How to measure tailcap current properly?

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dangerous
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How to measure tailcap current properly?

I thought measuring tailcap current would be very straightforward, but I am seeing some odd things…

Is it normal for the numbers to be bouncing up and down from roughly 2.2A to 2.4A with a given cell in a given light? Will different quality cells and different quality lights have higher variances in current when in use? EVERY cell I have shows these fluctuations except my VTC5s. This makes me think all other cells are inferior. :quest:

Do you only consider the peak current when evaluating the current if it varies like that?

The specific cells I’m testing are: Unprotected EVVA KK, Protected NCR18650B, Protected Olight 3400, Unprotected Samsung ICR18650-26C, Unprotected NCR1860PF, Unprotected EBL 2600, Unprotected VTC5…

The specific multimeter I am using is the INNOVA 3320 Auto-Ranging Digital Multimeter, which I am using on the DC 10A setting….

BLF

Edited by: dangerous on 07/27/2014 - 10:02
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do you use thick, short measuring cables?

thin ones raise the resistance a lot (for measuring purposes) and add to the inner resistance of the cell – that affects the Amps a lot.

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dangerous
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The cables are the standard ones that came with the multimeter – 22AWG (0.326 mm²) with a length of 40 in (1m).

BLF

Hikelite
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Those are some thin wires, some better standard ones are 18AWG, they could easily be 1.3-1.6meters.
You need to think about the entire circuit, so current travels 1m*2.

Use 12-14AWG with a max length of 1feet per cable, that is safe to get you better/correct results on low voltage-high currents circuits.

dangerous
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The thing that bothers me the most is how the NCR18650B cells have so much lower current than the VTC5 even though the current draw is less than 3A. I thought they would have been closer at such low current. This makes me reconsider using NCR18650 in so many of my lights…

BLF

Illuminaria
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dangerous wrote:
The thing that bothers me the most is how the NCR18650B cells have so much lower current than the VTC5 even though the current draw is less than 3A. I thought they would have been closer at such low current. This makes me reconsider using NCR18650 in so many of my lights…

I would throw my Samsung ICR18650-26C in the microwave if that would magically convert them to VTC5’s, no? Using 4 Samsung ICR18650-26C in my 4 cell, 11 amp, lights works well enough till I hit the lottery. The non high current drain batteries seem fine for more modest lights.

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Consider buying a external shunt modified DMM from me ($10 shipped), you can take accurate current readings up to 20A!

If you don’t you’ll need to, at the very minimum, upgrade your DMM leads, factory ones (even high quality Fluke leads) are only reliable to ~1A. Its best to use >14AWG stranded wire and solder them to the inside of the DMM (but this will make it only usable for current measurements) that’s why I sell the ones I do, so you can have an accurate current measuring DMM without having to make yours useless for other readings.

Also note, even tho the sheathing of your stock leads appear to be ~22AWG in size it’s most likely that there are only around 30 strands inside making it ~28+ gauge.

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dangerous
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Illuminaria wrote:
I would throw my Samsung ICR18650-26C in the microwave if that would magically convert them to VTC5’s, no? Using 4 Samsung ICR18650-26C in my 4 cell, 11 amp, lights works well enough till I hit the lottery. The non high current drain batteries seem fine for more modest lights.
Those Samsungs are great for the price considering I got mine for under $3/each, but my protected NCR18650B were the same price as my VTC5 ($11/each), which is why I regret buying so many NCR18650B. The NCR18650B are providing under 2.4A in the same light that the VTC5 are providing over 2.8A…

BLF

dangerous
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So most people think it is the cables that are causing the fluctuations in current? I would understand if the cables aren’t giving accurate reading, but I don’t really get why the current would fluctuate more with all cells besides VTC5…

I guess most people just don’t see these current fluctuations when taking tailcap currents…

BLF

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dangerous wrote:
Illuminaria wrote:
I would throw my Samsung ICR18650-26C in the microwave if that would magically convert them to VTC5's, no? Using 4 Samsung ICR18650-26C in my 4 cell, 11 amp, lights works well enough till I hit the lottery. The non high current drain batteries seem fine for more modest lights.
Those Samsungs are great for the price considering I got mine for under $3/each, but my protected NCR18650B were the same price as my VTC5 ($11/each), which is why I regret buying so many NCR18650B. The NCR18650B are providing under 2.4A in the same light that the VTC5 are providing over 2.8A...

3A current is not a big deal for NCR18650B, so don't blame the cells.  Fix the cable, or current measuring system. Don't ever forget that anything through a current has to pass will drop some of it.   X3 for example has a contact board then these some wires to the driver, just a bit of waste there too, we can easily call this a not so perfect concept for low voltage circuits and high currents.

Illuminaria
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your are seeing poor contact as mine are normally steady. Make sure battery post are clean and good contact on tube. Your meter may be in question, CK’s meter may be a good option if any doubt. Check your leads, on ohms, is the reading steady? What about measuring battery voltage at rest, should be dead steady on first 3-4 digits.

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dangerous wrote:
[Those Samsungs are great for the price considering I got mine for under $3/each, but my protected NCR18650B were the same price as my VTC5 ($11/each), which is why I regret buying so many NCR18650B. The NCR18650B are providing under 2.4A in the same light that the VTC5 are providing over 2.8A…

Just making an offer but I’d trade you one of my current reading modified DMM’s for a NCRB straight up.

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dangerous wrote:
The thing that bothers me the most is how the NCR18650B cells have so much lower current than the VTC5 even though the current draw is less than 3A. I thought they would have been closer at such low current. This makes me reconsider using NCR18650 in so many of my lights…

Can you tell me what did you measure with B vs the VTC5? how much difference there was, and at what amps?

Oops, now i read it you already answered, sorry. What light it was can you tell me?

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Hikelite
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Meter is in question here like many poor measurements that are talked about on the forum. You do not measure current over 2meters at 22AWG, the voltage will drop to 3.78V from 4.2V only because of the 2meters 22AWG wires, not counting other loses like springs, etc. Important to remember that an uncompressed spring is not going  to have as low resistance as a compressed spring that will also create what some call "unknown variable", so the numbers bouncing has at least one clear explanation, the one one would be poor contact or dirty contact.

dangerous
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Hikelite wrote:
Meter is in question here like many poor measurements that are talked about on the forum. You do not measure current over 2meters at 22AWG, the voltage will drop to 3.78V from 4.2V only because of the 2meters 22AWG wires>
These are 1m cables and voltage readings match the OPUS BT-C3100 within .01v every time.
dazed1 wrote:
Oops, now i read it you already answered, sorry. What light it was can you tell me?
The numbers I mentioned here were from the XinTD X3, but I reproduced the same pattern in other lights such as the Nitecore P12 (under 3A, but the VTC5 pulls .5A higher than the NCR18650B.

BLF

Hikelite
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dangerous wrote:
Hikelite wrote:
Meter is in question here like many poor measurements that are talked about on the forum. You do not measure current over 2meters at 22AWG, the voltage will drop to 3.78V from 4.2V only because of the 2meters 22AWG wires>
These are 1m cables and voltage readings match the OPUS BT-C3100 within .01v every time.

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.

dangerous
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Ah, I see now. Thank you.

BLF

Hikelite
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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.

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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.

Hikelite
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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.

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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.

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GW3 wrote:
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.

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I used 20miliOhm resistor and mV range multimeter.

then 1mV = 50mA

thulfiqar
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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) Big Smile

Thanks

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thulfiqar wrote:
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) Big Smile

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.
GW3
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I have a similar cheap multimeter and it is useless at low ohm readings.

Lexel
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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

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

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

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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.

 

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

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dmsoule wrote:
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.

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