Hi
a fluke clamb meter and a cheapo yellow unbranded.
I trust both,cause they are showing the same 
But a clamp meter is the best choice.
Regards Xandre
Kennybobby, but as thefreeman said, we’re affecting what we measure in a way that depends on driver and LED. Calibration is not possible with just the DMM in focus, only the error can be reduced by limiting the resistance. I find the idea to measure the voltage drop over a small resistor intriguing. But he might not have something like an Aneng AN8008 in mind when mentioning a precise DMM 
.
Oh well, just bought a clamb meter.
hahaha.. Unheard.. sorry about letting you buy a clamp meter!
Which one did you buy?
a word about accuracy
from where I sit, with no experience measuring with a clamp meter… all those measurements are accurate enough, and the variation between them is not significant, to me.
I think some people are overly invested in the idea of “accuracy” when in fact there are variations and differences in the measurements, that are due to variations not only in the tool doing the measuring, but also in the specific individual light being tested.
I do not expect accuracy to mean identical, when comparing data from different sources.
A uni-t 203+, I’m sure it is among the least precise, but it was really cheap. Hope to get it to half an amp right. Just to measure max. current.
I don’t trust my current readings at high currents.
I just use a shunt.
My nickel’s worth:
When I first came online I had the same issues as Chibi and opted for a clamp meter. Later I better understood the why’s and why not’s. In a nutshell, not enough voltage to push the current so the Vdrop of internal components/cables affects the readings beyond acceptable levels.
As for the clamp meter taking time to stabilize and the zero-reset – these use a HAL effect sensor which works by magnetic fields. There is a settling period depending on generation (maybe a few seconds). The clamp picks-up stray fields and the wire placement also affects the reading (background EMI).
I’ve opted for a BSide ZT-QB as it was on promo for less than the Uni-T 203+ 210E. I’m very happy with the results and repeatability of measurement – albeit the wire placement is detrimental. It can be seen the device is intended for DC measurement by default. The other settings have to be manually configured.
Addendum:
Chibi was inquiring as to which 7135 drivers would be used in the S2+ if the readings should be 2.80 or 3.40 Amps. This got me looking into my S21 (near equivalent – someone might clarify the difference) and got 2.91A w/ BSide clamp vs. 2.48A w/ AmpProbe DMM (not Fluke quality). I couldn’t find any info on any designation for the 380mA driver other than it would seem the 350 mA is a ballpark value ranging from 340 to 380 mA. Perhaps the higher binned ones are bundled together or someone deemed to market the 350 to its higher spec?
As the clamp meter accuracy is ±2% +30counts, it couldn’t be conclusive which regulator is used.
TL;DR – clamp meter gives a good ballpark value, better than the dropout from a DMM.
If price is not the utmost concern, the Uni-T UT210E has better specifications for clamp meter current measurements typical for flashlights compared to the Uni-T UT203+.
UT203+ lowest DC current range is 40A with a resolution of 0.01A and an accuracy of ±(2%+5)
Only other DC current range is 400A with a resolution of 0.1A and an accuracy of ±(2%+5)
UT210E lowest DC current range is 2A with a resolution of 0.001A and an accuracy of ±(2%+8)
Middle DC current range is 20A with a resolution of 0.01A and an accuracy of ±(2%+3)
Highest DC current range is 100A with a resolution of 0.1A and an accuracy of ±(2%+3)
UT203+ Manual:
https://www.uni-trend.com/uploadfile/2019/1122/20191122015258282.pdf
UT210E Manual:
https://www.uni-trend.com/uploadfile/cloud/English%20manual/General%20Meters/UT210E%20English%20Manual.pdf
I have two Uni-T UT210E meters which agree very closely with each other and I use them more than my Fluke 77 because it does not have a built-in clamp meter (but it can measure current using test lead cables which the UT210E cannot).
The UT210E is the most recommended budget clamp meter for several reasons. First, it has very good performance for the price, works great with DC and has sensible counts and current ranges. Second, you can mod the firmware, change the default to DC mode (from AC), tweak some other parameters and make it even better. Third: It is inexpensive, you can get it for less than $40 sometimes (two years ago there was a listing on Amazon DE for only 35 € IIRC – right before the checkout it was sold out).
And should the Convoy read 2.8 or 3.04?
I know 8*350 =2.8
but what if it's actually 8*380= 3.04?
I think I give up.
I've been looking at those shunts.. but have no clue what to get.. and I won't buy from Mouser, with their crazy expensive shipping options :D
I don't know whether to trust my 200mA setting or 10A setting on my DMM (or either of them), so I'll probably stop sharing Amp readings in my reviews.
The DMM readings with probes have lower values than the clamp meter from your analysis. Hence, these added connections lower the current readings as they too are resistive.
If you move up a couple of posts (link) I’ve added some info to my original post. It may be helpful.
A clamp meter is the way to go. You would have to make a four-wire method to account for the cable’s impedance even using a precise shunt.
Thank you very much for your reply. I just have the feeling that the clamp readings on the lower modes are just a bit off. 0.05A seems to be quite a bit higher than 0.01A for example.
At higher Amps, I probalby trust the clamp readings more. BTW. I used a solid copper wire about 20cm long (about 8 inches). Would a shorter one be even better?
And how about the DMM cables.. What if I get some, and shorten them to let's say 50cm or so.. wouldn't that help as well?
I don't need 100% accurate readings, but the differences are just a bit too much.
Not sure about the 350mA vs 380mA. I see that Fasttech sells 350mA and 380mA. When I look at mine, they 2 of them read: 7135 38S, another says: 7135 38Y, while the other visible one is just blank.
Not sure what they mean, and if that could be an indicator they are 380mA
It’s not only the probe wires that come into play. The internals of the DMM has a correcting multiplier (in my era of analogue meters/electronics) resistor for the shunt. That also adds to the impedance.
As for the tailcap wire lengths, I just used some 14 AWG muti-strands (for flexibility) of a convenient length (~9”). This isn’t high-end audio with Monster cables and superfine gold plated strands). Albeit, If I do find my leftovers, they would work better.
As for the lower currents, can’t be of help. My BSide has only the resolution to 2nd decimal and then has a 30 count error. Not of the required precision to reliably concur any values.
I don’t know of those 7135s. If someone (or myself if I wasn’t too short-sighted) would look them up and see if there is such a binning for the 380 mA or just marketing hype.
All I seen to get from some spec sheet is 350 to 380 mA – somewhere in a foregone search.
Don’t. A rough measurement is better than nothing imo. Why wouldn’t you trust your Fluke I wonder?
Why would anyone care a lot about low resistance springs or bypassed springs but in return not have the same requirements/care from the leads of the DMM?
It’s 2 long wires used for measuring current in series with a Low voltage Non-constant power supply (a 3.7V cell), so obviously those long thin wire add more resistance in the circuit.
There is of course things that confuse many, why when using short and thick leads then input current gets lower with certain flashlight and not higher. Take a buck driver for example where with 4.15Vin the input current is lower than the output current, oversimplifying a hypothetical: you measure 1.5A at the tail but the LED gets 2A and that is correct. If you add more resistance in the circuit (worse and longer leads) you may read 1.75A at the tail while the output current it is still 2A for that particular buck driver.
i thought you were trying to measure DC currents, but that was a bad assumption.
If the Convoy driver is using PWM to drive the 7135’s, then you are trying to measure AC, but not a sinusoid rather a high frequency square wave pulse with variable duty cycle. There will be quite a big difference in trying to measure DC or AC currents with any of your devices.
No DMM or clamp meter can accurately resolve such a high frequency signal, only an oscilloscope can show what is happening. All of your tools can only give some sort of average based upon whatever low pass filter is used in each device, the sampling rate, etc.
Same goes for a current shunt, it will respond to the HF current but the voltage measurement of the drop will be averaged by the voltmeter.
Very keen observation there. I was presuming he (Simon) didn’t use PWM on his linear drivers. But would that be on some models only? Store’s down, can’t backcheck.
Addendum:
S2+ low mode – 8 x 7135s
Most of this stuff goes over my head.. so I think that sharing Amps is less useful..
really considering to not share any Amp readings anymore..
Just tried with solid copper wires of about 20cm, and set the DMM to AC... it's impossible to measure the 3rd or 4th mode it will just go back to first or second mode looks like...