Electric Bike Articles
Why Build An Electric Bike?
You may be wondering why you should build your own electric bike when you can go buy an off the shelf electric bike or scooter at your local Wal-Mart or Canadian Tire for a reasonable price. The main reason is these bikes just plain suck. They are underpowered with small motors, low amperage controllers, and weak batteries. This is fine if you just want to cruise slowly at 30kph (18 mph) on a flat road down to the local corner store and back and don’t mind pedaling to make it up any hill, but I don’t see them as a replacement for a car. You see them pedaling like mad to make it up a small hill or sometimes pushing them because their battery died. Traffic gets backed up behind them on narrow roads because they are moving so slowly and cars cannot pass them.
There are a few companies that do make very nice high quality electric bikes but only if you are willing to spend up to $10000 and most of them are still not as fast as a bike you can build yourself for a fraction of the cost. If you are serious about replacing your car and cutting the umbilical cord to the oil companies you need to build the bike yourself, hand pick good quality components and modify some parts to increase performance and reliability. This way you can build a bike that perfectly matches your specific needs and will last for many years.
You may be thinking why not just build an electric motorcycle instead of using a bicycle as a platform. Well the bicycle has several advantages. In most places you do not have to license or insure an electric bicycle, which can save you thousands of dollars a year alone. You can also ride an electric bicycle on designated bike routes and paths. On a motorcycle you are obligated to obey the same rules as a car so you are stuck waiting in traffic with every other vehicle. A bicycle weighs much less than a motorcycle chassis, which means it will require less power to move it. This translates to a more efficient vehicle that can use a smaller (therefore cheaper) battery pack to travel the same distance. One final advantage of a bicycle is it can be locked up to a bike rack instead of parking in a stall saving you even more money by not purchasing a parking pass.
Electric Bike Batteries - Three Important Things To Know
If you are thinking about building an electric bike you will obviously need a battery pack. Many people get confused when they started shopping for batteries because there are so many different types and various specifications for each brand of battery. Hopefully I can help clear up some of the mystery for you to make you decision easier.
The first thing to consider is what voltage battery pack you need. The top speed of your bike depends directly on the voltage of the battery pack, the higher the voltage the faster the bike. If you want a motor just to assist you while you pedal your bike continously you will probably only need a 36 to 48 volt battery pack. On the other hand if you want to use the bike more like a motorcycle and cruise around at high speed without pedaling something in the 72 to 100 volt category would provide much better performance. You also need to make sure your motor and controller are rated for the voltage of battery pack you are using.
Next thing to consider is the battery capacity which is how long a battery will last on a single charge. It is measured by how many amp-hours (Ah) it can discharge before it is empty. If a battery can discharge 1 amp continuously for 1 hour it has a capacity of 1 Ah. The more Ah of capacity a battery has the larger its physical size will be if you are comparing the same chemistries. A 10Ah battery will be twice the size of a 5Ah battery if they are the same type and be able to get your bike twice as far if riding at the same speed. Multiple batteries can be connected in parallel (all the positive terminals connected together and all the negative terminals connected together) to increase the capacity or Ah to your desired level.
Last thing to consider is 'C' rating or discharge rate of the battery. The 'C' rating of a battery is a number that represents the safe continuous discharge rate (in amps) of the cell. A battery rated at 1C can discharge its rated Ah capacity in current without damage. A 2C rated battery can put out twice the number of its Ah rating in amps. If a 10Ah battery is rated at 1C, its maximum safe discharge rate is 10 amps, if the same 10Ah battery has a rating of 3C, it can safely discharge 30 amps. Likewise if that 10Ah battery is rated at .5C it can only put out 5 amps safely.
Hope this helps clear up some of the mystery of what to look for when shopping for batteries for your electric bike.
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 and push the limits of your battery pack every time you ride by completely draining it you will overstress 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 accidentally over discharge your battery pack.
Electric Bike Batteries - What is a Watt Hour and Why Do I Need to Know?
If you are considering purchasing or building your own electric bike then you need to educate yourself a bit on different technical terms so you can make an informed decision when purchasing batteries for your bike.
One term that may come up is watt hours or Wh for short. A Watt Hours is an important measurement when determining how much battery capacity you require to travel a specified distance. It represents the total energy available in a given battery pack. It is calculated by multiplying the amp hour or Ah of a battery pack by the total voltage of the pack. A 36-volt 20Ah pack and a 72-volt 10Ah pack both contain 720 watt-hrs; therefore they should both be able to get you the same distance provided you ride at the same speed. With the 72v pack you can accelerate faster and have a much higher top speed than the 36v pack. If you take advantage of this (it's really hard not to use all that extra power) and ride at a higher speed you will encounter more wind resistance using up more power. This will result in your distance traveled prior to the batteries running out being less than that of the 36v pack traveling at a lower speed but you will reach your destination faster. With a Crystalyte hub motor in a 24-inch rim and a motor controller set to 90 amps you will average around 35 to 45 watt-hrs per km (58 watt-hrs per mile). This is at a cruising speed of around 65KPH (40MPH) and no pedaling. How fast you accelerate and your top speed will influence your power consumption. It will also vary depending on how flat or hilly the terrain is and how much weight you are carrying. You can use less than 25 watt-hrs per KM if you ride really slowly (using the same setup mentioned above) on flat terrain or use over 65 watt-hrs per KM riding full throttle up hills.