safe plastic for a copper heatsink?

[js-lots]

I am modding my first flashlight and putting in a ssc-p7. I have a small copper heatsink that the pill will attached to with AA. I will be running it direct drive 18650. Is pvc safe to put inside the copper heatsink as a insulator between the + and - terminals or will it melt. What is safe? I am still learning, thanks for the help

 

[LukeA]

The PVC won't melt but it will render the thermal properties of the copper virtually null.

 

[PCC]

I may be wrong but I don't think any plastic is conductive. The problems with plastics are the poor thermal conductivity and relatively low melting point compared to metal.

 

[Illum]

conductive, impossible, but capacitive may be probable

 

[IMSabbel]

Capacitance doesnt really matter either.

The real problem is thermal conductivity.
a 100um thick layer between led and heatsink will add >10 C/W to the thermal resistance (ballpark figure , i did the calculations a while ago).

Compared to this, it wont matter if the heatsink is copper, aluminium or any other metal.

 

[EnabLED]

I have a small copper heatsink that the pill will attached to with AA. [...] Is pvc safe to put inside the copper heatsink as a insulator between the + and - terminals or will it melt. What is safe? I am still learning, thanks for the help

Perhaps you can clarify what you mean by "between the + and - terminals"? As others have noted, PVC is a poor thermal conductor so you do not want to use it between the hot LED and the cool case. It is, however, a good electrical insulator.

According to Wikipedia, PVC melts about 80 degrees C, which may be too low and so you may melt it, depending on where it is located and the rest of the heat path. Cree lists a maximum junction temperature of 145 degrees C, so even at ~10 degrees per Watt between junction and substrate, you could see a heat sink temperature over 100 degrees C.

 

[js-lots]

Thank you for your responses. the led will be resting on a star board. the star board will be attached to the copper heat sink. The pvc will go inside of the heatsink. The purpose of the pvc insert is to isolate the + and - contacts. I wanted to attach a bolt to the pvc for the positive end of battery and the + end of led. I want to be sure the pvc or vinyl plastic wont melt being that it is so close to the led itself. Ill try to take pictures of the this thing when Im done. Thanks:twothumbs

 

[shadow0000]

The PVC won't melt but it will render the thermal properties of the copper virtually null.

Ya you are right it is hard to melt the PVC but like you said LukeA it is render the thermal properties of the copper, but try to look some advice for those person that experiencing a problem like that...



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Copper Sinks

 

[diff_lock2]

You could make a hollow pill and fill it with pure water, this way the water can absorb lots of energy, but once enough has been absorbed the temps with rise.

EDIT: also the down time (off time) of the light needs to be long enough to rerelease the stored energy in the water. Off time should be longer than on time, depending on the power the led is run at.

I was just assuming since water has a high specific heat per mass, but I am not sure if there are better materials that have a higher volumetric specific heat.

 

[jankj]

Pure water is VERY hard to find. . . Even very minuscle amounts of pollutants makes water conductive. Try measuring the resistance of "distilled" water that you are supposed to refill on (old) car lead batteries. Don't rely on water being an isolator.

What I do like about this idea is that if the water is allowed to circulate it is a VERY good medium for heat transfer. (high specific heat capacity AND good heat transfer to adjoining surfaces, particular if the flow is turbulent). Don't make the water cavity too small and don't put the heat source on the top (hot water rises, use this fact to your advantage). Put the heat source (i.e. led) on the side and you're OK.