[ GXB172 - 50W Single Cell 17mm Boost Driver! ]

My lumen tube is calibrated to the set of maukka lights. So it should be close. I have looked over the test done on the xhp35HI several times, if you look at TA’s test he hit 2710 lumen from a cold start, that’s the little ramp near the end of the graph pushed at 3 amps. I don’t think anyone has done a death test on the xhp.35.2 which I’m using in a highest bin in the datasheet E2. 590 lumens at 350 ma. TA hit 2710 with a xhp35HI and the HD would be even higher. I’m not absolutely sure of the results I got but I’m pretty confident it’s close in the reading. The xhp50.2 in the same setup (6v) read I think the highest I saw was 3200 lumens at about 15 amps on the input side, still using the stock switch with two blue springs. Should do better with the LO fet switch. The xhp35.2 switch is stock with 20awg bypass.

On the driver 12v configured GXB172, using a .020 feedback resistor. I saw 3.2 amps from a power supply. I was worried the led may experience the blue tint shift at that current but I have not seen any blue yet. I was using a 30Q battery which will sag unlike the power supply.

If that’s an older test from TA then it was probably when his Lumen Tube was reading too high. That’s also the raw led with no reflector or lens.

Are you saying you saw 2600 lumen at “turn on” with the driver modded to output 3.2A and it was powered from your bench psu and not a battery?

All those things do make a big difference. I typically ignore the first second or two and let the output settle for 15 to 30 seconds so it’s more in line with the ANSI-FL1 specs.

I would be curious to see the complete light measured using a battery and after the output starts to settle. (Some lights settle after 10 to 15 seconds, some might need 30 seconds)

It’s awesome the led didn’t turn blue at 3.2A.

BTW, are you saying the psu drew 3.2A on the input side? That sounds way too low. A psu supplying power to the driver might need closer to 13-15A at 4.2v to output 3.2A at 16 or so volts, right? How did you measure the 3.2A? I’m a little confused.

30 dollars is quite a reasonable price for a couple of unique drivers. If there is a sale, then I will buy two drivers, one 17 mm one 20 mm.

The 3.2a was measured with my DMM in series with the xhp35.2 using the power supply to power the driver.
I can check the 15 second and 30 second readings if that helps.
The lumen reading was taken from the S2+ using a 30Q.
It be nice if we had some test data for the xhp.35.2.
I could do the test but then it’s still a variable comparison between what the other established members have already done.
It’s hard to have a set standard if you have more than one standard. :slight_smile:

I re-read my other post, yeah I guess that was a little confusing. I wasn’t to clear with the description.
My fault JasonWW. :person_facepalming: Maybe I got it all sorted out now.

wow moderator007 this is crazy, I like it a lot! I cannot believe you manage to drive Gxb172 at 17A! This seem like pushing both driver and xhp35.2 to limit! Very impressive! I womder if there is any other driver (maybe 2S or 4s) to drive XHP35 to such high power . Your work result in even more power than this one: http://www.thrunite.com/tn42c-v2-rechargeable-led-searchlight/ expensive $270 flashlight

I charged the 30Q up to 4.21v fully charged and saw 2800 lumens at 19 amps at the tail. This was measured using a 87V that’s only rated for 10 amps. I checked it more than once to make sure. It holds 19 amps for maybe a second or two then falls quickly to about 15 amps.

This driver is a Beast, doing the math 19a x 3.6v = 68 watts on the input side. Its only for a second or two, so its not of any real use but it will make Dale jealous. :smiley:
I’ll have to do some more testing to see what the actual use numbers would be. I can’t test the high end on my power supply, because it only does 15 amps. I could up the voltage to give it enough input power but that’s not helpful in our use.

I don’t have an 87V, but testing high amperage in series with a DMM, with all of its additional resistance, is hard for me to trust. I tend to do all my amperage readings with a clamp style ammeter. Have you considered getting a inexpensive UNI-T UT210E or something similar?

I need one for sure JasonWW. I’m about spent out at the moment or I’d get one, maybe next week. I don’t hardly trust it either seems awful high. I do use my custom made gold plated banana plug soldered on 12AWG stranded wire about 6 inches long for the leads.
If you run the numbers based off the lumen reading say 16v x 3.2a = 51 watts out, that’s pretty much a guess but seems reasonable compared to the input side.
I’ll try to get a clamp meter next week to give a little more trust in the reading.
You got any recommendations on a reasonable priced clamp meter.

There is also possibility the current shunt inside of your multimeter actually heats up at such high current levels.

Meaning, if it gets hots enough to get higher resistance, the voltage drop will go up, and so will the current measurement.

The one I mentioned, UT210E, is about $30-$35 and is used by lots of people on BLF because of the big group buy here a few years ago. There may even be some valid coupon codes from Freeme or M4D M4X, but I bought mine in the US on ebay.

It seems like this models price is always going up. I think I paid about $28 a year ago, but the cheapest I see now is $36 with $40-$45 the average.

It normally comes with test leads and a nice zippered bag. It will auto turn off to keep from running down the battery, etc…

I only get this reading within the first second or two. From what I was reading on the 87V it has a .03v burden voltage for every 1 amp in the 10 amp range. According to that the reading is actual lower but heat would increase the reading if it’s actualy heating up in that short amount of time. The 87V also comes with a 11 amp fuse and it’s not blew yet. This is getting to technical for me, I’ll buy a clamp meter and find out if it’s close. :+1:

I was checking that one out over at eevblog, seems of good quality and about right for my use. Ebay has a few for 45 in the us, so I may order from there to save the long shipping times. Thanks for the suggestions.

Fin17 has a code for the UT210E at Banggood that drops the price to 29.99. Archive topic - Banggood & Fin17

I’m not sure how accurate these things are, I can get four different readings on the same circuit by changing which way the meter faces and switching from the positive to negative lead.

I have tried using a milli-volt shunt on a buck driver, the noise drove it batty. Regular meter, true rms meter and every setting on my scope were all wrong measurements. The only way to get sensible numbers with the shunt was to use one of those one dollar led volt meters from Banggood.

If you can do it without shorting out the driver, maybe measuring voltage across the sense resistor and doing a bit of Ohm’s law might give an accurate current.

Are you talking about a clamp meter? They are sensitive to direction. You need to zero out the meter and not move it around before taking the measurement.

If you do move it around too much the reading is still pretty accurate. I only get picky about about zeroing it out when I’m doing really small measurements like under 500 milliamps. In this really low range I sometimes switch to a DMM.

Meter is set in place and zeroed each time with the wire in the middle of the clamp at 90 degrees. I’ve used these types of meters for a long time and have a hard time trusting them with measurements below five amps so whenever I get a new meter I test it. The 210E does ok for what it is and will give you a decent ballpark number but don’t expect it to be precise.

I started out trying to do tail cap measurements with three or four different DMM’s and every measurement would be radically different for each meter. The higher the amps the worse they measured. I quickly gave up on using DMM’s.

I do get repeatable results with my UT210E, but I don’t have a high precision, and I assume very expensive, calibrated meter to verify it’s accuracy.

The typical things I measure are flashlights at the tail cap and they can vary due to the battery, driver, led, etc… You get the usual peak when you first turn it on and it typically drops a little as the seconds go by so I don’t need super high precision.

Plus a lot of folks on BLF use the exact same meter. So if it’s got a wierd curve to its measurements or an inaccuracy, then hopefully everyone else measures about the same.

Repeatability is important to me. If a light measures 15.1A@30s and I switch to a better driver spring and get 17.6A@30s then I know it’s probably a legit 2.5A increase. Even if the meters calibration is 4% too high for instance, it’s still showing a legit 2.5A increase.

Us flashlight hobbyists are not working in a laboratory, so we don’t need super high precision. We just need something reasonably accurate for our purposes.

For it’s reletively low cost and seemingly “accurate enough” measurements, I think the UT210E is a good deal. Just my opinion.

Suggestion: use a low value precision current sense resistor with 4 wire measurement since most multimeter are very good at voltage/milivolt range.
You can buy this slightly expensive but good FPR2A-0R005F1 no-inductance resistor, 5 milliohm. At 20A, this will only have 100mV drop. Not the smallest in flashlight where every little bit is important, but easy to measure with 0.1mV resolution with most cheap multimeter. Then you can just put this across tail of flashlight and do quick measurement.

Are you suggesting we do this once in order to determine how accurate our clamp meter is or are you suggesting we do this every single time we want to do a tail cap measurement?

The uni-t clamp meter look like ±(2%+3) specification so it should be ok. But at low current measurement or if you want to make lower cost and very accurate measurement (but with some burden voltage), it seem like using a good current sense resistor and multimeter is easiest way, so it can be a backup or different method.


Using a current shunt is how I personally roll.

I’ve now also built one, using slightly different components though.

I am having some issues though, I think I might have fried the OpAmp. I’ll have to try replacing it. The mess on the bottom right is some fooling around with the current sense resistor, and I got a bit sloppy.