So this has been a very long time coming. I have come to notice that the most popular thing I have created on the internet happens to be my BLDC Alternator motor. So let’s try continuing with that. Here I have finally designed a PCB using Eagle that will control the alternator motor with less of a wire nest. With this board I can just pop the components on it and hook it up to the alternator! Let’s take a look at the list of components needed:
- Q1 through Q12: IRF2807 N-Channel Hexfets – These FETs were picked for their very low on-resistance, and high power dissipation capabilities at relatively high voltages. It is possible to use other N-Channel FETs, however they need to be powerful enough to drive a 0.5 ohm load with the voltage it’s given.
- IC1 through IC3: TC4420 MOSFET Drivers – In my original design I used the 555 timers to drive the gates on the Hexfets. This worked, but the 555 timers do heat up due to the high current the Hexfets can pull. The TC4420 fixes this by allowing up to 6 amps though it’s output, where the 555 timer was only supposed to allow up to 200 mA.
- IC4 through IC6: NE555 Timers – These 555 timers are configured as “Inverted Schmitt Triggers”. They take the sensor outputs and invert the signal since the output from the A3144 hall effect sensor shows HIGH when no magnet is present, and LOW when there is a magnet present. This signal then goes to the TC4420 chips to trigger the Hexfets.
- IC7: NE555 Timer – This 555 Timer is a throttle solution by providing a PWM signal the other 3 555 timers reset pins. It basically overrides the output by shutting down all three chips if it is LOW and bringing them back up if it is HIGH. The PWM frequency is controlled by the selection of C1 and the Potentiometer that is placed on THR+, /, and -. The pulse width then is determined by the position that the potentiometer is set at. In the last iteration, I used much to low of a frequency and it was very noisy (Chewbacca noisy! ha ha) So this time I plan on using a much higher frequency to quiet it down.
Really that’s it. The only other components on the board are the 12x 3.5mm 2 pin connectors, and about 6 inches worth of 3/4″ aluminum angle for mounting the Hexfets.
There was one big issue in designing this though. I was disappointed in not being able to place a positive power rail for the motor on the board. This was because the trace width needed to be just as big as the ground plane that’s already on the board (the size of the whole board) in order for it to work right. So the positive power for the motor actually just goes directly to the motor. Really though, the only reason I wanted it was so that I could maybe make it into a shunt resistor and measure the current off of it, but that can just be placed in line with the positive power to the motor anyway.
One small annoyance was that I could not figure out how to remove the middle pin from the TO220BV package in Eagle. My design does not use that pin as it uses the mount to pass the current through the drain, so I usually just break that pin off the component. However it was used by what seemed like billions of other devices in Eagle, and would have been a nightmare to clear it all up. In a future version I may just create my own library for it.
I have JLCPCB working on this board right now, and it should be finished and delivered here by the 15th. Once that shows up the fun can begin with assembling this little beast. I am having trouble figuring out what to do with 5 pieces though… I only really need one *wink wink! I will work on how I can possibly get rid of the extras to any super fans of the project that may want one!
Hope this is as exciting for you guys as it is me! Be back next week!