How to measure tailcap current properly?

I do not think you quite understand some basic stuff, I am only trying to help you.

1meter is in one direction there other direction is another 1 meter, so it is 2 meters that is how current travels. Reading battery voltage has nothing to do with reading the current you want to read on the same multimeter.

Ah, I see now. Thank you.

Get 2pcs of 1feet of 12-14AWG wire and use those as leads for your multimeter when measuirng current. You will see a big difference with the NCR18650B, also do not forget to chek how pressing the cell (compressing the spring) will change the current reading slightly, but since the cables are so thing now, the compression will not cause a big difference in current reading.

A real problem with measuring tail cap currents on multi-emitter lights is the total resistance introduced in the meter path. Most meters use a .01 ohm shunt resistor and even if one solders 2 - 1 foot 14 gauge copper wires to the insides of the jacks, there is an added .015 ohms in the path. (2 feet of 14awg copper is .005 ohm) Pass 15 amps through that setup as I do through my modded 6-XM-L2 SKR, and you will drop (V=IxR) 15 x .015 = .225 volts. That is a HUGE amount.
It’s just like running the light on 4.2V cells that are discharged to 3.975V. Couple that with the fact that LEDs when running in DD or with FET drivers on high and you will measure much less current than it would pull without that added resistance. Also remember that LEDs are non-linear in their current demands. Slightly increasing, or decreasing, the applied voltage will disproportionately affect the current draw. In other words a sight increase in voltage can greatly increase the current draw.
Of course when measuring smaller lights, as is the case in the OP, or current regulated drivers, the added resistance in the meter circuit does not matter so much.

Cereal_killer knows this, hence his suggestions.

The point I am trying to stress here is that NCR18650B are definitely capable of 3A if that is the load. You don't need VTC5 for 3A, if you got them that is good, useful cells, but NCR18650B has no problem delivering 2.8 - 3A, since X3 is using a Nanjg 105C driver.

Does the driver produce a PWM output? I’m wondering what would happen if a digital sampling meter, taking a sample at brief intervals, runs into that situation.

Most DMM's are fairly good at averaging measurements.

I used 20miliOhm resistor and mV range multimeter.

then 1mV = 50mA

Hi ,
What is the Typical Resistance in a Flashlight Switch , I just measured the resistance in my Flashlight switch and it was 1 ohm ?!
is it really 1 ohm or my multimeter is wrong ? (DT830D Multimeter) :smiley:

Thanks

Hi thulfiqar, in my signature line below you can my tests, and one of them is about switches. If I remember well, the typical small Omten switch should have roughly 0.01 Ohm resistance. These are values that normal multimeters will not measure well.

I have a similar cheap multimeter and it is useless at low ohm readings.

best is to measure the voltage over it with current you know flowing through it

R=U/I

for example

R=0,03V/3A=10mOhms

Exactly. If you don’t have a good resistance meter with 4 wire testing, check out HKJ’s article under the heading Low ohmic measurement:
http://www.lygte-info.dk/info/Measurement%20UK.html

Use a short piece of solid copper wire to bridge the battery to the flashlight case, and use a clamp a meter on the cable, the UNI-T UT210E clamp meter has an 1ma DC resolution, we had a group buy going a while ago as it`s such a great meter for the price.

John.

I thought that clamp meters only measured AC current, or at least the affordable ones. Does this UNI-T use a Hall effect sensor??

Yes, it does.

It`s all magic to me , here`s the original group buy it might fill in some gaps.

https://budgetlightforum.com/t/-/37314

John.

I would rather rely on Ohms Law
than the Hall effect
:wink:

for currents below 300mA The Clamp meter is not accurate enough
you can boost the sensitivity by doing multiplying the reading with more windings through it

the DC always needs set to zero depending on the natural magnetic field around it

Thank you, very helpful.