Disclaimer: These test were performed for my personal knowledge and use. They resulted in the forming of my personal opinions (listed later in this posting)…there is enough information contained in the resulting data for you to form your own opinion…and you should.
I have been working on enhancing the thermal efficiency of a P60 drop in for some time and the one thing I found is ‘no matter what modifications are made to the drop in, the heat transfer ultimately depends on the efficiency of the thermal wrap material’. Search the forums and you will find everyone has an opinion as to the best wrap material, but no one seems to have real numbers or real answers.
Also, I couldn’t find the typical range for a P60’s junction temperature –do you know your junction temperature? For all I knew, with the best thermal modifications (at higher drive powers), I may be pushing the 150° envelope.
It is a little challenging to measure the Tj of a P60 drop in in a host, but not impossible.
My setup:
I mounted a emitter on star (XM-L2 U2 1C) in a brass pill, then dilled a tiny hole adjacent to the thermal solder joint through the MCPCB and pill platform. I ran a k-type probe through the back of the pill, through the star even with the solder joint and set it with a thermally conductive silicone. I had to bore out the small opening in the reflector an additional 2mm to accommodate the silicone and probe tip.
These tests were preformed without a driver installed in the pill, instead, I used a lab power supply to drive the emitter at 3.00A. I used 16 AWG wire for the leads since they needed to run through the battery tube to the power supply.
I wrapped the drop in with various materials and tested each and plotted the first 15 minutes while monitoring the Tsp and light output simultaneously. (exceptions –when I tested with no wrap material, my Tsp reached 112°C at 8 minutes so I terminated the test. Even though my calculation to go from Tsp to Tj only added 25°C to the Tsp, this only works if the Tsp is stable…if the Tsp is climbing –the Tj will be more than 25° higher than the Tsp…if the Tsp is climbing steeply, the Tj will be much higher than the calculated 25°.)
I ran the test setup with various combinations of MCPCB materials and wrap materials. I have listed a few of the most common combinations.
The test setup was mounted in an integrating device with contact only at the mounting plate on the head of the host. Ambient temperature was 25° C with a +/- .2°. The Tsp and light output was recorded simultaneously.
Your setup:
Can you look at my graph and determine what your Tj or Tsp is…yes and no. These tests were performed in a controlled environment with a controlled power source and the host did not have the benefit of air flow or most importantly your cold hand wicking heat from it. If your P60 has a 3A driver and a fully charged battery, you can look on the graph and find your MCPCB material, find your wrap material, run it, standing on it’s tail cap, at room temperature for some time up to 15 minutes, then look on the chart and determine your approximate Tsp or Tj…but the real reason for all of this is just to compare thermal wrap efficiency.
Now the Results:
Some Clarifications on the above chart legend:
Al star = Aluminum MCPCB 16mm x 1.5mm
Cu star = Copper MCPCB 16mm x 1.5mm(Noctigon)
Cu foil wrap = .002” copper foil 5/8” wide
Al foil wrap = Reynolds® Heavy Duty
Cu tape = Copper foil tape w/ conductive adhesive 1/2” wide
As promised, my opinions:
1: wrap it or don’t bother going with p60 (at least anything over 1A)
2: forget the copper foil tape –the thermal resistance of the adhesive layer is too high to make it an effective wrap…aluminum foil performs much better and since you probably have some in your kitchen…it’s basically free.
3: if you run 2A or above…use copper foil
4: not list on the chart but a poor performer is aluminum foil tape (same issues as copper foil tape)
Why did Copper foil tape do so badly? (another one of my many opinions)
Our friends at 3M® have very good resources for their products, they consider the adhesive on thermally conductive tape to be a good conductor at 0.60 W/m-K…for an adhesive, it is good. Copper has a nominal conductivity of 385 W/m-K. Without using a calculator, you can see that copper has a thermal conductivity several hundred times greater than the adhesive (641.667 times greater if you use a calculator).
Copper foil –the best, but still has a drawback: every time the heat cross a layer (or wrap), no matter how tight, you loose some of copper’s thermal conductivity (you may have from 10 to 40 wraps)…but there are ways to minimum this problem, which I have tested and will address in a later posting including copper corrugated and dual gauge wraps.
MCPCB | Wrap | Tj Final C |
Copper | Copper Tape | 152 |
Aluminum | Aluminum Foil | 143 |
Copper | Aluminum Foil | 137 |
Aluminum | Copper Foil | 135 |
Copper | Copper Foil | 130 |
PflexPro | Copper Foil | 112 |
Now, Just for Fun:
During one test, at 32 minutes (after I had reached a stable Tsp) I decided to cool off the host before stopping the test. I read the host temperature with an infrared thermometer and decided I wouldn’t be cooling it with my hand. I used a freezer ice pack (the kind that never freezes hard) and wrapped it around the battery tube of the host. I continued plotting the resulting temperature and light output listed them on the same chart. Remember, the only change, at 32 minutes the ice pack was applied –notice how the light output increases as the temperature drops…just another reason to take thermal management seriously.