Is Dynamo hub supposed to be clicky when rotate?
 

I'm new to dynamo hubs and have a question regarding my recent buy. I bought this dynamo hub and wheel off ebay. When I rotate the wheel by holding with hand, I feel a clicky feel instead of a smooth turn/movement. I emailed to the seller and he recommended to put it on the fork to try it. I did that and it's bit less noticeable but still I can feel its clickiness especially when it's about to stop turning. I can feel in the frame too when it's spinning fast. I do expect some drags but I thought dynamo hubs are frictionless which means it turns freely and smooth.

Is my dynamo hub something wrong? Do all dynamo hubs do this or just mine does it? Is there frictionless dynamo hub?

You are feeling the coil passing the poles of the magnets embedded in the hub shell. It is hard to say with 100% certainty without seeing it in person (adjusting play out of cup-and-cone versions is not as straight forward, due to the magnets), but that operation is normal, even in high dollar hubs.

When it's on a bike and rolling, the "clickiness" usually disappears at most speeds, and is much reduced at other speeds. Feeling the poles is worst on a bare wheel spinning it by hand.

Perfectly normal.

If you're spinning it by hand, it's totally normal to feel it.

If you feel it when you're riding, there might be something wrong with it. It's definitely possible for it to be to clicky, but a little bit of clickiness when spinning by hand is normal.

Thanks for all replies. I'm relieved that mine is normal. I thought it was going to be totally smooth turning (little bit slow due to drag) not like clicky.

I have not ridden with it yet but just installed on the fork and turned the wheel. I could feel minor vibration through the bike frame with a high speed turning. I will try to ride with it once I put on a tire and a tube.

Just another newbie question, the drag will be same whether I turn on a dynamo light or not, correct? My dynamo light has a switch so just wondering if it would make any difference whether turning on or off.

My ultimate goal would be install dynamo USB charger to charge USB power bank to turn on lights and cell phones, etc.

It is unlikely you will notice any difference in drag with the light on or off.

Most dyno hubs, at least on the higher end, have more drag when they're powering an electrical load. Some of the less expensive hubs have fairly consistent drag. I can't tell from the pictures what model yours is, but it looks like it's close to the line between the two classes.

there have been a few articles/papers written about the drag of various hub dynamos, both with and without the light turned on. There usually is more drag with the light on, but it's usually just a few watts, and most people don't notice it (myself included).


Steve in Peoria

Drag will increase when you turn on the light, but not much, and you won't feel it in your legs. For that reason, I leave my lights on day and night. I have two of those hubs. I don't feel anything while on the bike until I hit about 20 mph. Then it vibrates through the handlebar.

I only notice the extra drag if I'm looking for it. If I'm on level ground and I switch it on/off I can feel it, but it isn't much.

I have the SON 150mm through axle fatbike dynohub, and it's the first one that I haven't been able to true in my stand because of the magnets. On the list of things to do today is make a 150mm through axle adapter for my truing stand.

The one thing I have seen and been told time and time again, DON'T TOUCH THE BEARINGS OR CONES on dynamo hubs. All the manufacturers say it and several mechanics have said the same thing.

The click is a little disconcerting the first time you hear it and then when you realize what it is, that goes away. My first reaction was "huh it's clicking a lit...WOWIE ZOWIE I AM GENERATING MY OWN LIGHT HOLY SH T THIS IS COOL, WOOOOOOOOOOO"

By way of clarification; the clickyness is the magnetic poles, but this is not drag. The poles pull and push equally, so lift the wheel off the ground and give it a spin and it should still spin freely, nearly the same as a regular wheel. With the light on, it will slow down a little quicker.

I've had the same wheel with the Sanyo hub for about 4 years or so. The notchiness is normal.

This is one of the hubs that performs basically the same whether the light is on or off, so it won't get much worse when you power a light.

It was one of the best things I've ever spent money on, by the way. I have an even-cheaper Shimano hubbed wheel that also has been great for me on my city bike.

a magnet has a North and South pole. you know..

I was wondering if putting a load across it will reduce the clickyness, but I haven't tried it. There is only one set of magnets, it must be generating a field in the windings when you move the axle. So you're right, it's not drag in the common meaning of the term. It seems strange that it would be so strong with no load.

Been riding dynohubs for 14 years. The one that old (SON) has never been serviced for bearings. It still runs nicely. Notchiness when spun by hand is normal. The speed that you can spin the wheel on the bike by hand is quite a bit slower than the speed the wheel will spin when you ride it.

Ride and enjoy the freedom of not having to worry about battery life... ever.

And yes, it is best to have the hub bearings serviced by someone who knows how to do it. Much has to do with the insulator's fragility and, IIRC, the direction it undoes, along with the tiny wires involved. Not even I have been game to fiddle with that aspect.

If my original dynohub does finally cease to operate efficiently, I might give it a go... it has done around 50,000km and certainly paid for itself time and again.

With no light attached, there's no current in the windings. The "clickyness" is just what you feel when the poles of the stator are aligned with the magnet poles. For reference, the stator is the non-moving part of the dynamo, which has a steel core that the wire is wound around.

Adding a load does increase the amount of resistance at each pole. As a fun little demonstration, you can short out the dynamo's terminals with a paperclip or such. You should notice more force required to rotate the axle. This is a handy test to use when troubleshooting lighting problems or buying a used dynamo.


Steve in Peoria

I wasn't thinking about the magnetic attraction to the stator, that's a good point. I wonder if Schmidt has decreased the air gap in response to SP having better efficiency. I assume that increases the "clickiness." SP's are noticeably more clicky than the high-end Shimano hubs, but also more efficient. My new fatbike hub is the clickiest yet, on par with the cheap Shimano and Sanyo hubs.

Out of Curiosity..

How was that 'efficiency' data collected? what was the test facility set up ?

Was it done by a 3rd party , or The SP marketing department?.

what was the fraction of a % difference.. micro watts?

It would be interesting to see where the various energy losses occur. Some will be due to eddy currents in the steel core. Cores typically use special steels, built up from thin insulated laminations intended to minimize eddy currents and their associated losses. Larger gauge wire will reduce resistive losses, but this adds cost and increases the size and weight of the windings. There's not too many other places to waste energy, at least in the magnetic or electrical realm.

Generally speaking, the gap reduces the magnetic field strength in the stator, which reduces the current out of the dynamo. I would think that the gap would be made as small as possible.

In the old days (10 years ago?), there was an e-mail list for bike electronics called "Bike Current". One of the regulars was Andreas Oehler, who worked at Schmidt. He didn't give away any trade secrets, but his knowledge of dynamos was quite handy and informative.

I've done a bit of work trying to map out the characteristics of my own SON dynamos, but there's only so much that a hobbyist can do.


Steve in Peoria