Powering a Lego EV3 all day

Powering a Lego EV3 all day at a Lego GBC show can be done in a few different ways depending on if your module is fixed or moving like a Train module.

Fixed Module Powering

If your module is fixed then you can power it directly from power adapter

Dummy battery and power adapter

This utilizes a pair of spacer batteries that are wired to a DC socket.

These batteries are then powered by a 7.2VDC to 9VDC adapter allowing the module to run all day
The power adapter should output at least 3A, noting that if you have 4 stalled motors they will be trying to draw 7A.

Do not exceed 9V when using this method as the motors are powered directly from the batteries output voltage

Ensure correct Battery polarity otherwise you risk fire and bricking your EV3

Lego rechargeable battery and power adapter

Lego produces a rechargeable battery for EV3’s. By using this battery and plugging in the charging power adapter a module will run all day

This works because the battery charging circuit sends power to both the EV3 and battery simultaneously

If your EV3 is under heavy load (more than the 700mA power adapter provides) it will draw power from the battery and could eventually turn-off if the battery becomes fully discharged

Moving Module Powering

For moving modules choices are limited to using Lego’s rechargeable battery for EV3’s.

Lego rechargeable battery (rolling swap)

As such you will need to have a rolling battery cycle, where you you will have 1-2 batteries charging, 1 in the EV3 and 1 fully charged, when the battery depletes you swap in a new battery and place it on the charge.

I’d recommend numbering your batteries and replacing them in sequence to ensure an even usage of the batteries.

EV3 Hot battery swap

Typically when you change an EV3 battery the EV3 will turn off and you will be left waiting for it to boot again, in GBC this can be especially problematic.

To mitigate this it is possible to modify the EV3 to enable Hot-swapping of batteries

The modification

You will need a spare Power Functions extension wire that you can cut in half

  • Drill 2 small holes near the EV3 battery terminals
  • Cut the Power Functions wire in half and strip the power wires and tape up the middle wires
  • Put the Power Functions wire into the hole and crimp against the battery terminal

Ensure the Power Functions wires are on the right terminals, otherwise you risk fire and bricking your EV3

Battery Hot-swap process

  • Connect Power Functions battery and ensure it is on
  • Remove the old EV3 battery and replace it with a new one
  • Disconnect the Power Functions battery