A question about a low resistance 3v build

LumenDisaster · 2018-10-09T02:53:01.000Z

I’ve got a convoy m2, with the “direct drive” 17mm fet driver,
xp-l v6, and a orbtronic 30amp continuous battery, it’s reading around 4.2 amps at the tailcap with the orb battery and same with my hg2, either i have to much resistance somewhere or my expectations were to high, what do u think, and also my soldering on the mcpcb isn’t the prettiest I’ve ever seen but looks solid to me

BlueSwordM · 2018-10-09T02:56:31.000Z

What are you reading the current with? A multimeter’s leads can add significant resistance in a FET build, to the point of reducing current draw from the LED, and therefore output.

Also, did you bypass the spring or not on the light or not? A steel spring has very high resistance. Over 3A, it can limit the current going to the LED, and therefore, the performance.

LumenDisaster · 2018-10-09T03:01:41.000Z

Ya a cheap multimeter, I’ve seen that it has at least .20ohm of internally resistance in the multimeter, and no the tailcap is not bypassed and has 2.0ohm according to multimeter,

ggf31416 · 2018-10-09T03:45:14.000Z

2.0 Ohms is just not possible, it would limit current to 4.2V/2 Ohm= 2.1A by itself even if the rest of the circuit was a dead short.

LumenDisaster · 2018-10-09T03:59:39.000Z

Ok then i read it wrong, but it’s got some resistance i know that much, i was expecting the amperage to be around 6 with this setup, but then again this is my test bed to learn about this stuff, still learning

mrheosuper · 2018-10-09T04:51:39.000Z

There are lots of things to caculate

First: Spring, spring has a quite high resistance, depending on its material, if you are not sure about your spring, just bypass it
2: Wire, the wire from driver to led also has resistance, so best to keep it short and use a thick wire( i usually use 22-20awg wire)
3: your method measuring current, cheap DMM usually use shunt resistor, it’s not bad, but what bad is the wire from the DMM to your light, usually it has very high resistance, so you can either use a thick wire, or get a current clapm meter( and use a thick wire)

LumenDisaster · 2018-10-09T14:23:47.000Z

Thanks for the tips, I’ll try the bigger wire on The driver see what happens the tailcap spring is gold, 0.02 ohms not enough for me to worry about

TheOnlyDocc · 2018-10-09T17:49:42.000Z

Doing a spring bypass will usually give you a big bump in current (if ledwires are big enough ~20awg) . If you use the spring that is delivered with the light i only can recomend to do the buypass.

LumenDisaster · 2018-10-09T22:25:00.000Z

I just bypassed it by manually holding a wire on the tailcap and body and it did get warmer faster then with the tailcap on,