wight wrote:
It’s been a while since I thought about this driver (and I still don’t have one myself). Glancing over your pics again, maybe it does not have a voltage divider. That shouldn’t be showstopper though, airwiring a voltage divider should be an easy thing. I think I’ve covered the component selection (two resistors) pretty well over here (#917). For such a large driver I’d probably just use standard 1/8w or 1/4w through-hole resistors, you probably have the room for them. Higher values are better, less power draw.
Tried out your above idea using 4S 18650's driving MT-G2 with HX-1175b here with STAR Momentary (Ramp Down at 130 and Sleep at 115) and it works. I need to fine tune it though as it may be stepping down a bit early at this moment. I didn't take notes during the process. So here is what I can remember.
- First tried 110000 Ohms for R1 and 5100 for R2. Ramped down way to early. Like 13.x volts.
- Second tried 110000 Ohms for R1 and 6200 for R2. Started ramping down modes around 11.3 and Sleeping at 9.x Too low.
- Third tried 91000 Ohms for R1 and 4700 for R2. Started ramping down too high again, like around 13.x.
- Fourth, tried 82000 Ohms for R1 and 4700 for R2 and adjusted Sleep in FW up to 120. Haven't tested this set up yet.
I think the Atiny13a used for the above has a high reference voltage. 10% either way from 1.1 volts per the data sheet. The resisters used were 1% accuracy metal films. I just used matched (resistance and capacity) healthy laptop pull cells.
Sorry for the slim data. I need to get a power supply. My take away is that wight's idea works and that these high voltage applications will require fine tuning on an individual basis.
EDIT: fine tuned wording (in bold).