-2003, 06:29 PM:

This may not help.... but I have been advised in the past to check and adjust the spark gap itself!

I know that the electronic ignitor used on some cinemecannica lamphouses do respond to adjusting the gap..... depending on the lamp in use. The wider the gap the higher the voltage to jump the gap. If the gap is boarder line then it may help? I admit I don't understand the theory or science behind it

Just a thought, maybe someone else can comment.

Posted by Darryl Spicer (Member # 711) on 08-18-2003, 06:59 PM:

I remember we used to have problems with a hot bulb starting on these years ago at the old theater I used to work at. What they did was replace the existing ignighter with one that if memory serves used to be used in strong lamphouses. Never had a problem again.

Posted by Paul G. Thompson (Member # 655) on 08-18-2003, 10:56 PM:

Ken, I was going to suggest the checking of the spark gap, but you beat me to it. [Smile]

Posted by Richard Fowler (Member # 893) on 08-19-2003, 07:50 AM:

Are you able to strike the bulb with the manual push button switch but the auto strike is unable when the bulb is hot, the spark gap is suspect. This is usually located on the non threading side of the lamphouse, mounted on the ignitor and looks like a plexiglas cylinder with a flat plate ( phenolic or nylon )on each side with some wires coming out of each end. The back of the tesla coil has two small wires that are soldered to the unit; since the tesla sits on a pin which is also the mounting point for the negative lead to the bulb, I have seen those fatigue and not allow for reliable sparking......take care in probing since you are dealing with high voltage if this should become energized while you are probing around. Kneisley parts are very reasonable so maintaining or overhauling this unit should not be a pain.

Posted by Brad Allen (Member # 470) on 08-19-2003, 01:11 PM:

Manual push button is how we always start it. Autostrike doesn't work at all.
Thanks for the info.
Been struggling with this for sometime, can't seem to put anyones finger on it.

Posted by Richard Fowler (Member # 893) on 08-19-2003, 02:00 PM:

The auto strike board ( single phase or three phase model ) and a new spark gap should be less than $100.00 to replace. The auto strike has a replaceable relay and voltage sense / trigger circuit ( for type of rectifier used )mounted on two screws for service. Check the wire harness around the auto-strike board for brittle insulation which may need replacement.

Posted by Ken McFall (Member # 845) on 08-19-2003, 07:23 PM:

Paul,

Nice to get one in before you....

I only siggested the spark gap because I'd been trying to sort out a strike problem in a cinemecannica lamphoue that was very unreliable.... There were four CX2100 lamphouses, three were perfect and struck first time every time with 1.6k lamps... one with 2k lamp was very unreliable. As they were running manual in that screen it had never been a real problem.... they just waited until the lamp struck! The lamp would flash about six times but it was quite feeble. However, when I installed a CA21 Pennywise automation the lamp strike problem played havoc with it!

I replaced the Irem striker, that had been put in to replace the original electronic striker becuase of the problems, can't rememeber the make sorry, with a brand new electronic unit so the lamphouse was back to its original spec. No joy at all. It only dawned on me at that point to try a 1.6k lamp!.... perfect first time every time.

Looking at the two lamps side by side you can clearly see the electrode gap is different...... unfortunatly I never got around to finishing the problem.... I won't go into that again... but here's a [fu]

for my employers at the time.

I was advised that by opening the spark gap it allowed the strike voltage to rise. It's funny that you never get these tips when you first dig.... I make no apologies for not knowing the theory behind all of this. However the problem had been long term and I was the first to at least try and sort it out.

The electronic strikers don't use ac input at all just DC from the rectifier. There was no problem with the open circuit voltage, which was 93+!

Hope my spellings ok on this reply... gibberish being my first language [thumbsup]

Regards....

Posted by Rick Long (Member # 213) on 08-19-2003, 07:47 PM:

Remember too, that enclosing cables in flex, (especially those carrying high-current DC.) diminishes their ability to radiate heat away from the conductor, thus reducing its effective current rating.

Take note also, that some of the Kneisley MI-series rectifiers used to put their ignitors in the rectifier, thus making the DC leads into wonderful radiating antennas for ignition noise.

Use of these, coupled with the extra pre-amplification required by the new red-l.e.d. readers, should result in hours of fun trying to de-sensitize your reader wiring from picking up lots of ignition noise at show start.

B.T.W. some of the Kneisley ignitors had a large potentiometer which allowed you to adjust the voltage at which they triggered. Have you tried adjusting this to cure the "hot bulb" striking problem?

Posted by Brad Allen (Member # 470) on 08-19-2003, 08:25 PM:

I have not noticed an adjustable pot for striking voltage.
I will take a look for that.
Thanks

Posted by Gordon McLeod (Member # 33) on 08-20-2003, 01:00 PM:

Latter autostrikes eliminated the pot
When a lamp is hot it typically requires a higher open circuit voltage to make it strike reliably
If you look through the view port and see the arc flashing through the lamp then the ifnigot is probably okay
Also check for highvoldtage arcing to teh relector fame around the bushing in the back fo the reflector it often is when hot they flash over more frequently

Posted by Darryl Spicer (Member # 711) on 08-20-2003, 08:59 PM:

quote:
Latter autostrikes eliminated the pot
When a lamp is hot it typically requires a higher open circuit voltage to make it strike reliably
If you look through the view port and see the arc flashing through the lamp then the ifnigot is probably okay
Also check for highvoldtage arcing to teh relector fame around the bushing in the back fo the reflector it often is when hot they flash over more frequently

Gordon, It's not cold up there in Canada yet is it? You got gloves on typing that last post? [Big Grin]

I just fed it through the decifer machine and everything was fine [Smile]

Posted by William H. Ward (Member # 1797) on 08-22-2003, 07:45 AM:

Brad... Let me add this also.... Normally Xenon bulbs tend to re-strike much easier when they are hot. As the bulb ages, they become increasingly harder to light. 4000 hours was the max I would allow a bulb to age. Check your PS for THRESHOLD VOLTAGE. This accours after power is applied to PS and simply charges some capacitors. Usually 90v dc or more. I liked 130v. The time to charge was 10 or more seconds after power on, depending on the PS. This allows a high discharge across the arc gap making a good strike more likely when the igniter applies the spark.