I suspect my Q8 doesn't output all 5000 lumens - Fixed

Some two months ago got my Q8 and after some fiddling tested my tail current at 6 amps. From these forums and by the specs the emitters should be drawing some 12 amps. I figured the batteries weren’t up to par and ordered new 30Qs. Today I received the Sams and re-tested. Again 6 amps. Took a look into the bowels and all solders are fine.
Some pics:

In the last picture, there is no R1 & R2. Would this be a fault?

I’ve simplified this thread…

I’m quite new to all this and treading slowly.

Your images aren’t showing up.

My bad, should load now.

I still don't see any photos.

Here's a thread on how to post images on BLF:


Something went wrong - redoing:

It doesn’t work because what you paste as image url is actually url to website.

Quite a learning curve - Must manually add <.jpg> extension to deploy and somehow doesn’t work with album.

Current at tail:

Primary inspection of driver:

Switch connections:

Detail of board:

R1 and R2 are relicts from when the predecessor of the Q8 driver had a voltage divider. They were abondoned in the design so it is ok that they are absent.

I do see a flaw in the way you measure current though. Accurately measuring high currents with a normal type multimeter is impossible because of the resistance of the multimeter leads and resistances inside the meter. The Q8 normally draws about 16A, and I’m not surprised that with the added resistance you are only leftover with 6A. Even using very short massive leads will limit current enough to get unaccurate low readings.

Accurately measuring current is easiest with a clamp meter around one of the led-wires, or at the tail using a thick copper shunt.

A few years ago I made a short video on 4 ways to measure high current, to show how they differ. The flashlight in the video only drawed 4.6A but already the differences are huge! Conveniently, the next video that youtube gives you automatically is a comparable useful video from vestureofblood :slight_smile:

https://www.youtube.com/watch?v=\_K_46vs_Zpk&feature=youtu.be , or see below.
vestureofbloods video: https://www.youtube.com/watch?v=5Tm6-D2oBE8&t=177s


Thanks Agro - Thought the URL would automatically open with proper indexed photos/album.

And thanks Raccoon city for the link. Much appreciated.

Well, I don’t have a DC clamp meter, only AC – they are rather rare and pricey.

And as for direct test leads; 16 AWG, internal shunt w/in multimeters (have tried 2) can measure up to 20 Amps (not sustained though). The discrepancy between the two meters is .8 Amps (6.9 vs. 6.1).

As for the missing resistors, I suspected a divider or some combo parallel.

I’m dumbfounded by such a loss - some 10 amps. Something should heat up fast. At 4 volts that would be about 40 watts.

And then I re-verified the specs on CREE XPL HD and they consume 3 A. at 1250 Lumens. I’m looking at 12 amps total charge. But if the emitters are pumped to the limit of the battery capacities (FET driver) and low loss, 16 is plausible. Mind that I have heard many a time the figure of 16 thrown about. So I can acknowledge that as an upper limit (and higher light output).
I’m sure you are much more knowledgeable in this field than I, and don’t take my apprehension as challenge of wit, mere curiosity.

Can you connect driver to external lab supply?

My Pwr Supply only has 5 Amps output. Do have a second one at 20 amps but not for low volts as 3 or 4.

So looking over those videos djozz linked; in his test flashlight, some difference between 4.21 A. and 4.58 A. makes approx. 10 % adjustment.

In my test w/ the Q8 I’m reading some 6 A. when should be 12 (minimum) - that’s 100% error.

My leads at 16 AWG can support 13 Amps without too much loss (I believe less than 5 % in the electrical code but I would have to test that).

And apart from the empirical data, subjectively, the flashlight gives somewhat more light than my TK-15 (1200 lm) but not 4 times as much. (sorry to compare to a weakling, all I have at hand).

Best to have another member with a Q8 test with multimeter and post picture(s). Direct comparison. I’ll search the forums.

Did you read through the mod thread? Cleaning all the mating surfaces for the earth and spring bypass can make a big difference.

Yes, I had. I’m having a discrepancy of 100% or more….

Besides, by-passing with my set-up.

Looking for some pics of current draws with Q8. It may not be me, it may be the flashlight.

Did you take into account the non-linear perception of light? Rule of thumb often quoted is it takes 4 times as much light to look subjectively twice as bright.

For example I can take 2 Convoy S2+ models, which are roughly 800-1000 lumens each, one warm (4C) and one cool (1A), one 6x7135 one 8x7135, and when I put the two beams together it looks just like my neutral white BLF A6, which, unbypassed, should be around 1200-1400 lumens.

Without that comparison you can see the A6 is brighter, but you would never say it is twice as bright, yet it is indeed fairly equivalent to the two Convoys together.

With how many amps the q8 pulls you’ll never get a accurate reading with that meter. As explained above. There have been multiple threads showing the differences between using a clamp meter and leads. Leads are always way off. Especially over 5 6 amps. It’s not the answer you want to hear, unless you get a clamp meter or take it to a friend who has one or send it off to a member here to test. You’ll never get close to the what the real Amps are.

So what your saying is your q8 doesn’t get hot on turbo?

Leads don’t make for 100 % and + error.

Yes, I have. The Q8 should be much brighter than my TK-15, yet only slightly outperforms. Both same type emitters.

Have you tested the current draw on a Q8?
Seems everyone thinks my error - yet I’ve taken the time test and ponder at the problem. The data does point to a discrepancy.

I appreciate your strong attempts to find a solid convincing answer. I have no advice, but I am intrigued nonetheless. I hope you find what you are looking for. I just was thinking about buying a Q8 so that’s why I’m here haha.