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Suggestion for the UI:

If the user pressed and held for a ramp-up within the last 3 seconds, have it so pressing and holding again ramps down (and visa versa).

That way you get 2-way ramping without having to go all the way to either end. Sorta like lumodrv.

Hey - that’s my GB… hands off… :wink:


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Will update op tonight

The BLF X5/X6 driver uses a Tiny25, not Tiny85. There's a 13A, 25, 45, and 85. The 25 has a version with the same exact footprint as a 13A, but the 45 and 85 need a bigger pad to mount them properly. For code space:

13A=1K bytes, 25=2K bytes, 45=4K bytes, 85=8K bytes

Currently, Narsil is sitting at about 6K of used code space. The 25/45/85 are all code compatible, slight variations from the 13A because of additional capabilities.

The 25 has the advantage of fitting in the exact space of a 13A, while the 85 needs slightly longer pads for the pins. Alternative is to bend the pins in on the 85, which a few of us are doing to re-use existing driver board designs. Could argue it weakens the solder connections, but for use doing hand soldering reflow, it works well. For this BLF Q8 driver, of course we designed it, and there's plenty of room, so we accommodated the 85. There's more to it, though, to properly support the 25/45/85. The BLF X5/X6 driver, for example, uses a 12 uF cap instead of the standard 10 uF cap because it wasn't stable with the stock 10 uF - not the ideal "fix" though.

For the BLF Q8 driver, we've taken a new approach, as others have, like Richard, to properly support the MCU and FET+1 based design, both from experimentation and pure digital design theory, with inputs and help from Electrical Engineers experienced in this.

Lot of the public research can be found in the 25/45/85 thread: https://budgetlightforum.com/t/-/34900

Sorry to go so techie, but might help some that are interested...

Maybe I wasn't clear enough, but the body tube of SRK is around 50mm, head of SRK is around 59mm. In my sketch diameter is been around 60-62mm so I think it could be 60-65mm. Best way to think it probably would be to pick SRK from the head and see how it feel's in your hand. Even in that where is 7x 18650 fitted largest diameter is 62mm with plenty of spare(for thicker walls). Handle of course would have to be big enough to fit your fingers, but If that's needed as option it probably cound be mounted for tripod nut thats planned in light. But as said before more comblex.

Sure, where I can buy one? Will this have enough power to light the dark side of the moon?

I cut your quote. That would be easiest way and probably what others expects, just wanted to share my thoughts. Since you all like that SRK tube I wanted to share one more sketch with using that.

Here it is more SRK like tube with same diameters. As before RED's are 18650 (and I know they are not exactly placed as in SRK but to give you and idea), GREEN 1x 26650 in middle and a bonus BLUE proposing as 32650 (only outer diameter as ring so it's more easier to view). That kind of design would be more easier. But it would have it own flaws. Using 1x 18650 you would probably have to use somekind of sleeve in middle (small circle inside green) and 2 or more cells it would also reguire somenthing in adition if drilled for 32650. With 26650 drilling I think they should be okey and walls would hold them nice.

EDIT: Angle of that pic is bit off so there is same free (white) space in top 2 cells even it looks like there is none.

That should not change too much I think, but would still give user ability to be versatile. Even thought some might think what would be advange on this. All I can say that would allow user to use the cell he likes and if using just a one cell it would be more balanced in therms of center mass of battery.


Pic is clear, idea too.
In this case we would need a 5th spring in the center for a 26650 of 32650.
And some sleeving/dummy addition to keep anything the 18650 cells in place when less then 4 are used.
A sleeve to fill gaps when a 26650 is used (or those dummies must be made of some elastic/easy to shape stuff)
all to be able to use the not much used 32650 format?

Hmm, two 18650 cells bring us 6800-7000mAh
1 26650 brings 5000mAh
IDK about top of the line 32650 cells

It seems like an awfull lot of adapting and rise in costs (we aim for double springs with a phosphor bronze spring to conduct better)
there is a limit in compability, 18650 are most used, have highest capacity for weight and size.

I have checked the option for a 26650 cell in the center, the 18650 would not be held into place as they are now.
Here upside down 18650 in SRK tube

And how a 26650 would fit

That is true for 32650, and it never was my goal either, Just while sketching, I realised that there could be space for that as well. That’s why I only draw it as ring. Point was that it could also be fitted if drilled larger ( by user if preferred to use those cells ).

So it pretty much about 5th spring in middle and and position of 18650’s. I know how it’s in SRK and I think it’s possible to more similar way. In SRK those holes are not “overlapping” instead they are little apart from others creating their own “tubes”.

I did try to say that in there earlier that they would have to move little bit from center to create same thing. Only problem I see is that I’m not sure if there is enough material to support only one 18650 cell in there. With 2 or more cells they would “bond” together and they couldn’t move. So one way is to use 1 cell in that middle spring with a 26650-18650 sleeve.

But I understant if you think that of too much complex and cost raise.


Well we are aiming for a very sharp price point here

So I wonder
A tube accommodating a 32650 cell in the center can be machined from a tube of ALU with relatively thin walls where the normal quad 18650 tube needs a much more solid bar to start with.
So I can imagine material for tube is cheaper (like the integrated shelf means a block instead of tube for the head)

But it means adding a fifth spring setup and some spacer stuff and I estimate that this would be costing more then a simple quad 18650 tube.

As all things it is very nice to have people shed their lumens on it and to seriously debate it.


Hard to say for others probably poll would find out. But please forget that 32650 as it was only there for illustration purpose.

That is regular SRK 4 cell design.

Got that!

Understood. It is very nice effort of you’r whole team. And also all members here that share their thoughts.

True, please forget 32650. It probably could be done by user if desired but it was never my goal. Just a toss in thought.

I’m not sure how much one spring and one plastic sleeve could raise the cost. Probably not that much.

Agreed, but I would think it more as express thoughts or opinions than a debate. It would be nice to hear more users about their opinion.


I think that 4x18650 is a great set-up: seriously more runtime as the usual 1x18650 light, seriously more current capability too. 3x26650 or any other set-up discussed is not adding much, and versatility is not really a good point either since 18650 is the most abundant and best battery, the other sizes are rarer and do not have nearly the energy density.

I admit that I have a weak spot for 7x18650 parallel, they fit so nice in a round tube, and it is a whole new runtime category :slight_smile:

@djozz I understand why you prefer 18650 (as do I, usually), and a 4x 18650 really is great setup. I must admit that my 3x 26650 idea was a silly in many ways since it would get too complex and could simply outperform them with 7x 18650 in smaller tube.

I’d still would like to hear you’r thoughts as valued tester about last sketch (ignore 32650 part), where simply adding spring (and possibly sleeve) would gain additional versatility. Even thought I understand that 18650 is best battery (and probably most versatile too).

I’d would be awesome to see someone building light with 7x18650 in parallel, whether it would be you or other :slight_smile:


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About the last sketch: I have been thinking about how a 26650 could fit in the middle of a SRK-type light, it takes boring out only 2 or so mm to make it fit. But unlike your drawing (that uses the battery dimension instead of the extra mm that a hole for a battery needs), boring out that extra bit to fit a 26650 precisely takes away the support that keeps the 18650’s in place.

@Sharpy: are you thinking of extra emerging dangers, apart from that 7 batteries in a tube are 1.75 times as dangerous as 4 batteries?

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311 new posts. Could you possibly date new info in the op and thread title so we know when to check and for what?

Yes, anything all should see is put in OP, with a CAPS title change and usually a link to rge post where discussion starts about it. (And least I plan on keep on doing it like the LED decision, head design, bezel discussion, Toms first ramping video (now new videos of Narsil have post 2))

After thinking more about it, I could see the 4x18650 and single 26650 compatibility working the best of what has been discussed. For me the 26650 would be nice as I currently don’t have any 18650 lights and really don’t plan to get any. I am planning to get the Convoy L2, L6, and BD06 which are all 26650 based lights. While I understand I would not get as good of performance on a single 26650 as I would 4x18650, I still think it would be sufficient for my uses.

I also feel like the 26650 cell is starting to gain more ground and becoming an increasingly popular cell resulting in better performing cells. How many amps will this light be pulling?

Could a nylon X be created on a plastic printer that would hold the 18650’s in place and still allow for a 26650 when not using 18650’s? Just a though…