# 4000 Watt short arc searchlight project



## WDR (Nov 17, 2015)

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.


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## BVH (Nov 17, 2015)

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 (Nov 17, 2015)

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.


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## BVH (Nov 17, 2015)

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.


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## WDR (Nov 17, 2015)

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.


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## PolarLi (Nov 18, 2015)

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 (Nov 18, 2015)

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 (Nov 18, 2015)

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 (Nov 18, 2015)

BVH said:


> 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.


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## WDR (Nov 18, 2015)

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.


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## BVH (Nov 18, 2015)

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.



WDR said:


> 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.


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## WDR (Nov 18, 2015)

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


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## BVH (Nov 18, 2015)

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 (Nov 18, 2015)

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


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## PolarLi (Nov 18, 2015)

WDR said:


> 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:



WDR said:


> 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.


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## WDR (Nov 18, 2015)

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.


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## WDR (Nov 19, 2015)

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?


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## BVH (Nov 19, 2015)

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.


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## WDR (Nov 20, 2015)

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.


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## NoNotAgain (Nov 20, 2015)

WDR said:


> 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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## PolarLi (Nov 20, 2015)

Two layers seems like overkill to me, and 1/8 - 5/32 is probably thick enough. High power lights like this either use a single layer of borosilicate or regular tempered glass, and none seems to have any issues with rain, or heavy seas. But there is hundred of different types of glass out there with different resistance to thermal shock. To be 100% sure, I would have ordered a small sample piece of the glass. Measure the light glass with a IR gun. Use a piece of heat resistant tape on the glass to take the readings off (normal IR guns have problems with readings on reflective surfaces) Then heat the sample piece up in a oven to the same temp and sprinkle water on. Increase the temp and repeat. To be comfortable, I would like atleast a 25-50 C reserve. You_ really_ don't want the glass to pop in rain. If it does, and water hit the lamp, that goes to, and may take out the reflector... 
Now that _will_ ruin your day 




:candle:


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## WDR (Nov 20, 2015)

I like your idea of ordering a sample, that's probably what I'l do. And yes, that is my exact concern, I already killed one lamp and at $200 or so each that gets expensive fast, and since I'm buying surplus I'd be lucky to be able to find the same lamp twice. Last time I wasn't so worried about reflector damage, it was cheap and foul tape could have repaired any issues, this one I am much more concerned about possible damage.


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## Searchlightexpert (Nov 21, 2015)

You have to chooose what you are going to obtain with your searchlight. That sets all parameters for which equipment, light source etc, to use. If a pencilbeam is what you want, it is only a Rhodium reflector combined with a Xenon lamp which can provide the best result. If it is more power offered to a larger covered area through a "softer beam" you want, then you must choose a aluminium reflector (with center hole) combined with a large double ended HMI lamp. It is only a matter of what result you would like to obtain.

I have tested both glass, Rhodium and aluminium reflectors for 24" size against HMI 2,5/4 kW as well as Xenon 3-6,5 kW lamps. The longest range was measured at apx. 30 km /1 lux from the 6,5kW Xenon lamp combined with the Rhodium 24" reflector while the most "useful beam" for instance for an icebreaker is obtained from the 4kW HMI lamp since it provide a wider beam before the caracteristic "dark hole" in the middle of the beam occours when using wide beam.

I will see if I can find some pictures from our testbed to add.


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## Searchlightexpert (Nov 21, 2015)

Wrong posting


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## Searchlightexpert (Nov 21, 2015)

Pictures:


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## Searchlightexpert (Nov 21, 2015)

There are only a few manufacturers in the world making such large searchlights for marine applications, and normally they are not visible in their "standard program". They are only being delivered on request to special applications like large icebreakers.

A bit off-topic but I add a few pictures of some very large searchlights the Norwegian searchlight manufacturer Norselight fabricated to some large anchor handling vessels in the 80's. These units were fitted with 4kW HMI lamps.











Some similar searchlights was also delivered by Norselight to two russian icebreakers in the 80's but then with 6,5kW Xenon light source. See picture below. Note the big difference in size compared to the two 2kW halogen searchlight on the bridge wings. These searchlights were really "ultra large" marine searchlights. Performance data was apx. 30 km. range (at 1 lux) when adjusted to narrow beam. Motorfocus was of course supplied as standard.


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## FRITZHID (Nov 21, 2015)

Idk about anyone else but picture links are broken for me.


*scratch, links working now*


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## medmike (Nov 21, 2015)

FRITZHID said:


> Idk about anyone else but picture links are broken for me.



I see pics ok....you obviously know Search lights!! Thanks for sharing your knowledge!


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## WDR (Nov 22, 2015)

I see them, another thanks for all the info.


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## Searchlightexpert (Nov 27, 2015)

How is your project proceeding, any progress?


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## WDR (Nov 27, 2015)

Slowly, I'm still considering how I'm mounting the bulb and reflector allowing for focussing.


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## BVH (Nov 29, 2015)

I stand corrected. The Anode of the VSS-3A Tank light lamp is in the Forward position towards the front of the light, not in the rear as posted above.


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## lightlover (Nov 29, 2015)

BVH said:


> I stand corrected. ... not ... as posted above.



Wow! BVH,

Must be a l-o-n-g time since you last posted something like that! 
*
Regards!!*


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## BVH (Nov 29, 2015)

That's what memory, or loss thereof can do. I look at all these threads as containing good documentation and everyone benefits for accurate information.


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## lightlover (Dec 3, 2015)

BVH,

I can confidently say that: *"You've forgotten more than I'll ever know"*

I've embarrassed myself by trying to joke ... 

My memory has failed me a few times - as life goes on. 

YOU - are an expert I admire.


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## FRITZHID (Dec 3, 2015)

BVH is definitely my "go to" short arc guy! Exp is everything.


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## BVH (Dec 3, 2015)

Hey, my head is already too big! Thank you both for the kind words!


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## WDR (Dec 6, 2015)

It's pretty easy to remember things differently then they are, I haven't even been on here very long and I am fully confident in your input BVH.

just want to let you guys know I am currently still progressing on the light. I have redone the ignition system with a noticeable improvement. I am retaining the same ferrite core, but now only using one ignition coil, and have replaced the two bottle capacitors with one small 50kv door knob capacitor. I also rewound the transformer with 9 turns of 2awg XLPE insulated wire and 3 turns of spark plug wire for the primary. This produces a notably brighter and longer spark for ignition. Next I will be working on building the support frame around the reflector. I am pretty close to having all of the mounting plans for the reflector and bulb worked out. I was having some conflicts between accessibility of components and order of assembly. I am maybe unnecessarily adamant on maintaining integrity of the pot and cutting the least amount of holes.


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## get-lit (Feb 29, 2016)

Regarding anode in vs out, the polar intensity is slightly higher toward the cathode, so it's advantageous to have the anode out for long FL reflectors and Anode in for short FL reflectors. But the lamp orientation is more likely dictated by the primary use of the light, as it's generally not as good for the lamp to operate with the anode down. So ground based lights tend to have the anode out and air based lights, anode in. This wouldn't be a concern for marine lights being primarily horizontal operation, so there must be another consideration for the ACR to be anode in. Could simply be that it's more effective to cool in the housing configuration.

EDIT.. Here's more specific info from *XBO Technology and Application* document... "Tilting the lamp with the anode at the bottom is the worst position. In this case, the convection forces act increasingly against the flow of the xenon gas and the instability of the arc worsens dramatically. Where a fairly large degree of tilt downwards cannot be avoided, it is therefore necessary to consider turning the lamp round in the optical system so that the cathode is at the bottom. Depending on the layout of the optical system, this can sometimes result in a loss of usable light, but it also results in much better lamp behavior."


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## get-lit (Mar 1, 2016)

Interesting note.. until the 70's, Xenon lamps could only be operated in the vertical position. This may be why the original tank light is configured as such.


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## WDR (Nov 7, 2016)

So, not just dragging this up for no reason, I've been working on the light lately with good progress. So far I have made a cage for the reflector and have it mounted into the cage, I'm currently constructing the mount and focusssing aperatus for the bulb and I've purchased another welder mainly just for this light that will have a 100% duty cycle at the required voltage and current output. 

At this point I do have a question, I realize it will be hard to get any exact information as I don't have that much info to go on. The literature for the lamp specifies 6m/s cooling airflow, my reflector has approximately a 3.5" center hole and I'd say the lamp occupies about a 1" diameter area in the center of the hole. With these factors in mind I'm wondering if anyone has an idea of the cfm I'm going to want for cooling this 4kw lamp? 

Using a calculator for ducts I'm getting about 70 cfm required for the area of the reflector hole including the subtracted lamp diameter. I'd suspect I'd want more flow than that as the air will imediatly begin to disperse and loose velocity after flowing through the reflector hole? I guess mainly I'm wondering if anyone has specs on the cfm of coolin fans used on lights of similar size?


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## PolarLi (Nov 7, 2016)

The airspeed you get over the lamp, will depend on how much resistence there is in the system and how much pressure the fan is able to create. 
Are you planning to circulate air inside a closed housing, or will you go for a intake and exhaust?
General tip on axial fans, smaller diameter, thicker, high speed fans, will create much higher pressure, than a big diameter, skinny, low speed fan, despite both have the same CFM rating.
I think 70CFM sounds a little low, but it would be impossible for me to say that for certain. The best option IMO, when tuning the system,
is to go for a more powerfull fan(s) with the option to slow them down with resistors or an adjustable power supply.
To do that tuning, I recommend you attach a temp sensor on the lamp base, and monitor the actual temp. 
You can buy complete K-type thermometer for just a few bucks on well known auction sites.


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## WDR (Nov 7, 2016)

Yeah, I know the airspeed depends on resistance over the system as a whole and such, I was just trying to get some sort of baseline idea so that I can choose a oversized fan that actually is oversized. that I can slow if required as you mentioned. I was thinking on testing with a thermocouple and also as a final system setting up an interlock to turn power off to the lamp and/or set an alarm for over temp such as if the cooling fan stopped for any reason. 

Anyways, getting back to the cooling I originally was going to have an open system with filters, but I'm now leaning toward a closed system with a air to air heat exchanger. Looking into that I found a automotive intercooler with 3" ports and a 12x11 radiator surface, thus was thinking of using a 3 or 4" axial inline fan(bilge vent) for the closed circuit and a electric automotive radiator fan for the external airflow. That was kinda what I came up with looking at available and affordable components. I'm not sure if I'm in a reasonable realm with that set up though.


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## PolarLi (Nov 7, 2016)

The heat exchanger can definitely work. I believe many of the Military Xenon lights use that setup. You can also see a "similar" system, but very simplified, if you take a look at the picture in this article: http://www.rbnett.no/lokal/molde/article314189.ece it's a 3 kw anti piracy light, and the only cooling (as far as I know) is air passing thru the two channels on top, circulating inside the light with some fans. 
I forgot to mention one thing about the temp sensor. Remember to insulate the wire for high voltage, and consider unplugging the sensor from the meter during ignition.


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## WDR (Nov 7, 2016)

Ahh, yes thanks for the remindor about temp sensor and the ignition voltage, probably would have overlooked that. It was my understanding that the military lights used a heat exchanger, I just didn't consider it feasible thinking conponants wouldn't be available until I thought of the automotive type stuff which I think may work out well. At this point the 3" ported echanger seams like the best fit.


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## Davekan (Nov 8, 2016)

Ametek Rotron makes the fans you want. If you get the dc versions, they are easy to control from dc/dc inverter. Look at Aximax, and Propimax from them. You lose pressure fast as you lower the speed so sizing in important. 70 cfm from a small 2" fan is better than 70 cfm from a 3" fan slowed down.

Dave


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## BVH (Jan 22, 2018)

WDR, it's been a while. Did you complete this light?


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