Can someone explain to me the importance(or lack of) of having a heat-sink on a mosfet in a 1590g unregulated box? I seem to recall hearing or reading that it is bad to use heat-shrink because it will overheat? Perhaps meaning lost power or a blown mosfet? Can someone please explain the deal with this?....
MOSFET heat-sink?
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Check your datasheet for the specific MOSFET in question... generally they limit the output amps based on temp. Heatsinks and Heatshrink or not the same thing, by the way.
Yes, I understand the difference between heatshrink tubing and a finned heat dissapation apparatus lol... just curious if it is bad to use heatshrink in general because it acts as something to keep the heat IN.
I figured you knew that
Yeah, heatshrink will act as a thermal insulator similar to how it acts as an electrical insulator. I wouldn't just heatshrink the whole MOSFET unless there was some good reason for it besides making it 'look clean', but that's me.
It should be noted though, that given the duty cycle we put the MOSFETs through, the amps we want to pull and the specifics of a particular MOSFET... they may only need a small heat spreader or a small heatsink to rapidly absorb the heat being generated and may not necessarily need that heat dissipated into the environment as quickly as other common items such as CPUs that are generating heat constantly. As a vaper, you might only be activating the MOSFET for 5 straight seconds and then letting it rest for 55 seconds or more before the next activation.
To summarize my opinion... MOSFETs generate heat and they will limit their output based on their temperature. I have never ran across a heatshrink tubing that also acted as a good heat conductor. The datasheet should describe the thermal characteristics of the device including how much heat you can expect to be generated given a specific load, how much heat the device package can dissipate as well as how much output you can expect from the device at given temperatures.
One last thing to consider is that if you use a proper size wire for the current, so as the wire itself is not joule heating too much, then you can consider this wire connected to the MOSFET to be a heat sink as well, but it will not work as well as a heatsink connected to the intended location.
I hope that helps.
Ok cool that makes sense, I plan on using 14 solid copper for the whole thing so I should be fine. Thanks
Very true, it just prohibits using the heat-shrink as talked about above. The other nice thing about this, is that many of the MOSFETs will have the heatsink connector shared with the drain connection... meaning you wouldn't even need to run a wire from drain to the ground on the 510 so long as the 510 makes good contact with the enclosure... in this situation you just have to make sure that your switch doesn't short the switch housing to either of the contacts for some completely silly reason.
I run mine naked on single and dual 18650s with open conductors. Zero heat anywhere. No fins No wrap.
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Which mosfet, at what expected current and what current are you measuring via ammeter?
With mosfets pick a low resistance one that you can be sure you always have the gate charged to a full on condition when firing and don't forget about battery sag when figuring that. Also make sure it is completely off when not firing. If you run the mosfet anywhere between off and full saturation it will start dissapating way more heat. Of course you must also make sure it can handle the current and voltages you are going to throw at it as well as dissipation.
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