Using aluminum body as heatsink?

[corrado33]

Hey guys, I have a quick question.  So if you've been reading my threads lately you know I'm building an aluminum bodied robot that uses 24v to drive the wheels.  So to convert that to 5v for my microcontroller, I'd need some kind of transistor.  And this transistor is going to get HOT!!  So my question is, could I simply touch the back end of the transistor to the body of the robot to act as a giant heatsink?

And by touch, I mean securely attach it with some kind of heat conducting glue.   

[galannthegreat]

Not recommend, but possible, but I wouldn't really suggest this as doing that could potentially put your system out of whack. Heatsinking is a huge industry in the electronics world. Invest in separate heatsinks for your tranistors, and maybe even a fan cooling system.

[ArcMan]

Absolutely, yes.  Using a chassis as a heat sink is very common.  The motor drive on my 24VDC robot is heat sinked to the electrical box / chassis.

Just keep in mind that your chassis should be grounded, so if the transistor has a metal body, it must either be ground or you must use an electrical insulator between the transistor and the chassis.  You can buy insulators and insulating bushings for just such a purpose.

[hgordon]

Aluminum body makes a great heat sink as well as a nice common ground (unless you are doing Robot Wars, in which case a grounded chassis is a bad idea).

[galannthegreat]

Speaking from a technician's view, it's not a good idea. But if it is working for others you might aswell try it.

[chelmi]

Speaking from a technician's view, it's not a good idea. But if it is working for others you might aswell try it.

Maybe it depends on the application, but it is a "common" (used in the industry) practice to use the enclosure as heatsink.
You can even buy enclosures designed for that purpose:
http://news.thomasnet.com/fullstory/535292
http://www.lawtronics.co.uk/heatsink.html

And I remember seeing electronic system with transistor or LVR in TO-3 packages mounted on the case.

Chelmi.

[Soeren]

Hi,

Hey guys, I have a quick question.  So if you've been reading my threads lately you know I'm building an aluminum bodied robot that uses 24v to drive the wheels.  So to convert that to 5v for my microcontroller, I'd need some kind of transistor.  And this transistor is going to get HOT!!  So my question is, could I simply touch the back end of the transistor to the body of the robot to act as a giant heatsink?

And by touch, I mean securely attach it with some kind of heat conducting glue.   

I guess it's the voltage regulator you keep calling a transistor?
A few points worth having in mind:
Heat conducting glue has a high W/K rating, so better bolt it on and use a very skimpy layer of heat conducting silicon grease.
The body comes nowhere near the low W/K rating of a large quality heatsink for a number of reasons (the surface are is much larger on a finned heat sink and the body is not optimized for the passing air flow to really be used well like in a finned heat sink and it's all a question of surface area and air flow).

Using the body is good up to a certain power rating (different for each body/box).
It's not very difficult (but somewhat time consuming) to measure the W/K of a box or a robot body - it just takes adjustable power, a variable (or several) load(s), and a thermometer.

[Admin]

Yeap, I think he means voltage regulator . . . hmmmm . . . and its getting hot?

How many mA are you using at 5V? Powering servos?

(24V-5V)*50mA = 1 W of wasted power

Might be better if you just used a 6V battery. You can also put voltage regulators in parallel.

[corrado33]

Hey guys, I was just speculating when I wrote this thread.  It's actually not a problem anymore as i'm using a switching regulator, but it's still a cool idea in theory.  And yes I did mean a "voltage regulator".  Thanks though for the clarification.