According to the xhp70 spec sheet there is a total clearance of .7mm between the thermal pad and power pads.
With a good tolerance manufacture you can get away with .16mm of clearance between pads, although .2mm is better for something like this. Lets go with .16mm though.
That leaves a maximum of .38mm of trace width.
That is roughly the same as a 36AWG wire. Or a wire about the size of a piece of sewing thread (.005” in dia).
Or to put it another way, it would have 38 times more resistance then a mere 20AWG wire. or 60 times more then an 18AWG wire (which is what is used in the Q8 and Tom has shown there are gains to be had be going even larger to 16awg).
Put simply with traces that small that would simply pop like a fuse if you tried to apply the amount of power we do to them.
It is a great idea, if the xhp70 thermal pad didn’t short out the xhp50 power pads, it would have worked perfect.
Oh aha
Then maybe just XML pads?
I mean go fancy on thermistor and resistor pads for series/parallel o people can mod xml2, luminous 40, XHP50, XHP50.2
For XHP70 (.2) they can use stars ad mod to make it all fit
Seems to me XML pads give such a wide choice with relatively easy modding that not many willever use the bigger XHP70 pads
Maybe add a few pads for colored LEDs which should be cool to use with translucent led gaskets and the Narsil switch led options.
Well, I just made a 7070 footprint and used Tom’s measurements (thanks for those Tom!) and did some basic layout work.
The 7070 footprint is huge, bigger then even I thought and the actual LED center spacing is closer then we had planned for to start. The combo of factors means that there is not room for everything even with the wire running on the outside. Here is a quick shot to show you how cramped everything is:
The space between each LED is less then 1.5mm with only about 1.2mm of that being usable for copper at most. Or roughly the equivalent of 30awg wire.
What was doable with 3535 and 5050 footprint LED’s becomes impossible with the 7070.
The only real options from here are as follows:
Option 1: permanently set them up for parallel usage. Being able to run in 4S does offer significant gains. Also you would not be able to use the mounting holes for the mcpcb at all, it is not possible to make them line up with the holes. It would also need a hole drilled for sure as you could not even use the factory mounting holes for the wire, they will be under the LED’s. There is no way to run the power from the center as it would have to neck down to a 30AWG wire at some point and that could just melt.
Option 2: Pick the 5050 or 7070 footprints and stick with one of them alone. This allows for the mounting screws to be used and the adjustable layout to be used as well.
Personally I don’t see many people actually using the xhp70 in this light due to the extra work involved and the cost of the LED’s. The xhp50 should more then max out the heat shedding abilities of this light at good efficiencies and it should still have a somewhat reasonable beam that is not pure flood.
This is my thinking on the matter as well, it makes things much simpler and for those crazy enough to go with an xhp70, they are also capable enough of using individual stars.
Ok, here is a 5050 based adjustable layout mcpcb. This has everything in the correct locations and spacing according to Toms measurements.
It allows for LED setups ranging from 4p to 2s2p or 4s using either solder bridges, wire or jumper resistors that can be applied while the LED’s are being reflowed anyways. It also allows for both connections to be in the center.
A side benefit is that you could install low value resistor on the jumpers to reduce the power if needed instead of using 6 feet of wire like I had to.
I like the Texas_Ace 5050 based design!
Now most of the mods are possible with the original or the 5050 board. The few people that want to go with 4 x XHP70 will also have to work on the thermal limitations. So we can guess that these people are also capable of using single stars for the leds. I would think that this is a very good solution if nobody has a different design that he wants to throw in.
So if anybody has something to add or if someone has noticed a flaw in the design please speak up.
The resistor-pads are verry close to the led-pads. thats a little problem for insulating gaskets. And the resistors ar possible visible through the LED holes of the reflector. Perhaps the resistors wolud be higher than the insulation gaskets around the led and the reflector will short the resistors/jumpers.
Nice work on the 5050 board TA! I really like the option of using current reducing resistors (well cooled!) individually for each led, that will be needed if you want to use a simple FET driver and XHP50’s. But I am concerned about the clearance that resistors will have under the reflector, you only have the thickness of the edge of the led center pieces.
The resistors come in .6mm thicknesses which should be fine for most centering rings. They are generally around .8mm+ thick from what I have seen. Although you could also jump it with wire or solder bridge it as well, doesn’t really matter.
Now the centering ring clearance is a bit of an issue but the mounting holes don’t leave a lot of room for alternative options.
The pads at 9 and 3 o’clock should be ok clearance wise but 12 and 6 are another story.
You should be able to use centering rings on the 9 and 3 pads and then screw the reflector down to hold everything in place and it should be perfectly fine without a centering ring on the other 2 LED’s. I have done this in lights before when I ran out of centering rings and it worked perfectly.
Technically yes but cutting traces on an mcpcb is a bit harder then a normal pcb since the cut trace can short to the mcpcb itself. If this was a factory produced item by thorfire then that would be a good reason to do that.
Since it is not and this will only be used by modders anyone that can reflow an LED, can also add the jumpers to the mcpcb at the same time is the way I look at it.
Agree on that, cutting traces on a MCPCB is very risky, soldering a thin wire over the jumper pads while you are reflowing anyway is easy and risk-free.
Cutting traces on a MCPCB is quite hard and you could ruin your board very easy. But maybe we could rearrange the 3 resistor pads so that we get a few more mm to work with.
It would not look as nice but maybee give you the mm clearence that you need for centering rings.
Not a bad idea. The 12 o’clock LED could gain enough space most likely but the 6 o’clock in screwed. It’s not possible to gain enough space on that one for a centering ring without vastly reducing the trace thickness to the ground ring.
I will play with it and see what I can come up with.
Here is a slightly updated version with more room for the 12 o’clock LED centering ring. The 6 o’clock LED is out of luck, the trace would have to be reduced more then it would be worth to move the resistors far enough away for it to matter. 3 centering rings is more then enough to keep everything centered and working properly though.
It sadly did take a hit in the looks department though, looks like I beat it with the ugly stick. lol
Do the screw holes need to be perpendicular to the wire holes? I think not because the wires go through one big hole in the shelf. So you can rotate the screw holes 10 degrees clockwise and get the jumper pads of the 6 o clock led further to the left.
