Choosing a dc converter/driver

Hi there!
Im Synergic and this is my first post.
Ok,im going to do a flashlight mod in a 3D maglite but i have some questions...
Im going to use a 12AA battery pack(14.4V) to power 4 Cree XR-E Q5 leds.Choosing heatsink and reflectors is easy,but the problem comes with the DC driver or converter...
As i know,maximun V in a Q5 led @ 1000mA is 3.7, so in the output of the driver/converter i will need 14.8V, right?
I was thinking abut Shark boost converter, but as i have seen (if im not wrong) Vout has to be 11.5V or 22V when jumpered... so is not a good option.
What a need is a boost driver to power it with 14.4V and keep my 4 Q5 leds at maximun rates, i mean 14.8 total Vout and 1000mA.
Any suggestions?
Thanks!!!

NiMH cells always run higher than nominal voltage, so your 14.4V pack will actually run about 17V.

Another option is to run the cells 3S4P in the light (you don't even need to make a pack, you just make some spacers and slide the cells in 4 at a time) and run each emitter off of a separate AMC7135-based driver. That's probably cheaper too.

The shark should work. Check out the maxflex http://www.taskled.com/maxflex.html and some of georges other drivers.

Synergic said:

Hi there!
Im Synergic and this is my first post.
Ok,im going to do a flashlight mod in a 3D maglite but i have some questions...
Im going to use a 12AA battery pack(14.4V) to power 4 Cree XR-E Q5 leds.Choosing heatsink and reflectors is easy,but the problem comes with the DC driver or converter...
As i know,maximun V in a Q5 led @ 1000mA is 3.7, so in the output of the driver/converter i will need 14.8V, right?
I was thinking abut Shark boost converter, but as i have seen (if im not wrong) Vout has to be 11.5V or 22V when jumpered... so is not a good option.
What a need is a boost driver to power it with 14.4V and keep my 4 Q5 leds at maximun rates, i mean 14.8 total Vout and 1000mA.
Any suggestions?
Thanks!!!

Click to expand...

Welcome to the forum. Here is a link to CPF from the Shoppe.
http://candlepowerforums.com/vb/showthread.php?t=105492

You probably already saw this since you have the spec's listed. I think the Shark will work well for your LED arrangement. According to this link, everything sold after Oct 2007 is Vout 26 volts and the J1 jumper has no function. I'm not an expert on this regulator, so anybody with knowledge to the contrary please feel free to correct me. Hopefully without the use of flames.

The 26 volt figure as I understand it is an open circuit regulated output that protects the regulator. Many cheap regulators blow up under no load situations. Also the max demand from your LED array has to be less than this figure. It is a boost regulator which means your battery voltage has to be less than the LED's are using, or there's nothing to boost. It is a constant current regulator, so it achieves a constant current by varying the voltage. Hopefully that answers your misgivings. Wayne's example in this link was greater than 1/2 Vout initially and at least 1/3rd Vout at the end of the battery pack's charge. As long as the battery drain doesn't exceed 4 amps.

Your example of 4 Cree's @ 3.7 volts each is 14.8 volts total. Your battery can't be any more powerful than that or it goes into direct drive. As LukeA mentioned, 12*NiMH is about 17 volts no load. Even with a load, it would blow out your 4 Cree's. If you only use an on/off switch, any pack as long as it's less than what the LED's require is good. In fact the regulator works at its highest efficiency as the battery voltage approaches but does not exceed Vout. A 10 cell pack would be ideal for your 4 Cree's. Well that's inconvenient so a 9 cell pack. Have you seen SilverFox's battery shootout? This will give you a good idea of what kind of voltage to expect from a freshly charged AA NiMH cell under load.
https://www.candlepowerforums.com/threads/79302

I think the reason Wayne mentioned a battery of at least 1/2 Vout is to allow for a dimmer. He has an option to buy the Shark and remove trimpot for an extra $3, or if you're good at soldering... If you used 9*NiMH's to drive 4 Cree's, you wouldn't be able to dim under 3.15 volts per LED. That would be at 100% regulator efficiency. By guesstimating from Cree's pdf, that's about 400 lumens for 4 Q5's. If you wanted to use a dimmer, the 6 cell pack would be better. At 2.1 volts per LED, the output drops to nothing. So you wire an amp meter in series with the regulator output on the LED side and determine the value necessary to get 1 amp. Then wire a resistor of that value in series with the pot you use so you can't blow your creation up.

Well as I said, that's my understanding of it so far.