Knowledge sharing: How many batteries are needed to run a ceiling fan, tube light and fridge?

This is an interesting and typical question that my engineers been asked all the time, let’s go through the calculate steps to see how much total power consumption of these appliances:

1. Ceiling fan - A typical ceiling fan consumes around 80-100 Watts. Let's assume 100W.

2. Tube light - A 20W tube light.

3. Fridge - Power consumption of fridges vary greatly depending on size and star rating. Let's assume a 120W average for a small to medium sized fridge.

4. Total wattage = Ceiling fan (100W) + Tube light (20W) + Fridge (120W) = 100W + 20W + 120W = 240W

5. Battery capacity - Deep cycle lead-acid batteries are commonly used for off-grid systems. A typical capacity is around 100Ah (amp-hours).

6. Calculate the number of batteries:

Total power (Watts) / Battery capacity (Ah) x Time (hours)

7. Time required - Let's assume the appliances need to run for 6 hours without recharge

8. Number of batteries = Total power (240W) / Battery capacity (100Ah) x Time (6 hours)

= 240/100x 6 = 14.4 ~15batteries

So to safely run these appliances for 6 hours without recharging, you would need a minimum of 15 x 100Ah deep cycle lead-acid batteries connected in parallel. More batteries allows for longevity and backup.

Actually, we are using lithium batteries to replace lead-acid batteries in these days, if lithium batteries are used instead of lead-acid batteries, the calculation would change a bit:

- Lithium batteries have a higher energy density than lead-acid batteries, so their capacity is rated in Watt-hours (Wh) rather than Amp-hours (Ah).

- A typical small lithium battery module has a capacity of 100-200Wh. Let's assume 150Wh per module.

- The total power consumption calculated earlier remains the same at 240W.

- To calculate the number of lithium battery modules needed:

Total power (Watts) x Time (hours)

Battery capacity (Wh)

- Plugging in the values:

Total power = 240W

Time = 6 hours

Battery capacity = 150Wh

- Number of batteries = 240W x 6 hours / 150Wh per battery

So with lithium batteries of 150Wh capacity each, around 8 modules would be needed to power the ceiling fan, tube light and fridge for 6 hours, as opposed to 15 lead-acid batteries.

The lower weight and higher energy density of lithium batteries allows for fewer batteries to be used compared to lead-acid in off-grid systems.