Hello, I want to drive 5A or more though an xml2
Here is the light:
basically 5x 18650’s in parallel powering 8x 7135. I plan to put more probably.
I am also using a step up dc converter to get 12V for my mini fan.
Wires are not put together right now because I am waiting for my switch from ebay to arrive.
I plan to have 2 modes. 30% and 100% most likely.
I need help on how much heat would be genereated from my driver. Since it is held together by hotglue, I am not sure this is enough.
I built a smaller version with one 18650 and 8x 7135, and it ran fine because of the my cheap battery’s voltage sag. But I forgot that now i have 5 in parallel, my voltage sag would now be very small! Any advice on how much heatsinking i need? I got plenty of aluminum scraps and thermal paste. I am able to remove the driver from DC converter at any time easliy because it is just hot glued.
On other topic, How many amps/7135’s should I do for this light?
Okay, yes, 5 Volts mini fans are a little difficult to find for a mini price…
I’ve been looking for 40 x 40 mm 5 Volts mini fans. I did find some though!
I can search for the links if you want.
They can be combined nicely with the 38mm alu cooling stars.
Can fit in a tube, if you remove the frame of the fan.
Wait, there’s this:
When you want to push 5 Ampère through an XM-L2, you may need more than 4 Volts…
You see the problem…
Let’s wait for someone who really knows the voltage needed to push 5 A through XM-L2
I would go for a 7.4 Volts battery setup, so you always have at least 6 Volts to work with.
But then you need a step-down driver, not 7135’s.
Charging will be more complicated too with a 2S setup….
I daydream of an MT-G2… That requires a 3S setup…
urr right… wow, I didnt even think of that… I just thought the 7135 just did all the “magic” to output 350ma. Well If 4.2v is not enough for 5A, does that mean I can just skip the driver and connect my battery straight into my xml2? This actually works out even better for me o.o
If the LED is on a copper board, and has good thermal connection to something that can dissipate the heat, it'll survive direct drive from any number of 4.2v cells in parallel just fine. But even with zero voltage sag under load the voltage will still fall as it runs as the cells empty, driver or no driver.
My Led is not SinkPad/Noctigon so it doesnt have that bypass that something layer. BUT, it is on copper! I use arctic silver in the middle and thermal plaster on the edge to glue it in place, then paperclips+ hotglue to hold it together.
I am worried about doing this because I killed my old xml T6 by testing my 1S5P battery by direct driving it. The led flashed once and it died. I am scared to try it on this one (the only xml that I Have)…
Do you think it will be able to handle it?
How many amps do you think it will be running on? (pretend there is no voltage sag to create the worst case scenario.)
I will look up the link to the topic about aluminium and copper boards with or without direct metal to metal heatpath.
But it turns out that the direct heat path, i.e. without an isolating layer, makes all the difference !!
Better to have Alu board with direct heat path than copper without direct heat path !
No number of 7135s will get you more current than that cell will do into that LED without the driver. Input voltage must be higher than the LED's forward voltage at your desired current, the 7135s cannot boost voltage or current, they can only restrict it.
They are essentially current limiters.
They limit the current to 350mA (or 380mA if you have those…) by burning off excess voltage, by acting like a resistor.
An automatic variable resistor which burns off the excess voltage when the 350mA limit is reached.
Alright, probably safer to not DD to battery. Comfychair, do you know if running all these 7135 create too much heat for my small driver? I could place them on a bigger heatsink, or just apply more thermal paste and slap on another piece of aluminum on the copper part?
Oh… so 7135 is basically a resistor…. nice explanation
It probably has the same engine (but with 5 Volts intestines.
And when you simply parallel it with the emitter, it will run along with the 3 to 4 Volts, which is slower than on the full 5 Volts.
When put in a pipe, it’s really quite effective
I have tried this. But I got a mini fan with a relatively large centre-piece, i.e. short blades, not much action…
No, it's nothing like a resistor, it's a complete current regulator circuit inside a tiny little block of plastic.
They don't need any special tricks for cooling, that's only an issue when you're really pushing them with more input voltage than what they're meant for. Single cell inputs don't stress them much at all. And besides, they have internal protection against overheating (they'll reduce output before burning up).
I read somewhere about 7135 burns off excess voltage?
VF of xml is 3.3 so ~4.0-3.3 is .7V x 5A is 3.5W of heat? I think that is quite a bit of heat. The problem is long before the protection kicks in, my hotglue is already flowing everywhere
It's only 3.3v at relatively low current. Higher current needs a higher voltage, so the 7135s have an easier time with it. They only have heat problems at higher voltages, like 4x or 5x D-cell NiMh. 4.2v max input voltage heat (from the driver itself) will not be an issue, and I'm not going to repeat that part again.
Another thing, DON'T mount the driver in/on the LED heatsink, it will run cooler mounted somewhere else on its own.
