Single 18650 DIY Bike Lights (front/rear) 3-up?

New here on the forums, have been lurking past few weeks trying to absorb all the wisdom (a lot like drinking from a firehose).

Anyhow, I'm looking to build a couple 3-up lights to use for bicycling. Most of the commercially made bike lights are overpriced and can't accept off the shelf 18650s without some modding.

So I'm looking for a suitable design solution that will run a 3 up xpg or xpe (red) with carclo optics. Prefer a smaller sized light since I'm going for fairly floody. As far as a driver, I'm liking the taskled L-flex driver, primarily due to it's bike-friendly firmware.

Goal is ~800L out the front and 1.5h runtime, ~200L out the back and 1.5L runtime. Desire for configurable flash/pulse modes since the standard strobe and beacon modes IMO aren't that great based on my current experience.

So a few questions I've not been able to get figured out.

In terms of lumens per amp of current would I be better with a single XML2 for the front or a 3-up xpg? This is basically a runtime issue for me, but I like to have full brightness for about the 90 minutes I typically ride in the dark.

For my 3-up head and taillight configurations, is is really feasible to run something like that off a single 18650? I'm not opposed to a 26650 or other chubby battery if that's what's needed to make this work. The goal is simply a bike light that doesn't need to be tethered to an external battery pack and that I can easily swap cells when they get discharged.

I realize the Vf is radically different from a white xpg and a red xpe. Also, this would be an unprotected 3500 mAH quality (panasonic, sanyo, samsung) cell.

The taskled driver is on a 20mm board. Are there smaller drivers with similar capability? I'd be probably more interested in a 7135 based driver like the Qlite (smaller form factor), but the firmware packages I've seen (admittedly limited) don't have a lot of strobe/blinky options suitable for cycling.

Speaking of firmware, are there any bike-friendly firmware packages I should look into?

Finally, what about hosts? If I could make it all fit, a Convoy S2 or S5 or S6 would be ideal. Again, that's assuming I can find a 17mm driver with multiple strobe/blinky options as well as steady modes. If that won't work, then I'm at a loss for a tube light that would work with 26xxx cells.

If this provides any context, I'm looking to take the Design Shine dual 3-up design and scale it down to a single, self-contained single 3-up design.

I expect I'll have more questions, so please have mercy on a clueless newb. If there are any places where some of this information is located already, links to previously plowed ground would be greatly appreciated.

Thanks in advance for the privilege of accessing the collective wisdom of the Wizards of the IlLUMENati (see what I did there?).

Ok lets start with the basics. Panasonic 3400 mAh are pretty much as good as it gets for 18650 cells. You want 1.5h run time. Starting with some rough calculations for a linear driver 3.4A for 1 hour = ~2.25A for 1.5 hours. I haven't mentioned volts as a linear driver burns off the excess voltage as heat. An 18650 ranges from 4.2v when full down to 2.5v (for the panasonic only, most batterys stop at around 3.0V) when empty.

What does that mean for you ? with 1 x xm-l2 U3, 2.25A = ~3.19 v = ~825 datasheet lumens with a thermal junction temperature of 85°C. Once the battery voltage drops below 3.19v, the light will gradually dim.

With 3 x xp-g2 S4, wired in parallel = 0.75A per led, ~2.9v, ~905 datasheet lumens with a thermal junction temperature of 85°C & the light won't start to dim till it gets below 2.9v.

Ie either way will get you in the ballpark.

Seeing as we are talking theoretical I have assumed you get the best available bins (U3 & S4) Personally I prefer a neutral or warm tint which usually means dropping back a bin. (As the leds come off the production line, Cree sort them according to the amount of light they emit, higher bins = more light, and also the colour tint)

Red xp-es are not particularly efficient with 18650s and a linear driver. They need less than 2.5v, so you have significant burnt off as heat. Personally I think you are not appreciating how different red lumens are from white lumens in perceived brightness. I have a couple of different light set-ups with single xp-e2s at 0.5A and 0.7A. Both are daytime visible and so seriously bright I use a diffuser to increase the point source of the light. At 0.7A, 1 xp-e2 driven by 1 x 18650 will run for more than 4 hours.

For your front I would go with housing - easy2led 20mm, leds - CREE XP-G2 S3 3D LEDs on Noctigon 3XP MCPCB, wired in parallel (make sure you buy the 4 jumpers), Carlclo tripple optic, Taskled L-Flex or Dr Jones mobydrv

Headlight Questions/Clarifications

Find Bruce -

Thanks for the responses. I'm still learning a lot here. A couple questions and clarifications.

Clarification: I am looking for a self-contained solution. I find that the external battery packs are a PITA, hence my desire to find something I can package into a single 18650 host. My current lighting set up runs on external batteries and is a DiNotte XML-3 headlight and a DesignShine DS-500 taillight.

Using those lights as a starting point, I was hoping to scale back to a single XML2 or triple XPE2 set up in the front and whatever might be suitable in the rear.

The DS-500 has two 3-up xpe2 red MCPCBs in series and a Taskled maxflex controller. I really like the light and the controller, but again, the external battery is a hassle for me.

Questions:

1. The XML2 U3 has 7825 datasheet lumens? I'm guessing that's a typo. I'm still trying to wrap my brain around datasheet lumens and what the thermal junction temperature means. I understand that hotter means dimmer, but much beyond that I'm still trying to learn.
2. From the above looks as if the 3-up set up gives a little bit more OTF lumens with a tad more runtime - is that right?
3. I understand TIR loses a little bit of light OTF relative to a reflector setup - is there a ballpark figure for how much loss?
4. Regarding the Carclo optics, would a 10511 be something to look into? Or would that be entirely too floody? The carclo optics are cheap so I can always buy a bunch and mix/match to see what works best for me.
5. I assume the mobydrv firmware runs on a 17mm controller?
6. Can you recommend a decent tube light host that will fit the 20mm board for the 3UP?

Taillight Follow Up

OK so using a linear driver on a red xpe2 results in a lot of waste heat since Vf~2.3V and Vbatt ~3-4V.

I haven't had any luck locating a boost converter to handle 3 in series (Vf ~6.9V) or a buck converter to step down. Does such an animal exist for my application?

If not, you mentioned (I think) you are successfully driving a single red XPE2 with a single 3.7V cell - did I infer correctly?

If so then I suspect, I *should* be able to drive three RED XPE2 in parallel, yes?

Regarding thermal management -

Assuming a single 18650, if I am driving a single red XPE2 at 750 mA vs. driving a 3-Up red XPE2 at 750 mA will one run hotter than the other?

And will the 3Up put out more light? (assuming that is the case).

Again, thanks for the education. Quite a lot to learn before I start really digging into this a bit.

Re: Headlight Questions/Clarifications

Tricycle Assassin said:

Find Bruce -

Thanks for the responses. I'm still learning a lot here. A couple questions and clarifications.

Clarification: I am looking for a self-contained solution. I find that the external battery packs are a PITA, hence my desire to find something I can package into a single 18650 host. My current lighting set up runs on external batteries and is a DiNotte XML-3 headlight and a DesignShine DS-500 taillight.

Using those lights as a starting point, I was hoping to scale back to a single XML2 or triple XPE2 set up in the front and whatever might be suitable in the rear.

The DS-500 has two 3-up xpe2 red MCPCBs in series and a Taskled maxflex controller. I really like the light and the controller, but again, the external battery is a hassle for me.

Click to expand...

Thanks for the clarification. Not my priorities, but that's your choice.

Tricycle Assassin said:

The XML2 U3 has 7825 datasheet lumens? I'm guessing that's a typo. I'm still trying to wrap my brain around datasheet lumens and what the thermal junction temperature means. I understand that hotter means dimmer, but much beyond that I'm still trying to learn.

Click to expand...

7,000 lumens for a single die would be imrpessive, but alas no, it was just my fat fingers typing. Should say 825. Don't worry about the thermal junction temperature - Cree likes to quote the lumens at 25°C which is entirely unrealistic in the real world. 85°C is closer to what you might expect. I include the TJ so it is clear what figure I am quoting and someone doesn't get confused and say "but the Cree datasheet says 950 lumens".

Tricycle Assassin said:

From the above looks as if the 3-up set up gives a little bit more OTF lumens with a tad more runtime - is that right?

Click to expand...

Any difference in runtime is coincidental - I chose amp figures to give approximately the runtime you want of 1.5 hours. 3 leds at lower amperage are more efficient in producing lumens than a single led, so yes a 3-up will always give slightly more lumens, other factors being equal. Whether they put those lumens where you want is a different question

Tricycle Assassin said:

I understand TIR loses a little bit of light OTF relative to a reflector setup - is there a ballpark figure for how much loss?

Click to expand...

That's what I understand too, not aware of any ballpark figure as it is going to depend on the specific TIR and reflector.

Tricycle Assassin said:

Regarding the Carclo optics, would a 10511 be something to look into? Or would that be entirely too floody? The carclo optics are cheap so I can always buy a bunch and mix/match to see what works best for me.

Click to expand...

For a triple on 20mm, your optical choices are flood, lots of flood or gigantic heaps of flood. Personally I go with the 10507 as the least flood, but it is not a narrow beam.

Tricycle Assassin said:

I assume the mobydrv firmware runs on a 17mm controller?

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Yes- that is what it is designed to do - it uses a cheap and cheerful, readily available linear driver and gives it a much improved UI.

Tricycle Assassin said:

Can you recommend a decent tube light host that will fit the 20mm board for the 3UP?

Click to expand...

There are probably quite a few options out there. Only one that springs to mind is the convey s3. Search for convoys3 triple and you should find some examples

Tricycle Assassin said:

OK so using a linear driver on a red xpe2 results in a lot of waste heat since Vf~2.3V and Vbatt ~3-4V.

Click to expand...

Now you are getting it. It is relatively inefficient, but I wouldn't go so far as a "lot of waste heat" - at 750mA, it is only 0.8 watts.

Tricycle Assassin said:

I haven't had any luck locating a boost converter to handle 3 in series (Vf ~6.9V) or a buck converter to step down. Does such an animal exist for my application?

Click to expand...

Nope, I haven't either

Tricycle Assassin said:

If not, you mentioned (I think) you are successfully driving a single red XPE2 with a single 3.7V cell - did I infer correctly?

If so then I suspect, I *should* be able to drive three RED XPE2 in parallel, yes?

Click to expand...

Yes & yes. A more efficient option is to use 2 AA batteries in series - gives you pretty close to the ideal voltage & 2 x aa battery lights are common enough. Don't know of any with a 20mm board though.

Another tailight I made runs a triple red using a 2s2p battery 8.4-7.0v for which a linear driver is very good, but you don't want an external battery

Tricycle Assassin said:

Regarding thermal management -

Assuming a single 18650, if I am driving a single red XPE2 at 750 mA vs. driving a 3-Up red XPE2 at 750 mA will one run hotter than the other?

And will the 3Up put out more light? (assuming that is the case).

Click to expand...

Running 3 leds at the same current will be 3 times hotter & put out 3 times more light. Running 3 leds at 1/3 the current will be more efficient, generate less heat & put out slightly more light. Won't happen with a linear driver though, because a 750mA linear driver uses 2 x 7135 chips, so you will be running 3 leds at 1/2 the current, so the 3 leds will run hotter (1 x 1.1v x 0.75A < 3 x 1.1v x .375A) & generate more light (128 lumens v 200 lumens).

Tricycle Assassin said:

Again, thanks for the education. Quite a lot to learn before I start really digging into this a bit.

Click to expand...

No worries, I am no expert and what little I know about leds comes from people explaining things to me followed by my own experimentation.