DIY Driver for MT-G2?

[macrosloth]

I am trying to figure out how to build a driver for the MT-G2…
I am thinking of doing something similiar to below… I was thinking of doing 2 groups of amc’s first group of 12 for approximately 4 amps… second group of 8 AMC’s off a switch that parrallel the first group.
So when the circuit is first turned on the MT-G2’s receive 4 amps..
When the switch is flipped and the second group of AMC’s is turned on the MT-G2’s receive 7 amps.
At 12.2 volts about 1000 lumens per led.
At 4 amps I will need a supply voltage of approximately 13.4 volts before the AMC’s start to regulate current and heat up.
At 7 amps I will need a supply voltage of approximately 14.2 volts before the AMC’s start to regulate current and heat up.
When the supply voltage drops below 10.5 volts or so, the leds wont light up… I am ok with this…
Does anyone see anything wrong with this idea? Also could I add a diode/Resistor as noted with the question marks to protect the system from random voltage spikes? If so what..
Also how many milliamps would 20 AMC’s require on their green leg to turn on?
Also I guess I could install a voltage boost circuit before this if I wanted to keep the incomming voltage at about 14.5 volts..

http://s15.postimg.org/ft9iip623/Driver.jpg

 

[climberkid]

One member on here that may be very interested and of much help is DBCstm. Just tell him he was recommended. He's done several mtg projects lately.

 

[DIWdiver]

I wonder where those numbers come from. The MT-G2 data sheet only characterizes the part for up to 3A. I'd be surprised if it survived long at 7A. Is this in a application with massive heatsinking?

If you're reading numbers off the graphs in the datasheet, remember those are only typical values; individual LEDs may be somewhat different from that. Also, the voltage across 2 LEDs is going to drop about half a volt as they heat up from 25C to 85C.

As far as protecting from voltage spikes, you'd have to give us a better idea of the application before we could advise on that.

The AMC7135 data sheet says it draws 0.2 mA on the Vdd pin, so 20 of them would draw around 4 mA.

The resistors you have are in the right ratio, but I would choose higher values. At 14.2V, the 100 ohm resistor would be dissipating (wasting) nearly a watt, and the 50 ohm one half that.

 

[DBCstm]

DIW, the MT-G2 can "survive" up to and over 16A. I have one running direct drive on 2 Samsung 20R cells at an optimum 11.88A, the point where diminishing returns starts taking the output back down. Hows 4000+ lumens sound? :)

There's a far simpler way to drive the MT-G2. I used a Qlite driver that is stock at 3.04A. Replaced the resistor at the LED red lead with a 200 ohm resistor. On the other side, I stacked a Zener diode on the capacitor. This enabled the 105c based driver to utilize 2 cells, lost reverse polarity protection and over discharge protection but am able to run the MT-G2 emitter as high as I want to stack the chips. So far I've run it this way at a bit over 6A, in too small a light so yeah, heat becomes a big factor. This modification of the standard driver is from some members of another forum. I just followed direction and it works beautifully. :)

 

[macrosloth]

DIWDiver, thanks for the MA rating of the AMC's. I'll size the resistors accordingly.. The MT-G2 is a beast, at 3500 lumens, things should be interesting..

 

[brandocommando]

Here is how I did my SST-90 Maglight.. I get just over 8 amps at the tailcap!

http://www.candlepowerforums.com/vb/showthread.php?335655-A-couple-Mag-mods-with-modded-SB-drivers

I was thinking of doing something simmilar with a HCRI M2-G2 at 5.0 amps or so.. :)