What Are Bike Dynamos And How Do They Work?

What Are Bike Dynamos And How Do They Work?

(cinematic music) – I hope you’re ready
for some serious tech, because in this video, we’re
gonna be looking at dynamos and we’re gonna explain what they are, how they work, and why
you should be using one. For this video, we’ve luckily been sent a nice new pair of HUNT
SuperDura Dynamo wheels, which, I have to say,
I’m genuinely impressed and surprised at how
normal-looking the front hub is. Granted it is bigger when
you look at it front on, anda bit more bulbous than a normal hub, but especially once it’s on a bike, it’s hard to tell the difference. (cool jazz music) There are two main types
of dynamo, hub and bottle. Now, bottle dynamos attach
either on your seat stay or your fork, and they’re designed to contact your tire, and as the tire moves, it moves the dynamo. Now, these aren’t great. They’re not the most efficient. They’re quite hard to set up. They can move, and they can
also wear out your tires. So in this video, we’re gonna focus on hub-based dynamos because
they’re the most common type of dynamo you generally get today and they’re also far more efficient and this particular model we
have here is called a SONdelux and it’s got some pretty cool tech in it. First of all, how do
dynamos actually work? Well, it’s quite simple. There are a series of
magnets inside the hub that move around a copper coil. Now, the action of the magnets
moving around the copper coil actually induces an electrical
current in the copper coil, which can then be used to
charge and power your devices. And this process is
electro-magnetic induction, and it’s essentially the same process that occurs in any electrical
motor, albeit in reverse. (smooth jazz music) What can you actually use dynamos for? Well, fortunately, we have some top tips from the 2015 trans-continental
winner, Josh Ibbett, who certainly knows a thing or
two about endurance cycling. So, according to Josh, you can charge most things from a dynamo, including phones, laptops,
electric blankets, whatever, but if you are gonna be charging
your phone from a dynamo, Josh suggests not to use the dynamo directly into your phone, but instead, charge a USB battery pack first and then charge your phone
from the battery park. The reason for this is that the DC current coming directly from the dynamo can damage your phone’s battery. Why would you need a dynamo? Well, there are several reasons. The first reason is that they’re
great for people like me, who constantly forget to charge batteries, but if you’ve got a dynamo,
you can simply plug it in and you can still ride
and you’ve got power and you can charge your devices. That brings me on to the
second great use for dynamos, commuting. Now, I like to commute on
bike whenever possible, including in the winter,
when it’s often dark, and my commute is
typically around an hour, maybe even sometimes longer if I’m doing a bit more training. Now, this means that I have
to charge my lights daily and you don’t wanna be stuck at work because you forgot to charge your lights, so having to wait for
them to get some charge. And having a dynamo means
you’ll never have to do that because you can simply run
your lights off the dynamo. Finally, dynamos are loved
by ultra-endurance cyclists and the bike-packing community. And the reason for this is that if you’re riding for days on end with no civilization in sight, if you want to keep your
computers, your GPS, and your lights, and
other devices charged, then you either have to use a dynamo or carry loads of
additional battery packs, which not just add
loads of bulk and weight but also is just another
thing to worry about once you invariably
ready civilization again. It really is rare to see
an ultra-endurance cyclist leave the house without a
modern dynamo these days. What are the drawbacks to a dynamo hub? Well, there are two main disadvantages. Weight and drag. So firstly, weight. A SON 28 dynamo hub weighs 440 grams. We put this into context. A DT Swiss 240 hub, which is a really common
and good quality road hub that’s fairly standard
across a lot of wheels weighs just 96 grams. So nearly four times
more for a dynamo hub. In terms of drag, hub
dynamos produce more drag than a standard hub. A SON 28 hub dynamo produces one watt of additional drag at
25 kilometers an hour when it’s not turned on. And admittedly, this
doesn’t sound like much, but once it’s turned
on at that same speed, it actually increases
to six watts of drag. Now, this, again doesn’t
sound like a huge amount but over a huge ride,
this adds up significantly to a huge amount especially if, like me, you don’t have many
watts in the first place. However, with modern
road-specific dynamos, the penalties are somewhat diminished. So with the SONdelux hub we have here, it’s actually 50 grams
lighter than the SON 28 we mentioned previously. And actually, when it’s built up into this HUNT SuperDura Dynamo wheel set, it actually comes in at
less than two kilograms for a complete wheel set, which, for a, with a dynamo
and disc, very specific, it’s pretty impressive. In terms of the drag, well, six watts is quite a lot if
you’re doing a time trial or road racing, but you’re
not really gonna use this kind of hub for those applications. If you’re bike-packing or doing something like the trans-continental, then that six watts isn’t gonna make a huge amount of difference once you’re riding a fully laden bike and also, the advantage
of being able to charge all your gadgets on the
fly vastly outweighs having to stop all the
time to recharge them. If we’re being technically correct, then most dynamos actually aren’t dynamos. Confusing, I know, but they’re actually what we call magnetos which come to think of
it is a much cooler name. (smooth jazz music) What’s the difference
between a proper dynamo and a magneto, then? Well, those of you who
are fans of rock music may be familiar with ACDC. Now, proper dynamos produce
DC or direct current, whereas magnets produce
AC or alternating current. The different is, is that a proper dynamo requires a piece of kit
called a commutator. Now, this is a bit techy, but a commutator reverses the polarity periodically to create the DC current. This sort of power generator wouldn’t really work in the way that a bicycle dynamo functions and it’s really easy for lights to have AC to DC converters, so
it’s not really an issue. As to why bicycle dynamos
are called dynamos and not called magnetos,
I don’t really know, I have to be honest to say.
Maybe one of you knows. You can let us know in the
comments section below. Well, I hope you’ve enjoyed this deep dive into the world of dynamos. And if you have, why not
give the video a thumbs up? And also, check out the GCN shop. If like me you demand the finest T-shirts available to humanity
and you demand them now, then the GCN shop is the place to go. And if you wanna watch another video, why not check out our video
on the trans-continental race, where you’ll see loads
of people using dynamos? See ya later.

About the Author: Michael Flood


  1. Do you have a dynamo on your bike? If not, would you get one now? Let us know your thoughts in the comments below 👇

  2. I've been strapping skinny northern magicians to my forks for years, with awful results. I now realise my mistake.

  3. You can’t charge a USB battery directly from the dynamo like you seem to suggest.
    You attach a USB converter from your dynamo battery, such a sinewave revolution. Then from this you can connect your phone and charge. Rather than a USB battery pack. Charging your phone straight from the sinewave revolution is more efficient than charging to battery back up and then to phone.

    So you advise I feel is not strictly correct.

    So dynamo to usb converter to phone or a USB battery, which ever you prefer.

  4. MY eyes got fixated on those GP4000s II's, because i know I will never be able to afford one hahaha(really crying)

  5. I kept waiting for you to tell me that I could win this wheel, which would have been tremendous, but you didn't, and now I'm sad. I'll tell you what, if you want to make it up to me, you can send me the wheel.

  6. I tried charging battery pack using dynamo hub, but it goes awfully slow. Not recommended. Charging iPhone or Wahoo ELEMNT directly from it, works perfectly.

  7. You didn't include anything about connectivity, lights, chargers, power banks. I know some basic stuff about electronics and I can tell that no gadget uses 6V. USB standard voltage is at 5 +-0.2V and 3W is close to half power than a basic USB 1A charger. I suggest you do a follow up video on everything about the peripherals of a dynamo.

  8. Eh, bottles have a big advantage in that you can easily switch the drag on and off entirely. Not to mention switching out wheels when you're in BFE.

  9. Don't have dynamo……yet but after this brilliant video i'm one step closer to get one:-) Very good work one of the best from Ollie brilliant.

  10. '…that's nearly four times more.' Um, it's actually 4.5 times more than 96g. Great video nonetheless Ollie as been wanting to know about the benefits and drawbacks of dynamo hubs for a while.

  11. So the most important question, how is the power transferred from a spinning wheel to a wire to charge stuff?

  12. Is there a battery in the hub so you charge devices when off the bike? or somehow you use a wire while the wheel is spinning?

  13. Poor Ollie; seems he has been struck down with a terminal form of Richardson’s disease…the compulsive need to put on glasses merely to appear geeky

  14. For what its worth there is big differences between a Magneto and a Dynamo . A Magneto produces AC voltage with permanent magnets and a Dynamo produces DC voltage using a commutator ..

  15. You say it costs 6 watts at 25kph turned on, how many watts does it produce at 5 volts? A normal smart phone charger needs around 1.2 amps at 5 volts to charge at its intended charging speed (actually ranges from 1 to 2 amps, depending on the phone), which is exactly 6 watts. If these dynamo/magnetos are producing 1.2 amps (or 6 watts at 5 volts), then technically there is no loss, just redirected power. If they produce MORE than the 1.2 amps (more than 6 watts), they are more efficient than the DT swiss hubs, as not only are they redirecting power, they are producing additional power.

  16. You're wasting power charging up a powerbank to charge the phone. If the charging circuitry is well designed, there will be no problem charging the phone directly

  17. When I was a kid I used love my old bottle dynamo(s) I had this awesome front lamp on the right hand fork that would light up tree canopy dark roads in Bedfordshire. My mates had these crappy Ever Ready battery lights that used a pair of AAs that were just no comparison. The last time I used one was around 2000 but was experiencing problems with the contact wheel slipping on the tyre in the wet and without a proper mounting boss on the fork used a hacked solution that utilised a bracket that used the cantilever boss. Just use modern LEDs now but when I spec up a new touring bike, probably a Condor, I'll have one of the Son hubs. As others are saying though it is necessary to add somekind of circuitry to maintain steady current.

  18. I have a Son28 dyno hub, hooked up to a Supernova e3 triple heads light and a e3 tail light. I also have  a sinewave Revolution usb charger. This setup was expensive but its worth it knowing that I have lights any time I need them, and I can charge a powerbank witch I can then use to charge my phone, ipod, gopro and gps while I'm out touring.

  19. Dynamos are awesome! I've been using a Shimano Alfine dynamo hub with B&M lights(front and rear) on my commuter bike for almost 2 years and the lights are great to have whenever I want. They are also pretty bright compared to alot of the midrange bike lights I've used in the past.

  20. Maybe they aren't called Magnetos because you need a Sony Pictures license for it. Maybe a Marvel license too.

  21. As always, great vid. One question though. I tent to buy cheap power banks because after some time they don't work as they should, e.g. they take super long to charge and I just get a new one. I'd be willing to buy a good quality one if I had it recommended. Would you or Josh recommend any specific power bank for bikepacking with a dynamo?

  22. can someone explain why a dynamo that is switched on causes more drag than when its not when the size and weight of the dynamo hasn't changed???

  23. Nice review. Used to have one on my bike back in the 70’s to run my lights. May well consider one again after watching this👍🇦🇺

  24. An AC-DC "converter" is called a rectifier. It's not something anyone needs to know, but when you do know it, you can never help but correct those who aren't aware of it.

  25. If someone is intrested, there are some nice information on some dynamos on: https://fahrradzukunft.de/14/neue-nabendynamos-im-test/
    Its german but you should be able to comprehend the graphs in the lower part of the article:
    (1): mechanical input lights off
    (2): electric output on 12 Ω
    (3): mechanical input on 12 Ω
    (4): electric output on 24 Ω
    (5): mechanical input on 24 Ω

    There is actually quite some difference in quality.

  26. Someone should develop a dynamo hub that uses regenerative braking so it charges more when you are slowing/freewheeling

  27. I love how Ollie puts on a Midwest American accent when he wants to sound like a scientist. Those of us across the pond typically don an RP British accent when we want to sound smart. Hilarious!

  28. I thought about going dynamo on my adventure (gravel) bike set up but for all the extra cost and effort it just seemed easier to get a solar rechargeable battery with 25k mAh which lasts 3-4 days. If you intend to cycle through the night or go a very long time in crap weather and no access to electric then I can see why you would usea dynamo.

  29. Maybe its because I was much younger, or maybe its because it was ancient 80's technology but last time I rode with a bottle dynamo it was a hell of a lot more than 6 watts of drag and was like cycling through treacle. But then it was powering a bulb not a nice modern LED.

    Oh the torture of hand me downs……

  30. A fantastic video for people who already know everything suggested by the title. For others wanting to learn, not so great…. no description of exactly what it is to a cyclist, no view of how it connects to the bike or how it's actually used in practice. It's said that you can use them to charge equipment like phones and computers and heated blankets(?), but not even the slightest hint at the charging capacity (e.g. a 10-minute ride will charge your heated blanket for a toasty night's sleep?).

    Not up to GCN standards.

  31. Was it said not to charge a phone directly because of the Direct Current from a dynamo, then later we're told that they're not dynamos but magnetos and produce AC?

  32. Do e-bikes use dynamos? I would think that front & rear hubs generating a constant 12 watts would significantly extend battery life. They could probably rig an on/off switch so that the dynamo was only engaged when the motor wasn’t. Also, why not develop a braking system like hybrid cars use to add a little more boost to the battery? How about solar panels on a helmet or backpack? Add all of that up and the re-charge might peak as high as 60 watts. Or is that crazy? (It’s 2am here and I have insomnia!)

  33. What I'm curious about is if it is a brushless design or not, which would be WAY superior to anything else out there and much more efficient. I looked at one of Hunt's videos and it showed the guts of one and it does look brushless, hence no commutator. It that is the case, it would actually be an syncronous alternator and use a rectifier internally. That would be slick indeed and be practically maintenance free… except for the bearings.

    But somehow, "syncronous rectifer" just doesn't roll off the tongue, does it!?!? It's the antithisis of a sexy name. Yeah, stick to Dynamo.

  34. Well, Ollie definitely did a better job then Dan or Si ever did with the science glasses gag. That was entertaining, I laughed hard. No offense to Dan or Simon it's still funny when they do it.

  35. Always so many myths about electronics, how much current flows into your phone has nothing to do with the current that the dynamo produces, the voltage provided to the phone will cause the phone to draw current, they all have voltage regulators, so unless you supply way too much voltage they wont draw any more current than usual. Electricity works on the principle that if you apply a voltage across a circuit a current will flow, it does not work by supplying current, none of these devices supply current, they produce a voltage and the circuit you attach them to will draw a current. You could have a dynamo that can supply 10amps of current but if you put it on a device that only draws 1amp, it will only draw 1amp. The only way to push more current through is by increasing the voltage.

  36. Informative video, but more to the point, i'm quite impressed with how Ollie has managed to fit in so well with GCN. Chapeau!

  37. Do you need a dynamo specific wheel?… so do you generally buy them separately and then take them to you LBS to build???

  38. Title of video: "What Are Bike Dynamos And How Do They Work?" And yet, you never told us WHAT a bike dynamo is. At about 1:40, if you're paying attention, you can finally figure out what a dynamo is. So, for those of us that thought, "what's a dynamo?" and came here to find out. Well, eventually, you can divine it. But, you might consider starting a "what is" video by saying, well, what it is.

  39. I use a SON28 with a sinewave revolution,just connect anything with a USB socket to the sinewave and Bob's your uncle

  40. 6 Watts of drag at how much electrical output power? It depends on the load you're drawing. I can't afford the SON kit so I use the Shimano ones, they're fine as long as you stay away from the "DH-32" model that's nfg.
    You can get phone adapters with rectumfryer and surge protector that let you charge from the dynohub without intermediate powerbank, LiPo batteries are pretty efficient but you always incur at least 10-20% loss by storing the energy in a battery and then getting it out again.

  41. A standard phone battery has about 13 Wh (watt-hour) capacity. You're at a loss of 13 Watts if you charge your phone fully in an hour. I think phone batteries can charge at 13 Watts.

  42. Drawbacks for hub dynamos: weight, drag, and……price, low output and maintenance. I believe both SP and SON hubs have to go back to the manufacturer for bearing replacement, which, if you ride a lot of miles, could be every 1-2 years. And the hub has to be removed from the wheel for that…..so then you have to have the wheel rebuilt. And the amount of light you get with a hub dynamo light is pretty sad compared to a battery light system you can put together for $30, as I have. And I can move that battery system to any of my bikes, even though they have different wheel sizes/brake systems. I really want to like dynamo lights, but I just can't get past the hundreds of dollars extra cost for far less performance.

  43. thanks but would've liked some info on output and what sort of limitations on the amperage you can pull from these, as well as different models and specs. on to the next vid on these…

  44. I love my hunt dynamo wheelset. The drag is negligible, and it's a nice piece of mind to know that your lights won't run out of batteries.

    Oh, and one minor correction: the dynamo hub generates AC current, not DC. This is why the lights tend to flicker at slower speeds. In fact, if you freeze the frame at 3:18 you'll see a neat little sine wave on the flange letting you know that you need an AC to DC converter for your USB devices.

  45. Just a few nitpicks from a geek… take this with a pinch of salt.

    > DC current from your dynamo can damage your phones battery

    As you later divulge, these things output AC, so I can't say I'd recommend charging any DC device using them (not even a battery)… unless you like explosions? You would need a bridge rectifying diode.

    The USB connector that is commonly used to charge mobile phones uses DC 5V. 6V isn't far off; in fact, by the time it gets through 3 feet or so worth of cable it's probably down to 5.5V (which is within 10%). A lot of phones will happily accept nearly 20V anyway. 3 watts is a bit on the high side, but I think that's more likely to burn up the cable. Intermittent connections might damage some batteries, but mobile phones usually detect that and refuse to charge from what they consider to be a faulty charger.

    In terms of computers, I would recommend not charging one of those. Your average PSU for a laptop is rated somewhere between the 45-60 watt mark. You'll be riding for quite some time to charge that! Additionally, they draw 115V in the states and 230-250V everywhere else, so I think they're unlikely to work on 6V to begin with; on top of the bridge rectifying diode, you would need a transformer, which will probably make the diode seem light-weight.

    > loads of additional battery packs

    I happen to have a solar cell that would be suitable for charging a mobile phone; it occupies about the space of your hand and outputs 6V, 1 watt.. all that's needed is a soldering iron and a sacrificial USB cable. The weight is probably less, and of course the power source doesn't come from pedalling… plus there's the benefit that it actually does output DC. Maybe have a look for something like this in a mobile phone shop, since I'm pretty sure I've seen them for somewhere around the $25-30 mark.

  46. You can't run a car on the streets in most places without integrated lighting and fenders, so why would you run a bike like that? Fenders and dyno lighting, or its basically a dune buggy!
    Also, where I live marijuana is legal so I just assume every single driver is stoned all the time. I want to be as visible as possible, day or night, so I run lighting 24×7. With a dyno you never think about it. It's always on.
    Finally, there are a few clips in this video where Emma is running a flashing red tail light. I've read that there's some evidence suggesting that flashing lighting "mesmerizes" intoxicated drivers in a way that solid lighting doesn't, but I haven't actually seen the source material.

  47. Why not show a dynamo hub with disc brakes? And why not slowly charge a battery then use that for lights???

  48. "The DC current coming directly from the dynamo can damage your phones battery" – nope, current is irrelevant. My 5v 40amp power supply is fine for charging a phone, my 12v 1A power supply would kill it. Besides, how is anyone going to wire up a Lightning connector directly to a bike dynamo… You don't have to use a USB battery pack, you could use the same DC-DC convertors that dash cams use, both of them are bucking the 6/12v input to a 5v USB output.

  49. My friend is adamant that if you put a dynamo on the front and an electric motor on the back, and use the dynamo to power the electric hub motor on the rear, you will have an infinite supply of power. He genuinely believes he has discovered this and believes I'm being ignorant for dismissing his idea… He also thinks Boris Johnson and Donald Trump are bold & competent leaders… So you've got some idea of what Im dealing with.

  50. Late to the party, but it seems no one answered the question "Why are magnetos on bikes actually called dynamos?". The same reason photocopier is called "xerox". First energy source for bike was actually a bottle dynamo. The name just stuck.

  51. I have a son dynamo hub on my gravel bike with an edelux light and a Shimano Nexus with a non branded plastic light on my commuter, I love dynamo lights, not worrying about batteries is excellent. I want to upgrade my mountain bikes to dynamo lights too.

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