Tuesday 20 November 2012

Never Ending Power

One of the great things about cycle touring is that it's much easier to go for long periods without any planned stops than it is with hiking. Sure, you can carry 2 weeks of food in your pack but the one thing you will likely run out of long before food is power! Most of us are heavily reliant on gadgets nowadays, be that with smartphones, cameras, tablets or whatever. Even if you are willing to carry heavy additional battery packs, or unreliable solar chargers, you will eventually have to hook-up to a power-point. This isn't so with a bike, get the right kit and you will never have to worry about power again. The only problem is it can get very expensive.

The two most important components in the charging system are the generator and the rectifier/regulator. These two parts are what give us useable power. After that you have two options -
  1. Charge a battery pack up during the ride and then recharge  your gadgets from the battery pack in the tent overnight (cheapest). 
  2. Charge a buffer battery pack up during the ride while also charging/using the gadget (more expensive). 
If you want to do option 2 then you need a buffer battery while option 1 can use any rechargeable battery. More on that later.


This critical component takes the rotational movement of the wheel and converts it into electricity. A simple design all it contains is a coil of wire and powerful magnets. As the magnet is rotated around the coil electricity is generated. How much electricity is generated (Voltage), and with what force (Current), depends on the rotational speed of the wheel. Climb slowly up a steep hill and the output will be a lot less than zooming down the other side. These are AC (Alternating Current) devices and not suitable to charge any gadgets directly. These all require DC (Direct Current), normally at 5V. You don't get anything for free and it takes a certain amout of force (drag) to rotate these magnets around the coil, and that has to come from your legs. So now when you are climbing a hill not only are you fighting the gradient but also the generator. Fortunately this additional drag is so slight on modern hubs that, as a tourer, it can be ignored.

There are two types of generators available. These are hub (above) and bottle. Bottle generators attach to the bike frame and use the tyre sidewall to rotate the magnets. A useful feature of a bottle generator is that they can be disengaged completely when not needed. There is no additional drag when it is not being used and they are normally much cheaper. However, they are noisy, can slip in the wet, need adjusting, wear out your tyres and are less efficient. Hub generators on the other hand are built into the front wheel and are completely silent, have less drag in use, are very reliable, maintenance free and more powerful but always add some drag, even when not being used. For the tourer the hub generator is the only way to go.

When choosing a generator, if cost is not an issue, then you want the lightest and lowest drag hub with the most powerful output and that means the German Schmidt SON range. The one I have fitted is the SON 28 and costs £189.99 and is guaranteed maintenance free for 50000km. The table below shows a number of different generators and how much drag they produce. From then table it can be seen that when riding at 20km/h the rider is using about 5W of their pedal power to charge the gadgets. When not charging it's less than 1W.


The job of this component is to take the raw power from the generator and convert it into something stable we can actually use. The AC generator voltage is converted (rectified) to DC and then smoothed and regulated to the chosen voltage and current setting. I have experience with two units which are the B&M E-Werk £139.99 and BioLogic ReeCharge £78.99. The ReeCharge kit is a bit of a bargain because it also includes a Buffer (read on) which the much more expensive E-Werk does not. However, all is not equal! The Biologic has a fixed output of 5V, 400mA while the B&M has a variable voltage and current output at up to a impressive 1.5A. What these means in the real world is that potentially the B&M can charge a gadget up to 3 times as fast as the BioLogic. It's not quite as simple as that as most of the devices you want to charge do not want more than 1A. Then, the B&M should be around twice as fast to charge a device as the BioLogic. The second problem with the BioLogic is a warning in the instruction manual that the device can be damaged if it is operated without the Buffer attached AND turned on. I could see this easily happening on a tour. The buffer lives in my valuables bag so when I leave the bike anywhere I take this bag with me. That means disconnecting the buffer from the regulator and it's possible I could forget to reconnect on return. The risk is too great. I use the fuss-free and more powerful E-Werks set to 5V 1A.


If all you want to do is charge a battery pack so that you can charge your gadgets overnight in the tent then you do not need a buffer. Get yourself a USB rechargeable battery pack such as a powermonkey and off you go, nothing else is needed. But, if you want to directly charge, or operate, gadgets from the bikes rectifier/regulator then you will almost certainly need one. Some gadgets are particularly fussy about being charged, with Apple among the worst but they are far from alone. Also, as you cycle along you will have to slow down and stop at junctions so power will be interrupted to the gadget which can cause all sorts of problems. Warning messages flashing on screens, rebooting and refusing to charge at all is likely. The solution is a buffer battery. What you are now doing is charging the buffer battery from the hub which, in turn, is charging the device. When you stop the buffer battery is no longer being charged but the device is. This buffer battery is also an additional source of power and can be used like the Powermoney when in the tent and not connected to the regulator.

Unfortunately most USB rechargeable battery packs, like the previously mentioned Powermoney, are not capable of being charged while charging a device at the same time. They cannot be used as a buffer and the solution isn't cheap! B&M sell a matching buffer which they call a cache battery for £71.48, but if you use Apple devices then it is not capable of charging the latest iPhones. If you're not an Apple user then this might be the best option but I've never tried one and they also can't be charged from a power-point. For Apple users the buffer battery that comes with the BioLogic ReeCharge kit works perfectly with the E-Werk set to 5V 1A. The ReeCharge kit comes with a special adapter that you must use with Apple devices and it works well. It also comes with a mains charging kit which is overly large and heavy so I've replaced it with a smaller unit. This allows the buffer to be charged from a power-point should you have access to one, a useful feature.

That's it! For a total of £408.97 you can have endless, reliable power, or a little less if you omit the buffer. Is it worth it? Only you can decide.