Electric Bike Batteries - Why You Shouldn't Completely Discharge Them
Electric Bike Batteries - Why You Shouldn't Completely Discharge Them
If you are thinking about buying or building your own electric bike then there are some things you should know to help make maximize the life of your expensive battery pack. DOD or depth of discharge is one of these things.
When calculating how much battery capacity you need for the distance you want to travel on your bike you should only plan on discharging the pack to 80 percent DOD. Most battery cycle life (how many times it can be recharged) specifications are based on 80% DOD. If you discharge more than this each time the cycle life can be reduced. The batteries will also slowly lose capacity over time so the extra 20% capacity gives you an added buffer zone before you need to replace them. Don't forget to add any electrical loads from accessories that are powered from your battery pack such as lights and a heated jacket if you intend on using one. Something else to consider is your battery capacity will decrease as the temperature gets colder. You will have approximately 15% decrease in capacity when riding in temperatures close to or below freezing so you may need a larger capacity pack if you intend on riding in cold weather. On an average daily commute it's best to only use about 70 to 75 percent of your battery pack with all accessories running so you have a little extra capacity if you decide to take a detour and run some errands on your way home. If you need to use close to 100 percent of your battery pack to reach your destination you will be constantly worried about using too much power accelerating or fighting a headwind which could leave you stranded with a dead battery. That's why you need a good buffer zone of power so you can ride stress free. If you try to push the limits of your battery pack every time you ride by completely draining it you will over stress it and not get the specified cycle life from it. It pays to treat your battery pack with care.
To prevent you from over draining your battery you can add or buy a battery pack that has a LVC or low voltage cutoff. A wire connects from the battery pack to the motor controller and if the voltage of any one of the battery cells drops below a preset voltage, the LVC will trip and cut off the power to the controller stopping the bike. Once the voltage rises the power is restored and the bike will move again. A LVC is a great safety device and will guarantee you never accidently over discharge your battery pack. I hope this helps you understand why you should never completely drain your battery pack.