The crux of every single electric vehicle is battery capacity. Although there have been some amazing breakthroughs recently batteries still can't compete with gas for the amount of energy that they store. That doesn't mean that we can't try though. With electric vehicles the secret is efficiency. The more efficient you make your system the longer one full charge will last you. Let's take a look at how I'm going to be saving energy with the electric bike.

We'll start with the basic ways that you can re-capture power with an electric bike.

Regenerative braking is probably one of the best know ways to re-charge your batteries. What this means is when you apply the brakes the motor is going to turn into a generator and pump some juice back into your batteries. You've probably heard about this method before with hybrid cars as they were the first widely used application. This method works great the only problem is that you don't drive with your brakes on so the amount of energy that you capture isn't going to be a lot (although every little bit counts).

The second method that can be used with electric bikes is while you're pedaling and not using the electric motor. This adds some drag to the bike though so it will be a last resort. This type of charging will be something that you have to 'turn on' so that you have the option of charging while you pedal.

Of course we have coasting as well. This is a great opportunity for recharging batteries although it is plagued by the same problems as braking. You can't coast forever so the amount that your able to capture won't be that big (unless it's all downhill to where you're going).

The last method is to re-capture energy while the motor is running. Now that's the craziest thing you've probably ever read, but I'm experimenting with this right now. To understand we need to take a short electronics lesson (it won't be difficult I promise).

We don't drive motors by varying the voltage to the motor anymore... we control the speed by something called pulse width modulation (PWM for short). What this means is that small pulses are sent to the motor many times a second. The picture below will help.

You can see from the above picture what PWM looks like. At 100% load it looks like 1 continuous pulse, but at 50% load the pulses are spread out. Pulses are measured in Hertz (pulses per second). We'll be working with 500 hertz (or 500 cycles per second). At 100% load each pulse is high; however, at 50% load only every other pulse is high.

What does that mean?

Since we're not likely to be driving the motor at 100% all the time it means that for quite a bit of time the motor is actually just spinning. A motor that is spinning isn't a motor... it's a generator. We can use the intertia from our weight to keep the bike rolling and the time that the motor is off we can use the charge our batteries!!!

Let's take a look at how profound that is. With braking/coasting/pedaling etc. You can recapture some power, but if we're going to capture energy while we're using the electric motor we can capture a whole lot more.

If for example we used the bike at 75%... that means every second 1/4 of it we'd be generating electricity for the batteries. Over the course of an hour we'd have 15 minutes of charging... which means that you'll be able to go alot further with the same charge.

The how to build this part of the electric bike will be fully detailed in my building an electric bike guide which is going to be started in early septemter. It will be available for members only so if you want to learn how to build one you should sign up now while the membership is still cheap and covers all new projects (it's going to be split up shortly).

If you have any questions about this just leave a comment or send me an email.