Hi all,
I’m obviously missing something, but at rest, I thought the only device drawing power was the Pi (and anything else connected to the Pi)? But I’m guessing given the discussion that the ESCs also draw power? Any idea what sort of load? I had a look for the AfroESC specs but couldn’t find anything.
I’m just wondering for myself the tradeoff between a simple switch on the BEC for the Pi to save most (maybe) of the power draw, vs the options discussed here for an absolute power cut.
I believe the ESCs draw about 0.5 Watts when they aren’t running. The microcontroller and other circuitry draws about 30 mA at 5v, and since it’s powered through a linear regulator, it uses the full 30 mA at battery voltage (16v). So that’s 16*0.030 = 0.48 W.
Why don’t you simply switch all the control power off with the Blue Robotics switch. i.e. switch on / off tether interface, Pi Computer and Pixhawk. Problems with high amp relays gone. The only thing left to draw any energy are the built in esc’s for thruster control.
I think the principal objectives of being able to turn off power in the ROV are to prevent unnecessary battery power loss and to render the ROV “safe” without having to open a housing. Turning off power to the control systems might meet one of those objectives but not both.
Yes, the ESC’s will still draw about 3 Watts according to earlier posts, but simply having ability to turn off controls and reboot without opening still has a lot of value. I do like the idea of topside on off capability though even if just to reboot while subsea.
I am considering adding a 100A SSR to the battery compartment, with a Blue Robotics external switch in the endcap. I have the BR battery pack. Any issues with using the charge balance connector as power source for the control circuit? The datasheet for the SSR states 15mA maximum input current for the control circuit. Also they say inductive loads must be diode suppressed, but I assume that because the motor loads are managed through the ESCs that doesn’t apply in our application… is that a correct assumption?
I know power switching is being considered for our next ROV version, as part of a broader electronics overhaul. Beyond that, I don’t believe we’re working on a self-contained power-switch that could be added to an existing ROV.
The biggest issue with an ROV power switch is being able to handle the significant current levels that the thrusters can draw. If “low power” is an acceptable “switched off” substitute then you might want to consider using a switch to control a MOSFET that can switch the power inputs for everything other than the ESCs, or possibly just the input to the 5V converter. Both those options mean the flight controller can be switched off, at which point it cannot send any control signals to the ESCs (which means they’re safely stopped), and should reduce most of the idle current draw.
I thought I’d share this solution. My preference would be to keep the SSR in the power enclosure (vs. the electronics enclosure) so have used:
BlueRobotics wet switch
SSR 100A 30VDC
1N4002 diode as flyback
Mounting plate made from 3mm phenolic board (artwork PDF under photos).
4 x BlueROV2 short standoffs
4 x M3 x 8 bolts
2 x M4 x 8 bolts / nuts / washers
Longer AWG11 (ideally) or 12 red/black DC power wire.
This solution JUST fits the 15Ah battery with the standard enclosure length. Battery access is from the front of the ROV with the longer power cord fitted.
NOTE: The flyback diode needs to be mounted in the electronic enclosure across the bus bars (earlier photos had it across terminals on the SSR - daw!).
Thanks @EliotBR. Super impressed with the BlueROV2 product. Well done to the whole team - and big ups to Matt at Bay Dynamics, your NZ distributor, for great support.
@PeterM@EliotBR
This thread helped me a lot I myself used a 120a constant duty 12v relay with a diode across the coil like you have there. I then send 12v down my tether to activate the relay, I haven’t had much real world usage so it could fail on my one day but I am positive buoyant so hopefully I can pull her back in from up top.
I really wanted to do SSR like you did but I only know of crydom and they are wow expensive for 100amp. I used some china ones 40amp for my printer and nearly burned my house down.
I put a switch on the front of the BR surface box and use a spare pair in the tether to turn it on/off. No issues after a few years of use so far! The SSR fits easily in the main enclosure.
Now that is slim and pretty, Kinda surprised heat is not an issue, but I guess quality of gear matters. the china 40a DC relay when operated at 10amps got hot enough to char wood, however the crydom 20 AC relay that powers my 1500watt heater remains cool with nothing more than a small 40mm fan.
