I have made many electronic loads in the past. For instance this simple harddrive cooler housed small dummy load, this more sophisticated constant current/constant programmable load and this heavy-duty electronic load that is capable of sinking over 1kW under peak load. In this blog post though, I am going to take a look inside an Array 3711A DC electronic load I recently purchased on eBay. You can find a video of this teardown towards the end of the post.
The Arrary 3711A can sink 300W with a maximum load current of 30A and maximum load voltage of 300V. It can be used in constant current, constant power or constant resistance mode and can be controlled remotely via an RS232 interface.
The entire unit is actually quite compact given the amount of power it is capable of dissipating. This can be largely attributed to the efficient forced-air cooling system it uses. There are four fans all together. Two are sitting at the bottom of the chassis that sucks in air. The air then flows through the heatsinks and the hot air gets blown out from the back via another two fans.
To achieve this compact design, some sacrifices need to be made. This becomes apparent after opening up the top cover. As you can see in the picture below, the power module boards are mounted directly on the heatsinks and the microcontroller board is tucked away behind the front panel. And to access any components located on either the front panel digital board or the analog board located at the bottom of the case you have no choice but to partially dissemble the unit.