Voltage drop when using new recommended batteries


#1

I am using the new recommended batteries

My electronics is different though, it include raspberry pi and arduino. I have separate LiPo batteries to power the electronics.

I have 6 (3+3 in parallel) of the newly recommended batteries to power my motors. At no load the voltage I get from the batteries is 9.9V. When I run 2 of the motors inside water at maximum speed the voltage drops below 6V and often the motors shutdown and restart immediately. This leads to a series of jerky on-off cycles.

Do you guys have any solution? One thing I can think of is not to run the motors at full speed. I am also considering switching to lipo batteries if things don’t work out.

If there is any better solution let me know. Thanks.


#2

Hi Prasanna:

The stock batteries should be able to handle 2 motors running at top speed just fine. I would check your wiring to make sure that current is being drawn out of both battery packs.

If you have the OROV cockpit running, you can see the battery currents in the telemetry pane on the right hand side of the screen. The names are something like BATI1 and BATI2. If the currents you’re seeing aren’t roughly equal, then you either have some bad wiring or perhaps a bad cell in one of the battery stacks.

If you’re not running the OROV cockpit, you can experiment manually by removing the batteries from one battery tube and repeating the experiment. Look to see if there are changes in behavior when only running on one battery tube. If the ROV won’t run at all, then you know you’re found your problem :smile:

Let us know what you find.

-W


#3

Hi Walt,

Thanks for your response. I put a current sensor in series to measure the current drawn by the motors. I used only 1 battery tube and 1 motor at a time for testing. I will give the results below.

Initial voltage (no motors running): 9.6 V 0 A
One motor running in air at full speed: 8.5 V 0.5 A
One motor running in water at full speed: 3 V 5 A

The voltage mentioned here is the voltage measured across the motor terminals. I am getting a 6 V drop inside water. The motor sometimes shuts down and restarts. The voltage of the batteries return back to the original voltage as soon as I switch off the motors.

Any help would be great. Thanks.

I am testing in a small kitchen sink. I am wondering if the boundary effects from the wall could cause high resistance towards the motors causing this drop.