Dynamo lights have many advantages.They’re always on call, lightweight, and extra- bright, but traditional dynamos are noisy, inefficient and unreliable.These days, there’s a renewed interest in hub dynamos, which are virtually silent and more reliable, but expensive to buy and fit.We’ve looked at the best bottle dynamos we could find, to see if they’re: (a) worth the extra over a conventional bottle and/or (b) comparable to a hub.
Two manufacturers dominate this business – Swiss company Dynosys, manufacturer of the LightSpin, and Busch & Müller from Germany, manufacturer of the Dymotec.The LightSpin is basically a high-tech version of a conventional six volt bottle dynamo, with improved bearings and electronic voltage control, while the Dymotec comes in three forms: the ‘6’, a more efficient version of a conventional dynamo, the ‘S6’, like the ‘6’, but with voltage control, and the ‘S12’, with everything else, plus a greater output. All can be fitted in place of a conventional bottle or hub dynamo except for the S12 which has an output of 12 volts (all other systems are six volt) and thus needs dedicated lamps, or hard-to-obtain 12 volt bulbs if upgrading older (ie, electronic-free) lamps.
While we’re on the subject, if adding a new bottle to an old system, it’s worth bearing in mind that some ‘medium-tech’ lamps may contain zener diodes to dump surplus voltage and improve bulb life.With the exception of the basic Dymotec 6, these posh-end dynamos contain more sophisticated voltage control and should not be used with zener diodes, because the dynamo will do its best to supply power to the bulbs and zener, which will simply throw the surplus overboard. If in doubt, it’s a good idea to replace the dynamo and lamps at the same time.
We’ve tested the LightSpin against the top-of-the-range B&M Dymotec S12.The 6 and S6 are cheaper, and broadly similar, but with lower output. For the purposes of making the test as realistic as possible, we fitted the dynamos to a hack bike with slightly wobbly wheels, although if spending this sort of money you’d be well advised to have the wheels trued, because a wobbly wheel will reduce efficiency. Both the designs dealt manfully with wobbles and inclement weather.
Dymotec S12
The Dymotec 6 costs £38, the S6 £110, and the S12 (complete with 12v versions of the Lumotec Oval Plus front light and Toplight Plus rear lights), no less than £300. Sounds like a reasonable budget for a bicycle. But for engineers everywhere, this is more or less the dream spec for a dynamo: 12 volts, 6.2 watts and 60% efficiency. For the rest of us, let us just say it’s solidly made, reliable and efficient.
So, what do all the numbers mean? As any woman will tell you, it’s largely a man thing: big numbers meaning a generous wallet, unrivalled fertility, and so forth, but a 12 volt dynamo really does make some sense.
Most battery lights are three volts, and dynamos six volts – the voltage being a measure of the electrical ‘pressure’. On its own, this tells us nothing about the light output, but the greater the pressure, the easier it is for the power to fight its way through those embarrassing dodgy joints held together with sticky tape. In short, a 12 volt system is more reliable.
Efficiency is the difference between the power you put in and the electrical power that comes out of the dynamo. Some are atrociously inefficient, turning only 20-30% of your hard won effort into light, while the rest floats off into the night as heat and noise. Fortunately, dynamos are small, absorbing 15 watts or less for an output of three useful watts. For those who’ve forgotten their school physics, voltage (electrical pressure) multiplied by amps (the current or volume of electricity) equals watts – the measurement of electric power.
Fifteen watts doesn’t sound much, but if you’re tooling gently home on a bicycle at a modest 13mph, your total power output may be less than 75 watts, so a crummy old dynamo could be absorbing nearly a quarter of your leg power.
Better quality bearings, and other much more complicated things, bring greater efficiency. Busch & Müller claim 40% for the 6, 55% for the S6, and 60% for the S12.That efficiency is used to cut the overall power consumption on the six volt units, but with the S12, B&M has chosen instead to provide a greater output: 6.2 watts, plus the 40% chucked away as heat, giving a total drain on your legs of 10.3 watts.All a bit complicated, but the result is a bit less effort, twice as much light, and a very tiny reduction in global warming.
In practice, our test yielded a whopping peak output of 8.7 watts (the extra power recharges the standlight lamps in the first few minutes of operation). But with a steady output of 15.2 volts above 8mph, we suspect the S12 might be powerful enough to eat bulbs relatively quickly. Don’t care, eh? You will when you find the bulbs cost £12.99 each.
Rolling resistance is barely discernible.When we tested a down-market three watt dynamo in October, it knocked 1.4 mph off our typical coasting speed.The S12 (generating 8.7 watts), only reduces the coasting speed by 0.5 mph – noticeable, but insignificant.
Fitting
…not a bad chat-up line…you could ask them to come up and inspect your zener diodes…
Fitting the S12 is quite straightforward, and we managed to assemble a complete system including the front and rear lamps in about an hour. One bit of advice – do solder the connectors if you can.There’s no point in spending £300 just to see the wiring fall apart on the first soggy night. If you don’t have the technology, trim the wires to length and seek out a man or woman with a soldering iron (not a bad chat-up line, all things considered – you could ask them to come up and inspect your zener diodes too). Otherwise, assembly is fairly self-evident.The dynamo needs to be carefully aligned, like any other, but the Dymotec units also feature a crafty contact pressure adjustment, which should be set as low as possible for any particular tyre/weather combination. If the lights flicker, increase the pressure a bit. For rough conditions, the rubber roller can be swapped (hardly a roadside job) for B&M’s ‘weather-proof’ design, a rotary wire brush that would do a decent job of buffing up your small parts.This should be kept well away from frail tyre sidewalls and small fingers for obvious reasons. B&M make the point that it should only be used ‘temporarily’ in ‘rainy, snowy or icy’ conditions.We didn’t need it, but it was nice to know it was there.
Light output
We tested the S12 with Busch & Müller’s wonderful Lumotec Oval Plus front lamp and Toplight Plus rear lamp, produced in 12 volt versions specifically for this dynamo. Both have a standlight function too – the rear LEDs continue to burn at full brightness for about five minutes, while the front switches to a single white LED that lasts for ‘at least’ ten minutes. Ever tried waiting for a standlight to go out when there’s something good on the telly? Should your unsoldered connectors drop off, the front standlight is as powerful as some elderly filament bulbs, and easily bright enough to get you home.
As for the halogen main beam, don’t expect two or three times as much light as normal, just because you’re generating two or three times as much power, but in terms of brightness and spread, the Lumotec is unrivalled. Country roads are easily navigated at speed, and oncoming cars tend to assume you’re motorised, treating you with a bit of respect. Our only criticism is that enough light scatters through the transparent rim of the lens to dazzle the rider in open country, which is a bit counter- productive.The easy answer is a strip of black masking tape, but surely this should be sorted at source?
LightSpin
Unlike the B&M S12, this is a six volt device, so you can use it with conventional six volt lamps, provided you seek and destroy those pesky zener diodes. It’s also relatively cheap at £70 – a full £40 less than the B&M S6, which has a lower output. Efficiency is claimed to be 65-75%, so with our measured power output of only 2.6 watts, we estimate a power requirement of less than four watts.With such a low demand, the wheel can be spun quite easily – you can’t feel it on the road.The coasting speed was reduced from 15.3 to 15.2 mph – a barely discernible effect.
Incidentally, the low power output on our graph doesn’t necessarily make this a seven stone weakling amongst dynamos. Traditional bottle dynamos tend to call it a day at three watts, but the LightSpin provides whatever the bulb demands, up to a recommended maximum of 4.8 watts. It just happens that our bulb combination demanded only 2.6 watts. With this dynamo (and the B&M S6 too) it is permissible to fit a three watt bulb at the front and 0.6 watt at the rear, making 3.6 watts in all.
We paired the LightSpin with the neat little Hella Micro FF front lamp.The result was noticeably less exciting than the B&M S12, but the lamp throws a smaller, well defined pool of light just where you want it. Or at least, it does if you take great care aiming the lamp.
Conclusion
Value for money is a difficult concept at this level. After all, you can buy a basic dynamo for less than £10, but we wouldn’t recommend cutting corners to that extent if you commute on a regular basis.The B&M in particular is frighteningly expensive, but it offers unrivalled light output.The cheaper B&Ms and the Lightspin have a more conventional power output, but great efficiency.
They’re all better than the cooking variety, but are they as good as a hub dynamo? They’re certainly noisier, and compared to the hubs we’ve tried, the useful power kicks in at a slightly higher speed – 5mph instead of 4mph.That might seem irrelevant, but a hub will keep the lights close to full brightness at a smart walking pace, whereas the bottle dynamos will not.They’re relatively vulnerable too, both to the elements and vandalism.
On the positive side, a bottle dynamo is quick, easy and cheap to fit, and there’s no drag when it’s turned away from the tyre, although drag has been virtually eliminated from the hubs these days anyway.
Our instincts are moving towards the weather-proof, no-nonsense hub, but there are plenty of reasons why you might prefer something easier to fit, and if you want hub performance from a bottle, one of these might suit. If you’re looking for low rolling resistance above all else, the LightSpin is the best, but if power matters, go for B&M’s S12. There’s enough oomph here to recharge a mobile phone, or even a lap-top, provided you can find a suitable adaptor.
Specification
Dymotec S12 (c/w lamps) £300
Power output (claimed) 6.2 watts
Efficiency (claimed) 60%
Manufacturer Busch & Müller tel +49 2354 9156 mail info@bumm.de web www.bumm.de
UK distributor AMBA Marketing (UK) tel 01392 840030 mail sales@amba-marketing.com
Dynosys LightSpin £70
Power output (claimed) 4.8 watts
Efficiency (claimed) 65-75%
Manufacturer Dynosys tel +41 62827 4828 mail info@dynosys-ag.ch web www.dynosys-ag.ch
UK Distributor Gearshift tel 0700 0700 531 web www.gearshift.co.uk
