3 x XPG Maglite 3C build

[pulstar]

Hi guys,

I'm getting more and more joy watching all those nice mods that i decided to build my own too Well, i got the idea of building 3 cree XPG's, parallel connected to 3x ni-mh C-cells in series(3.6 volts, pretty close to leds forward voltage). I wonder if i could protect my cells by wiring a suitable diode in reverse direction in series to main circuit ( to protect cells being overdischarged. Diode should conduct nicely when battery maintains voltage higher than Vbr, and stop conducting while voltage drops.)

I really don't know how to regulate the damn thing, but i thought i could use some kind of a current regulator(i saw a few, but there aren't many that could provide around 3A) to hold a current at desired level(1A per led or 3A for all together. I'm not a native english speaker and i really can't express myself in appropriate way so i hope you got the idea what i try to tell. So: battery plus wire, switch, protective diode in series (optional 3A current regulator in series) 3x XPG in parallel(optional 1A current regulator in series to LED in all three branches), wire to battey minus. Would this work in our space?

 

[pulstar]

Would AMC 7135 be suitable for my needs?

 

[Justin Case]

A Mag mod has a lot of room for drivers. You can wire configurations such as 8xAMC7135 to get 2800mA (using two single-mode 4xAMC7135 drivers connected in parallel), or 9xAMC7135 to get 3150mA (three 3xAMC7135 drivers in parallel). The XP-G datasheet says a typical Vf of 3.3V when driven at 1000mA. I'm driving a Cutter triple XP-G R5 parallel star using a 6xAMC7135, two-board sandwich. Power source is either 1xIMR26500 Li-ion or 3xAccupower C NiMH LSD cells. Both battery configurations work great.

See StefanFS's Maglite mod guide, especially if you want to build a multimode, AMC7135-based sandwich driver.

 

[HarryN]

Hi - nice start on a project.

I assume the purpose of the diode in series is to raise the total Vf ( LED Vf + diode Vf) above the lowest desired battery discharge voltage. You are hoping that the power draw will just stop when it hits this combined Vf.

The idea would work if the Vf of LEDs and diodes were really just a single number, but it isn't. Every diode, including LEDs, actually has a Vf curve. In the case of your description, as the voltage drops in the battery pack, the current will also drop, and the Vf will also drop - tending to level things out some.

If you used some decent quality NiMHs (ones with a relatively flat discharge curve) your concept will work just fine. You could also use a resistor in place of the diode and obtain very reasonable results. In both cases, there is heat to be dealt with, which is the power that these devices are dissipating. It can be estimated by using

(V battery - Vf total) x current = power dissipation.

There are many lights made this way and they work just fine. The low battery discharge point though is something that will be indicated by YOU - not this circuit. When it gets dim - turn it off and recharge. Or - recharge regularly.