4000 Watt short arc searchlight project

WDR

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Hello all, this will be my first post on here, although I've spent a bit of time reading around on multiple occasions(warning, long. Anyway, I'll get to the project(was completed, now inoperable, will explain).

I've wanted to build a searchlight for awhile and after coming across a new surplus 4200watt xenon short Arc lamp I decided to go for it. I bought the lamp and also ordered an Edmund optics 24" reflector, and worked to fit them into a large metal can from a parking meter lot light. I used the fan from a old dehumidifier for cooling and my welder as the power supply.

One thing I have noticed is there doesn't seem to be a lot of info on the high voltage igniter. I was able to find only a couple YouTube videos on how to make one but I am happy to say I did so sucessfully and would encourage those on here to do so as well to be able to operate short arc lamps. The circuit is very simple, and doesn't require many components. Basically I used two ignition coils connected with capacitors and a dimmer to 120v as the high voltage source, and then imposed that onto the high current source(a welder) with high voltage capacitors made from wine bottles and a spark gap to transformer wound on the ferrite core from a old tube tv. This circuit worked very well and would ignite the bulb quite reliably and almost instantly once I insulated the cables going to the bulb more carefully.

I tested the light a few times before destroying the bulb with reversed polarity. Which brings me to some questions. I just found another surplus bulb and was planning to replace the one I damaged, however it is not the same size. So I plan to use this as an opportunity to improve. 1) The Edmund reflector was obviously inferior and I would like to find something better. I would not hesitate to spend $200 or so, not sure if that is a reasonable price range. 2)Aditionally is 24" a reasonable size for a 4000w lamp? 3) I expect mainly to have the light pointed horizontal or above, previously I mounted the lamp coaxialy with the mirror, the larger electrode furthest from it, is this still probably the best orientation?

I would be interested in any input and gladly answer any questions or provide more details requested, thanks.
 

BVH

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I had a couple of 20" or 24" (can't remember now) electroformed reflectors made for a couple old ORC Gunfire Simulator SA lights by an advertiser here on CPF - Phoenix Electroformed. They used the tooling from a stock reflector which matched what I already had so I think I paid about $250 to $300 each for them shipped. Phoenixelectroforms.com
 
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WDR

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Thanks, I'll look into that. One thing is I'm not really sure how to specify the details to order the reflector. I'm not even entirely sure what I need. I kinda just threw the whole thing together and it actually worked pretty well so now I want to do it right.
 

BVH

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I didn't save my email exchanges with the guy at Phoenix. He's very technical with reflectors and as such, you can tell him what you have and what you're after and he should be able to steer you towards the right product.
 

WDR

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I was looking on their site and one of their stock reflectors is a 20", that seems like it may work, but I'll contact them regardless.
 

PolarLi

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24" would be fantastic, bigger the better! On the other hand, there is nothing wrong using a smaller one. You just end up with less throw:mecry:
Most commerical searchlight and skybeams seems to use reflectors from 12-16 inch for 2-7 kw xenon lamps.

A good pick from Phoenix would be 2.35" focal length, 14, 16, 18 or 20"
Vertex hole size, as small as possible, but big enough for clearance around the lamp base so you don't risk an arc over, plus for air flow. 2.5-3" should be good.

Anode (big electrode) forward is the common setup in most reflectors. If you download this document, and look at the illustration on page 13 You will see that the anode create a bigger "shadow" than the cathode, so the light emits in around 40 degree angle over the anode, and around 20 degree over the cathode. You want the most light to hit the reflector, and when the lamp is in the focal point, you will easily see what's the best for your reflector.
 
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BVH

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I find that in all the military and aviation SA lights that I have, the Anode is towards the back of the light. The Spectrolab SX-16 NightSun, the SX-5 Starburst, The VSS-3a tank light, the Marconi radar Systems 1000 Watt light, The Locator, The M134 Minigun light, The ACR-RCL Marine lights, Megaray, 150 Watt Bourns Communicator and my ORC 500 Watt Gunfire Simulators. The VSS-1 had its lamp oriented vertically so it's not comparable. The only exception is the 60" carbon Arc which had the Anode forward. All the arc intensity profile drawings that I have seen show the most intense point of light in the arc itself is sitting right next to the tip of the Cathode. The way I see it, if you have the Cathode at the rear of the reflector, then a large portion of the circumference of that most intense point is blocked from a good portion of the rearward portion of the reflector and a large portion of the circumference of that most intense point is facing the front of the light where none of it is projecting towards the reflector. If the Cathode is in the front, the vast majority of the light from most of the circumference of the intense portion of the arc hits all of the reflector save a tiny portion blocked by the Anode. And most of that area of the reflector is the hole.

On the other hand, all the aviation SA lights and the marine light I have are made to point down when in use so having the Anode at the rear - or on-top so to speak when in-use makes sense since the flame/heat travel direction would be in the upward direction against the larger Anode which is designed to take it. The VSS-3, Megaray and Carbon Arc lights are horizontal use lights so I can't explain that one.

EDIT: Removed Maxabeam from list of lights.

I believe the 20", 2.35FL model is what's used in the VSS-3a. It projects a 1 degree beam or a bit less.
 
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WDR

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Thanks for the input. I just got an email back from Phoenix, they suggested possibly the 18", preferably the 20" with a 3.5" hole as being the best and probably only suitable reflector from their product line, cost is $580 with the rhodium coating. I wasn't looking to spend that much but may anyway for better performance. My thoughts on the first build were that as you confirmed the brightest portion of the arc would be the cathode tip. My thinking was with the cathode in front(furthest from the reflector) a big portion of the light would project forward and not be columated by the reflector and would spill out at an ange, where as with the anode in from that light would be primarily directed rearward and collected by the mirror. I may be invision the properties of the light emission in correctly though.

and PolarLi, thank you for pointing me to that document. It answered almost all the other questions I had about this project mainly pertaining to lamp cooling.
 
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PolarLi

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I find that in all the military and aviation SA lights that I have, the Anode is towards the back of the light.

That's really interesting! Because all the commercial light's I've seen had the anode forward (medium to long focal length) Except the one you mention. For a moment I thought I had been completely at sleep here, so I just spent 30 minutes googling user manuals for skytrackers and marine searchlights, and all I found documentation for, had the anode forward. Francis, Tranberg, Glamox, Griven, Strong, plus various chinese ones. Also found lamp change videos on youtube for Xenon Cinema projectors, Barco, Christie, Nec they also had anode forward (Although, the projectors use a slightly different reflector setup) So I would love some more input on the subject.
 

WDR

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I am imagining the positioning may be somewhat dependent on the expected trajectory of the light. I'm thinking the military lights are expected to be aimed primarily below horizontal so the anode would most often be the higher side, where as commercial lights are expected be aimed above horizontal thus having the anode in front to again have it on the higher side. That's all just a thought, could be wrong.
 

BVH

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I think there's something to this as I tried to say above. I was told that if you point a running SA lamp up and its Cathode is on the top side, the flame/heat will initially be directed down towards the Anode but instead, will roll back up on the smaller Cathode electrode (heat rises) which is not usually "built" to withstand it. I suppose you could build a lamp to withstand it. I'd guess there are more factors that go into the orientation of the lamp than just the flame/heat issue.

It makes perfect sense that the commercial lights would be Anode-up as their use is usually at least 45 degrees up if not more.

I am imagining the positioning may be somewhat dependent on the expected trajectory of the light. I'm thinking the military lights are expected to be aimed primarily below horizontal so the anode would most often be the higher side, where as commercial lights are expected be aimed above horizontal thus having the anode in front to again have it on the higher side. That's all just a thought, could be wrong.
 

WDR

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I am thinking I'll go with anode up. I will mainly be pointing the light up, and only briefly horizontally if ever.
 

BVH

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I wish I had kept my info on the Phoenix reflectors. I'm thinking now that I paid $600 each, not $600 for both. Not only did I have them Rhodium coated, they had to remove the mounting hubs from the old reflectors and re-install them on the new ones.

EDIT: Nope, it was $680 for both.
 
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WDR

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Hmm, I went ahead and ordered it at 580, curious price difference.
 

PolarLi

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I am imagining the positioning may be somewhat dependent on the expected trajectory of the light. I'm thinking the military lights are expected to be aimed primarily below horizontal so the anode would most often be the higher side, where as commercial lights are expected be aimed above horizontal thus having the anode in front to again have it on the higher side. That's all just a thought, could be wrong.

For the skybeams, that make sense. They 'always' point up, and aviation lights 'always' point down. But marine searchlights are horizontal or just slightly up and down (more down than up) Same goes for military/weapon lights, horizontal or slightly up or down. Xenon lamps made for horizontal use, usually have a 10-20 degree window up and down anyway, so the lamp can handle it regardless of anode in or out, yet, the military lights have anode in, but not the marine lights :thinking:

Hmm, I went ahead and ordered it at 580, curious price difference.

Congrats! That will be a killer light :twothumbs as for the price difference, was the reflector in stock, ready coated, or did he have to make it first? Either way, you will get a better deal if you order two or more.
 

WDR

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I'm not sure if it is made or not, it is one of their stock sizes. I did figure pricing would be better in quantity. I am looking forward to the finished result.
 

WDR

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So I have been looking into glass for the front lense of the light. I found this supplier of borofloat glass and was thinking the 1/4" thickness.

http://www.sandysindustrialglass.com/product/14-borosilicate-plate-glass-45-x-33-sheet-copy/

it looks as as though at their standard pricing would be around $120 for a 21" circle if they will cut that, haven't spoke to them yet. That seems like a reasonable price though.

I am wondering though, I would like to make the light operable in rain just in case, will the Borofloat glass crack of the light is hot an it gets rained on? I don't imagine it would get that hot with the cooling air for the bulb though. Would it be good to have two layers of glass, with air flow between so that rain water could not hit the hotter inner glass?
 

BVH

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The front window on the NightSun is only 1/8" Boro glass. It flies at up to 120-130 MPH on helicopters. Don't know on the cracking question.
 

WDR

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Hmm, that light is much smaller though. Mine will have a much larger surface area but then I don't expect to ever go flying with it either.
 

NoNotAgain

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Hmm, that light is much smaller though. Mine will have a much larger surface area but then I don't expect to ever go flying with it either.


Have a read here. http://abrisatechnologies.com/docs/Guide to Glass Final April 2011.pdf

I'm not recommending these guys as I've only spoken with them on the phone, but they appeared responsive.

No one said building a high powered search light was going to be cheap. I figure for my project, I'll be $2k into it just to "show off" a bit.
 
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