Angry Bird Air Conditioning from Batteries

Details: Category: Smart marine blog

Many yacht owners have thought about how nice it would be to have air conditioning at anchor, quietly, without running the generator. In this testing phase, we only operated the air conditioning in the two cabins from the battery, not the salon air conditioning.

The total capacity of the installed LiFePO4 batteries on the boat is 12V 1120Ah, which is 14.33kWh. Two separate wires were needed for this: one from the inverter to the air conditioning fuse, and another from the inverter to the air conditioning cooling pump. A 32A smart switch was installed at the inverter, and we installed a relay for both the air conditioning and the pump. These relays switch the air conditioning and pump from shore/generator power to inverter power when inverter power is activated. Once switched, the air conditioning system operates the same as before, just on inverter power.

At this point, the power consumption from the LiFePO4 batteries required for air conditioning ranges between 5-80A, depending on the operating phases of the air conditioning, with a CruisAir unit cooling the two cabins.

On the day selected for testing, it was quite hot. At 10 PM, the temperature in both cabins was over 31°C. Nobody was on the boat, and all doors and windows were closed all day. At 10 PM, the outside temperature was 25°C, and the situation would have improved significantly if we had ventilated the boat earlier.

The air conditioning is started by an automation system, where we can set the time for the air conditioning to turn on and off.

We considered the test results very good. Starting from an extremely high cabin temperature, the service battery charge dropped by 35% over 8 hours.

In the morning, we began recharging the batteries with the Victron Multiplus II and the supplementary charger, at 200A.

The chargers charged the batteries in BULK mode from 6:53 to 7:38, then in ABSORPTION mode from 7:38 to 8:38, and switched to FLOAT mode at 8:38, marking the end of charging for us, which took exactly 1 hour and 45 minutes. In practice, this means that we got through a whole night's air conditioning with 1 hour and 45 minutes of generator running.

Bulk mode: charges the battery with full, pre-maximized current.

Absorption mode: continues to charge the battery at full capacity but does not allow the charging voltage to go above the pre-set absorption level.

Float mode: keeps the battery voltage at the set level with the minimum necessary amperage, maintaining the battery charge.