4000 Watt short arc searchlight project

[WDR]

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?

 

[PolarLi]

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.

 

[WDR]

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.

 

[PolarLi]

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.

 

[WDR]

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.

 

[Davekan]

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

 

[BVH]

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