P7 driver/emitter combination for DIY lantern design

[aranyak]

Firstly I want to thank cpf for telling me ALL that I know about LED flashlights! I have purchased a few of them (few more on the way).

I would like to design a basic LED 'lantern' for use during power outages. Since it doesn't need to be particularly aesthetic or rugged, I was planning on mounting one (or more) LEDs on a CPU heatsink and using a battery pack + driver circuit to drive them.
As a prototype (before I cough up the $$ for more expensive parts) I put together a driver (DX SKU 7880) and a Q5 emitter that I had lying around on a heatsink, connected to a single AA NiMH, and it's pretty functional..a design that I can live with, so now I'm figuring out what components to use for the 'real' bright version. I don't know how to upload pics yet, once I do I will upload photos of my prototype 'lantern' (if you can call it that).

I have a spare CPU heatsink which I can use. I am aiming at a runtime of about 4+ hours on high, and planning to use a 6xAA NiMH or 8xAA NiMH (2000mAh each) as the battery pack. My initial thoughts on the components are:

LED: 1xSSC P7 mounted on the heatsink directly with thermal glue. Any tips on where to purchase reasonably priced bright P7s are welcome. Are http://www.dealextreme.com/details.dx/sku.12721 or http://www.dealextreme.com/details.dx/sku.11809 options I can explore?
Since I will be mounting the LED(s) on a heatsink, should I mount the bare emitter or should I purchase one with a star?

Driver - undecided - I don't know yet, I checked out http://www.kaidomain.com/ProductDetails.aspx?ProductId=1866 and http://www.dealextreme.com/details.dx/sku.20330
but I don't know if they are the most suitable ones for the project. Any ideas?

Battery pack: 8x2000 mAH = 16000 mAh
1xP7 driven at 3.0A gives 5.3 hrs. 6xAA gives 4 hrs (is this calculation accurate?) Also any idea if such packs are available or would I need to build one?

I'm want this setup to give out approx 1000 lumens(or more!) so is a single P7 enough or is it possible to drive 2 or even 3 P7s from a single driver? Where can I buy such drivers? Is this the most efficient way to get 1000 lumens from a lantern or should I use multiple Q5s? Is a small 6v lead acid battery suitable for this application?

Any thoughts on the heatsinking? Any help is appreciated!

 

[spencer]

Your calculations are a bit wrong. For me it is easier to work in watt hours for batteries.

2000 mAh = 2 Ah

so 1.2V x 2Ah = 2.4 watt hours x batteries = 19.2 watt hours.

A D bin P7 emits only 800 lumen so thats a bit less than what you want but at 2.8A a P7 has a Vf of about 3.75V according to the LED testing thread.

The LED uses 2.8A x 3.75V = 10.5 watts

Take into account driver losses (lets use an optimistic 85%) 10.5 watts / 0.85 = 12.35 watts.

19.2 watt hours / 12.35 watts = 1.55 hours

That is considerably shorter than your 4+ hours and it doesn't give the output you want. Consider using XP-G LEDs. They are more efficient. As for heatsinking you should be fine. I run about 7 watts of old Luxeon LED's (less efficient so more heat) through the smallest computer heatsink I could find and with little air movement I find it to be an acceptable temperature.

A lead acid battery could be considered. They are cheaper but heavier. In a lantern weight shouldn't be an issue.

One think I thought of though is a computer heatsink only has one side to mount on so this light will be pretty directional (not 360 degrees).

 

[Stereodude]

If you want a P7 in the brightest bin head to CPF Marketplace and buy from Shdwkeeper. He's got DSWOI P7's.