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

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edited with new info

Hi loneoceans, I’m planning on changing some values to the following…….

Vbatt x R4 / R3 + R4 =Vref
• When battery level drops below 3.30V, Light up Red.————————- 3.3V x 360K/116K+360K = 2.5V
Vbatt x R6 / R5 + R6 =Vref
• When battery level drops below ~3.00V, Turn off all LEDs.————— 3.0V x 360K/ 72K+360K =2.5V
Does this look right or should I decrease R4 to keep R3 at a lower value, sorry I looked up the datasheet and i couldn’t figure it out, what’s the rule when setting R2 value in a voltage divider circuit pertaining to the MAX9052BEUA+ datasheet? Also how do I factor in the voltage drop across the bleeder resistor to have compensated values for R3&R5…. Vi= Vt x Ri/ RB+R4+R3

So to set a trigger point of 3.3V, bleeder resistance= 100R, R4=360K, R3(compensated for bleeder)=115K. drop across R4= 2.5V

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If any one need help setting different trigger point or led brightness, just PM me.

note a 100ohms bleeder is required… any higher value messes up the ref voltage for the compactor even if your calculations are correct, the video loneoceans posted implies that he’s hooking up a bench power supply without any resistance and I’m sure his driver must have some sort of resistance from positive to ground other wise it’ll short circuit, also not shown is an internal hysteresis of about 0.02V where both channels are trigger.

Also note that the 100R bleeder will be in parallel once the flashlight is turned on.. consuming 37mah average, a minimum of 1/5 watt power rating required, 1/2 watt recommend for reliability to cope with the heat generated from the led, easily available in 0603 package.

Lexel
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I would add a 2.8V LDO to the tail cap, so you get constant brightness of the LEDs

R4/R6 should be large to have a low current over the voltage divider, so do not lower them
their current draw is even present when all LEDs are shut down

The reason the calculated brightness varies from calculated resistors id that the bleeder consumes voltage,
the drop differs with the current drawn from the LEDs, so constant current is at least easier to calculate

for example if your 6 LEDs draw together 0.3mA then on a regular 100 Ohms bleeder the voltage drops 30mV
Each LED draws 50uA
LEDs are powered over a 2.8V LDO so we do not have to mess with different currents on different battery voltages
LV 3.2V
SD 2.9V

on this example the current drawn of the 3 regular LEDs is removed when you hit 3.2V
so the current drops from 0.3 to 0.15mA also the drop on the bleeder jumps from 30mV to 15mV
so the comparator notices when 3 LEDs shut down a voltage rise of 15mV
The question is how big is the hysteresis of the comparator is this basically dictates how big the bleeder can be

With such a low hysteresis not really big LED currents or big bleeder of 1kOhm are possible without flickering

I looked in the datasheet of the comparator and adding 2 resistors per channel from Output adds hysteresis,
this would mean a bigger bleeder possible

I also noticed the comparator shows 130uA supply current which is more than many low brightness tail caps consume, so storing the light without checking tail color is not a good idea

Using an LDO would pretty much remove the need of a comparator with internal reference

[Reviews] Miboxer C4-12, C2-4k+6k, C2, C4 / Astrolux K1, MF01, MF02, S42, K01, TI3A / BLF Q8 / Kalrus G35, XT11GT / Nitefox UT20 / Niwalker BK-FA30S / Sofirn SF36, SP35 / Imalent DM21TW / Wuben I333 / Ravemen PR1200 / CL06 lantern / Xanes headlamp

[Mods] Skilhunt H03 short / Klarus XT11GT,

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Thanks Lexel, makes a lot of sense… I finally got it to work exactly as I want it, changed LEDs current & R3/R5 – R4/R6 values works good with no hysteresis noted, ill upload a video in a little bit. I have the compactor set for 3.7V LV and 3.5V SD.

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old values showing hysteresis

new values, works better
contactcr
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Video shows off the switch design nicely. Good job

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contactcr wrote:
Video shows off the switch design nicely. Good job

credit goes to loneoceans, its his design, hope he shows up again with his driver release!
Lexel
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I have made a new enhanced version

2×3 colors above first shut down
1 single LED for low battery signal

28uA 2.8V LDO up to 5.5V
dual pad for a 10V LDO for 2S lights
capacitors for LDO

2.8uA comparator without reference voltage, significantly reduced standby drain
the reference voltage comes from the 2.8V regulator and a voltage divider

added for each comparator a hysteresis voltage divider, so a larger bleeder like 470 or 1000 Ohms should be possible

17/20mm version

20mm with trimmers for LED brightness

[Reviews] Miboxer C4-12, C2-4k+6k, C2, C4 / Astrolux K1, MF01, MF02, S42, K01, TI3A / BLF Q8 / Kalrus G35, XT11GT / Nitefox UT20 / Niwalker BK-FA30S / Sofirn SF36, SP35 / Imalent DM21TW / Wuben I333 / Ravemen PR1200 / CL06 lantern / Xanes headlamp

[Mods] Skilhunt H03 short / Klarus XT11GT,

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Wow.. awesome job Lexel! Did you just design this in the past 24 HR !? Well when is this gonna be available to buy?

djozz
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Wow.. awesome job Lexel! Did you just design this in the past 24 HR !? Well when is this gonna be available to buy?

Lexel is from a different planet somewhere distant in the universe, the life forms from over there work at a much faster clock rate than we humans.

“I used to think that top environmental problems were biodiversity loss, ecosystem collapse and climate change. I thought that thirty years of good science could address these problems. I was wrong. The top environmental problems are selfishness, greed and apathy, and to deal with these we need a cultural and spiritual transformation. And we scientists don’t know how to do that.”   (Gus Speth)

wildstar87
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Apologies if I missed it, but where did you get the stainless steel switch?

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wildstar87 wrote:
Apologies if I missed it, but where did you get the stainless steel switch?

If your referring to the switch on page 1 of this thread…, they come with the flashlight, I think they are standard on the red and clear anodized s2+.
contactcr
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If, like me, you have one of the S2+ lights with a black metal switch you can buy the stainless metal switches from Banggood and the light will shine through the clear gasket (barely). So my Tan/Sand colored S2+ has a stainless metal switch I replaced and then added a lighted switch to.

wildstar87
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Yeah that is the switch, do you have a link on Banggood?

contactcr
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wildstar87 wrote:
Yeah that is the switch, do you have a link on Banggood?

https://www.banggood.com/Convoy-Metal-Clicky-Switch-DIY-For-S2-RedGreenB...

It only works on the ones already threaded for a metal switch though.

wildstar87
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Thanks!

vinte77
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So Lexel, are you going to have these switches available for purchase?

Firelight2
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vinte77 wrote:
So Lexel, are you going to have these switches available for purchase?
Yes… where’s the group buy on these switches? I need at least 10!!!

skinny_tie
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Lexel wrote:
I have made a new enhanced version

2×3 colors above first shut down
1 single LED for low battery signal

28uA 2.8V LDO up to 5.5V
dual pad for a 10V LDO for 2S lights
capacitors for LDO

2.8uA comparator without reference voltage, significantly reduced standby drain
the reference voltage comes from the 2.8V regulator and a voltage divider

added for each comparator a hysteresis voltage divider, so a larger bleeder like 470 or 1000 Ohms should be possible

That’s awesome Lexel. Are you planning to sell these?

The_Driver
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Will the FET switches also fit in the tailcap of a Convoy C8 v2? Does anybody know how that lights tailcap compard to the one of the S2+?

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The_Driver wrote:
Will the FET switches also fit in the tailcap of a Convoy C8 v2? Does anybody know how that lights tailcap compard to the one of the S2+?

Convoy C8 v2? Do you mean the new Convoy C8+? if that what you meant… I should have one arriving in few days, I’ll check and let you know.
The_Driver
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The_Driver wrote:
Will the FET switches also fit in the tailcap of a Convoy C8 v2? Does anybody know how that lights tailcap compard to the one of the S2+?
Convoy C8 v2? Do you mean the new Convoy C8+? if that what you meant… I should have one arriving in few days, I’ll check and let you know.

I meant this one , not the plus-version.

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Just checked with FET switch alone and FET switch + lighted pcb and they all it fit perfectly.

The_Driver
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Just checked with FET switch alone and FET switch + lighted pcb and they all it fit perfectly.

Thank you! Great to know!

This means mine will go in this light from kiriba-ru which uses the body tube of the C8:

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Cool, let me know how that works for you,

Has anyone else used this FET switch, they seem not to last more than 2 weeks before they stop working… for some reason the coin cell just craps out. ill Raise R1 value to 4-5kohms to slow down the charging current and see what happens.

Schoki
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The charging current should be fine. But maybe the discharge current stresses the cell too much. The maximum continuous discharge current is 0.1mA.
Try increasing R2, by a lot.

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Schoki wrote:
The charging current should be fine. But maybe the discharge current stresses the cell too much. The maximum continuous discharge current is 0.1mA.
Try increasing R2, by a lot.

I thought about that as well.. but the weird thing is that they just die on there own, the light would be sitting unused for a week with a fully charged 18650 in it, than the next thing I know when I try using it is its dead, the coin cell voltage is at 0. anyway I have some more boards on order, ill increase R2 like you said and see how that effects the battery and the FET gate.
Lexel
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old values showing hysteresis
new values, works better

I got a major problem here on my builds I can not firgure out
I removed hysteresis and adjustable reference, but it is still odd

If I put the board on my PSU and it is on I can connect it it is lightning up, reducing the voltage makes it go red and then turn off
But when I increase the voltage it does not turn on anymore or go from red to the other color

I measured the voltage on the ina+ and b+ and it is higher than the reference, but I got to disconnect the PSU to turn it on again

PS

finally found it running the comparator on 2.8V LDO with a higher voltage from your voltage dividers at levels above the 2.8V did not work
running the Maxim 9022 with 2.8V reference from LDO and Vcc on battery supply works now

seems it can not compare higher voltages than its Vcc or close to it

[Reviews] Miboxer C4-12, C2-4k+6k, C2, C4 / Astrolux K1, MF01, MF02, S42, K01, TI3A / BLF Q8 / Kalrus G35, XT11GT / Nitefox UT20 / Niwalker BK-FA30S / Sofirn SF36, SP35 / Imalent DM21TW / Wuben I333 / Ravemen PR1200 / CL06 lantern / Xanes headlamp

[Mods] Skilhunt H03 short / Klarus XT11GT,

Lexel
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So final results for the Tail and Aux boards are found
2S atm untested

Vbatt x R4 / R3 + R4 =Vref
When battery level drops below 3.30V, Light up Red.
3.255V x 360K/270K+360K = 1.86V

Calculate divider for LDO reference R8 360k fixed for one and 2S
1.86V=2.8V*R8/(R7+R8)
R7=0,531*2.8*R8-R8
R7=182k

on 1S is max 4.35V, the calculated reference voltage should stay below 2.5V for 2.8V LDO
4.2V x 360K/270K+360K = 2.485V

2S
is max 8.7V, the calculated reference voltage should stay below 2.5V for 2.8V LDO
8.7V x 390K/1M+390K = 2.44V
6,63V x 390K/1M+390K = 1.86V

Vbatt x R6 / R5 + R6 =Vref

When battery level drops below ~3.00V, Turn off all LEDs.
for 1S
3V x 360K/220K+360K = 1.86V
for 2S
5.88V x 390K/845K+390K = 1.86V
calculate like above just with another battery voltage 2.8-3V

The tail boards run with an 1kOhm resistor as bleeder this works with relative low current drawn from LEDs
Note the more current the LEDs draw the more voltage drops on the bleeder so battery voltage is higher than the calculated values

With standard hysteresis there is a fade between both LED groups and LVP shut down
this is PWM because when the comparator switches the LED off, then the voltage drop on the bleeder is gone,
so it switches on again just to notice that with the voltage drop again it is too low, aso
with battery voltage dropping the PWM cycle gets shorter and fades out

without a resistor like with new Aux boards it has a devent hysteresis

[Reviews] Miboxer C4-12, C2-4k+6k, C2, C4 / Astrolux K1, MF01, MF02, S42, K01, TI3A / BLF Q8 / Kalrus G35, XT11GT / Nitefox UT20 / Niwalker BK-FA30S / Sofirn SF36, SP35 / Imalent DM21TW / Wuben I333 / Ravemen PR1200 / CL06 lantern / Xanes headlamp

[Mods] Skilhunt H03 short / Klarus XT11GT,

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Nice work lexel!

1. If I put the board on my PSU and it is on I can connect it it is lightning up, reducing the voltage makes it go red and then turn off
But when I increase the voltage it does not turn on anymore or go from red to the other color.

I had the same problem & it turned out to be because of the high bleeder value I was using.

2. finally found it running the comparator on 2.8V LDO with a higher voltage from your voltage dividers at levels above the 2.8V did not work
running the Maxim 9022 with 2.8V reference from LDO and Vcc on battery supply works now
seems it can not compare higher voltages than its Vcc or close to it

The 9052 has a set Vref of 2.5V also a VCC of less than 2.5v will put the compactor to sleep, the 9039/9039 is set to 1.23V and the 9040/9043 is set to 2.048, which one are you using?

3. Vbatt x R4 / R3 + R4 =Vref
When battery level drops below 3.30V, Light up Red.
3.255V x 360K/270K+360K = 1.86V

I’m surprised you having it trigger at 1.86V, this is where I lost you.

4. 1.86V=2.8V*R8/(R7+R8)
R7=0,531*2.8*R8-R8
R7=182k
on 1S is max 4.35V, the calculated reference voltage should stay below 2.5V for 2.8V LDO
4.2V x 360K/270K+360K = 2.485V

Now I’m getting back on track again.

Whatever magic you did, I hope you’ll be releasing them for sale soon!!