Project off-road lightbar featuring SST-90's

[icalbert101]

I'm building almost the same light only using 6 SST-90-W57S-F11-GN200 s, are you still using the Aluminum u channel for the housing? that was my planis I was going to use a 2x2 billet aluminum rod then get a channel milled out and heat sink fins milled on the back side of the channel PROs/CONs?

 

[DIWdiver]

That big chunk of aluminum will be great at absorbing heat, but if you run it a while, it will eventually heat up.

The thing you really want to do is transfer the heat to the air and get rid of it forever. That's what fins are for. Surface area and airflow are the keys to heat transfer to air.

Your six LEDs will be generating around 200W. You want your heatsink temperature rise no more than 50C, (less is better), so you need around 400 square inches of surface in calm air (more is better). With airflow (from driving around or a fan blowing on the surface), you can reduce the surface requirement by a factor of up to 5 or even more depending on the airflow. The fins give you more surface area in a smaller package. You can get an improvement of 2 to 20 times or more in surface area / package area.

Your 2" square billet might be okay in still air if it were 50" long and its entire surface were exposed to the air. Driving around slowly, you might reduce that to 30" (just a guess - I'd have to do some calculations to get a better number). At highway speeds 10-20" would probably be enough.

 

[icalbert101]

2x2 billet aluminum rod then get a channel milled out and heat sink fins milled on the back side

the back would have fins milled in to the billet not really thin but I was thinking it would turn out similiar to to the apearance of a dirtbike/atv cylinder head so each fin would be about a 1/16" and a gap of 1/16" and maybe a slot or two in the oppsite direction to add just a bit more surface area. so the back would have 16 horizontal fins and then maybe 8 channels milled out vertically and all aprox 1 inch deep

 

[DIWdiver]

The slots probably need to be wider to optimize airflow, unless you are using a fan. And a 16:1 aspect ratio on the fins (length to thickness) is higher than most aluminum heatsinks. Plus it's hard to mill slots 1/16" wide and 1" deep, unless maybe you are sawing them. Say you have 12" of rod, with 1/4" slots and 1/8" fins. That would give you about 32 fins, each with 4 square inches of area, for a total of 128 square inches. When you count up the tips, edges, lost surface, etc, I calculate you now have 208 square inches total, compared to 96 before the milling. Sticking with your 1/16" slots and 1/16" fins, you'd have a lot more surface area, but perhaps no better performance for your trouble due to restricted airflow and limited heat conduction down the length of the fins.

If you have the ability to mill those slots, it would be interesting to see what happens. Maybe make a 2" long test piece with thin fins/slots, and one with wider ones, then measure performance?

 

[DIWdiver]

Oh, and the slot in the opposite direction doesn't increase surface area unless the slot is thinner than the thickness of the fins. It would increase turbulence, but I have no idea whether that's good or bad.

 

[icalbert101]

and that's why I'm blad I posted here that makes alot more sense the way you where describing. not to mention milling 1/4" only 2"s makes way more sense than milling 1/16" 12"s the refletors I'm using are
two sst-90w s and 4 sst-90s because it's a "stealth" bar. would it be more benificial to up the reflector slightly I could probably jump up to a 1.5" or 2" but it wouldn't be as "stealth".
http://www.mouser.com/Optoelectronics/LED-Lighting/LED-Lighting-Reflectors/_/N-8x9c7?P=1yzsouo link to reflectors I ordered


I hate to ask so much on someone elses build but my build is so similiar it seems convient if there are any complaints please let me know and I will start a new thread.

 

[DIWdiver]

The only reason to use a bigger reflector is to get a tighter beam. If you are happy with the beam, then it's a good reflector.

 

[cmacclel]

Very Cool project I also looked into building a light bar as I have a 04 Rubicon myslelf. I never like the SST-90's as they never seemed practical with all the heat they put out and optics where hard to find. I would go with XM-L Led's myself. If you VF matched the LED strings you could run 9 from each driver.

Mac

 

[cmacclel]

I wimped out and wound up with the Rigid Dually D2's for $330 shipped from Ebay. They output 5200 lumens (2600 each).

 

[Diman]

well. no news yet. I just got home from hospital to discover that neither IR-meter nor the heatsink have arrived.

The main idea is still the same. 5mm thick u-channel with heatsinks glued to the back using thermo adhesive.

I'm playing around in solidworks and here're some pics of the design.

The u-channel need to be modified - wings must be machined down a bit to ensure proper distance between reflectors in the front panel and the leds on the bottom of the u-channel.

This is of course only preliminary sketches...

 

[icalbert101]

 

[Diman]

...collecting parts....
not much happening yet...

 

[HB021]

It's going to be great!

 

[Diman]

some minor updates...
I've ordered (and received ) one driver from DerWichtel, they are (what I think) switching drivers.
It's more expensive than DIWDivers and handles only two SST-90s in series. But the fact that it is a switching driver and generates alot less heat that I have to deal with is intriguing.

So I will evaluate it as soon as I can... too much at work before Christmas, too little time...

I've been thinking about my design.. had an idea, I'll just run it by you...
What if I'm to add a small fan to the housing... I already know that i will need a vent hole, so that the housing is not hermetically sealed. This vent will probably be a small pipe beginning somewhere at the top of the housing and pointing downwards along the backside to prevent rain and dust from entering the housing. couple of inches in length.
But what if I add another vent at the other end of the housing.. the same design a little bigger pipe/channel originating at the top and running down the backside... And place a small pc-fan inside the housing at the top hole where that second pipe begins... blowing the air out.

difficult to explain.. I have it only in my head

the question is would the air movement inside the bar have any cooling effect on the leds (in addition to the passive cooling with my original heatsink idea)... I mean would that fan help cooling so much that it's worth the extra work or would it's effect be so small so it's worthless...

sorry for somewhat blurry explanation...

 

[DIWdiver]

The explanation seems fine to me. And yes, it would help. The faster you drive the less you need it, but if you are creeping along it will make a big difference.

 

[Diman]

well, the intended use of the bar is in the woods and it seldom goes over 5 km/h there...
and I need the lights to be on for long periods of time...

I'd love to do a thermal simulation/calculus, but I've never had to deal with heat before so I don't even know where to begin.
So the only way for me is to over-dimension things.
I'll give that fan idea some more thought.

 

[HB021]

If it is a roof bar, can't you have someone calculate how big heatsink you'll need? It will probably be a massive heatsink but does it matter if it's on the roof? And maybe some active temperature control that lowers effect to half when say its over 80 degrees? And maybe 2 housings combined, build one air and waterproof housings with heatsink on the back and then another housing(vented) on the heatsink with fans blowing directly on the heatsink?

 

[Diman]

allright.. some more thougths.

Here I was, working on another project... small one but involving LEDs.
My liftgate (as a liftgate supposed to) opens upwards and provide excellent roof for me standing in front of the rear hatch. I have some stuff there.. water tank, propane-kitchen, tools and other stuff one might need on the trail. I then figured it'd be nice to have some lights there and liftgate was a given place to mount them to.

So I bought two drivers for two cheap LEDs I had laying around since forever.. nothing special - chinese crap Leds http://www.ebay.co.uk/itm/10W-Power...790?pt=LH_DefaultDomain_0&hash=item256ade4a06

drivers:
http://www.ebay.co.uk/itm/12V-LED-D...452?pt=LH_DefaultDomain_0&hash=item5ae06b1f8c

assembly in the rear plastic of liftgate

Then I tried to turn them on and connected drivers to Jeeps battery. 12V. Jeeps engine not running!
I was listening to radio at the moment and when LEDs turned on I got very strong interference noise from the radio. My garage FM-radio is a old stationary hi-fi box, cd is dead only radio is working. So it's not radio in the Jeep = no physical connection through power wires.
I use my iPod with attached FM-transmitter to play music in the garage. The music was almost entirely replaced by that noise. At the moment the iPod was laying next to the radio and I estimated distance between me with leds at the battery and the radio to be 5-6 meters. So it's far away...

After googling a while I wrapped that plastic box where I placed the driver in aluminum tape, but it didn't help. Still getting alot of noise as soon as the LEDs turn on.

What I really want to know is if will I get the same kind of noise from my LED bar? is it LEDs or driver that are the cause? And if anyone had the same kind of problem
and how to fix it...



Happy New Year to all of you

 

[CKOD]

The drivers you linked probably happen to have harmonics running way out up high. I'l look at a low-pass T filter on the output to squelch the noise. I'd avoid a low pass pi filter, as the capacitor on the output could potentially blow out your LED if it was big enough and you get an intermittent connection to the LED. (i.e. it charges up and then the connection is remade and it dumps into the LED) The inductor between the cap and the LED in a T filter would at least give it a chance.

 

[DIWdiver]

The noise is generated by the switching regulator, not the LEDs. Those nice long wires make pretty fair broadcast antennae in the FM band.

As CKOD suggests, you need to filter the noise at the point the wires attach to the driver. You should filter both the input and output wires, though the output may be more important. However, at those frequencies you don't need large capacitors. Either a T or pi filter with 0.1uH and 0.1uF components should provide 70dB attenuation at 100 MHz. If you can enclose the driver in a 'Faraday Cage' (any metal enclosure that's mostly sealed), and tie the grounds of the filters to the cage, and the cage to power ground, you should be good to go. Aluminum foil tape may suffice, but a box would be better. The Faraday cage may not even be necessary, if the filters are nice and close to the driver.

The IS1006 drivers you bought, being linear drivers, will not exhibit this problem. Der Wichtel's driver is a switcher, so it will generate noise, but there's no telling whether it will be as bad, until you test it.