So you want an ebike but what type or how to start?
There is a lot of detail about this on the web but it is hard to find in one place. Endless Sphere has great detail and many there are happy to answer questions but it can be a trawl through the details.
Basically other than a suitable bike an ebike needs three extra major components. A motor, a battery, and a controller.
You can see my other blog for details on chain driven motors but I think the neatest and simplest is the hubmotor. Hubmotor replace the centre of the normal bike wheel with a brushless electric motor. These motors come in two main types, direct drive or geared. This has nothing to do with the bicycle gearing just how the internals of the motor is built.
Direct drives are usually larger and heavier but can be more reliable (less moving parts) and can do regenerative braking where the motor charges the battery when decelerating or braking.
Geared Hub motors are similar motor but with internal plenary gearing. This usually allows for a smaller and lighter motor. Because of the gearing these motors usually have a built in free wheel so when the motor is not working the rider does not have to work against the magnetic “coging” of the motor amplified by the gearing. I’ve have had two geared hub motors one with a freewheel and one without (going on the spare bike) the one without was totally fine except when the electrics failed and really then the bike was unridable.
Motors are usually rated in terms of power described in Watts. Electrical power is a simple matter of multiplying Amps by Volts. 7Amps in a 36 volt system would give 252Watts but by the time you account for power losses through electrical inefficiency, and mechanical losses in the gearing and wheels, there would be less than 252 Watts in “mechanical power” getting to the ground. So really rating for Motors and ebike is generally called “nominal” which to me means we just took a guess. This can be tricky when you want to ensure (as do I) that your bike is legal for road use.
Also motors can have similar Watt ratings but differ in other aspects like top speed (RPM). You would for example want a higher RPM for a small wheel like a 20 inch than for a 700C wheel. to maintain a similar top speed. Motors are usually designed (wound) to run a given top speed at a giving voltage input.
While this all sounds confusing, the simplest way to choose a motor is by it’s “nominal” Watt rating with maybe some attention to what wheel size it suits.
Until recently lead acid batteries (just like a car battery) were very common on ebikes, and I think they still are in China. They are cheap, recyclable and easy to buy. But they are also heavy, have a short life and short range. This is where more exotic battery chemistries comes in. Mostly these days that means some form of Lithium battery, but you really need to be careful here because “oils ain’t oils” and there are several popular forms of Lithium Batteries all with their pluses and minuses.
Current champ in Lithium batteries are Li-FePO4 which are safe to charge and discharge and hold lots of electrons to get you long distances with low weight. There are lots of other versions or chemistry variations of Lithium batteries and unfortunately most vendors seem to just refer to them as “Lithium” which can be misleading and can cause you to buy a battery that at best has a shorter lifespan (500-700 charges, verses LiFe PO4 upwards of 2000!) or at worse could set your house on fire!
Most made up battery packs (ping battery for example) come with a Battery Management System (BMS) to protect the battery from overcharging or discharging and to keep the battery healthy or in balance. Balance just means that the individual cells the battery is made up from all have the same voltage.
Other than the chemistry ebike batteries are rated in three important aspects. Voltage and Amp Hours and C Rating.
Voltage is easy, choose the voltage suited to you motor (and controller) or add more volts for higher speeds. 24, 36, and sometimes 48 Volts are common on commuter ebikes.
Amp Hours basically relates to capacity and in ebike therefore range or how far the bike will travel. Kind of like how much petrol the battery has . More Amp Hours mean higher capacity. with 10 to 15 Amp Hours usually giving a commuter bike about 30-50 kilometre range with some pedaling.
C Rating is a little more complicated and examples are the best way to explain it. If a battery is a 10Amp Hours capacity and rated for 1C then that battery can comfortably output 10 amps at any given moment without “sagging” (lowering voltage) or damaging the battery.
If a 10 Amp hour battery is rated to 2C than it can output 20Amp Hours.
A 20 amp hour battery rated to 30 C could theoretically output 600Amps at any given moment.
LiFePO4 batteries often have lowish c rating of 2 or so but with a large enough capacity (AH) this is not usually a problem for you average commuter bike.
Other Lithium chemistries can have higher C ratings and A123 brand batteries have nice safe LiFePO4 chemistry with very high (30?) C ratings.
Bottom Line? It is important to get a battery with enough amp hours and a high enough C rating to power the motor (and controller) in the way you need without damaging the battery in the long term.
This is the electronic “brain” which takes the battery power in and distributes the power to the motor in an efficient manner. Connected to the controller is usually a throttle, or a PAS (Pedal Activated System) to tell the controller when to apply the power.
Controllers can come in various types and models and with various features including cruise control, speed limiting and battery regeneration or braking.
Often a controller is a little (or big) silver box with a spaghetti of wires coming out of one end, however some motors (Cyclone, and Golden motor Magic Pie) confidently have the controller built in.
Like batteries you need to match the controller to the battery and motor. Controllers often have some kind of Lower voltage limit, a bit like the BMS to avoid overdischarging a battery. Often within limits controllers can accept higher voltages than they are rated for, but this is certainly not universal.
Some controllers can be programmed with an appropriate USB cable and software, to alter power and speed features.
Controllers input battery power and controls (throttle) and output 3 phases of power to run the motor. Often then controller needs additional input via sensors in the motor to help the motor run correctly however “sensorless” controllers are increasingly popular and simpler to connect up.
Again the controller need to match the motor and battery in terms of voltage and amps.
This has really been a brief run through to just get the basics of current electric bike technology out there. So you can of course obtain your electric bits and pieces individually and build your own ebike. Alternatively (and this is what i am doing) almost as cheaply you can buy a ready to go plug and play kit which save all the matching this with that and learning to solder wires together.