Tail Cap Current Reading Issues - Very Strange!

Trying to read the tail cap current on one of my modded flashlights. In it is a modded 105c driver with 12 x 7135 chips (380ma) each. I am using a mid-grade Radioshack 22-805 meter to read the tail cap current. I figure I should be getting a reading somewhere around 4.56 A.

FYI, the light takes two 18650s in series. Test below with all freshly charged batteries.

My OLD SolarForce 2400mah cells are giving me a reading of 4.55-4.56A at the tail. YAY! All good here!

Here is where things stop making sense:
With my NEW trustfire flames 2400 mah i am seeing currents around 3.5A
With my NEW trustfire flames 3000 mah i am seeing currents around 3.7A
With my NEW efest IMR 18350s i am seeing 3.8ish A.

I cannot figure out for the life of me what is going on here. Repeated the test many times… always the same result.

Too add on to this, just got myself two elcheapo Harbor Freight multimeters. $2.99 each, red in color, SKU 98025. Both meters are reading 1.45 A!!! consistently crappy?

this will sound as a repetitive answer, but …
are the DMM probes good ones?
did you make more efforts to lower the resistance of the complete flashlight, such as copper braids in springs, proper gauge wires, etc?

yes, consistent crap. those higher resistance probes will give you consistent low readings

The last brand new 2400mah 18650 trustfire black/red flames would not even hold 3v under a 3 amp load right after being fully charged. Tested with a hobby charger.

All of a sudden… for no apparent reason, i am getting correct readings with my Radioshack DMM. Getting between 4.5A and 4.6A on all the batteries tested above. I have no idea why…

Regarding the cheap Harbor Freight DMMs… i plugged in higher quality probes/leads and got good readings identical to my Radioshack unit. Now i need to find myself some new CHEAP but low resistance test leads for 3 meters. Anyone have any experience buying cheap ones that end up performing well?

My Harbor Freight DMMs give decent and repeatable readings with decent leads. I ended up just soldering some 18 AWG silicone wire directly to the input jacks. Works great for me!

and to answer your question, yes i have performed a bypass mod on the tail cap spring with copper braid. No mod on the driver spring yet.

Should i be getting any readings greater than 4.56A? If in fact that is all the current my batteries should see (LED and driver current consumption included) then i seem to have a pretty low resistance setup :slight_smile:


Harborfreight test leads have a resistance of 2 ohms… POS!

Still, I’ll keep the DMMs because they were only 3 bucks each.