How to work out what capacity battery to buy

To work out how far your ebike will go on a single charge you need to consider battery capacity, efficiency, road and riding style. We have supplied some industry averages so the hard work is done and and that is

10wh per km of travel plus 5wh per km of travel every 250w after.

What you need to calculate

Battery Capacity (Wh)

Energy of the battery

Motor Power (W)

Measured in watts

Average Power Consumption (Wh/km)

Calculated avereage

Efficiency

Efficiency of the motor and controller, usually around 70-90%. This can be factored into the average power consumption we use the lowest value of 70%

How to Calculate Range

You have a 52V battery with 14Ah capacity and a 500W motor.

Step 1 Work out your battery Wh (Watt/Hour)

52V × 14Ah = 728Wh

Step 2 Estimate Average Power Consumption:

10wh for first 250w plus 5wh for every 250w after

10wh + 5wh = 15wh/km travel

Step 3 Calculate Theoretical Range: Watt hour (Wh) battery divided by Watt hour per Kilometer (Wh/km)

728Wh / 15 Wh/km = 48.53 km

Step 4 Factor in Efficiency (hills, rider weight, wind, bike weight etc)

48.53km – 70%  or

48.53 x 0.7 = 33.97km

By using the efficiency factor of 70% this ensures your battery isn’t over worked and wont heat up thus extending the life of your battery by up to x2

Battery Systems Comparison

Let’s compare three identical motors, each 2000W, but with different batteries (36V, 52V, 72V) all with 20Ah capacity.

Key Points to Consider

Battery Capacity (Wh)

• 36V Battery: 36V × 20Ah = 720Wh.

• 52V Battery: 52V × 20Ah = 1040Wh.

• 72V Battery: 72V × 20Ah = 1440Wh.

Wh/km

• 30 wh/km - 10wh per km of travel plus 5wh per km of travel every 250w after.

Range Calculation

1. 36V System:

   • Theoretical Range = 720Wh / 30 Wh/km = 24 km

   • Adjusted Range = 20.57 km × 0.7 = 16.8 km

2. 52V System:

   • Theoretical Range = 1040Wh / 30 Wh/km = 34 km

   • Adjusted Range = 34.67 km × 0.7 = 23.8 km

3. 72V System:

   • Theoretical Range = 1440Wh / 30 Wh/km = 48 km

   • Adjusted Range = 57.6 km × 0.85 = 33.6 km

Conclusion

• 36V System: 16.8 km on a single charge.

• 52V System: 23.8 km on a single charge.

• 72V System: 33.6 km on a single charge.

Which one is the most economical and why?

72V  

1. Higher voltage systems are more efficient because they draw less current for the same power output. 

2. With higher voltage, same amount of stored energy (watt-hours) is utilized more, longer range.

3. Higher voltage system requires lower current to produce the same power, less stress on the components and less heat generation, more efficient.

Tips

• Use Online Calculators: Several online range calculators allow you to input specific details for more accurate calculation.

• Test Real-World Range: Actual range varies on real-world conditions. Test your ebike under normal riding conditions for more accurate measurement.

• Monitor Power Usage: Use a display or app that shows real-time power consumption to adjust your riding habits for better range.

By following these principles you can make informed decision on which battery voltage and capacity is best for you.