This is a thread all about the Shark driver. I am more of a Direct Drive person whenever possible so I haven't really read up on this.
http://www.candlepowerforums.com/vb/showthread.php?t=105492
One thread by Elektrolumens stated, IIRC, that the most number of Cree optics he could fit into the Mag head was 3. ah ha
http://www.candlepowerforums.com/vb/showthread.php?t=150586 3rd post. But maybe you can think of 4 Crees. 3 with optics, one without.
However, given that you are going for the max 980mA for each Cree, that would mean an output power of 0.98A X 3.2V X 4 = 12.544W. Assuming 100% efficiency (don't know the exact efficiency...) with 3 NiMH D cells, you have voltage of 1.2V. that means a current of 12.544 / 3.6V = 3.48A. That is threading too closely to the limit of 4A of the shark driver. However, if you are using 9AA NiMH using a 9AA-3D holder (sold by fivemega and modamag), the input current would be 1.161A which is pretty safe.
If you should decide to do direct drive, with 3 NiMH D cells, you can get pretty much run any number of Crees you can fit into a mag head with each seeing a current of 350mA or so. This would definitely be less impressive than the setup with the shark at 980mA but you should have zero heat issues given a decent heatsink.
Runtimes - in the 3 setups above, runtimes are approximately as follows:
-3 NiMH D cells (10Ah each) with shark driver => 10 / 3.48 = 2.87h (provided when the cells' voltage do not fall below 1.2V. Otherwise, it may fry the shark driver first.)
-9 NiMH AA cells (2.5Ah each) with shark driver => 2.5 / 1.161 = 2.15h
- 3 D NiMH cells (10Ah each) direct drive => 10 / 1.4 = 7.14h
All calculations are assuming you use only 4 Crees.
Downboys could be used as well but i think the only way to use them with 4 Crees would be to use 12NiMH AAs and i think regulation would only be for a while before they go direct drive. 14.4V supplied and (12.8+1 )V required.
I may have some calculations wrong here so if anyone should spot any, please let me know.
