Here you can see the charging without charging station. If you don't want to use a charging station (or for your first tests), the charger can be connected directly to the Ardumower:
For the charger, we are using a Lithium Ion e-bike charger (29.4V, 1.5A current limitting) that can be purchased via the shop . The charger is placed in a protected area (house etc.) and connected to the robot charging station. The charger should accomplish the following things (in this case Lithium-Ion, lead battery is similar, but less critical):
- Charge battery pack via the charging pins of the robot
- Maximum cutoff voltage / charge voltage compliance (charging voltage limit)
- Maximum charging current compliance (charging current limit)
If you are using an existing charger, these things are implemented with high probability already in it. If you don't want to use a charging station, the charger can be connected directly to the Ardumower.
Total power balance
- 2 x Gear motors each 1A (under heavy load): 2A, 27 volt (measured at max. 80% accuracy by motor drivers)
- 1 x Mower motor 1A (under normal load): 1A, 27 volt (measured at max. 80% accuracy by motor drivers)
- PCB: 1A, 5 volt (not measured by PCB)
Total: 3A * 27v + 1A * 5v = 81W + 5W = 86W
For the battery, we are using a 'Sony Konion 7S2P' Lithium Ion battery pack (Sony Konion US18650V3 2250 mAh cells, Li-Mn), 29.4V x 4500 mAh = 132 Wh, 500 recharge cycles, 126 x 36 x 65 mm (LBH).
Using this battery with the Ardumower motors, the mowing time is about 1.5 hours (132 Wh / 86W).
battery charge/discharge conditions for optimal battery life time:
- charging per cell: max 4.15v (0.3A - 0.1A charging cutt-off)
- discharging per cell: min 3.1v
Standby-off / Under-voltage protection
You can add an undervoltage protection to your Ardumower. There are two reasons for a battery switch (standby-off mechanism):
Reason1: If the robot was not started within 5 minutes, it should turn battery off to save energy.
Reason2: Modern batteries should not be completely discharged. When the robot isn't able to charge for some reason and when the battery is below a certain threshold, it should be able to switch off the battery itself (undervoltage protection)
In the robot itself, the battery voltage is monitored (see diagram below). So it can be determined when the robot must go to the charging station. The robot and the voltage and the current during charging is controlled. So it can be determined whether the robot has reached the charger and when the battery is fully charged again.
Via pfodApp (Android) you can monitor the charging process.
By the help of the perimeter wire loop, the robot finds its charging station where it can be charged again. So, it drives along the perimeter wire (in clock-wise direction) until it detects a charging voltage at its charging pins. There the robot stops and recharges its battery. Due to the standby/charging current, the perimeter sender can detect if the robot is in the charging station and can then switch off the perimeter sender.
Here you can see the charging via charging station: