Batteries - drewnoakes/bold-humanoid GitHub Wiki

Batteries require careful handling in order to get the most out of them. Of the original batch of batteries we received, many died and became useless because we did not exercise correct care in their handling. We currently have 9 working stock batteries, and some newer batteries with slightly higher capacity.

Thankfully the rules are very simple:

Tether a robot immediately to a transformer when it gives a low voltage warning and take out the battery
Disconnect them from the charger as soon as the light is green
Don't leave them connected to robots that are not in use

Keep full/empty batteries in clearly marked containers. For batteries that have them, slide the charge indicator to show red whenever taking it out of a robot, and back to green when disconnecting from a charger.

Battery Cavity

The housing for batteries on the robot has the following dimensions:

44mm width
33mm height
80mm depth

The door that screws onto this cavity adds a little more to the depth, but not at the full width.

39mm width
6mm extra depth

Connectors

Each battery has two different connectors.

Balance is a 4-pin plug (JST-XH) which provides access to the potential across each of the three cells within the battery.
Power is a 2-pin plug (Deans type) which provides high-current access to the potential across all cells within the battery.

Both connectors have the female plug attached to the battery, with the male counterparts on the robot and chargers.

LiPo batteries

LiPo (lithium-polymer) batteries are the most common type of batteries for robotics.

They can be dangerous when damaged, and fires and explosions are not uncommon. Be careful!

LiPo batteries are divided into cells. Each cell has 4.2V when fully charged, and should never be discharged below 2.8V, otherwise will be damaged. Battery voltage ratings use 3.7V per cell, i.e. a 3 cell battery will be labelled as 3 * 3.7 = 11.1V.

The DARwIn-OP requires 3-cell LiPo batteries (written as 3S), with a nominal operating voltage of 11.1V (3x3.7) and a maximum charging voltage of 12.6V (34.2). Note that the DARwIn will shut down when the voltage drops below around 10V, which is above the 8.4V (32.8) rating on the batteries. However a used battery left for a long while will continue to discharge slowly and may cause itself damage. Therefore batteries should be left sufficiently charged, and tested and potentially recharged after long periods of storage. Storing LiPo batteries for a long time (several months) when fully charged is also not good for them. The iCharger has a 'storage charge/discharge' mode which uses 3.85V per cell as target voltage.

Battery Stock

We currently have two different type of lipo battery:

1000mAh 11.1Wh 10C (red) Yuntong (3S YT503560HH) that came with the DARwIn robots (66x37x20mm)
1300mAh 14.4Wh 25C (blueish) Gens (B-25C-1300-3S1P) bought for the German Open 2013 (73x36x25mm)

(View larger) (View larger)

The 'C' ratings of the batteries indicate the maximum safe discharge rate, measured relative to the battery's capacity: A rating of XC specifies that the maximum rate in Amperes is X times the capacity in Ampere-hours. So, the red batteries with a capacity of 1000mAh and a rating of 10C can discharge at 10 * 1000 = 10,000 mA ( = 10 Amps); the rate for the blue batteries is 25 * 1300 = 32,500 mA ( = 32.5 Amps).

For charging, the charge rating is important. Similar to the discharge rate it gives the maximum charge current relative to the battery's capacity. The blue batteries are rated 5C, so they can be charged with a maximum of 5 * 1300 = 6500 mA ) = 6.5 Amps). The rating for the red batteries is not given, a safe default guess is 1C, i.e. 1000 mA.

Transformers

We have two types of transformer.

Bundled

One of these was provided per robot, so we have seven.

Batteries - drewnoakes/bold-humanoid GitHub Wiki

Battery Cavity

Connectors

LiPo batteries

Battery Stock

Transformers

Bundled

eBay

Chargers

Yuntong

Junsi iCharger 106B+

Standard charging procedure

Alternative charger