Powering with DC power supply? How much current and voltages?

power
electronics

#1

Hello,

I have the motor set (3 brushless DC motor) and ESCs (Turnigy 18A) from OpenROV 2.6 (or previous version, I’m not sure), without other parts, and I’m planning to design my own system with DC power supply. I received these items without manual or spec sheet and am clueless right now, about how much voltage and current do I need to supply to the ROV at max, that is 3 motors running at full speed?

I have tried with the old configurable power supply I currently have on hand which can supply ~5,5V, ~8,5V, and ~10,5V at 1A, it probably a bad idea though? Only tested for like 30 seconds.

I haven’t decided on what cable to use and whether to build the power supply and how, or bought one, any recommendation?


#2

It uses about 0.5-0.8A @ 10V driving only the computers.
Here is the specs on the motors: (at least on 2.8) http://www.hobbyking.com/hobbyking/store/_52808__Turnigy_Aerodrive_DST_700kv_Park_Fly_Indoor_Motor_EU_Warehouse.html

So you need to have to manage at least ~20A at peaks.


#3

I would say it is not doable in a meaningful way. If you power with 10V dc, you need a massive cable area to compensate for voltage drop. Powering with AC and have an onboard converter might workout, but is very, very dangerous.
Here is a link to a calculator for calculating voltage drop etc.
http://photovoltaic-software.com/DC_AC_drop_voltage_energy_losses_calculator.php


#4

Thanks that’s what I’m about to do since the voltage drop is became too much to handle, I also read that professional ROV is using this method as well by sending thousands of voltage over AC, I’ll just use regular AC from the net at 220V/50Hz though, but what is the very very dangerous danger you speak about? I’m thinking to put the converter in separate container on the ROV and lots of heatsink due to the heat.


#5

Water + High voltage AC is very dangerous. With wet/damp hands a small zap that you would easily survive on dry land could easily kill you. It only takes a few mA through the heart to die and water rapidly lowers the resistance of the human body. A small nick on the cable while managing the tether could provide a path for you to come into contact with full mains voltage. When you said “I’ll just use regular AC from the net at 220V/50Hz though” and you didn’t mention RCD’s, earth leakage detectors, double insulation or any other safety devices, I became concerned that this is not a safe project for you to construct. Appropriate wiring standards need to be observed when dealing with mains or the setup could be quite illegal in most countries. If you have a small leak in the converter you could have a fire and lose your ROV. Professional ROV’s use appropriate standards to manage safety with AC and water. You could lose your life if you don’t know what you’re doing. That’s the very very dangerous danger.


#6

What Brendan said.
220V AC is lethal. And in combination with water in an amateur project it is not a question if someone would get seriously injured or most possibly killed. It is about when.
Just do not try this.


#7

Agree with @marcus2. DO NOT TRY THIS. Go buy some 18650 batteries like we discussed in ROV Peak and Constant Current Draw It’s not worth dying to save a few dollars.


#8

Agrees that you should not use the mains and a transformer downside, at least not without a state of the art ground fault monitoring system, a certified and proven unit like Bender or Megacon.
There is a old way od doing this used on the Sprint vehicles. They had two conductors, I guess around 2.5 sqr mm for power and a twisted pair for feedback from the vehicle in the tether. The twisted pair then feed back actually voltage at vehicle to the surface powersupply.
I guess you could easy make up a power unit using a lawn mower motor and a car alternator. The feedback would then feed the subsea voltage back up to the regulator. The alternator output would then become 14 volts plus the voltage drop in the cable.
This would provide unlimited dive time and independency from the grid.
I strongly recommend installing a DC/dc converter subsea to power the fragile electronics.