What is the expected runtime of a 12V fridge using a 120AH battery?

Calculation of Runtime

1. Convert Watts to Amps:
   • The formula to convert watts to amps is:
     Amps=Watts/Volts ​
   • For a fridge using 60 watts:
     Amps=60W/12V=5A 
2. Daily Consumption:
   • If the fridge runs continuously, the daily consumption in amp-hours (Ah) can be calculated as follows:
     Daily Consumption Ah =Amps×24 hours 
   • For our example:
     5A×24h=120Ah 
3. Runtime Calculation:
   • With a 120AH battery, if the fridge consumes 5A continuously, theoretically, it could run for:
     Runtime hours =Battery Capacity Ah / Fridge Consumption A ​
   • Thus:
     120Ah/5A=24hours 

Factors Influencing Actual Runtime

While the theoretical calculation suggests that a 120AH battery could power a 12V fridge for up to 24 hours, real-world conditions will often reduce this runtime due to several factors:

• Duty Cycle: The fridge compressor does not run continuously; it cycles on and off based on temperature settings and ambient conditions. This can significantly extend runtime.
• Ambient Temperature: Higher temperatures increase the workload on the fridge, leading to more frequent cycling and higher energy consumption.
• Fridge Efficiency: Different models have varying efficiencies, affecting how much power they draw.
• Battery Discharge Limits: For lead-acid batteries, it’s recommended not to discharge below 50% to avoid damage, which would reduce usable capacity to about 60AH, limiting runtime.

Practical Examples

• A typical mid-sized fridge might draw around 6A during operation. In this case, the runtime would be approximately:
  120Ah/6A=20hours 
• If using a more efficient model drawing only 4A, you could expect:
  120Ah/4A=30hours 

Conclusion

In summary, with a 120AH battery, the expected runtime of a 12V fridge can range from approximately 20 to 30 hours, depending on its power consumption and operating conditions. Monitoring actual usage and adjusting settings can help optimize performance and extend runtime.