GFS16 - Battery Indicator Tailcap Light & 1mR FET Tailswitch! (Rev B)

Flashlight Modding and DIY Parts
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Today I complete my Gfs16 mosfet tail switch and led tail light with battery low indicator!! Here is the result. After soldering both pcb, first I test the led board.

I use warm white led for nice glow effect. Since this is good, I solder both board together, + to + and - to -. Then I understand why loneoceans make oval cutout on pcb, since the battery need to stand up and fit through. This was perfect fit!!

I use thick copper spring from noctigon and I use lfpak33 mosfet in the middle. Finally I test low battery indicator with power supply and it work very well, turning red when battery is low, and turn off below 3V. very happy.

When I first measure battery, it is at 2.5V. Then once I finish the Gfs16, I connect it to 4V powersupply and let it charge battery for half day, and the battery voltage is now about 3.0V and going up. Because it look like it is charging through 2.2k resistor, it will take a while to charge full.

Next, I realize I make big mistake.

The Convoy S2+ is not all the same! Sad that my gray S2+ is actually using black rubber boot and not working with stainless steel switch!! So other people trying, you need to be careful! Lucky that I bought clear rubber boot in the past so I use that instead.

Before I install into tailswitch, I make some measurement.

Resistance Measuremenet

  • Original convoy switch - 47.2milliOhm (lowest measurement, click a few times get very different result..)
  • Original convoy switch with wire bypass 22 awg - 15.2milliOhm
  • Gfs16 mosfet switch with battery at 3.0V - 6.4milliOhm

This measurement include the spring. I use power supply to generate 5A constanct current and measurement taken using multimeter for voltage, to find actual resistance.

My tiny battery for above experiment is 3V, maybe waiting a bit longer will be 3.3V, which drive gate of mosfet in tailswitch, so maybe in the future performance is even better. This result is good enough that I do not use bypass spring.

Last I adjust Gxb172 and add bypass resistor of 220 ohm using 0805 resistor solder on the jumper pad (ground side) and the center spring.

Finally my entire Gxb172 flashlight is COMPLETE!

Review for gfs16:

This project is easier to solder together than Gxb172. The hardest one is soldering the tiny mosfets on the led board. The rest is easier than Gxb172. I am not sure why schizobovine have problem with battery, since mine work first time.

Same as Gxb172, I recommend to use magnification to solder with smaller solder tip, thin solder wire. I only use hot air for the lfpak33 mosfet.

Before assemble, I suggest to make sure lfpak33 have no short, battery have no short, and led light system voltage working with power supply. For me I use oshpark 0.8mm pcb for both and they fit Convoy S2+ good.

I recommend the hobby maker to order more tiny mosfets before you blow them on the floor, and I recommend making sure you buy the correct Convoy s2+ light to make sure it fit the stainless steel switch! Make sure you handle tiny battery carefully! Also I use very thin wire (awg30?) to solder + and - pad together. I make sure I keep the switch screw tight, but not overtight to prevent pcb from breaking because it is not as strong as aluminum washer.

Difficulty - 6/10

Cost - 5/10

Result - 9/10! Very nice! I remove one point so it is not perfect so loneoceans can motivate to improve it

I recommend loneoceans add more led on the tail to make ring of light, but I understand how it may have no space since need two bank of leds, and any smaller is harder to solder.

Big thank and appreciation to loneoceans for this cool project and for everyone here who also make their own and inspire me to build this successful project!!

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Is it too late to get on the list for a switch?

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No, not at all.

There’s one left.

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Actually, in my experience the result is much better with a clear rubber boot. The stainless switch requires 3-4x as much light/power and still barely shows through the tiny gasket. It’s not worth it.

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Please put me down for 1 blueswordm.

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If still available I would like to purchase one.

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Great work. I ordered the GFS16 boards with the hope I can solder such small pieces. If I fail, at least I got BlueSwordM giving it a go. I want it mainly for the reliable power capabilities. Not so much for lights. Has anyone tested the upper limit of these? Total novice here but wouldn’t that mosfet get fairly hot. Especially in the context of its vicinity to the switch. Maybe not such a concern, since you could only run a 50 watt led for so long.

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I think the limit for reliability is 30A.

At a Vgs of 3-4,5V, the max resistance if 3,00mOhms.

That means, at 0,003Ohms of internal resistance and a driving current of 30A, that would mean power dissipation would be around 2,7W.

For the MOSFET, that should not be an issue if it is soldered down well. No light has reached that power consumption yet for continuous operation.

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Very nice job clientequator, a big :+1: from me.
It looks like hot air may do the trick. I’m just glad loneoceans didn’t use another DSBGA4 Digital Temp IC if you know what I mean. :stuck_out_tongue:
I’m still waiting on Oshpark. Hopefully I’ll have the boards in a day or two.
Thanks for the resistance measurements. This should help out the GXB172 alot.
I’m really impressed with the low resistance.
Thanks for sharing and very well documented clientequator. :slight_smile:

I’d like to give a big thanks to Loneoceans also for sharing his creations with the members of BLF. :+1: :wink:

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Thank you! Yes this project much easier to solder than Gxb172. if you can do Gxb172, this is no problem.

After using this lighted switch at night and discuss with moderator007, I agree that the design I build is too BRIGHT at night! For the white led on tailcap loneoceans recommend 30k resistor, but this is because he is useing stainless steel switch which has thin gap for light to go through. moderator007 recommend using 100k resistor instead when using clear rubber cap like what I use. Maybe I will adjust it next time!

145

So, I’ve received my GFS16 PCBs. I now just have to wait for the Omten 1288 switches to come by.

Now, a question.

Where do I actually put the super cap/battery on the PCB that one of the members actually modified?

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I would assume it goes where the battery goes (B1, top right pic) but I’m no expert here.
My boards still haven’t made it yet. If you get the super cap working, please post up your results. It might save me some headache.

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Oh yeah, forgot to say the problematic PCB is on the left.

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Schizobovine used this battery retainer. https://www.digikey.com/product-detail/en/mpd-memory-protection-devices/BK-414-TR/BK-414-CT-ND/2079911
So my guess is that’s it dead in the middle, battery to the round circle and the two rectangles hold the retainer and the switch goes on top of that I guess.
Center circle should be negative and the retainer positive.

149

Oh, then the build is easier than I thought. I did actually know that the cell was in the center, but wondered how it would get retained.

So, here are the bill of components:

0,70$US each for the boards.
2,33$US for the supercap. Still cheaper than the lithium ion battery, and much safer to solder.
0,38$US for the LDO.
0,24$US for the SMD cap.
0,06$US for the resistors
0,45$US for the schotky diode
0,87$US for the FET
0,40$US for the Omten switch
0,40$US for a single BeCu spring, and 0,80$US for a dual spring

So, if everything goes well, the FET switch should cost, with labor, about 7,00$US.

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:+1:

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What battery fits in the holder design by schiobovine? It seem to me that the battery is under switch? This maybe cause the spring to sit out a little high from Convoy S2+ housing because the battery holder is over 2mm thick. In this case, the aluminum case of flashlight may not be in good contact with aluminum of the back of tailswitch. Do you know what battery you are using for that design?

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I’m using a supercap for the design rather than a battery, and I’m not going to use a holder for it for the schiobovine design since it’s actually pretty easy to connect it directly to GND:
https://www.skilhunt.com/product/h03-rc-magnetic-rechargeable-led-headlamp/

It’s also safer :slight_smile:
And I can use a lower value resistor to charge it since it can be charged faster.

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I built one GFS16 fet switch with the rechargeable battery and 2 with the Super Cap that BlueSwordM linked from digikey.
The Super Cap is much easier to work with. It comes drained at .001 volt. It doesn’t care if you short it with tweezers. It with stands soldering very well. You can bend the tin tabs without having to worry about shorting and destroying it. I recommend trying the Super Cap for anyone who might be having trouble with the battery. The Super Cap is almost the exact same size as the battery.

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This is the SC (super cap) soldered in the same position as the battery. The only difference is the SC is backwards with the casing soldered to the smaller outside pad.

In this pic you can see the SC sticks up above the switch and will hit the original S2+ washer or lighted GFS18. That’s the reason Loneoceans added the oblong hole in the GFS18 led PCB. If using the washer it will need to be modified with a hole for the battery or SC to stick up through, then some way to hold the washer in place so that it doesn’t spin hitting the top of the battery and ripping it off the PCB when installing the switch holder ring. Maybe glue or epoxy.

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I came up with a different solution that could work without hitting the original washer or having to have a hole in anything. I only tried this with the SC because it seems a little smaller and is a whole lot easier to work with.

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The tin pads can be bent if very gentle, so that the battery can lay back towards the switch. Its a little tricky to get the right bend, and a little tough to solder on the outside pad. It can be done though. I bent the the center tab of the SC on about a 45 degree angle and the arrow looking tab on the case I just cut off as it’s not needed. Laid the omten switch in position and checked clearance. Done that a few times bending the tab back further until I had good fitment. Once the SC was lower than the switch shelf I placed the SC in the right position for contact to the pads with no shorting once soldered. I then applied a small drop of UV glue in one corner of the SC tin tab on the big PCB battery pad and turned on my UV light and presto its held in place. Soldered the big pad first with a small soldering tip and then very carefully soldered the case to the small outside pad, with just enough solder to make a good connection. Doesn’t need much as this is very low current.

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Now it will clear the washer or GFS18 with out shorting or having to have a hole for clearance.

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I used the Q2 LFPAK33 and added the larger Blue spring. If you use the Q1 PowerPAK SO8 then this will make the switch assemble taller but adds more clearance of the SC or battery because the switch shelf is higher. This option would be the easier to build without having to lean the SC or maybe just slightly to clear the washer or GFS18.

I changed R1 to 500 ohms and the SC takes about 1 to 2 minutes to charge up before I could operate the GXB172 in turbo. This is after the battery is installed in the light and screwed together in the off position. The lower modes would work but turbo flashed 3 times indicating low battery voltage, after a minute or so of being off, turbo began to work when the SC became charged. If the light was drawing a few amps I suspect it would work within a minute if the switch is in the off position. On the second SC GFS16 I built I used a 220 ohm for R1 and after screwed together and being off, turbo will work between 30 to 60 seconds. Might could go even lower but this 200 ohm range seemed very usable to me.

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Yep, that looks like really nice.

BTW guys, I’m just waiting for the Omten switches to come to start building these FET switches.