Hi there! I’m working on a project and could use a bit of help. I need to power two T200 thrusters attached to a stationary frame at a depth of 130 feet. I have access to a 120v power supply at the surface, and they’d only need to run for about 5 minutes at a time. Any advice or information you could share would be greatly appreciated. Thanks so much!
Hi @darren.horler -
I’s assume your 120V at the surface is AC, and not DC voltage?
What power level do you need to run the thrusters at?
Converting to a safe DC voltage (<24V) and sending power along sufficient copper to the ESCs, located in an enclosure at depth alongside the thrusters is likely your best bet. This calculator can help you determine how much copper would be necessary based on your power consumption, tether length, and cable used. Or, placing a battery on your frame and just sending a control signal to the ESCs down the tether could also work.
As always, take extreme precautions when sending power down a cable in the water! A GFI or other safety system to prevent voltage reaching the water is an absolute requirement.
Thanks for the information. Yes, it’s 120V AC. Unfortunately, I can’t leave a battery at the frame since it would have to stay at depth for its entire functional lifespan.
I aim to operate the thrusters at the maximum feasible speed
Hi @darren.horler
Two T200s at maximum power is quite a lot to send down a tether! It will require significant copper to do so. Here is an example of how you can make it work:
You’ll need a single 9 AWG, or 2X 12AWG wires for positive, and the same for the negative. You’ll also need a twisted pair for ground and servo-style PWM signal, to control the ESC. You may run into issues sending this control signal down 150’ of tether! A thruster commander could help with this, if control could be local to the equipment. You may need 200 foot or more to reach the depth!
This is only enough power to run a single T200 at full power, so you would double everything to run 2x!
You’d need to convert your 120AC to 24V DC with a sufficiently large power supply - Running at this voltage will mean if the cable is damaged, no one gets hurt, but they may feel an unpleasant sensation!
Would it be practical to send the 110V AC down to depth and connect it to two AC-to-DC converters, then route the output to the thrusters? The 110V AC would be powered by a 2000W Honda inverter generator with GFCI protection. Additionally, I’m not quite sure how to handle the ground and transmit the servo-style PWM signal. Your information has been extremely helpful and appreciated.
Hi @darren.horler -
It would be possible, but incredibly dangerous, to send the 110V AC down your tether. 
The GFCI on the generator is likely to have a very slow trip time, if it trips at all if/when the cable conductors are exposed to seawater - you may need to run a ground wire from it to the seawater to have this function at all. A better solution would be a line insulation monitor - these can be quite expensive, for good reason, as they will detect and trigger a connected relay to open fast enough that no one dies! AC voltage in water is incredibly dangerous, so we can’t endorse that approach…
You can generate the PWM signal with a simple servo tester, only the GND and PWM output pin needs to run along your tether to the ESCs - if you’re sending the same signal to both the signal and ground lines can be linked together. This has the best chance of working over that distance if you use a twisted pair to carry this signal.