Thermal Compound – Another Experiment

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NeutralFan
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Thermal Compound – Another Experiment

One regret I had with my Cheapo AA Flashlight Mod was that I didn’t use any thermal compound between the LED MCPCB and the copper pill. Why didn’t I?

  • I didn’t have any.
  • I didn’t think it was necessary since it was only a single AA flashlight so not much heat to worry about. Plus I used a direct thermal path LED MCPCB.
  • The LED MCPCB and the copper pill are clamped together tightly by the retaining ring. I thought the contact alone should be enough for the pill to absorb the heat.

But with my Convoy C8 Mod, I knew better to risk not using thermal compound so I bought some. Now that I have some compound, I thought I would perform a small experiment to see if it has any impact on the AA flashlight.

To establish a base, I took the temperature of the flashlight sitting on my workbench.

I then turned the flashlight on and kept measuring the temperature of the flashlight head until it no longer got hotter. Please note that the entire flashlight body is made out of aluminum so a lot of metal to absorb and dissipate heat.

The flashlight head got approximately 8 degrees Fahrenheit hotter.

I then took out the LED assembly and separated the LED MCPCB from the copper pill. I put some thermal compound on a toothpick and put it in the middle of the pill (middle dot method). I pressed the LED MCPCB back onto the pill and twisted it slightly back and forth to squeeze out any excess compound. And then put the flashlight back together and ran the second part of the experiment.

With the thermal compound, the flashlight head got approximately 20F hotter. Very impressive!

I shared this experiment with some of my family members and they initially thought the thermal compound should have kept the flashlight cooler, not made it hotter. I told them that a flashlight should quickly take heat away from the LED and the increase in temperature was a good thing. I then started to get blank stares and obligatory head nodding so I knew I had once again gone too far talking about flashlights.

My conclusions. Without thermal compound, the heat from the LED was slowly being distributed and dissipated throughout the entire flashlight. With the thermal compound, the heat was more readily absorbed by the pill and thus more heat dissipated through the head. The same amount of heat was being produced by the LED, but with the thermal compound, the heat dissipated faster.

I’d rather use my flashlight around the house than turn on the lights.

kennybobby
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What was the ambient temperature in both test cases?

chinooker
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that looks like a pretty big Uncle Ben grain of rice
could the compound be filling more than just microscopic imperfections in the surfaces?

NeutralFan
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kennybobby wrote:
What was the ambient temperature in both test cases?

Same as the initial temperature reading of the flashlight – 60.7 degrees Fahrenheit.

I’d rather use my flashlight around the house than turn on the lights.

NeutralFan
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chinooker wrote:
that looks like a pretty big Uncle Ben grain of rice could the compound be filling more than just microscopic imperfections in the surfaces?

Probably since a copper plumbing cap may not be perfectly flat on top.

I’d rather use my flashlight around the house than turn on the lights.

chinooker
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well, it made a big difference in your light
and that is good
your audience needs a bit more erudition