Power Distribution Boad
The power distribution board converts the 48V from the surface to 12V and 5V to power all ROV systems
Sure, here is the edited version:
All ROV power distribution is managed via the power board PCB. It receives power directly from the 48V power supply on the surface, which is converted to 12V using a BMR4800102/002 flex power module. For the control loop of this module to function correctly, the ESR on the output must be under 1mΩ. To achieve this requirement, low ESR capacitors were configured accordingly.
The 48V Mean Well power supply on the surface produced random high voltage transients above 60V, which is the maximum input of the BMR4800102/002 upon power-up. While the tether alone provides a substantial amount of inductance, our team also integrated filtering capacitors and zener protection to ensure protection against these transients. A zener diode with a breakdown voltage of 56V was chosen in series with a 10Ω resistor. The 10Ω resistor was specified to avoid excessive power dissipation, which could lead to failure of the component. If the inductor-capacitor filtering fails, the zener diode will pass its breakdown voltage, causing an instantaneous short and preventing the transient voltage spike from entering the power board.
The 12V board supplies power to the ESC carrier boards and the Pi Hat. A 5V 1/16 brick converts the 12V to 5V to supply power to the Pi Hat. The board delivers a peak power of 900W to the ESC carrier boards. Both of these power modules have built-in over-temperature protection and short circuit protection (on the output side). The Pi Hat is able to read the temperature and power draw of the BMR4800102/002 using the PMBus. The heat from the system is dissipated into the water via conduction. This board is made from 2oz copper to reduce internal resistance.
Testing
- used a ~10:1 VD to test the top side supply, need to do this so you do not blow up the scope
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With out filtering, this would occur about 1 in 100 power cycles resulting in power modules being killed: see scope recording video
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With filtering we were able to dampen this spike
- This is the IC on the power module that failed
Current Status
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V1.0tested and functional
- The only problem is the MR-30 connectors have the wrong polarity, but the ESC carrier boards do too. If I was to do a 'V1.1', I would fix this, but this does not effect functionality in anyway. Just noting this if anyone ever does bench testing on this line of boards, make sure that your polarity is correct
To Do
V2:
- Fix popularity of MR-30 connectors, but if you do this need to make sure that it is done in line with a new REV of the ESC carrier board
- Add better circuit protection: would like to look in to having something on the input side that waits a specified amount of time at topside power up providing power to anything sensitive. Would likely consist of a 555 time, liner voltage regulator, and large mosfet or realy