I got the board fully populated yesterday, plus I made a heat sink out of a piece of ¼” × ¾” aluminum bar stock. The heat sink makes an enormous difference. Before using it, running a small motor at low power for 20–30 seconds was enough to make the H-bridge uncomfortably hot. Now running the same 12v motor stalled at full current (3A) for a full minute raises the temperature only to 100ºF.
The motor got warmer than that, and I think I burned it out, since it no longer runs and has a 400kΩ resistance. I’m not really surprised—it was a cheap door-lock actuator, and only intended to be used with fraction of a second pulses. Further testing will require a more robust motor.
As you can see from the photo, the screw terminal for motor 4 (second from the bottom) is a bit crooked—I’ll have to unsolder it and straighten it. For the HexMotor 2 board, I’ll use slightly smaller holes so alignment is easier.
The thermal grease I used (Cooler Master IceFusion High Performance Thermal Compound 40G RG-ICF-CWR2-GP) was more liquid than I expected, especially since it comes with a little spatula for applying it. I had to put on a fairly thick layer, because the aluminum extrusion was not very smooth, and when I tightened the bolts the stuff oozed out making a sticky mess. Next time, I’ll sand the aluminum smooth first and use much less thermal grease.
Closeup, showing the excess thermal grease puddling under the H-bridges, where it is very difficult to wipe off.
This closeup photo, in addition to showing the pooled excess thermal grease, shows the header pins with shorting jumpers to configure the H-bridges for either lock antiphase or sign-magnitude control. (Because of the last-minute change from TLE-5205 to TLE-5206 chips, the silk-screen labeling of the header pins is wrong—this board is actually configured for sign-magnitude throughout not lock antiphase.
The photos also show that I did not leave room for the heat sink between the electrolytic capacitors. The HexMotor 2.0 board will fix this problem also.
The HexMotor software now can handle 3 different boards: the HexMotor rev 1.3 board shown here, the Adafruit Motor Shield, and the HexMotor rev 2 board, which I am just about done fussing with the design for. I’ve only tested with an Arduino Duemilanove board, but the software should work with an Arduino Mega as well.
Tagged: Arduino, H-bridge, heat sink, motor controller, Printed circuit board, thermal grease
[original story: Gas station without pumps]