I needed a 5V 1A source in the car but didn't want to have some ugly adaptor plugged permanently into a fag lighter socket so used one of those jellybean TO-220 package monolithic regulators for the job. Mounted it to a steel tab on the chassis via mica washer and silicon gel. I thought that would do, and it may well, but the damn thing is getting hotter than I'd like running flat out and of course when the engine's running it's working even harder still dropping from ~14V down to 5 rather than the usual 12V. The heat is confined to the reg (which is too hot to touch for long) and the very close proximity around it on the steel tab. It's like it's not leaching away very efficiently into the rest of the tab, which is quite cool. I know copper and aluminium are supposed to be better heat conductors, but would it really make that much difference to switch metals?
Heat Sinks
Jul 13, 2024
Last reply: 2 years ago
13 Replies
In my previous car which didn't have any USB outlets I fitted 12V to 5V USB panel mounted sockets very much like
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Search ebay for "usb car panel socket"
You will find a variety of discrete panel sockets requiring just a hole or sockets already mounted on small panels.
These days USB C is becoming more popular so you may be able to find something physically smaller if you opt for a USB C output rather than a USB A output.
In the past I've opened and discarded the casing of a USB mains adapter to reveal the small PCB, then directly connected it via wires and packaged the whole device in my own very much smaller enclosure. You may find that if you strip apart a car 12V to USB adapter you will find a small PCB which you can wire directly and it will not run as hot as your current arrangement.
The type I purchased was 12V to 5V with a specification for output current.
The listing above gives no details so best avoided but the same physical socket can be found elsewhere with a detailed electrical specification.
You can safely have the chip running hot enough to boil water I think if it gets too hot it will shut down safely
Thick alumininm better than thin steel
Yeah, I know you're right from the strict technical pov, but coming as I do from the 'germanium generation' it just feels wrong.
What about 0.5mm thick copper sheet?
well I am firmly of the 'silicoin' generation an d power circuits to boot I have had one of those s*it down. Crashed my model Tiger moth. Switched it off and on again ant it worked fine.
Well you can try. I'd rather go for 2mm Al.
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That picture reminds me of a supplementary question: ISTR from *way* back in school that matt black surfaces emit heat more efficiently than bright surfaces. With that in mind, would painting the tab matt black help meaningfully?
IIRC correctly, what counts is the emissivity of the surface, and from what I have read that of a black painted surface differs not a lot from a white painted surface; neither is a good approximation of a black body.
Might do. Matt black is the best for losing heat; shiny chrome is the worst. I have no idea why. They reckon to get the most reliable reading from a 'point and squirt' IR thermometer you need to paint the surface of the subject item matt black or apply black insulation tape to it and aim for the taped area.
Yes, that's because the IR thermometer looks at IR. This has little to do with how much heat is being dissipated by the heat sink, which is mainly being absorbed by the surrounding air in the consequent convection current. I recommend mounting the heat sink vertically to encourage air flow.
Well no. The amount of radiated energy from a heatsink 50 degrees above ambient is negligible compared with convection.
And in sunlight, the absorption of radiation from a sun 3500°C hotter than the earth is CONSIDERABLE.
I havent used a Germanium Transistor since I was at IBM in 1986. Got some Esaki Diodes around.
In message snipped-for-privacy@4ax.com, Dave W snipped-for-privacy@yahoo.co.uk> writes
There's possibly a case for mounting a heatsink surface at an angle to the vertical, so that the air is forced to 'rub against' it instead of 'slipping smoothly over' it.
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