I needed some single mode drivers to power a red XP-E2 in a C8 with the option of running 1x18650 or 2xCR123. I figured 2A would be about right.
The best I could find was This Driver on the Alibaba wholesale sight. It’s listed as 2.5A, which was a little high, but I figured it would have to do. When ordering, Ruby asked me how I would like it, so I said 2A and she changed the specs and sent me an invoice.
I didn’t really expect them to arrive and test at 2A, you know how it goes.
Got them today and did a quickie test on one. This is kinda general as it was done with the usual bunch of wires held together with alligator clips, magnets and manually touching the the positive wire to the driver.
First I tested one cell with an old XPE (I think) on a non DTP mcpcb.
Initially on cell gave me around 2.2A and two cells gave me around 2A. Three cells also gave me around 2A. This is not exact science, as things were fluctuating from my manual dexterity.
I’ll have to test more with it installed in a light for a more accurate reading, but it seemed to run a little higher current with one cell.
As I held the driver, I could feel one of the component heating up. Not sure if this is fairly normal for a small buck driver. With two cells it heated a little faster, but as I kept holding it, it didn’t seem to be increasing. Hot, but not too hot to hold. I’m not sure if it wa my imagination, but it seemed less hot with two cells than it did with one. With three cells, it got real hot, real fast. I noticed the current dropping down to 1.8A, but realized that the little XPE on Non DTP aluminum board was just experiencing heat sag.
Does anyone have experience with this type of driver? Besides mine being single mode, I think it might be fairly common. Mostly I want it to drive a red XP-E2 Mounted on a noctigon with 2xCR123.
I have been looking for something like that. I see that it may have a sense resistor that could be adjusted. Would be a fun one to play with in a light that has the option of one or 2 batteries.
Once I get this installed and running with better heat sinking, and find it runs steady at 2.2-2.5A, how would I go about lowering the current to 2.A.
It’s probably fine as it is, but I wouldn’t mind playing with some options. Like I said, once I deal with the heat sag from my quickie tests, I may be dealing with a slightly higher current.
If R100 is a sense resistor, one would increase the resistance by a small amount. I would use trial and error, there are some here that could give you a good idea how to calculate it. My interest lies in it from the standpoint of a 2x18650 red rifle light as well. Something like a C8 with extension tube.
I have not pushed that far yet, mounted on copper with a good heat path... maybe? I have one running 2.1 amps, did not have more emitters so did not push any harder.
I think I built a flashlight like that. Red XP-E2 on a Noctigon with a 7x7135 driver for around 2.45A. Seemed fine to me. See here: djozz - blue and green XP-E2, output tests
Single cell to single emitter it might have been ~10-15% driver losses but certainly from 2 cells you would expect Ib to be closer to 1A. In any case it will be less efficient as the voltage differential increases.
I’m getting the 2-2.2A readings at the emitter, from the Neg. wire between the LED and driver. Reading between the cell and driver is 1A with two cells.
Thanks wight, and glad to see you’re back. I’ve been gone for a long while myself and need to shake the cobwebs out. I read the link you gave for the QX9920 and the SF. That board is two sided, whereas mine is only one sided and probably more basic. I realize it’s the nature of the beast for a buck driver to give off heat, and generally they have double sides or two boards with larger toroids, so I’m just wondering if is should worry about the heat this little driver puts out, or just ignore it and let it do its thing. I mean bad things can always occur in any situation, but do you foresee any real problems cropping up using two CR123s with this driver. Is the heat it produces really a big deal, or should I just “let it bleed”.
My cobwebs are in full force, so I might not always give the best advice. I don’t think you should worry about it based on your description in the OP. If you can keep your finger on it indefinitely you are OK. 2xCR123A primaries is probably this driver’s ultimate sweet spot. They should be around 2.5v each at 1amp for 5v total input - That’s plenty to keep the driver regulating for a red LED, but not too much extra. Very efficient.
FYI I wouldn’t say that SF’s board is really a more complex implementation of QX9920. Note that the PCB you see is around 15.6mm and uses a contact board. Their inductor has around an 8mm diameter base. The back has an MCU and stuff if it’s the multi-mode version.
Okay, back to this thread. I was having problems understanding my tail readings so I started a Separate thread here.
Now I’m back to heat. I looked closer into the heat coming from the driver. It’s coming from the R100 resistor. I powered the driver with one and two 18650s and two CR123s with my fingers clamped down on the resistor. It’s seems to get equally hot no matter the cell configuration. Real hot. Can’t keep my fingers pressed down on it. How much heat can a resistor bleed off? Is it going to fail, or are these tough little buggers. I built the light anyway, and left it running for quite a while. I’m sure that resistor must have been really hot, but the light didn’t fail.
I don’t hunt, but these red lights are for hunters and I’m not sure if they’ll have them running for extended periods, or just for one to five minute bursts.
Resistor package size determines the power they can handle.
That resistor should be the load-side current sense resistor and will see the same current, regardless of the input voltage.
At 2.2 A, the R100 resistor will be dealing with 0.484 W.
A 0.5 W resistor will too close and will get too hot. A 1 W resistor will do better. It also depends on PCB layout, fat tracks connecting the resistor helps to sink some heat.
Maximum rating for resistors is usually much more than 60 C (60 C is about the limit to keep your finger on it), but are linearly de-rated above 70 C. So at 100 C, a 1 W resistor may be only rated for 0.65 W, for example.
I suppose a driver like this based on ATtiny 13 does not exist? Otherwise all would have been sorted? Richard has this, which is what I’m currently using, but its not cheap. ATtiny 13 is a must for me for custom mode setups.
There is room on the board for an extra resistor soldered along the side of the r100, so if you are worried about the heat, you may swap the r100 out for two parallel r200's.
Do you mean remove the R100 and squeeze two R200 in its place? Would stacking an R200 on top of another be the same.
Will this change anything else in the drivers operation.
Let me know. It’s early morning here, and I have the day off. I’d like to try this first thing…after I change the cats litter box.
