Collecting parts for my first DIY P60 drop in. And I have a few questions.

[mattw]

First off, if this is in the wrong place... move it please!

I am collecting parts to build my first P60 module. So far, it looks like it will have either a CREE XM-L2 T6 4C or CREE XM-L2 U2 3C mounted on a Noctigon copper board. Since I plan to drive it with 1x18650 high output cell I have selected the QLITE REV.A 7135*8 3.04A LED DRIVER with NLITE firmward and a 120 second automatic step down. I have selected the above LED's because of the neutral white tints.

I have not selected an actual module to build it on, I may gut a Solarforce for lack of a better donor. If there is a shell that all of you could recommend that is roomy and well designed, let me know. I think I will go with a smooth reflector to maximize throw.

Now, for the questions... I do not fully understand potting the led for strength and I see that people use heat transfer grease or epoxy in the process. I assume that this goes in between the driver and the pill and the LED and the pill? I would also need something that would allow better heat transfer from the LED to the reflector and at the same time to prevent the reflector from shorting the LED.

I know, this is re-inventing the wheel... but I want to try the process, so that in the future I can work with other LED's that may have a tint or output level that I like and drivers that can be programmed or support a good 4 mode option.

I think I am on the right track, but would like some confirmation from the experts here.

Thanks Matt

 

[magellan]

I'm no expert but I believe potting is mainly for shock and vibration resistance. Things are less likely to break loose if the light is dropped. Perhaps the experts who know more than I will chime in on this.

 

[mattw]

It appears that potting can provide strength and a heat path. I am not sure I need both. I know I will need to get heat away.

I am also curious about my choices of emitters with that driver and a single 18650. I guess I will just build and see.

 

[m4a1usr]

Potting is a technique used for insulating driver components. Not the LED MCPCB. It is meant to be a thermal barrier and not a conductor. When I pot my drivers I do it in 2 stages. After reflowing a driver board (something I personally prefer for my builds) I clean the flux residue off the electrical components and cover the parts with a layer of Fujik (there are lots of different potting compounds). Once it has dried sufficiently I then test the driver board for proper function. When it's time to solder the driver to the pill I than fill the inside of the pill with enough potting compound to fill all the possible voids.


When attaching the LED MCPCB to the pill you can use Artic Silver or similar adhesive to center the LED MCPCB in place or if your knowledgeable in the technique, you can direct bond the copper MCPCB, which is the best method of attachment if possible. That means you will be soldering it to the brass pill. But that also means you wont be able to solder fill the pill which to be honest is a technique subject to debate among builders. Myself I like doing a solder fill since it adds thermal mass and a larger thermal path to the pill and reflector body. That's where the heat needs to travel to. And hopefully to the head/ bezel/ body. But when using a copper MCPCB in my builds I have been using the assumption that the solder under the MCPCB will perform pretty much the same job (just less of it) and get the heat moving outward. Either way a good thermal path should be the goal.

 

[DellSuperman]

For the thermal grease between the pill & MCPCB, i use Artic Alumnia (doesn't harden but not an issue since the MCPCB is pressed down by the LED gasket & reflector). It is easy to align the LED as well since i can slide the MCPCB around.

For the potting of the driver side, I use Fujik thermal compound available at those Dealextreme or FastTech sites.
These will harden over time & hold the wires in place to prevent unnecessary movements. Reason for not using the Artic compounds is because some of them contain small traces of aluminum (to increase thermal property of the compound) & those aluminum will cause shorting on the driver.

As mentioned by M4A1user, i used to fill the driver side of my pill with solder to provide slightly more thermal mass.. It does make ur dropin slightly heavier.
These days I use 16MM bare copper MCPCB (filed off the circuitry portion) & solder 2 pieces together, than put in into the pill's driver cavity & solder them onto the pill again. That way, I have extra heatsink like the solder filling method but this time it's copper! Haha..

 

[DellSuperman]

It appears that potting can provide strength and a heat path. I am not sure I need both. I know I will need to get heat away.

I am also curious about my choices of emitters with that driver and a single 18650. I guess I will just build and see.

Extra strength in your dropin allows u to use your flashlight with more confidence without fearing of malfunction when dropped..

When I build dropin for my friends who is unlikely to dismantle the dropin, i even apply the potting compound through the holes the wires are threaded through, the 2 wire points at the emitter side & also on the threads on the pill where the reflector screws in.. Too much, maybe but it definitely makes the dropin stronger when applied properly.

And thermal compound on ur driver allows ur driver to cool off better when it heats up & works more efficiently.

Btw, your choice of driver & emitter works well with a single 18650. No worries...

 

[magellan]

Great information, all, thanks. I was thinking the thermal control was secondary to the shock and strength advantages, but it appears this is not the case.

 

[m4a1usr]

Great information, all, thanks. I was thinking the thermal control was secondary to the shock and strength advantages, but it appears this is not the case.

No I think mechanical as well as thermal isolation is sound reasoning as the thermal insulation explanation that some of us builders use. Since potting, also known as encapsulating, accomplishes both. Hence my prior comment as the builders protection logic. The one obvious down side to potting is that once done you might as well as consider the build a throw away should the build fail at some point in the future. I should get off my duff and put together a sticky about common build techniques for building LED drop in's. I know there are some bits and pieces here and there on CPF but a more modern centralized build log, followed up with many CPF members contributions would likely be of help for future developing builders. It is after all a process of improvement and that ultimately comes from individual experiences.

 

[mattw]

I for one would love to see a sticky that contained the process, pictures and bonding agents or thermal path agents that are used. I am just starting down this road and I am trying to build some inventory of parts for mods, budget limits me right now. I am not concerned about having the latest, brightest LED but rather I am concerned about getting the process right. So, if anyone is canning old LED's, drivers or abandoning P60... please let me know before you just toss anything.

Thanks Matt

 

[kosPap]

I have not selected an actual module to build it on, I may gut a Solarforce for lack of a better donor. If there is a shell that all of you could recommend that is roomy and well designed, let me know. I think I will go with a smooth reflector to maximize throw.

get the empty XML modules from Fastetech. the one with NO ring around the led opening.
VERY good beam