I hooked up two LiFePo 14500 batteries in series directly to a MT-G2 emitter, the led draws 1.5A, the voltage sag prevents higher current. I have some A123 LIFePo 18650 cells coming in the mail. When they arrive I am trying those directly on the emitter on a copper Noctigon. I will let you know....
I’m ready … 8)
The cells should not sag much under 3.2V and easely deliver the 2.8 A for the MT-G2 (at 3.2Vf).
ok, I received the a123 lifepo 18650 batteries, 4 of them, and they all measured 3.56V upon arrival, I guess I could call them fully charged (right?). A charger for them is still in the mail somewhere, but since they were as good as fully charged I tried them out. Reflowed the MT-G2 on the noctigon plus two thick lead wires, screwed the board onto a sizable block of aluminium with Arctic silver in between, and connected two batteries in series to the led with my DMM in between, everything thick wires and soldered when possible. Result: 1.8 A , already lots of light but rather disappointing I thought, hoped for 3+ amps. Tried with all combinations of two of the four batteries with similar results. I have to try again when the batteries really charged fully, but I would be surprised if the current would be much higher with that last bit of juice. Hmmm..., is this a matter of bad batteries or is this just what you get with LiFePo-batteries: the voltage stays just not high enough for this led when under load? I am tempted to try some IMR's directly connected to the led :evil: (exept that I do not have two matching IMR's lying around).
On the other hand, you may not be able to build that smokin' hot MT-G2 light with this set-up, but it is a way to build a simple and efficient direct drive MT-G2 light with actually some runtime on safe batteries.
What do you guys think on a TrustFire 3T6 as a host with different reflector of course?
I have 2 of them so, I could chop one, just waiting to see a proper driver, one that is actually build for MT-G2, with real 6A :P
"Constant current circuit (2 cell only)"
Actually the LD-29 can output 2.77A even on 1 cell until 3.6V, as follows
Input 5.0V - input current 2A - output current 2.8A
Input 4.5V - input current 2.21A - output current 2.8A
Input 4.2V - input current 2.37A - output current 2.8A
Input 3.8V - input current 2.63A - output current 2.77A
Input 3.6V - input current 2.77A - output current 2.77A
I think you're missing the point. It's not a buck driver when run from two cells. If it were, it would drive a 6v LED from a 8.4v input. And you already said it won't do that. Unless it's a really poor design, or defective, a buck driver shouldn't need more than 2v difference between the Vf and input voltage. I don't know what else to tell you.
I only showed my readings, my point is not prove it's buck. The update is to show that the "constant current 2 cells only" is not exactly so.
The driver can do 2.8A out only down to 6.60V, at 6.55V falls out of regulation.
You can also see that here on the Balder BD-4 which uses that driver http://lygte-info.dk/pic/Balder/BD-4/Balder%20BD-4%20High.png