Current draw measurements on Fenix TA21 and LD10

Hey guys,

This is my first attempt on current draw measurement, tested on a Fenix TA21 and LD10, but I'm getting different readings. Has anyone done measurements on the Fenix TA21? Do compare with my data below, I would like to know if my measurements is how someone would measure current draw in LEDs. I'm still learning, and would like to be corrected and learn more.

I'm using an Ace Digital Multimeter (affordable), DC current measurement only has 2mA, 20mA, 200mA and 10A range. Positive pin is placed on the body (non-anodized part) and Negative pin placed on the center battery, which is one AW18650, voltage reading before test is at 4.01

I've excluded the strobe, beacon and sos modes (The TA21 has 12 modes).

Stages (lumens rated by Fenix) --- Tested at 10A on DMM:
1) 4 lumens --- 0.00 (no reading because of high resistance)
2) 18 lumens --- 0.03 (30 mA)
3) 35 lumens --- 0.06 (60 mA)
4) 50 lumens --- 0.11 (110 mA)
5) 80 lumens --- 0.19 (190 mA)
6) 120 lumens --- 0.32 (320 mA)
7) 160 lumens --- 0.51 (510 mA)
8) 190 lumens --- 0.67 (670 mA)
9) 225 lumens --- 0.88 (880 mA)

Stages (lumens rated by Fenix) --- Tested at 200mA on DMM:
1) 4 lumens --- 12.7 mA
2) 18 lumens --- 39 mA
3) 35 lumens --- 75.4 mA
4) 50 lumens ---123.4 mA
5) 80 lumens --- DMM showed 1, which was above 200mA


Now for the LD10, voltage reading before test was at 1.70, Energizer Ultimate Lithium.

Stages (lumens rated by Fenix) --- Tested at 10A on DMM:
1) 9 lumens --- 0.11 (110 mA)
2) 45 lumens --- 0.36 (360 mA)
3) 90 lumens --- 2.3 - 2.5A

Something was very wrong there, I'm not sure if it's my DMM, but 2.3A on high mode is insane? I switch off my DMM and then back on, tested not more than 2 secs to get a reading on high and it's around 2.3 - 2.5 again. I stopped there, did not bother to test on turbo. However, the brightness level on each mode appears to be the same as with the tailcap on.

So I've decided to check the LD10 tailcap for resistance. DMM resistance was set to 200 ohms. Direct pin to pin test showed 0.4 (This would be zero value):
- Tested on tailcap at switch off = nothing.
- Tested tailcap at switch on = 0.4 - 0.5, very low resistance, almost as zero.
- I did the same for TA21 tailcap with similar results.

Anyone can help me here with the LD10 measurement too? I know I'm using a budget DMM, but I've used it for other voltage readings, resistance reading and other current draw measurements on other flashlights I have after this tests, it seemed to make sense. I think I'm not understanding certain things correctly.

Not so bad, but there are a lot of caveat's when measuring current on flashlights. On regulated light the current is depend on the battery voltage and will increase with falling voltage. When you are near the maximum level, the led will heat up and this will often reduce the current, i.e. measuring after 5 seconds, gives a higher current reading than measuring after 60 seconds.

My current measurement with a 18650 fresh of the charger is and without waiting for the led to heat up: 14.8mA, 42mA, 76mA, 121mA, 195mA, 324mA, 506mA, 665mA and 862mA
If you are using 2xCR123 you will get a lower current draw, due to the higher voltage.

When close to full scale a DMM has a snigficant voltage drop and this will give a higher current draw (In my guide about measuring on flashlights I recommend to stay below 10% of full scale).

My measurement on the LD10 gives: 90mA, 540mA, 1320mA and 2100mA, this is done with a eneloop (They are very good at holding the voltage under load), maybe you battery could not keep the voltage up and the regulations increased the current to keep stable output?

HKJ, thanks for your reply, I saw your brilliant website guide for flashlight measurement.

I've compiled a comparison based on your data. I assume your are using your Fluke DMM right (which is a lot better than mine).

TA21: mine --- HKJ's

1) 12.7 mA --- 14.8mA
2) 39 mA --- 42mA
3) 75.4 mA --- 76mA
4)123.4 mA --- 121mA
5) 190 mA --- 195mA
6) 320 mA --- 324mA
7) 510 mA --- 506mA
8) 670 mA --- 665mA
9) 880 mA --- 862mA

My 18650 has lower voltage than yours fully charged. And I left the light cooled for 5 minutes after usage. Just making sure the light is working before and after tests. Based on your comments and my knowledge, the different reading showed could be affected by DMM difference, temperature on LED and environment, battery temperature, state and voltage, LED lifetime reduction?

LD10: mine --- HKJ's
1) 123.7 mA --- 90mA (my DMM started at 0.09 too, when the light was cool)
2) 360 mA --- 540mA
3) 2.3 - 2.5A --- 1320mA
4) Did not test on turbo ---- 2100mA

HKJ said:

My measurement on the LD10 gives: 90mA, 540mA, 1320mA and 2100mA, this is done with a eneloop (They are very good at holding the voltage under load), maybe you battery could not keep the voltage up and the regulations increased the current to keep stable output?

Click to expand...

Can't come to any conclusion yet. I've tried with a Powerex NiMH at 1.25v (low and medium only, the next day before post), the readings were like your eneloops, 0.09 and 0.50 above. Then, I've used an energizer max alkaline at 1.4v, low and medium only at 0.11 and 0.35 above. I'm guessing because lithium voltage was higher than both. That explains the boost only circuit. Now... because of this, it might also explain why Fenix does not recommend 3.6v batteries on their LD10, it may reach to higher amps that could be fatal to the electronics, make sense?

Btw, your measurement for LD10 is a relieve, I thought I may have done some damage, I actually inspected the LED for few minutes to see if there were any burnt signs, I had mistaken how it 'behaved'.

Okay... As for the TA21, since the current draw differs from 18650 and 2xCR123 because of its voltage difference, so the actual current measurement to the LED can only be done in between the LED and the electronics regulating that constant output, which is inside the bezel? All the measurements we did above was find out how much current draw was needed for a regulated output at each mode?

pseudoblue said:

HKJ, thanks for your reply, I saw your brilliant website guide for flashlight measurement.

I've compiled a comparison based on your data. I assume your are using your Fluke DMM right (which is a lot better than mine).

Click to expand...

Yes, I am using the Fluke meter.

pseudoblue said:

My 18650 has lower voltage than yours fully charged. And I left the light cooled for 5 minutes after usage. Just making sure the light is working before and after tests. Based on your comments and my knowledge, the different reading showed could be affected by DMM difference, temperature on LED and environment, battery temperature, state and voltage, LED lifetime reduction?

Click to expand...

There are many reason for different values. A lower battery voltage gives higher current draw, on a regulated light. Difference in Vf on the led, will also affect the current (low Vf gives low current).
Measuring 200mA on the 200mA range will probably give you a 0.2 volt drop in the meter (maybe more), and that is rather significant in a 4 volt circuit.
The actual current draw is probably in pulses and not all meters handles that equal well.

pseudoblue said:

LD10: mine --- HKJ's
1) 123.7 mA --- 90mA (my DMM started at 0.09 too, when the light was cool)
2) 360 mA --- 540mA
3) 2.3 - 2.5A --- 1320mA
4) Did not test on turbo ---- 2100mA

Click to expand...

I do not believe that the 123/90 has anything to do with led temperature, but more with the driver. I did a couple of measurements and most times the meter showed 90mA, but a few times it stabilized on 110mA.
The 350/540 might be partly because you battery has a higher voltage.
The 2.3/1.3 might be because you battery could not sustain the output voltage at this load and dropped down to a low voltage.

pseudoblue said:

Can't come to any conclusion yet. I've tried with a Powerex NiMH at 1.25v (low and medium only, the next day before post), the readings were like your eneloops, 0.09 and 0.50 above. Then, I've used an energizer max alkaline at 1.4v, low and medium only at 0.11 and 0.35 above. I'm guessing because lithium voltage was higher than both. That explains the boost only circuit. Now... because of this, it might also explain why Fenix does not recommend 3.6v batteries on their LD10, it may reach to higher amps that could be fatal to the electronics, make sense?

Click to expand...

The reason that Fenix does not recommend 3.6 volt batteries, in lights with boast only circuit, are because they are 4.2 volt of the charger and the led only need about 3.6 volt for maximum output.

pseudoblue said:

Btw, your measurement for LD10 is a relieve, I thought I may have done some damage, I actually inspected the LED for few minutes to see if there were any burnt signs, I had mistaken how it 'behaved'.

Okay... As for the TA21, since the current draw differs from 18650 and 2xCR123 because of its voltage difference, so the actual current measurement to the LED can only be done in between the LED and the electronics regulating that constant output, which is inside the bezel? All the measurements we did above was find out how much current draw was needed for a regulated output at each mode?

Click to expand...

You are correct, it is rather difficult to measure the actual led, you have to open the head and unsolder a connection to the led. The only light where you can measure the led current at the tailcap is lights with direct drive.

HKJ, thank you for all the clarification! :twothumbs I understand more now compared just hours ago.. you :rock:

:thanks: