Overview (written 2012)
The bicycle is a simple machine. A fantastic design that has changed little in 100 years.
So , why on earth would you add a complex electrical system to it ? The answer is because just like better gearing systems and nicer saddles, the system increases my enjoyment of days on the bike by letting me know where I am, take all the digital pictures I want, call for help if I get hurt, see and be seen better, make unexpected changes in reservations mid-day. All of these things are easy now with cell phones, rechargeable batteries, GPS units, tablets, cameras etc. The main drawback to the wealth of benefits they have is keeping them alive. I am willing to make the trade off for the benefits I get out of them. You need to make that decision for yourselves. The choice of a generator hub to me was a no-brainer, (see 2016 updates below) solar is still pretty big and another “loose” item to pack and carry, and throwing away batteries or being chained to wall outlets is out. Lets not even start with different battery sizes, types, charge cords and wall adapters.
The approach I took is to make the system as unobtrusive and easy to use as I can. That meant doing some planning. First order of business was to make a christmas wish list of the things I would like to have that require some kind of electricity.
- Taillight (steady)
- Taillight (blinky)
- Cell Phone
- Camp flashlight
- Cellular Modem
OK so how many of these things can get cut from the list?
NONE ! I have all nine items from the wish list by making things do double duty and using a front hub generator. I got it down to 4 items and lost no functions. I prefer to use a cheap throw away phone or I could have got rid of more. Only 2 of the items needed are attached permanently to the bike, the Generator Hub and the Primary Taillight. Here is how they combined, and how I get away with no wall adapters, only 2 cords, 4 extra AA batteries and 2 AAA batteries.
- Headlight (charges 4 AA batteries at a time for the following)
- Camp Flashlight
- Taillights X2
- Netbook (replaced by Nexus 7 Tablet)
- Cell Phone
- Cellular Modem
I created a video of the bike’s charging system. It’s already a little outdated since I’ve made the parts much smaller and added some cool features. A new video is coming in early April (2016). Here’s the original one.
Schmidts Original Nabendynamo or “SON” (Schmidts Original Hub Generator)
The SON 28 is arguably the best bicycle dynamo hub ever made. It is German engineered and produced by a small group of folks in low production numbers. The inherent drag these produce is lower than any other hub made and they produce the requisite 3 watts of power as dictated by German traffic device laws. You can read on the internet all kinds of personal opinions and test results using different methods to determine how much of a penalty you pay compared to a regular hub.
Here is one more. In my opinion the drag from this hub doesn’t matter a fart in a hurricane. I do not ride at TdF levels of efficiency so I don’t care if I “could have” been 3.1 feet further ahead after that last 2 1/2 hour climb. In my opinion you can’t feel it at all. If you pick up the wheel and spin the tire slowly you can feel the magnets and coils working, if you put the bike on the ground and push it you can’t so your not going to tell me you can feel it after adding your body weight to the package and pedaling. Sorry, I’m just not buying it. I said in the wheel article that if you sneeze twice, the break in your breathing and cadence is probably equal to the efficiency loss of what this thing takes in a entire day.
The exact model I chose is actually designed for a tandem, this was needed to get the 40 hole flanges. The newer model of the SON 28 is smaller but only comes in a 32 or 36 hole style. This model is still produced as a tandem hub in 40 and 48 hole configurations.
In order to get the juice out of the hub you need to attach to the two small tabs as seen in the photos . This spade terminal system is very good but it can be a little fussy attaching and detaching the connectors when you want to drop the front wheel. This is especially true if you have a front rack and fender struts attaching down at the eyelets near the dropouts. I decided that I would make a quick disconnect since I hate anything fussy.
I decided that a standard trailer connector would be well suited to the job and built a short pigtail to extend the connection point of the generator up the fork leg a little ways where it is easier to get at. These connectors are rubber, and very tough, I used a braided polyester sheathing on them and double heat shrink tubing on the solder joints. The bright yellow shrink tube is to make the connector easier to see in low light conditions. If I’m dropping/mounting the wheel in bad light, I’m probably already irritated and don’t need to compound it by looking for the black connector halves on the black wire on the inside of a dark blue fork in the dark.
The matching part of this cable connector is attached to the inside fork braze on opposite the front rack mounting point, having a threaded boss there on the inside of the fork is a convenient place to attach a P-clip to hold the bike side of the connector securely.
The cable that runs up the fork goes to a distribution box that allows the connection to the taillight and provides a connector to redirect power to the headlight when needed, more on why you would do that in the headlight article. The connector box is designed to mount on the fork leg but I wanted it to be more convienient since I was going to be using the generator output differently. I mounted it up on top of my stem to allow devices to charge inside the handlebar bag or map case without an additional wire hanging down. The important thing to note is that you can tap into this 6 Volt AC current anytime you want, you will see why.
Wiring and Schematic
The wiring attaches the front hub to the taillight via the power port on my stem. That is the only wiring that needs to be installed on the bike. Specifically there is :
- One wire from the front hub to the stem mounted box
- One from the stem box to the taillight
The switch box on the stem is really just 4 terminations connected to a 1/8″ stereo jack. The photo shows the internal board from the stem box. It only has 2 states it can be in:
- If nothing is plugged into the jack, the power goes to run the taillight.
- If something is plugged in, the the power goes there, and the taillight runs on its batteries automatically.
This is the beauty of this system, the taillight knows if its getting power from the generator and can switch between it and its (2 AA) batteries automatically. This is important when you stop since there is no gen power. This light also has a sensor to determine if your moving, it will shut the lights off after 4 minutes if you have it in the “auto” mode. You can also put it in “always on” or “always off” mode as well.
The second thing about this is that by plugging into the stem box you now can do anything you want with the generator output. I use that output two ways. The way I use it most is:
To send the power to an adapter I built that contains a bridge rectifier to change the AC output to DC and a line conditioner and voltage regulator to output the USB current of 5v DC. That box is just an adapted version of Lady Ada’s Minty Boost, which is normally built from her kits into an Altoids tin. You can see the difference in my box between a professionally designed board on the left side of the case and my rectifier circuit on the right side. I have built and sold about 50 of them so far for other folks with generator hubs. They cost 30$ and have about 22$ in parts in them and take me about 4 hours to build one at a time.
(March 2016 Update) :
I have been able to shrink the size of the converter box to about 50% of the one in this original article, the new box also has a display that shows the output in Volts and Amps so you know exactly how much power your devices are getting at any given speed. New post on that coming soon. The new cost for a GenHub to USB with the display has dropped to around $4 ! total for parts and take less than 30 min to assemble. I expect to be able to make them for anyone who wants one for about $10. I will also give a parts list, schematic and my sources to anyone wanting to build their own (free).