Battery charge capacity and browning out

Our team is having issues with the robot seeming to “brown out” during matches even at times that the robot should not be “browning out” such as when the robot is not doing high output activities or during skills matches. The brown out would not act like a typical brown out since instead of just stalling or having significantly decreased movement it would occasionally “sputter” or seem to disconnect but have some small “ghost” movements such as slightly drifting to either side.

Upon inspecting factors which could potentially cause this we identifies that the batteries which are typically rated for 7.2 V were being charged to a range of 8.8-9.2 V instead. One of our alumni argued that the potential “brown outs” could be caused by the batteries discharging more than they were designed for into the cortex which would cause it to trip the circuit breakers which would normally cause these brown outs.

The motors which suffered from this were all on the cortex and did not exhibit this issue on power expander motors

Since this happens to some extent on all of our robots we believe that the some external factor such as the batteries could be causing this problem.

Also, could this type of brown out cause disconnection issues by effectively “browning out” the part of the cortex which affects the vexnet keys and wireless signals?


You are correct - if the battery voltage gets to Low, the Cortex will reset causing a break in the VEXnet Link. This could be a “brown out”. It would help to give as many details as possible to what is happening and what is not happening.

If a Breaker Trips or you lose the VEXnet Link, your Motors stop working. That is to say that all Motors stop working with a lose of the VEXnet Link, but only some Motors stop working with their associated tripped Breaker.

You could have a bad Battery, Cortex, Joystick, or VEXnet Keys - any of these can cause a break in the VEXnet Link.

Also, you should watch the LEDs on both the Cortex and Joystick when this issue happens to help guide you to the cause.


But would the higher than specified battery voltage be detrimental to the cortex or could cause the brown out or would that be be unlikely?

The LED and Cortex were both green during the brown out instead of the yellow which should normally occur during a brown out, which makes us suspect that the issue is not normal such as when the motors cause the brown out

The Higher Voltage would not hurt the Cortex or cause the “brown out”, but you would be pulling more current causing your Breakers to trip and temporarily stop your Motors - note: you have Breakers in the Cortex and in the Motors.

On the Cortex, the ROBOT LED color indicates your Battery Level - Green is Good. Yellow is Low, Red is very Low and you would probably not be able to run any Motors.

Normally if you have Good Batteries everywhere and only some of your Motors stop working, your are tripping Breakers.