I replaced all the sense resistors with a piece of wire with 28mOhms, which should result in ~2.4A output. The wire is 0.025” diameter solid copper and 50cm long. It’s not coiled so shouldn’t have significant inductance. I get the same results as above, around 2.4A with 1s input but still ~3.5A with 2s input. Is this a symptom of a component being operated out of spec? like the inductor being saturated or something?
I switched back to the two R100 stacked resistors and the driver behaves as it should; 1.4A with 1s or 2s input.
Well, the odd behavior I’m seeing does indeed have something to do with the wire sense resistors I made. I made a 50mOhm section of wire and the driver did not behave the same as with the 2 stacked R100 resistors. I guess I’ll just wait until I get the proper sized resistors.
Yeah a wire that long, even not coiled up will present a fair bit of parasitic inductance to the circuit which could certainly cause the strange behaviors you see.
I will play around with the H2-C a little more when I get a chance, now that I know it is an external switch we can push past the 10A input limit of H1-A. The switch should be good for around 15A, though the stock inductor isn’t.
Using 2S input levels should prove to be very good on H2-C based on my initial test. I bet we can get around 2.5A output safely using 2S input and the stock inductor, as barkuti said. Which could make one heck of a light using XHP35 HI.
I will be sure to post KX70 results when I get the driver. Just got my tracking number a few days ago. I may make a new thread for all the KD boost drivers to document everything. I am also hoping for around 5A output with modifications, the inductor may need changing for that though, as it doesn’t look much bigger than the ones used on the H1-A and H2-C from the pictures.
I got some proper sense resistors from digikey to continue modding the H2-C. With a 0.030 Ohm resistor the output current was right around 2.37A to the XHP35, with 1s and 2s input voltages. But the output was still not stable in 1s mode; after a few seconds the output would start to blink.
Some efficiency measurements. Voltage measurements taken at driver.
Input: 3.46V, 13A, 45W
Output: 14.1V, 2.35A, 33W. Leads to 73.6% efficiency.
I also ordered some toroidal cores to make my own lower resistance inductor, but I got T38 core material which has a high relative permeability (10,000). This leads to the inductor having too high an inductance. Even with 1 turn the inductance is about 100x larger than 2.2microH. I’m using this calculator. With this inductor installed the output current was lower and the output was not stable (it would start to blink).
I took off the stock inductor and measured the DCIR, and it was only 7mOhms. Here is a similar inductor I found on digikey. It is rated for 12A and has a 27A saturation current. Any idea how high the current pulses are with this driver?
Look out for a triple build using H1-A from me soon. Just finished modifying one of the triple pills from kiriba-ru to accept the 20mm driver. It is do-able, but the driver will have to be soldered to the pill, not enough material left to do a retaining ring. Not a problem for me though as I usually solder the driver in the S series lights anyway.
Just need to decide what emitters to run. I wanted to go with 219C 3000K from clemence, but I may go with XPG3 3000K for now since the 219Cs are not available yet. Maybe XPL2.
Quick notes on the KX70 driver. I received my sample yesterday, and it is a decent driver as is, but not much modding potential.
Uses the same TPS61088 as the H1-A, so we are limited to 10A on the input. Stock it is drawing almost 9A. I plan to try to push it right up to the edge, but I don’t think more than about 4.2 - 4.5A will be possible if we want regulation right up to battery cutoff.
Mode spacing is fairly close too, I really wish low was lower, as it stands low is about .75A to the emitter.
Once I get some full testing done I will be making a new thread to document all these KD boost drivers.
What i did was to grind out as much as i could for the driver and it did fit but i was afarid the components would Touch the wall so i stacked a ring made of solderwick on top of the pill to gain space… horrible move.
Had to grind the inside to realy jam the driver down and the outside so the pill woulf fit in the threads.
And flatten the backside of the reflector and remove the lens oring due to longer pill lenght.
And driver spring cut in half.
No bypassed springs and original 24 awg led wires so output is probably lacking but it works that was the main goal.
Could probably make a pill that would fit the driver better.
What if I just put the driver on the pill and screw back the battery tube to make a sandwich ?
The driver would be stuck between the pill and battery tube and I would change the battery by the tail…
Of course it would require some adjustments, like a thicker oring or maybe some solder to thicken the driver ground ring…
Probably do-able, I thought about that myself, however I have access to a lathe so I machined out a pill to get mine to fit, and it does indeed fit, just have to solder the driver to the pill as the retaining ring won’t work. I have a couple of nice S2+ builds coming up using this driver, just waiting on parts and another host.
I got another inductor core to try to continue modding the H2-C driver. The core I ordered was a T44-52 (0.44” OD, –52 core mixture), but it was actually –18 core material. This was OK because their relative permeabilities are pretty close. I could go larger than 0.44”, but I was having trouble finding the right core size with the right core material. So I wound an inductor with the T44-18 core with 4-6 turns. The DC IR was 3 mOhms, compared to 7 mOhms of the stock inductor. The new inductor did not improve the performance of the driver. With R030 sense resistor the output was still not stable with 1s input. The inductor still got very hot. I still don’t know what’s going on with the driver, but I suppose I’ll keep my eye out for a larger suitable inductor core, in case saturation of the core material is the cause of the output instability.
I ended up putting the stock inductor back on and putting the driver in a convoy L2 for use with 2x26350 cells. See more info here.