First off I would like to say the number I threw out there was just a guess off the top off my head, with no real data to back that number up. I have pushed a MT-G2 with 2 20r”s and got over 10 amps. In this thread DBCstm states he seen 12a at the moment of hook up direct drive with 2 20r’s. Now where dealing with 3 li-ion cells, is 15a possible? If you take a buck driver and bypass the sense resistor (solder across it) I would think there is no more regulation, because with no sense resistor it doesn’t know where to stop or regulate the current. Running 2 cells basically becomes direct drive, where the driver keeps trying to push current until there is not enough supply voltage to support the demand of the vf of the led. So if you use 3 cells its trying to buck the voltage and doesn’t know where to stop with the current, so it push’s it as hard as it can until the cells voltage stops it. Now what interest me is we can all look at HKJ’s useful graphs and know about what the predictable voltage of a cell will be at a given current load. But look at the very first second of those graphs, the cell’s have not had sufficient enough time to adjust to the load, so the voltage is much higher, almost at the 4.2v charged voltage. So if 3 good li-ions (not exactly sure which cells where used to blow this MT-G2 in this thread) where fully charged and hooked up direct drive (which I think this driver would basically be with the sense resistor bridged) At the moment of hook up what would be the current to the led?
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In my testing with 20r’s direct drive, the current actual increased as the cell’s became warm, which is common with li-ons. I never actual tried fully charged cells and checked the current at the very second of connection, but I do believe as DBCstm says, that 12a is possible with only 2 cells so what could 3 good cells do, especially if they where pre-warmed.
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@ImA4Wheelr, we know power in has to equal power out plus losses, so I’m with you on the math. I don’t know for sure but, at the moment of connection it looks like to me the cells voltage would be much higher and the driver losses maybe far less at that moment, since nothing has had a chance to warm up yet. This is all just me thinking out load, ya I know quite dangerous. :bigsmile: If anyone has something to ad or disagrees with my thoughts above, please post away. I don’t mind at all. I’m always willing to listen and learn.
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I have 2 more 20r’s coming from RMM in a day or two, so I can sacrifice a MT-G2 to find out what 3 will do direct drive if need be. I just hope I don’t blow my meter up. 