Shimano hub dynamo

[nez]

Could anyone comment please on the real world differences between the various levels of Shimano dynamo N20 to N80? On Spa's website there is a doubling in price over the range and I just wonder if it's worth going more expensive. Or is it a question of wheel bearings? Or do I dig deep and go for the Son? Oh, questions questions. I'm a heavy fellow with a Galaxy, so the use is predicted by that probably. I'm hoping to go on a few week long tours this year so would rather save the lolly for that if I can but then I would rather not have breakdowns.
Thanks

[Brucey]

there are small differences in bearing quality and parasitic drag in the shimano range. Actually the %age change in parasitic drag isn't that small, but the overall effect on you is rather small.

For a utility bike any will do, for a 'posh' bike or one requiring some special aspect of generator performance, you can get as spendy as you like....

BTW I'm planning to get an SA hub dynamo with a hub brake built in for my utlity bike...

cheers

[Meshuga]

As far as I know it's to do with weight and resistance, both progressively lower the more you spend.

I know we should support British companies and all but Rosebikes (http://www.rosebikes.co.uk/search/find/?q=hub+dynamo) in Germany are unbeatable on dynamo prices. £55 for top end shimano dynamos, £100 for complete 700c wheelsets. £5 delivery to the UK.

[The Mechanic]

I think the higher the number (quality) the lighter the hub. I have a 3N80 and it performs faultlessly. BTW you can get them considerably cheaper from Germany ay Bike24 or Rose Versand

[nez]

I'm horribly tempted by buying one from Rose and having a bash at making the wheel myself. Oh there will be a muddle and I'll end up paying someone with proper skills to re-do it eventually (one look at the method of establishing spoke lengths makes me dizzy). But the temptation... and the satisfaction if I get it right.

[stewartpratt]

(one look at the method of establishing spoke lengths makes me dizzy)

My method is always to look up the measurements for the hub and rim and put them into the DT Swiss calculator and see what comes out. No dizziness required.

[nez]

Thanks Stewart. That seems painless enough. Now I'll just have to choose a rim...

I'm quite excited by the idea of building one.

[interestedcp]

Could anyone comment please on the real world differences between the various levels of Shimano dynamo N20 to N80? On Spa's website there is a doubling in price over the range and I just wonder if it's worth going more expensive. Or is it a question of wheel bearings? Or do I dig deep and go for the Son? Oh, questions questions. I'm a heavy fellow with a Galaxy, so the use is predicted by that probably. I'm hoping to go on a few week long tours this year so would rather save the lolly for that if I can but then I would rather not have breakdowns.
Thanks

IMHO, if you expect to ride more than 1500-2000 km per year, then you shouldn't buy the cheap 3N20/3N30 models. The main difference between these and the "sport" models like the 3N72 and all similar priced models, is the bearing races, cones, and ball bearings. The sport models have "ultegra level" bearing races, meaning that Shimano uses Borazon (http://en.wikipedia.org/wiki/Borazon) abrasive tools to polish them with. In theory at least, that means they can polish the bearing races with extreme precision even if the races are made of very hard metal. The point here isn't the better performance, but longevity of the hub; the fine polishing prevents wear/damage and it is assumed that the races are made of a much better and harder metal since Shimano uses Borazon to polish them with. The problem is that there is no official way to service the cup-and-cone bearings on a Shimano dynamo hub, so once sand and other hard particles enters the bearings, they stay there and grind away until the end of life of the hub. The official way to service a Shimano Dynamo hub is to exchange the entire "Internal Assembly" which is quite easy to do for anyone who has serviced a cup-and-cone bearing hub, but since the right bearing race is part of the hub shell which doesn't exist as a spare part, the entire hub is dead when the right bearing race gets pitted.

In my limited experience the cones on the cheaper dynamo hubs are made of clearly inferior materials and to a much lower standard than the "sport" models, they also uses grade 200 carbon steel ball bearings instead of the much better grade 25 stainless steel ball bearings, again, the point here isn't performance, but that carbon steel rust much more easily and that soft cones gets worn much more quickly. Again, the problem is that one can't easily exchange these parts on the hub. The sealing is also much better on the "sport" models, further improving the hubs life expectancy since water ingression is a major cause for damaged hubs.

IMHO, four season riders and people who rides "a lot" are much better served with the Shimano "sport" hub dynamos since these hubs are likely to last much longer due to better materials, fabrication and design (sealing).

BTW, all the Shimano "sports" dynamos are identical when it comes to electrical output and performance, they differ mainly in weight, colour and features like QR, Center-lock disc or not etc. The 3N80 is lighter than the 3N72 and T-660 because of a lighter hub shell and a (weaker) aluminium axle instead of steel, but measures exactly the same in the lab when it comes electrical output. If you want light and expensive, get the 3N80, if you want strong and cheap, get the 3N72/T-660.

[Brucey]

the cups, cones, and seals vary on different quality shimano hubs for sure. This is perhaps more of an issue with dynamo hubs because of the difficulty with servicing the RH bearing.

If comparing the DH-3N30, DH-3N70, DH-3N80 series here;

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/DH/EV-DH-3N80_2N80-2732A_v1_m56577569830637958.pdf

the steel balls used are the same part number (Y-000 91210) in each case, even if the other bearing parts are different.

IME the two main things that kill hub bearings are water ingress and bad adjustment. All shimano hub dynamos have at least some shields; 30 series, 70 series and 80 series seals are all differently constructed. I don't know just how much they vary in effectiveness. The adjustment of the bearings is especially critical with any hub but especially the QR hub; if set with no play, a QR hub bearing will be excessively preloaded once the QR is tightened, and this will very greatly reduce the life of the bearings. This wear may be less rapidwith higher end hub bearings, but (barring water ingress) if correctly adjusted the less expensive bearings last well enough.

The other thing that commonly kills hub dynamos is the magnets coming adrift inside. This can and does happen, although I have no idea if it is systematically more likely with some shimano models than others. When the magnets come adrift the wheel will turn only with some difficulty, and may continue to produce electricity.

Shimano presently list over twenty different models of hub dynamo

http://techdocs.shimano.com/techdocs/blevel.jsp?ASSORTMENT%3C%3East_id=1408474395181679&FOLDER%3C%3Efolder_id=2534374302051151&bmUID=j7tjMq9

For the ones in question here the model designation might be;

DH-2N30 where;

DH means 'Dynamo Hub'
'2' means '2.4W' power output (and '3' would mean '3W')
'N' means 'Normal hub for rim brake' (and R would be for roller brake, D for disc brake etc)
'30' means model number (20, 70 or 80 series being alternatives)

70 and 80 series models are advertised as having lower drag than 30 series models. I have no idea how much difference there really is, although there are measurements out there somewhere. It appears that in some cases the same model number is used for variants with nutted or QR fittings.

For utility cycling the nutted versions are probably better suited since they are less likely to be stolen and the bearing adjustment is easier since tightening the wheel doesn't affect the bearing adjustment in the same way as QR versions.

cheers

[johnb]

Could anyone comment please on the real world differences between the various levels of Shimano dynamo N20 to N80? On Spa's website there is a doubling in price over the range and I just wonder if it's worth going more expensive. Or is it a question of wheel bearings? Or do I dig deep and go for the Son? Oh, questions questions. I'm a heavy fellow with a Galaxy, so the use is predicted by that probably. I'm hoping to go on a few week long tours this year so would rather save the lolly for that if I can but then I would rather not have breakdowns.
Thanks

IMHO, if you expect to ride more than 1500-2000 km per year, then you shouldn't buy the cheap 3N20/3N30 models. The main difference between these and the "sport" models like the 3N72 and all similar priced models, is the bearing races, cones, and ball bearings. The sport models have "ultegra level" bearing races, meaning that Shimano uses Borazon (http://en.wikipedia.org/wiki/Borazon) abrasive tools to polish them with. In theory at least, that means they can polish the bearing races with extreme precision even if the races are made of very hard metal. The point here isn't the better performance, but longevity of the hub; the fine polishing prevents wear/damage and it is assumed that the races are made of a much better and harder metal since Shimano uses Borazon to polish them with. The problem is that there is no official way to service the cup-and-cone bearings on a Shimano dynamo hub, so once sand and other hard particles enters the bearings, they stay there and grind away until the end of life of the hub. The official way to service a Shimano Dynamo hub is to exchange the entire "Internal Assembly" which is quite easy to do for anyone who has serviced a cup-and-cone bearing hub, but since the right bearing race is part of the hub shell which doesn't exist as a spare part, the entire hub is dead when the right bearing race gets pitted.

In my limited experience the cones on the cheaper dynamo hubs are made of clearly inferior materials and to a much lower standard than the "sport" models, they also uses grade 200 carbon steel ball bearings instead of the much better grade 25 stainless steel ball bearings, again, the point here isn't performance, but that carbon steel rust much more easily and that soft cones gets worn much more quickly. Again, the problem is that one can't easily exchange these parts on the hub. The sealing is also much better on the "sport" models, further improving the hubs life expectancy since water ingression is a major cause for damaged hubs.

IMHO, four season riders and people who rides "a lot" are much better served with the Shimano "sport" hub dynamos since these hubs are likely to last much longer due to better materials, fabrication and design (sealing).

BTW, all the Shimano "sports" dynamos are identical when it comes to electrical output and performance, they differ mainly in weight, colour and features like QR, Center-lock disc or not etc. The 3N80 is lighter than the 3N72 and T-660 because of a lighter hub shell and a (weaker) aluminium axle instead of steel, but measures exactly the same in the lab when it comes electrical output. If you want light and expensive, get the 3N80, if you want strong and cheap, get the 3N72/T-660.

Excellent and informative post.

I have been thinking lately would the new 3N80 be as good as the older 3N72 or would it be a similar comparison to that of the new XT vs the old Xt hubs, you seem to have answered that for me, thanks.

[andrew_s]

In general, the older hubs (10, 20 & 30) give higher drag, most noticeably with the lights off. The 10 gave more drag lights off than lights on at over about 20kph.
Since the 70, the hubs have been good in terms of drag (roughly comparable to the Schmidt).

[PW]

I spotted Brucey's comment about the thing which commonly kills hub dynamos. The only one I've come across with Schmidt, and I don't know if it also applies to Shimano, is water getting in via a drainage hole in the skewer. I didn't realise until too late that Schmidt skewers are not to be greased, deliberately to let the water out. Block that hole and the bearings get a dowsing, with associated rust especially in the salting season. If you're also daft enough to go out with a soggy hub when it's -15C ( ) the ice will wreck the windings. (Been there too!). When you take the skewer out and if there's a drain hole in it then put it back in with a little oil by all means but don't let grease anywhere near it.

[Brucey]

I think that the feezing water issue may well be part of the trouble which causes the magnets to pop off in shimano ones; certainly its people who ride in freezing conditions who seem to have had this trouble worst, but then these cold places are the places it is dark, too.....

cheers

[andrew_s]

The only one I've come across with Schmidt, and I don't know if it also applies to Shimano, is water getting in via a drainage hole in the skewer. I didn't realise until too late that Schmidt skewers are not to be greased, deliberately to let the water out. Block that hole and the bearings get a dowsing, with associated rust especially in the salting season.

The hole in the middle of the axle isn't to let water out, but to let air in & out.

There is a reasonably large volume of air inside the hub, and if you cool the hub down it contracts, reducing the pressure inside. The difference between the internal pressure and the external pressure can suck water in past the axle seals unless there's an easier route in for the air via the axle hole. Once there's moisture inside, it doesn't get out and you get rust on the generator parts. The clearances are very small, so you can get enough rust to jam things up.
I believe there's a little rubber balloon on the inside of the axle hole to keep water out if you ride through a flood.

It's a problem that used to occur when you kept a bike indoors, and took it out into cold and rainy weather, followed by a period of non-use that allowed the rust to get thicker without being scraped off. It would also occur if you rode a bike through a deep ford on a hot day.

[PW]

Mine occurred winter 2010/11 when we had heavy rain followed by that severe cold spell. I just didn't realise what was happening until too late. The bike was in an unheated shed overnight, -15c, When I wheeled it out to go to work about 6 ish the front wheel was solid. I picked it up straight away, took it inside to ease off by the hallway radiator and 15 minutes later the wheel was smooth again - but the generator was dead. The lights still worked with a 6V gel cell so I got to work that way for a while but I assumed the ice had wrecked the windings. A month later I was about to send it off for a rebuild when I found the hub was solid again, no ice this time, so the bearings were rusted up. I binned it and bought a new one. The hub was a SON 28, I've had no more trouble with its replacement or another SON 20R so I'll stick with Schmidt and be a bit more careful in future.