1

So, guys, I’m currently planning to build a Sofirn C8F with a regulated driver and 3x351Ds, for some beautiful beams and usability.

I’ve got everything set up, except for the driver choice. I’ve looked at linear drivers, and buck drivers, as I still haven’t found a compatible 17mm boost/buck driver.

Knowing that I want to drive 2.4A through the emitters, meaning at about 800mA per emitter, the emitters would exactly need 2.97V, I would like to know which type of driver would give me the best efficiency for the emitter combination, to get the as constant brightness as possible?

Thanks in advance to all of you for the answers.

Edit: It is 800mA per emitter, not 2.4A. That would not be sustainable if that was 2.4A per LED”

2

How about mtn FET 17mm?

3

Nah, I’ve got enough lights with FET already.

I want some more… sustainable output.

4

Are the led’s in parallel or series, I assume parallel. In series you would need 7.2 amps out of the driver to get 2.4 amps to each led.
Using a single cell, the run time is going to be short at that current 20 to 30 minutes depending on cell and driver.
What size is the driver?

5

I meant 800mA per emitter, not 2,4A per emitter. I edited the OP.

6

I see you edited the post with more info. I believe I would just use a simple 17mm amc 7135 driver. Lots of options with UI and one 7135 can be removed to give you about 2450 ma to the led’s. That’s if you use the 106c driver. Mtn drivers you will need to remove two 7135’s for 2440 ma from the driver. Mtn uses 380 ma 7135’s and the 105c uses 350 ma 7135’s.

7

Would that be more efficient than a 1S buck driver or not?

I do know quite a bit about buck/boost drivers, but I don’t really know about the behavior of buck drivers with non-linear current devices such as LEDs. From what I’ve researched, it’s quite strange.

8

With a single cell li-ion 4.2v, starts at about 75% and increases in efficiency until the vf of the led is reached then becomes direct drive. With a vf of 2.97v it should be pretty efficient.

Its about middle way down the post

9

You don’t need a boost/buck driver, as a simple 105C would work fine. Get one with 7×7135 (add one to a 6, remove one from an 8).

7135s saturate at about 0.1V, so at 3.0V at the LEDs (rounding up), you’d need ~3.1V at the battery, which is almost at its cutoff point anyway, so you’ll be in regulation for most of the battery’s life before it desperately needs a charge.

You gonna use the host with a pushbutton side-clicky? Dunno any 17mm drivers that would use it. a 105C, 105D, AK47, etc., would all be “blink” driven (tailcap switch interrupting power).

If you could get one of the old C8Fs, with only the tail-clicky, you’d be set.

10

If using say a Sanyo NCR18650GA you can look at HKJ’s graphs to see how the battery sag will react to the driver and the vf of the led used. There will also be a small amount of other voltage drop losses too.

It’s a very simple decent efficient solution. I think that’s probably why there’s not that many single cell buck drivers around. The amc7135 linear regulator driver pretty much took the market and is a cheap, good reliable driver.

11

In series the amperage would still be 2.4A but the voltage will be higher.
In parallel the voltage stays the same but the amperage is increased. The amperage will be shared between each led.

BlueSwordM, with that setup there is no need for a buck or boost driver. You’ll need a linear driver do have regulation.
The above named drivers could work.
Another option is the LD-A4 from led4power.com.
https://led4power.com/product/ld-a4-2-12amp-17mm-constant-current-led-flashlight-driver/

12

Yeah, I must have been upside down when I wrote that. :stuck_out_tongue:
I assumed parallel then jumped to series with specs. It’s been a long day :weary:

13

The problem with the LD A4 driver though is that it doesn’t work with a side switch.

14

Good point, forgot that the current versions don’t work with a sideswitch.
The previous version did…

15

Its also 85% efficient at 3vf.

16

Also, for tail switch operation, could I just take any C8 tailcap and just screw it on?

17

So, could I use a generic C8 tail switch with the Sofirn C8F or not?

18

Convoy c8 tailcaps thread on but don’t make adequate contact. They won’t work without modification, IME.

The sofirn c8t clicky tailcaps work though.