Just when I thought I had the basics all figured out, I find out I'm not that smart. I just got my first DMM, and was learning how to test for continuity. First I touched a lead to the spring, and the other to the + Led wire on a Nanjg driver and got the expected beep, indicating continuity. Next I did the same with the - Led wire and the outer ground ring on the driver, and...nothing. I thought there was something wrong with the driver, and tried it on another. Same result.
Now I'm really confused. I thought that the outer trace ring on drivers was a continuation of the negative pathway, and there would be continuity, but obviously I'm wrong.
Could someone out there please explain to this rather addled neophyte modder what I'm missing, and where does the neg. LED pathway lead to.
The INPUT circuit (battery-to-driver-input) path connects to the + side of the battery and the - side of the battery. The OUTPUT circuit path (driver-to-emitter) connects to the + and - sides of the emitter.
It’s not “necessary” that the - side of the INPUT circuit be the same/in-common with the - side of the OUTPUT circuit. They could be the same, but they don’t need to be the same.
You can think of the driver as a box with 2 input lines (+ and ) on one side of the box, and 2 output lines (+ and).
The LED- wire goes to the 7135s, and the 7135s control how much current is allowed to pass thru. So with the light 'off', there's no path connected between LED- and GND. If it DID show continuity, that would tell you you have a short, and the light would run in 1-mode direct drive at all times... no current regulation, because the short bypasses the 7135s.
Don't get too dependent on using the diode test mode, try to only use it when you're either actually testing a diode, or when you can't see the meter's display while working (like hanging upside down under a car dashboard). Diode test when used on things that aren't diodes will just give you a yes/no, which isn't always good enough for a circuit with resistors and capacitors and other things in the path. Using the actual ohms mode will give you a real measurement in numbers you can use for much much more than if you only get a binary yes/no result.
edit: you may not be working with 7135-based drivers, but if it has continuity on the LED+ to BAT+, and none from LED- to GND, then you have a driver that does the regulation on the ground side of the circuit, regardless which actual components it uses to do it.
…so, if I want to direct drive, I would just unsolder the negative LED wire from the board and re solder it to the ground trace, and get the same output whether the driver was 1A or 5A?
Yep! That is, as long as you've confirmed you're working with a driver that regulates on the ground side (or a common one you know well enough you don't need to check with the meter).
Thanks for the help guys. While I’m here I might as well ask if those brass sleeves over the spring in the tailcap add resistance, and if removing them would help improve amps?
I believe Foy in one of his reviews of a shadow light removed the brass cover and it DID reduce resistance. I’ve tried it with my XinTd light and thought the spring looked ugly and ‘long’ so put it back…
That little brass cap adds another contact point to the circuit, from the spring to the inside of the cap, and from the cap to the cell. Without it you just have from the spring to the cell. Get rid of all the 'extra' parts like that and it can help a lot. (I think about 2/3 of the parts in a C/D cell Mag can be thrown away and it only makes the light work better)
