Wednesday, 11 January 2012

Selecting and installing dynamo lighting

Dynamo lights installed on our delivery bike
(or... everything we know about dynamo lights for bicycles).

Why dynamo lighting ?

Much nonsense is written about dynamo lights. The objections usually come from people who don't use dynamos, or have not used them for many years.

According to some "experts", dynamos either slow you down or wear out your tyres or don't produce much light, make noise, or perhaps they commit a combination of these sins.

Actually, modern dynamo lighting is efficient, reliable, quiet and produces so much light that the best headlights now have optics which shape the beam to prevent those coming in the opposite way from being dazzled.

For utility cyclists we recommend dynamo lighting. There are many advantages over battery powered lights:
  1. It's low cost in use as no batteries need ever be bought.
  2. It's reliable for day to day use as there are no batteries to go flat and have to be charged or replaced.
  3. Dynamo lights are permanently mounted on the bike, meaning you don't have to detach things and take them with you when you park your bike.
  4. Permanent mounting also means your lights are always there. An unexpected delay doesn't result in cycling in the dark with no lighting.
  5. There is quite a lot of power available to run lights from a dynamo so dynamo lights can be very bright.
  6. Because the power source is you, your lights stay bright even on long rides. They can't fade out half way home because the battery ran out.
Dynamo lighting is a "fit and forget" option. Set it up properly once and ride with the minimum of maintenance thereafter.

Selecting dynamo lights
There are a wide range of dynamo lights available, from the very cheapest all in one sets through to expensive systems which can cost more than €200. Any system of dynamo lights consists of three components, the dynamo itself, a headlight and a rear light,

AXA and Nordlicht bottle dynamos, Shimano hub dynamo
Choosing a dynamo
There are two types of dynamo - those built in a wheel ( "hub dynamos" ) and those which run on the side-wall of a wheel ( "bottle dynamos" ). Each has advantages over the other:
  • While no good quality dynamo will slow you down by enough to make a difference unless you're in a race, hub dynamos offer lower drag when the lights on are than bottle dynamos do. However, because bottle dynamos completely disconnect from the wheel when the lights are out, bottles offer no resistance when you are not using the lights, while hub dynamos still have a small amount of in-built drag relative to a normal well-maintained hub.
  • Hub dynamos cannot be knocked out of alignment, and will continue to work well even if your wheel is damaged and the rim bent. However, bottle dynamos do not need to be replaced if you damage your wheel and have to replace it.
  • Hub dynamos are heavier than bottle dynamos.
  • Bottle dynamos can slip in the wet (meaning your lights can be unreliable) though this is rare with correct setup.
  • Hub dynamos cost more to retrofit because you must buy or build a wheel. However, they don't require brackets to be fitted to the bike and the wheels probably don't cost as much as you think.
  • Bottle dynamos are much more straightforward to retrofit to a bike which already has hub or disk brakes or to a rear wheel with hub gears.
A cheap "all in one" dynamo
lighting set. We don't sell these.
If you're struggling with a set like
 this, see our guide below.
We sell both bottle and hub dynamos. We've used both types over the years. At the moment, most of our own bikes are fitted with bottle dynamos. Our favourite bottle dynamo is the Nordlicht. This is made of metal, robust, very reliable and light running. We're still using one that we bought 15 years ago. A lot of quality for something so inexpensive. We also rate the AXA HR which is a little less expensive and perhaps runs slightly lighter. We also have a range of wheels with Shimano hub dynamos. These start at under €50. Very good value for what you get.

Very nearly all currently available dynamos, whether hub or bottle, have the same output of 6 volts at 3 Watts to power both front and back lights. 2.4 W is allocated for the front light and 0.6 W for the rear. Just a few models of hub dynamo produce 6 V 2.4 W making them suitable for powering just the front light.

This means that all dynamos are compatible with any available dynamo lights and you can mix and match to achieve a combination which has the performance and price that you want.  Even the cheapest all in one set has the same output, so even if you have started with a set like this, you can swap one component at a time for those of better quality until you have a satisfactory lighting setup.

There's just one thing to bear in mind with headlights - with a hub dynamo you want either a manual or automatic light sensing switch on the headlight so that you don't run the lights even in daytime. This switch will also operate the rear light.

Oh, and something I must point out about having 2.4 W for the front lights. This is quite a lot of energy for bicycle lighting. Most battery lights of old used 0.75 W front bulbs as higher power led to very short battery life. Contrary to many people's opinions, dynamo lights were always brighter than battery lights. While some high end battery lights available these days are brighter than dynamo lights, many battery powered lights still do not attempt to produce so much light as even low cost dynamo headlights do, because trying to do so results in a short battery life.

Dynamo headlights
Three of our favourite dynamo headlights, the remarkably
good value AXA Sprint and two from the Philips range. 
In days of old, dynamo lights used sometimes incandescent bulbs. These were often used with reflector designs which spread the light too broadly and could result in a not very effective light pattern. Halogen bulbs improved the situation considerably as they increased the light output for the same power, and better reflector shapes helped even more. However, they were never quite adequate for fast cyclists.

The introduction of LED headlights has changed everything. 2.4 W (the headlight share of the 3 W output of a dynamo) is enough to produce a considerable amount of light from LEDs. Also, LEDs last and last and last. There is no need to replace bulbs.

Even at a low price, modern dynamo LED headlights work extremely well. At the mid and high price ranges they become yet more effective.

An important advance is shaped lenses and use of indirect light from the LED source. This has made it possible to build extremely bright lights with a sharp cut off at the top which won't blind oncoming cyclists and drivers. It also means that more light goes where it is needed for you to see by because less is wasted in the wrong direction.

We currently have five favourite LED headlights which we particularly recommend. Each also includes a retro-reflector which shows up in car headlights:
  • Philips SafeRide 60 lux - relatively expensive ( €80 ) but produces a lot of light from two high power LEDs. Powerful enough to be legal lighting for small motorbikes in some countries. Keeps glowing for up to four minutes after you stop riding. Mechanical switch for hub dynamo use.
  • AXA Luxx 70 plus - ( €70 ) Enormous light output. When you're not using the light, this also provides a USB outlet to charge mobile devices.
  • Philips SafeRide 40 lux - lower cost ( €50 ) but still an enormous amount of light. With an automatic light sensing switch which in combination with a hub dynamo means your lights come on automatically at night. Keeps glowing for up to four minutes after you stop riding.
  • B&M Lumotec Lyt - a mid-price light ( €17 ) still with high output and a good beam shape, including standlight and optional switch or sensor for dynamo.
  • AXA Sprint 10 lux - a much lower cost light. In fact, a bargain at just €12.50. It's not so bright as the B&M Lyt or the Philips lamps, but still well in advance of what we used use ten years ago and I find it entirely adequate for riding in town where there are street lights. Optional switch and stand light functions.
Dynamo rear lights
Some of our favourite dynamo rear lights. All include a stand light function
which means they store electricity and continue to glow after you stop.
Dynamo rear lights have also been revolutionized by LED technology. It made it possible to have a "stand light", where the light would charge up and store electricity so that it can continue to glow after you stop cycling.

With rear lights, there are other factors to consider, such as where you will mount the light. Some rear lights are designed to mount on the rear mudguard (fender) while others are designed to mount on the rear rack.

Our favourite rear dynamo lights are as follows. All include a stand-light function and a reflector to give extra visibility when lit by car headlights:
Finally, note that running the rear light from the dynamo is optional. You can also use a dynamo front light together with a battery rear light. Some people prefer this due to not having to run so many cables along their bike. We have battery rear lights to use together with dynamo lights which can be mounted permanently on the bike.

Other things you'll need

We sell wire and zip ties but not tape
As well as the main parts of dynamo, front and rear light, there are other parts that you will probably need.

Some lights come with wire, but not all. You will probably need wire to attach between the dynamo and headlight or between the headlight and rear light. We sell wire fitted with the correct size of push on connector for our lights.

You can use zip-ties and/or electrical tape to run the wires along the forks and frame of your bike. We have inexpensive zip-ties but do not currently sell tape because you can almost certainly buy it as cheaply as we can in a discount store near your home, and you may be able to find colours which are a good match to your bike.

If using zip-ties, which we recommend you do, please don't do them up so tight that you cut through the insulation of the wire. Also, remember to leave a little loop of wire around the headset so that the handlebars can be turned without putting undue stress of wire which is heading to the rear lamp.

Dynamo mounting brackets. Left to right: front wheel,
rear wheel, Canti / V brake boss.
If fitting a bottle dynamo to a bike which doesn't have a bottle dynamo mount on the frame or fork, you will need to buy a bracket. Of these, we think the Cantilever / V brake mounting bracket works best, so if you have mounting points for these brakes, whether or not they are in use, this would be our first choice. Like most things we sell, we use it ourselves as you can see in the first photo on this page.

While the electricity from the dynamo is AC, it is still important to make sure that you keep the "earth" connection consistent through the wiring of your lights. The reason is that the "earth" is connected to the frame of the bike within both the dynamo and some of the lights. Confusions over "earth" can lead to faults such as the switch on a headlight not actually switching off your lights because electricity is flowing through the frame of your bike, or the lights either being very dim or not lighting at all due to a short circuit through the frame.

The "earth" side of each light and dynamo is made obvious by labels on each component. If unsure, use the wiring diagram. The black wire in the diagram denotes the earth connection. The outside of the wire does not of course have to be this colour. With the wire that we supply, both are black but the earth wire has a white stripe along it.

When there is no switch on a headlight, the input and output are the same. Just connect the wires from the dynamo and to the rear light together at this point (doing it this way makes it easier to change to a different headlight at a later date).

Switching a dynamo on and off
Not all bottle dynamos work in an identical manner, but it is usually the case that you press a button of some kind to release the spring to allow the dynamo to push against the wheel to switch the dynamo on and pull the dynamo gently away from the wheel until you feel a click to switch back off.

In this video I demonstrate with a Nordlicht dynamo, the type that we recommended most highly

Setting up a bottle dynamo
The dynamo should run on the dynamo
track on the side of the tyre.

There are a few factors which should be taken into account when using bottle dynamos. If you take care of these small issues then problems with bottle dynamos are rare:
  1. Run the dynamo on a tyre with a dynamo tread and make sure that the dynamo is aligned so that it runs correctly along that tread.

    Skinwall racing tyres are not designed for use with a dynamo and the sidewall of such a tyre could be damaged by using a dynamo against it. All the tyres that we recommend for everyday use have a dynamo track on their sidewall. However, if you prefer skinwall tyres, note that the Nordlicht dynamo can be run on the rim, which makes it compatible with skinwall tyres.
     
  2. Take care of correct pressure against the sidewall of the tyre.
    In the "off" position, the gap
    between tyre and dynamo
    roller must be right.

    I find that setting up the dynamo so that in the "off" position it is about one cm clear of the tyre works best. You may find that this varies a little with different combinations of tyre and dynamo.

    Note that when you change between different tyres of different widths this distance may need setting up again.

    To adjust the gap between the rubber or steel roller of the dynamo and the tyre you can bend the brazed on bracket until this spacing is correct. If the gap is too wide or too short then it may result in there being inadequate pressure. Your correct distance may not be the same as mine. Excessive pressure results in more drag and can also sometimes result in the dynamo slipping.

    The Nordlicht dynamo with rubber wheel can also be set up to run on the rim. The same rules apply.
     
  3. A straight line between the axis of the dynamo and the centre
    of the wheel is important.
  4. The dynamo axis must be lined up so that it passes directly over the centre of the wheel. Not doing this will roll out the roller on the dynamo more quickly than normal and can even damage bearings in the dynamo.
     
  5. Slipping can occur if the roller is worn out. Replacement rubber rollers can be bought in our shop for both the AXA and Nordlicht dynamos. In both cases you simply pull off the old one and push the new one on to replace it.
  6. Bent wheels result in intermittent lighting behaviour because the dynamo stops operating as the low point comes around.

    Solving this problem requires either a new wheel or rebuilding of the existing wheel. Minor problems can sometimes be solved by tweaking with a spoke-key. Loosen spokes on the side which is convex, and tighten adjacent spokes by the same number of turns on the side which is concave.
  7. A squealing noise from the dynamo quite possibly means that the internal bearings are worn out. It's usually accompanied by much more drag and can result in intermittent light. This happens quite quickly with some cheap dynamos, and is aggravated by incorrect setup with the axis of the dynamo not going past the centre of the wheel. If your dynamo has reached this point, you may well need to replace it. A better quality dynamo will last longer than a cheap one.

    However, before you dispose of the old dynamo, try applying some light oil, just a couple of drops, to the bearings. You may need to remove the roller to do this. If the dynamo is old, but still in good condition, it may simply have dried out.
  8. Periodic noises: If a noise occurs roughly twice or three times a second with a bottle dynamo setup, this is caused by the wheel, not the dynamo. Wheels on bicycles rotate roughly two to three times a second at a normal rate of cycling. A warped wheel, a defect on the tyre or other problems with the wheel can cause slipping or jumping of a bottle dynamo at the frequency of wheel rotation and can make quite a lot of noise. If you experience this problem, turn the wheel slowly and watch for defects.

Conclusion
This article is quite long because I've tried to cover everything. However, setting up dynamo lights isn't difficult to do. Once it's been done, you have "free" lighting with lights which are permanently attached to your bike and cannot be easily stolen (you need tools). A great bonus for utility cyclists, as you don't have to carry things with you when you leave your bike.

For some kinds of sport cycling, for example road racers who want to carry absolutely the minimum of weight and be able to easily remove their bikes for daytime racing, or night-time mountain bikers who want enormously powerful lights which flood the entire area in front of them with light1, there is no real choice but to use battery powered lights. For the rest of us, dynamos really are the best option.

FAQ
Q: Do bottle dynamos wear the sidewall of your tyre ? A: No. The roller has very little pressure compared with that of the bike on the road so wear on the sidewall of the tyre is very much lower than that of the tyre against the road surface. Normally you will notice no sidewall wear of significance in the lifetime of a tyre. You should, however, only use a sidewall dynamo on a tyre which has a dynamo track printed on it.

Q: Do bottle dynamos slip in the wet ?
A: With a quality dynamo this is unlikely to happen unless the dynamo is not set up correctly. See the setup section

Q: How much does a dynamo slow you down ?
A: Almost not at all. I wouldn't expect to be slowed by more than 1/20th of my normal speed by a well set up quality bottle dynamo when the lights are on. A hub dynamo will slow you even less and of course when lights are off there no no drag from a bottle dynamo and very nearly none from a hub. The stronger you are, the less the effect can be felt.

Q: Which dynamos keep the lights glowing when you stop ?
A: None of them. This function is always in the headlights and tail-lights themselves, and it's present in all of the rear lights and almost all of the front lights in our shop.

Q: Don't the lights go out when you stop ?
A: No. Almost all good quality dynamo lights these days include a "standlight". This is a circuit including a capacitor which stores some of the energy generated to keep the lights on when you stop. It works for up to four minutes with some lights

Q: What happens if I use a headlight without a switch on a hub dynamo ?
A: The lights will come on whenever you ride your bike, even in the daytime. Some older hub dynamos were actually more efficient with the lights on than with them switched off. However, this isn't true for the hub dynamos that we sell now. It's better to have a switch.

Q: If I have an old dynamo lighting set and one component has failed then do I have to buy everything new again ?
A: Almost all dynamo lighting sets ever made are rated at 6 V 3 W. If yours has this rating (it's usually written on the bottom of the dynamo) then it is safe to substitute any of the front lights, rear lights or dynamos that we sell and use them in any combination with older parts for the same system.

Q: I have an old Sturmey Archer Dynohub. Can this work with modern headlights ?
A: The original Sturmey Archer Dynohub had a slightly lower rating. 6 V 2 W. Headlights expect 6 V 2.4 W. This means there isn't enough output to run a normal headlight at full brightness. However, in practice, the combination of one of these venerable dynohubs with a modern LED headlight will result in much more light than you ever could have produced with the original lights which matched the dynohub. It is best in this case to use a battery rear light so that all the energy from the dynohub goes to the headlight. Modern "dynohubs" produce 6 V 3 W and can run both front and rear lights.

Q: Where is the best place to buy good quality dynamo lighting ? A: The Dutch Bike Bits webshop, of course. We also have a wide range of battery lights if you would prefer them.

Q: Why can't you use just a dynamo rear light without a front light ?

A: The simple answer is that a rear dynamo light will always be damaged if used without a front light. The explanation of why is quite long and technical, but you'll find it below:


It is perfectly safe to use any of our dynamo front lights with our dynamos without also connecting a rear light. This will not damage the headlight. However, you must never use a dynamo to power a rear light without a headlight also being connected as this is quite likely to cause damage due to driving the rear light with too high a voltage. The reason why is as follows:

Sources of electrical power can approximate either a constant voltage or a constant current.

Constant voltage: A battery is an example of a constant voltage source, and it will attempt to supply the same voltage whatever load is attached. If you short-circuit a battery, then the battery will attempt to discharge at an infinite current and this is why lithium batteries, which are capable of very high currents, can cause fires.

Constant current: A bicycle dynamo is an example of a constant current source. Bicycle dynamos are rated at 6 V 3 W but what this really means is that they are current sources which attempt to deliver half an amp across whatever load is connected. The expected load of a rear and front light together is the equivalent of 12 ohms. A dynamo tries to supply sufficient voltage always to deliver the same current. With a short circuit, the dynamo will still deliver about 0.5 A at zero volts, but with an open circuit the dynamo will produce so high a voltage as it can in an attempt to deliver 0.5 amps.

You don't need to know any maths to safely connect dynamo lights. Simply pick a front and (optional) rear light, and wire them to a dynamo. However, if you want to know why you should never use a rear light on its own, read on:

The 12 ohm equivalent resistance for front and rear lights together comes from the front and rear lights being connected in parallel. The front light has an equivalent resistance of 15 ohms while the rear light is the equivalent of 60 ohms. To combine the two we use 1 / (1 / 15 + 1 / 60) = 12. Now that we know the equivalent resistance of each light we can calculate the current and power for each if used on their own.

For a front light alone, V=IR, V=0.5 * 15 = 7.5 V. P = IV, P = 0.5 * 7.5 = 3.75 W. This is a little over the rated value of 2.4 W, sufficient to damage older front lights with bulbs unless the bulb is changed to 3 W. However, modern LED based front lights can cope.

For a rear light, V=IR, V=0.5 * 60 = 30 V. P = IV, P = 0.5 * 30 = 15 W. This is a long way over the rated values of 0.6 W and 6 V and this is why dynamo rear lights do not last long if connected on their own to a dynamo. The front light is required to keep the voltage down to the correct level for the rear light.


1Please don't use mountain bike type lighting when you're not in a mountain bike race. It's anti-social and potentially dangerous to other road and cycle-path users who can be blinded by the amount of light scattered too high in front of you. It's analogous to driving a car with the headlights on full beam. The lights that we recommend here, especially the Philips lights, are very bright while being specifically designed to avoid this problem.

4 comments:

  1. David great article! Are you planning to add a segment for velos? Or are velos with drum brakes not applicable? I would love to add some sort is dynamo to my Mango. Have A great week.
    Larry in Leduc, Alberta

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  2. Great article, David. I'm a convert for commuting having picked up a Shimano hub dynamo built into a wheel from an ex-hire bike for £5. Helena then bought me a set of lights for my birthday.

    I won't be going back to batteries and in the longer term want to look at dynamos for off-road night riding too. Powering a helmet light is something of a challenge though...

    ReplyDelete
  3. I wish we had such thoughtful and elegant retailing where I live in Canada! Thanks for the !

    ReplyDelete
  4. Excellent article. I am surprised how little there on the setup of these older style bottle dynamos on the web.

    ReplyDelete