Say you're riding off into the sunset on a big bike tour or bikepacking trip.  Lights are an essential part of your kit - for riding after dark, or increased visibility during poor weather.  In the 21st century, small electronic devices also appear to be essential for many people - smart phones, GPS units, or even tablets and laptops can be useful during a tour.  Of course, keeping your lights and devices fed with power can be a major pain.  Carrying batteries around makes for heavy bags, and places to recharge can be few and far between.  Enter the hub dynamo system.

System overview

A hub dynamo is just what it sounds like - a front bicycle wheel hub that generates power as the wheel turns.  It's possible to power just a headlight off a dynamo hub, but you can also power a taillight, AC-to-DC USB device chargers, and cache batteries to store power for later.  Here at VC we've been using dynamo hubs since 2008, and our experience is that it's amazing to do away with batteries.  Your lights are always there when you need them - no worrying about charge levels, or if you'll run out of power.  The concept is simple; getting a solid system set up and working properly for your needs takes a little more work.  So we decided to help out by writing this primer!  Below you'll find each part of a dynamo system described in detail, along with suggestions on how to choose your system based on your intended usage.  We stock almost everything covered in this primer - you can find the parts listed below in our shop or on our webstore.

Here's a basic dynamo power flow chart we made, for all you visual learners...

The Hub

Many people hear "dynamo" or "generator" in association with "bicycle" and think of old-school bottle dynamos - those annoying little devices that bolt onto your fork or frame and literally rub against your tire in order to spin a small wheel and generate power.  If that's one side of the spectrum, modern dynamo hubs are on the completely opposite end.  A nice hub in this day and age is small, relatively light, extremely efficient, and has incredible longevity.  Paired with modern LED lights and efficient devices, you can make great use of the power produced by nothing but your forward motion.  There are several nice dynamo hubs on the market, and we can source others for you if you wish, but we stock only the Shutter Precision PD-8X, for a few reasons.  1) It's the most efficient dynamo hub on the market.  2) It's the lightest-in-class dynamo hub on the market.  3) It's compatible with 15mm thru-axle AND normal QR.  4) It's less expensive than any comparable dynamo hub on the market.  In short, it's hard to find something to dislike about the PD-8X, and so we decided to just offer the one we prefer to use ourselves!

The most common question we hear about dynamo hubs is "how much drag is there?"  Indeed, when you feel the PD-8X's (or any dynamo hub's) rotational resistance by hand, it will feel exceptionally notchy and difficult to turn.  You're not feeling misadjusted bearings, or interference between mechanical parts, but the inherent attraction between the magnets and the poles in the dynamo.  When the hub is used on a bicycle, even at very slow speeds, these "notches" essentially disappear as opposing magnetic forces cancel each other out, leaving a smooth-rolling hub with electricity to spare!

Modern dynamo hubs have a 6 volt, 3 watt output, which is compatible with virtually all modern dynamo lights and device chargers we're aware of.

The Light

Just like older dynamos, older bicycle dynamo lights left a lot to be desired.  Happily, LEDs and circuitry have come a long way over the years, and modern lights are nothing short of amazing.  LEDs take very little power to achieve full brightness, which means that your bicycle's light is very bright even at low speeds.  Furthermore, many high-end dynamo lights have a built-in capacitor that allows the light to continue burning (generally for several minutes at a slightly reduced output) even when stopped.  This is extremely handy at stoplights, or on the trail if you need to see something while you're stopped.  Dynamo lights wire directly to the hub and generally mount to either the fork crown or the handlebar.  We stock Supernova's E3 Triple 2 headlight for off-road use, and Busch & Muller's Luxos U for road use.  (The Luxos U also has a small internal cache battery and USB output for device charging, similar to the USB-WERK; see below.)  The beam patterns are very different - the Supernova has a large, round, flood beam for great trail visibility; the B&M has a very wide beam with some shaping to avoid blinding oncoming drivers.  Both are German-made and are extremely nice, long-lasting products.  At VC we've been using a couple now-older B&M headlights for years, without any issues whatsoever, and we are also currently using the Supernova light for bikepacking trips with great results.

Dynamo taillights, while not necessary, can be used and are wired to the headlight, not directly to the dynamo.  We currently use a battery-powered taillight on most long trips because LED taillights run forever on small batteries and using one eliminates a long span of wire along the top tube - less to potentially break!  There are wired-in taillights on the VC commuter fleet, though...

The Device Charger

Your dynamo can be used for so much more than just powering a light.  It can also be used - alone or in conjunction with a headlight - as a power source for small electronic devices.  GPS units, cell phones, or smart phones are common examples.  Dynamo hubs only put out so much power, so you generally can't charge devices and have your headlight on at the same time (or, if you do, neither works well).  But with some basic planning - charge devices during the day, burn lights at night - you can have your cake and eat it too.  It isn't as if you can just wire your iPhone to your dynamo directly, though, and that's where device chargers come in.  Dynamo hubs put out AC current, just like the outlets in your house.  But your device needs DC current - and that's what the little box on the end of your wall charger does, converts the current.  Dynamo system device chargers convert the current from AC to DC, and provide a controlled-current USB output for your device's USB charge cord.  They wire into your dynamo hub in parallel with your headlight.  We stock several device chargers: Supernova's The Plug III, Busch & Muller's USB-WERK, and PedalPower+'s Super I Cable.  They have several differences, but in the end they all serve to charge your device.  Supernova's The Plug III is the slickest little charger we've ever seen, replacing your headset's top cap.  Since it simply converts AC to consistent DC, you must maintain a minimum speed of about 10mph to charge your device, or use a separate cache battery (see below) to store power for charging.  The USB-WERK is small and light, has a small cache battery (~175mAh) inside its housing, and can maintain steady current to your device even during slow speeds and while stopped (as long as the cache battery lasts, of course).  The Super I Cable also has a cache battery, but it is much more capacious (2200mAh) - while also heavier and larger, this means that your devices will charge even during extended stops.  The Super I Cable is also the only device charger we carry that comes complete with many different device adapters and international wall chargers so that, if you'd like, you can charge up the internal battery at the hotel room before hitting the road!

The dedicated Cache Battery

Say you're using Supernova's The Plug III as your device charger.  Since it only converts the current and provides a USB interface - but doesn't store any power - you need to maintain a speed of about 10mph to charge your device.  For road touring, that's probably fine, but not if it's mountainous or if you're riding off road.  Or, say you have multiple devices, or you're even carrying a tablet or small laptop.  You need more power than even something like the Super I Cable, with its 2200mAh internal battery, can provide.  In these types of scenarios, a dedicated cache battery makes tons of sense.  You plug it into your USB charger during the day; it charges to capacity; then you can charge whatever you'd like off of it until it's empty.  We carry three flavors of dedicated, USB-interface cache batteries: Brunton's Pulse 1500, Metal 4400, and Heavy Metal 5500.  (Note: What we call cache batteries are often referred to as device chargers in the electronics world at large, not to be confused with device chargers as part of a dynamo system, described above.)  The numbers in Brunton's model names correlate to the batteries' capacity in mAh (milliampre-hour, if you want to know).  As a point of reference, the 1500 will charge most smart phones once; the 4400, four times; the 5500, five times.  You can purchase cache batteries with 20,000mAh capacity, but they get big and heavy, not to mention impossible to charge from a dynamo hub on a realistic timeline.

Cache batteries are a compact, sleek way to store power that you generate, and unlike something like the Super I Cable (with an internal cache), you can easily detach it from your charger and take the power with you, say, into your tent.

Specific usage considerations

Now that you (hopefully) have a greater understanding of the parts of a dynamo system, we can take a look at how to set up YOUR system.  The foundation is, of course, the hub.  Once that's in place, you can customize to your heart's content.  Run a headlight, or none at all.  Same with a taillight.  Same with device chargers and cache batteries.  Below we'll run through a few ideal scenarios - which one sounds the most like your needs?

1) The Minimalist - this rider is moving fast and light.  Road touring in non-mountainous terrain, or dirt road touring with minimal device charging needs (perhaps a GPS unit).  A nice setup would be the PD-8X hub and the Luxos U headlight w/ internal cache battery; another would be the same hub with The Plug III.  To either setup we could add the small Pulse 1500 cache battery.

2) The Off-Road Minimalist - this rider is fast and light, but on terrain that keeps average speeds down.  Still minimal device charging needs - a GPS unit or a smart phone.  A nice setup would be the PD-8X hub and the E3 Triple 2 headlight, along with The Plug III charger and Pulse 1500 cache battery, OR the USB-WERK charger and the Pulse 1500 cache battery.

3) The Normal Touring Cyclist - this rider is like most of us, riding for fun, on- or off-road, with perhaps a cell phone and a GPS.  A nice setup would be the PD-8X hub, the Luxos U or E3 Triple 2 headlight (depending on whether on- or off-road), and The Plug III, USB-WERK, or Super I Cable charger, along with the Metal 4400 cache battery.

4) The Long-Term Tourist - this rider is on the road for months or years at a time, and is carrying devices to update a website, etc.  Device charging needs are high.  A nice setup would be the PD-8X hub, the Luxos U headlight, the USB-WERK or Super I Cable charger, and the Heavy Metal 5500 cache battery, or even multiple cache batteries if the charging load is high enough.

The End

Yet again, my fingers are sore and it's time to go for a bike ride.  Thanks for reading.  Hopefully this was helpful to you, and if so, please consider supporting VC with your next purchase!