Improving Heat Dissipation

Every motor controller produces heat — it’s an unavoidable side effect of managing electrical power. As current levels rise, so does the heat generated inside the components. If that heat isn’t properly managed, temperatures can climb to the point where performance suffers or the controller is permanently damaged.

Effective thermal management is therefore essential to ensure reliability and long service life. Broadly speaking, there are two ways to remove heat from a controller: conduction, where heat is transferred into a heatsink or mounting surface, and forced-air cooling, where airflow carries the heat away.

First let’s look at conduction. The aim is to get the heat from the controller heatsink away into something else as quickly as possible, to do this we need that something else to have the following properties…

• Have good thermal conductivity – aluminium is 4x better than steel. Do NOT mount the controller on a wooden or plastic surface, these will insulate the controller and prevent heat dissipation.
• Be as large as is reasonably practical for your installation. The more mass it has then the larger is the “bucket” to pour excess heat into, the more area it has then the faster that excess heat can leak away.
• Have a smooth flat surface with no air gaps [use thermally conductive paste].
• Be rigid enough not to bend or flex when the controller is mounted to it. Remember that there may be vibration that causes the mounting plate to flex.

 

 

 

 

 

 

 

 

 

We recommend mounting the controller vertically if possible, this allows natural air convection to better assist with dispersing the heat from the mounting plate.

Now let’s look at forced-air cooling. The aim here is to get the excess heat into the air and then away from the controller as fast as possible, to do this we need to pay attention to the following…

• Fan airflow rate. Although PC cooling fans look superficially similar, there are big differences in the airflow that they can actually shift. Have a search through Farnell or RS to find one with a good CFM rating – around 80 gives good results on our test bench.
• Mount the fan on spacers so as not to “stall” the airflow.
• Give the heated air somewhere to go, have vents in the top of the compartment, consider a 2nd fan to drive the heated air out of the compartment.
• Allow cooler air back in, have vents in the bottom of the compartment.
• Top tip: power the fan from the controller parking brake socket, then the fan will only come on when the controller is working.

We have recently done some tests with the outside of the heat sink spray-painted matt black. This chart shows that the controller ran 5 – 10 degrees cooler than with the bare aluminium finish.

If you still get overheating after that, then it may be time to consider either a bigger controller, or a finned or water cooled heat sink.