Maximum supply voltage for OpenROV 2.8 Developer's Controller


#1

Hi All,
I have purchased an OpenROV 2.8 Developer’s Controller Kit that I plan to use with three Blue Robotics (BR) T100 Thrusters. The BR Thrusters can work off of a voltage range of 6 - 16 vdc and consume 135 watts each when run at full speed.
I plan to power the OpenROV 2.8 Controller with two 3S LiPo batteries which when full charged will reach a voltage of around 12.6 vdc. Is this an excessive input voltage for the OpenROV 2.8 Controller or can the Controller handle this voltage. Under load I am sure that the battery voltage will probably run at 12 vdc or a little under.
Since I plan to use 12 vdc batteries the BR T100 Thrusters will draw around 11.25 amps each maximum which does not leave much headroom if I use the present OpenROV 2.8 Controller 12 amp ESCs. Will it be a smart move to replace the existing 12 amp ESCs with say, 20 amp ESCs of the same physical size?
Regards,
TCIII AVD


#2

The voltage is fine. The controller is designed to work up to a 4S battery pack.

The current draw is a bigger issue. The OpenROV thrusters draw about 7A each at full throttle, and the controller board is designed to work with this load. People have had success using the controller board with T100 thrusters using the stock LiFePO4 batteries, which gives a nominal battery bus voltage of 9.6V. The T100 thrusters will draw a little more current than the OpenROV units, but things still seem to work OK. With LiPo batteries and a nominal battery bus voltage of about 11.1V (12.6V peak), then the current starts getting a bit out of hand.

You can replace the 12A ESCs with 20A units, but there are other areas on the board that start to break down- the current through the DB-25 connector, the current through the battery blocking diodes, the current through the various current sensing resistor shunts, and on and on. In a nutshell, full-throttle operation of the T100 thrusters with LiPO batteries is going to push things to the point where I suspect something is going to fail.

I think in your case the best move would be to wire things up the way you currently have planned, and run your ROV for a while while being careful about the use of full throttle. Once you have a design that you like, you can re-evaluate the hardware and figure out what you need to do over the long term to make the electrical system reliable.

Alternatively, if you haven’t purchased your batteries yet, look into using a 9.6V LiFePO4 battery pack in place of the LiPo packs.

Hope that helps.

-W


#3

Hi Walt,
Thanks for the insights, much appreciated. I will look into the LiFePO4 battery packs, but most of the brick style packs have very low discharge rates compared to LiPo batteries.
Regards,
TCIII AVD


#4

Hi Walt,
Would it be possible to power the ESCs separately from the controller board, not though the controller board, and still use the 3S LiPos for both the ESCs and the controller board?


#5

Sure, that’s actually the smart thing to do if you want to drive a large ROV using the OpenROV controller board. Just remove the 3 ESCs (they won’t be needed), and plug the servo wires of the external ESCs into the appropriate servo connections on the controller board.

The only tricky thing on this is how to turn power on and off to the remote ESCs. There are a couple of ways to run a signal from the controller board to an external switch that turns the external ESCs on and off, but you’ll need to study the schematic of the controller board a bit to figure out how to do this- there’s not a handy place to hook up a signal for an external switch. That’s one thing that’s on the Github issues list right now to add to the 2.9 Controller Board.

-W


#6

@Walt,
I have decided to keep the Controller Board in its present configuration, though I might upgrade the ESCs, and use 5000 mah 9.6 vdc 40 amp discharge rate NiMH batteries. The batteries can be purchased for around $72USD each plus shipping. I will then limit the thrust to the T100 Thrusters to less than 4.
Regards,
TCIII AVD