Power Distribution Board
This Power Distribution Board (PDB) is specifically designed for Phoenix Solar Racing's Phoenix solar car and hopefully future solar cars.
I designed the board to handle 10 Amps of current. This is probably more than we will ever use, even in peak situations. To design the trace sizes I used simple geometric calculations of trace L*W*H, to get 0.01ohms from farthest-input to farthest-output. At 10A that's 1W of power dissipation and 0.1V drop. I used 2-once copper PCBs and removed the solder mask on the ground traces around the outside of the board, just in case I needed to increase the current handling by piling on solder.
I tried to keep power traces on one side, and signals on the other. Power-traces had to jump up to the top to connect to surface-mount current sensors.
>Flir photo >In tests, 10A of current showed no clear signs warm traces. Only fuses and input diode are warm >temperature resolution is very fine so if the traces were dissipating
>small PCB photo with Google photos link >micro scope photo?
-Got from PCBWAY.com for 74$ & 22$ shipping, That's for Ten, 175mm x 120mm boards with 2-once copper. Please excuse me as I shill, but I am really impressed with the quality and price of PCBway as well as their advanced website that shows the status of your PCBs on the assembly line. A real person makes sure your Gerber files are not screwy, and the boards are tested with flying probes before they are shipped, but that might be for protecting their own reputation. >facebook post ;)
I simulated the input protection in Multisim and experimented and tested many different Zener Diodes. The diode I chose is a special type of Zenar called a TVS diode. Unlike normal zeners, TVS diodes can conduct thousands of Amps when in breakdown (for a few micro seconds). The simple cheap automotive fuses used on the board take relatively a long time to break. The TVS diodes "burn up" and fail closed by the time the fuse breaks. if the PDB experiences an Over-voltage situation, one or more TVS diodes will need to be desoldered and replaced. I chose this input protection circuit because of its simplicity, low cost, and feature-set.
I added 5.1V zener diodes on the 5V rail just in case a high voltage tries to find it way onto it.
15 Red-Green combo LED s display
Current & Voltage Sensing
We use one kind only of micro-controller on the team for applications like this, a Sparkfun "pro micro" (20$) or equivalent knockoff (5$) loaded with the Arduino Leonardo boot-loader, not the Sparkfun boot-loader. It is coupled with a MCP2515 CANbus Controller IC to give the setup the ability to report the PDB's status to the bus.
Reverse Leakage Current
The reverse leakage current of the power input diodes is something that caught me off guard, 150uA or more at 13V. The leakage makes it appear as though there is a 11.5V ghost battery connected to empty ports. The 100k+10k voltage divider to ground dose not drain enough current away so I have to bodge in a 5K resistor in parallel. Even wth the 5K, the ghost voltage is about 3V, but in software I can say that anything below 5V will mean that there is no battery connected.
The relay coil power is sourced from the wrong side of the relay. That is, the relay needs to turn on... in order for the relay, to get power, to turn on... I noticed this problem when I was laying to the board, but forgot to change it! I also had no room left to route a trace and would of had to use a jumper anyway
The current sensors output a ratiometric voltage per current, meaning for every 1A increase, the output voltage increases 5%vcc. This is great because the ADC on the micro-controller works the same way if you set the reference voltage to VCC as well. The problem arose when I supplied the the Arduino pro micro board with 5V on it "RAW" pin so the VCC that the 32u4 saw was only 4.2V, because of the voltage regulator on the board. The fix was just to put a jumper wire to short the VCC and RAW pin on the Arduino, lucky break.
If I Was To Do It Again