I have ordered a power bank with led, the led is a standard 1W Chinese LED with a tir.
Here is a picture of what I guess is the “driver”, it’s the bottom of the whole electronics. The led gets switched on with a long press of a electronic switch which also enables the power bank features.
The two resistors are parallel and have about 2.5 ohm resistance, the small device has 2300 printed on it.
I guess it is a transistor with a current reducing resistor to drive the led with some hundreds of mA.
What do you think am I right?
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First mod thought, reducing the resistance increases current. problem is I might burn something I can’t fix again.
Second thought additional driver and additional switch for it. Problem switches are huge and I have no space. Additional switch on outside is possible but ugly.
Third thought, bigger transistor.
Or some 7135, would it be possible to use maybe a 4x7135 driver and use the existing transistor to enable the 7135s?
Is this possible? Just remove the mcu and wire the power line to the enable pin?
Edit: just measure a bit, it seems that the positive line is directly connected to the led and the negative is switched.
Measured while turned of between bat- and led- 0.8V
Might still possible with a electronic switch programmed nanjg…?
i think a pic of the reverse side might help some people…
i’m no electronics expert, but with time you can at least test the effect of the sense resistor
read/measure the stock resistance, connect a trim pot (inf in parallel?)… then determine if it’s the one by slowly adjusting trim and noticing current/temp change.
my guess is in the end you will be limited by the host’s heatsinking at any rate, so for a small gain it might be worth it…
btw, have you measured the stock output current connected to a cree yet?
So I have further tests, it is a npn switching the negative line like you painted it down.
With XML I get 0.4-0.45A with battery at 4V. I added another resistor/pot and got 0.85A but I am sure the transistor will burn if I increase the current.
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The base contact is not strong enough to deliver the voltage/current to enable the 7135s. The voltage is there but breaks in if I connect the enable line.
Another thing I haven’t thought of is that if I would make it like on your picture the 7135 are always connected to power and this will cause some quiescent current…
I have no measured number but from the datasheet I guess four will take about 0.5mA=>8month…not super bad but you know less would be better.
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I have checked my spare parts and I have some bc817 npn in sot23 laying around, can handle 0.5A.
So I checked opportunities and the best way would be a transistor with more power(e.g.: FMMT617)…so if I need to order anyway The stock transistor isn’t so important anymore……then I went the dumb brave way and did this
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Worked on 1A a while, then I thought maybe 1.5A would also work and it worked…
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I soldered two additional 1ohm on top of the resistors(resistance before 2.5ohm, after 0.4 ohm) and got 1.4A. Also I fujiked a very small piece of copper on top of the transistor. It run for 20 minutes while I checked possible optics. Nothing burnt this little guy is tough. I now charge the battery and test maximum current.
All test were done with a XML first gen.
By the way I roasted a Alusinkpad while reflowing a xml2 S6 on it, between the dielectric layer with the traces and the star is now a gap, the colour is not white anymore and it smells like burned electronics…
Couldn’t wait until the battery is fully charged, stopped charging and started another burn in…
Maximum current was 1.69A, decreased to 1.4A in 20 minutes.
Copper shim gets hot just tested it with my finger and I guess it is around 72.7°C, the whole circuit is warm( from charging too) and it smells a bit “warm”.
Still testing with XML and not assembled.
Edit: 1h and 15min, now pulling 1A. It works. 2h 0.76A, battery 3.25V.
Just want to inform you(even if nobody has interest)that everything worked.
Despite the tir got a bit dirty, the host has cheap anodizing and tiny gap between the parts I am super glad how everything worked.
The xml2 S6 has super nice colour rendering(was the first I ever used) and a very useful amount of light, current is about the same as the tested XML. The USB charger charges my phone like a breeze and the single button UI is superb.
I used an old alu star grinded to the inner diameter of the tube underneath the led as additional heatsink and a big bunch of Fujik to fill the gaps and make additional contact to tube. I also added a GITD oring around the lens.
Glued the copperpiece with AA on top of the transistor and covered all with AA, grinded the tube a bit so that the thicker transistor fitted in and finally fujiked all to the tube while assembling it. Gets hot from both ends :bigsmile:
Insulated the PCB and solderpoints to the battery with plastidip, I also shrinked an additional layer around the battery, I used the paper discs on the poles and fixed them with insulating tape.
Everything fitted nicely together, no hassle with the wire length, battery thickness or so, there is enough room left.
The current is not regulated so it dims with decreasing battery voltage, I measured the current after charging the battery with the inbuilt PCB (4.16V) it was 1.7A, decreases fast to around 1.4A for a while then goes further down. That’s exact how I wanted it.
Used it yesterday night to play around and it is now a power bank with flashlight like intended.
The case is just the same as shown on the kaidomain pictures, the top and bottom cap are a bit different anodized and it has some scratches from assembling and putting it in and out my maxpedition gear…
I thought about to cover it with an additional paint or so but I decided against as I will carry it with me in a case every day and wanted no shelf queen.
