# Battery run time question

I’m hoping you can help me as my head is spinning attempting to calculate the run time of a Dometic Fridge on a portable power bank, which I will eventually add solar panels to the system.

Im planning on using a 12v Dometic Fridge CFX 40, and the power bank is the Jackery 500.

The Power bank battery is rated capacity is 518Wh (24Ah, 21.6V), and I will be plugging the fridge in the DC 12V, 10A “Car Plug” of the power bank

According to some youtube videos, once up to temperature the Fridge used 27 Wh and 2 Amps in 4 Hours, averaging 6.75 Wh and 0.5 Amps.

1 – If I calculate via Wh, using the manufacturer formula of (Working time = 518Wh* 0.85 / operating power of your device) = 518 * 0.85 / 6.75 = \~65 Hours
2 – if using a similar formula for AH, battery life = capacity / consumption * (1- discharge safety) = 24Ah / 0.5 * (1-.015) = \~40 Hours

Now I’m guessing my discrepancy is the battery voltage vs the appliance voltage, but which result is correct?

Thanks!

• That seems consistent with the consumption in the Manf data sheet that says 64kWh/year. Average 7.3W. Commented Jan 3, 2020 at 1:01
• 10A may or may not be enough to start the compressor motor. Overcurrent may or may not shut down the power bank. But if you can start it, should be OK.
– user16324
Commented Jan 3, 2020 at 15:17

The 0.5 A and the 6.75 Wh seems not consistent. the voltage has to be $$\\frac{6.75 \text{Wh}}{ 0.5 \text{A}} = 13.5 \text{V} \$$.
The voltage at the output of the powerbank is $$\ 12 \text{V} \$$.