Good update RMM. Thanks for keeping us posted. Looks like I need to eat my words a little about the output capacitance not helping ;). Low ESR seems to be the key to a lot of things. I assume that a shielded, 10.5A, 47uH inductor must be very large physically? Between the two large caps and the giant inductor, you seem to have assembled a real brick :p.
Can you try increasing the sample rate the next time you capture a trace? The outlier samples seem to be a long way out.
I see what you were thinking now. The HX-1175b is constructed using a chip meant in part for controlling high voltage LED strings. The HX-1175b itself is marketed as a driver for SST-90 of course, but I’ve seen little to indicate that it shouldn’t work for higher voltage loads. Thinking more about what I already said, I can’t really see how the PSU section (zener and resistor) for the buck controller would be the problem. I’ll probably pick one up sooner or later to try to learn a little more about it.
Took measurements with 2S and 3S driving an MT-G2. Cells were King Kong ICR's charged to 4.2ish volts. The cells are older and have internal resistance of about 40. Current to the MT-G2 with no driver was 6.5 amps.
2S
3S
High
Low
High
Low
Input Current (Amps)
5
2.5
5
2.5
Emitter Current (Amps)
5.1
2.5
6.7
3.4
Sensor Bank (mV)
162
77
166
82
The driver used is completely stock. The HX-1175b1 only has High, Low, and Strobe modes.
EDIT: Fixed typos in table.
Ouchy,
If you get a chance, please post a pic of the 13amp driver. Also, it would be helpful to know what current 2S of your 18500's deliver when connected directly to an MT-G2.
How do I increase the sample rate on the DDS? I haven't seen any place to do that.
The inductor is actually the same size or smaller than the stock one, although I think it has higher DC resistance (more heat losses.) so it may not be the most efficient but it works well, is small enough to fit in most lights, and runs smooth. The saturation point is what I was really after since I think what happens with the stock inductor that wreaks havoc. With the stock inductor you can run pretty smooth up to a certain point then it just spikes like crazy! Sometimes you can have an LED working fine then you move the LED wires by the inductor and then it blows.
The driver fits well in the TK61 and my little mini intimidator. If you are happy with 6.5A-7A you can get away without the output capacitors but I've added them for extra insurance.
I tried to guess cell voltage under load and Vf of the emitter to get a rough idea of efficiency. Does it make sense for the driver to be more efficient on High mode?
Again, good info - thanks. It sounds like the included software with a DDS-120 doesn’t allow you to manually change that, but if you make a small time/division it will increase the sample rate on it’s own. This is the thread that leads me to believe that. It should be easy to tell since it displays the samplerate on the screen? There may be alternative software which would allow you to force a higher samplerate, but just making a smaller amount of time/div would do what we want here. Based on the specs I assume that the actual limit is either 50MSa/sec or 200MSa/sec.
EDIT: I could be wrong, but I think that in HKJ’s driver reviews he uses 1μs - 2μs per division.
I’m not sure, but I see that you did not adjust cell voltage sag for the different loads. Considering that we’re talking about 5A vs 2.5A, I’d say you’ve got to do that.
I’m not sure, but I see that you did not adjust cell voltage sag for the different loads. Considering that we’re talking about 5A vs 2.5A, I’d say you’ve got to do that.
Good point. I need to find a HKJ chart for the KK and adjust. I will do that later. What I really should do is set up a driver testing rig so that I can collect all the relevant info needed for this type of stuff.
Right now I only have two Efest IMR18500 handy. This is all jury rigged with different wires, alligator clips and magnets, but I got a reading of 5.9A.
Okay wight, I tested the voltage across the resistors while running the MTG at 13.45A and got a reading of .049v. I tested each resistor, and got that reading. What it means, I don’t have any clue. Hope I did it correctly.
Ouch! I went to take another reading before I disassembled everything, and smoke was coming out of both resistors. I sure am glad I checked this driver before it went into a light.
I looked it all over with a jewelers loop and didn’t see anything different from the other ones. No burned or charred spots. I even tested a few solder spots with my DMM. Then again, my eyes aren’t that good.
Thanks for testing this. You definitely got .049 and not 0.49? 13A across a total of 0.034 ohms should give about that much drop (1/2 volt). Sounds a lot like you are getting DD or as close as this driver will come (with the FET and inductor in the mix).
Could be I suppose. With QX5241 that just gives you a dead driver, but the pinout for QX9920 is different enough that it might give you DD; I’m not sure.
I think that it could also simply be a defective controller chip.