I have a project that require me to use 120VAC through the tether, and then use a AC-DC converter inside the battery housing to run a Bluerov standard config. I will only run the motors on 25-50% gain.
The tether i have available is a 100m long Deltarov power tether with 2x0,75mm2 power conductors.
My plan is to use this Ac-Dc converter in the rov:
Hi @Jhans -
Before you go any further, I would strongly push you to identify, obtain, and test adequate safety components for your project. Putting AC voltage in proximity to water can be very dangerous, especially at high voltage (anything above 24V, AC or DC, becomes pretty nasty!) At the minimum you should use a ground fault interruptor circuit, with a ground line in the body of water you’re deployed in. Other ways of detecting leakage current are possible, and worth doing!
When you used the calculator, you increased your wire area above what you said your tether had?
400-600 watts is a good estimate for 50% power consumption of the standard ROV.
Keep in mind that the power loss as heat can cause issues, especially for portions of cable not immersed in the water or coiled on a spool. Divide the energy loss by the length of your tether to understand how much heat energy per meter will need to be removed, to prevent wires from melting.
Upon reviewing your power supply system, it appears that it may not perform as expected. The issue does not seem to stem from the conductor size; the voltage drop across the 50-meter tether is within the specifications of your AC-DC converter.
However, a significant concern arises when considering the use of brushless motors. When decelerating (e.g., transitioning from full forward to a stop), these motors function as generators. This generates a reverse flow of power that must be properly managed.
In systems using a battery, like the BlueROV2, this reverse power flow is absorbed back into the battery without issues. But in your setup, which uses a direct power supply, there isn’t a straightforward path for this back current to dissipate. Consequently, it will feed back into your AC-DC converter, potentially causing an increase in the output voltage. This spike in voltage could trigger the overvoltage protection mechanism in your converter, leading to a shutdown of your power supply.
It’s crucial to address this reverse power flow to ensure the reliability and safety of your system.
I would send 200v DC down expecting 30 volts drop or more in the tether, then use a switching regulator in the ROV.
Shock hazard for nearby swimmers.
Galvanic corrosion for any leak to water.
You need a battery in the ROV to handle surges and store the charge.
Installing a power diode in series with your PSU output could prevent the overvoltage trigger on your PSU. However, this approach has a significant downside. While the diode would block the back current from returning to the PSU, it doesn’t provide an alternative path for this current. As a result, you might see an increase in voltage within your circuit. This heightened voltage could potentially exceed the maximum voltage tolerance of your devices, posing a risk of damage.
Regarding the brushless motors, one avenue to explore could be adjusting the settings in QGroundControl to modify or disable the braking function of the motors. If feasible, this adjustment might help manage the back current issue but I’m not sure if it is possible to do.
I’m also curious about the operational duration and specific tasks your BlueROV2 is intended for. Depending on these factors, incorporating an additional battery could be a viable strategy to extend its runtime. Could you please provide more details about the intended duration and nature of your BlueROV2’s tasks?
P.S. It’s important to note that constructing a reliable and efficient power supply system, especially one that deals with high voltage input and high current output, is a complex task. This complexity extends beyond just preventing overvoltage; it also involves integrating additional components like capacitors and resistors. Moreover, managing heat dissipation is a critical aspect that cannot be overlooked.
At SubseaLED, we devoted two years to research and development to perfect our 1500W power supply system. Given this context, if you’re working within a tight deadline and wish to avoid the extensive investment required in developing a bespoke power supply system, I would strongly recommend considering alternative solutions.
One such alternative is to focus on extending operational time using batteries. This approach is generally simpler and can be more readily implemented without the complexities and risks associated with designing a custom power supply system. If you decide to explore the battery option, I would be happy to discuss potential configurations and strategies to maximize the effectiveness of this solution.
