what issues did yours have that warrant replacing? I’m now questioning the authenticity of my HG2s and VTC6s because i can’t get my c8f to draw more than ~3.6amps on my meter, even on turbo. My next hottest light is an S2 w/ 8x driver, which draws about 2.7, which is pretty close to spec, but not enough to tell me that it’s definitely the c8f and not the cells, or i suppose the resistance in my meter?
any insight, Tracy? tests to perform, or maybe a driver replacement?
@ownmyeyes, what kind of multimeter are you using? If it’s a regular multimeter with long leads, the resistance is going to increase dramatically. You need as thick current leads as possible that are short as possible to measure current accurately.
an innova 3320 with long leads, so that could be the culprit. i’ll hack together some heavier gauge short copper leads and give it another shot. it’s also possible that the difference between ~900 and ~2600 lumens is not as dramatic to my eyes as i expected…
You can have the shortest, thickest leads in the world, but there is no getting around the fact that the current shunt on a DMM adds significant resistance. On my UniT 139c I just measured the shunt resistance as ~20mOhm. That works out to a burden voltage 200mV at 10A.
That’ll make a big difference in the draw of a direct-drive light. It’ll make no difference on a regulated light (like the Convoy 8x7135 driver, as long as the cell voltage is high enough to overcome the burden voltage and the regulator drop-out voltage.
For my part, rather than trying to approximate the spring & contact resistance, I’ve made tailboards with a (bypassed) spring and heavy gauge wire for the clamp measurement loop.
Earlier I experimented with measuring the resistive voltage drop across flashlight body tube. It worked pretty well with my precision bench DMM, but calibrating it was a pain.
Measuring the resistance using the DMM was problematic. Two-wire measurements had a lot of variability. Four-wire measurements were hard to manage in an assembled light, and also had a lot of variability. Increasing the signal-to-noise ratio with higher currents was a pain to rig up, and brought its own sources of error. It was sort of doable with FET+1 drivers because I could use the regulated modes as an internal calibration but thermoelectric effects were a significant source of error, even at 350mA, and made lower-current secondary calibration points pretty much useless.
I had it in the cart with the coupon applied………deleted it. It looks like a nice light but I just couldn’t see the niche that it would fit for me. I mean, I like lights of all shapes and sizes, but before I click the “buy” button, I like to envision a scenario in which this particular light would outshine all others—so to speak. Ya know, a time and place that this light will do what my others can’t or at least do it better. Couldn’t find one. Maybe next time.