Shimano DH-3N30 dyno-hub - Any Good?

[CREPELLO]

I've just bought an apparent bargain Shimano dyno hub http://www.rosebikes.co.uk/article/shim ... wwodDyQA6w (actually a 3N31) for the princely sum of£13.

I bought it with the intention of putting it in a town run around bike. A couple of days later I ended up buying a 2nd hand a CB Dalesman. Having decided to use some spare Mavic MA2/3 rims, the Dalesman could have the making of a reasonably nippy little number. Except the hub doesn't feel anywhere near as free wheeling as my higher spec Shimano LX hub. The approximate difference in a crude wheel spinning test (hub unloaded) was 5 seconds (just) for the 3N31 hub and a full 30 seconds for the LX. I had an idea that the 3n31 was a bit less efficient, but not this much.

Coupled to some old high current Solidlights, I just wonder whether this combination will prove ponderous if I want to take the bike for a spin in the hills?

The hub is laced up into the rim but not fully tightened up/stress relieved, so it's not too late to change for an RSX hub (matches the back one)

Possible alternative is a Lightspin bottle-dyno (and Soubitez canti bracket -£2 from Rose) with an old Halogen lamp I have. I don't want to use a battery front light.

What would you do?

[Brucey]

I'd try it and see.

I don't think that it is anything like as bad as you might think to ride with a slightly draggy generator like that. I would expect the bearings to be badly adjusted and for the seals to be draggy too. Could be why they were cheap, eh...?

cheers

[NUKe]

I have 3n80 on my Audax bike, when I built a new pub/town bike I wanted the same convenience so I bought a 3n30. This bike gets used to go round town and to commute in the worst weather. Yes it is slightly more draggy than the 3n80 but you only notice it when comparing the two and still negliable when compared to my last bottle dynamo which was excellent for a bottle dynamo. uphill it does dim below 8mph but is still working at 4mph below that your nearly walking and it will flicker slightly. It should run the lights you want.

[pete75]

There's some figures here on the drag of various dynamos including the 3N30. A Son 28 has about half to a third less drag with lamps off depending on speed and about 10 - 15% less with lights on. http://www.bikequarterly.com/VBQgenerator.pdf The report actually says "Overall, the SON28 still is the most efficient hub generator, but the Shimano DH-3N30 does not lag far behind."

I bought one of these but what they actually sent was a 3N31 as well, a little strange as they're advertising the 3N31 at twice the price of the 3N30. No idea what the difference is.

If you really want to compare it with an LX hub you need to mount both wheels in a bike and do free wheeling distance tests. I suspect the difference will be negligible.

[stewartpratt]

Speaking from experience of the 30, the 72 (both on my commuter) and the XT (on my audaxyish bike)…

The 30 did seem a little more draggy, and I certainly wouldn't choose one for a long distance bike. I also found it had a little vibration at walking pace - noticeable when slowly filtering through traffic or when puching the bike.

But what I also found was that it failed after 6 months of commuting: no output at all. The XT has done two years on the road bike without a blip. The 72 is good so far (and "feels" much like the XT, ie not really noticeable at all) but it's only been on there a few months.

Maybe mine was faulty from the off. But I certainly found that example to be inferior to the more expensive models in pretty much every respect, and I wouldn't buy the cheaper hubs again. YMMV.

As to the "what would you do?" question, given the stage you're at, I'd leave it in the hub and ride with it and see how it goes. It'll probably be just fine.

[Hackfall]

sounds like a bargain to me especially if you can build your own wheels. If I could I'd snap it up as its a better one than my shimano dyno hub which can only really power front light and is not quick release.

[JamesE]

I can't comment on its dragginess compared with other dynamos but I've been running a DH-3N30 for a year now, around 4000-5000 miles including some very long days in all kinds of weather, and I've had no problem with it at all. So +1 to "give it a go, see how you get on".

[Brucey]

The 30 did seem a little more draggy, and I certainly wouldn't choose one for a long distance bike. I also found it had a little vibration at walking pace - noticeable when slowly filtering through traffic or when puching the bike.

But what I also found was that it failed after 6 months of commuting: no output at all. ..

-presumably it was replaced under warranty?

cheers

[CREPELLO]

Thanks for your thoughts folks. I'll try the hub out and readjust the bearings (there was no sign of slack with the skewer loose, so it's probably too tight) and have a peep inside the removeable side bearings for signs of grease.

[CREPELLO]

Checked for grease inside and there was plenty there. Re-adjusted the bearings. This can be tricky with hub dynamo's because of the magnetic friction. Apart from feeling for a little slack with the hub out the dropouts, I'm satisfied when the hub nearly stops, then rocks quickly between a couple of poles.

I recorded an improved rotation time in the wheel build stand of ten seconds (up from five), then a further ten of the wheel just rocking like a pendulum (there was little rocking before). Any further slack can be adjusted out tightening the QR skewer.

I must say that the bearings sound louder than anything I've had before, but that must be expected at this level and I can't argue with the price (£13), if the thing works - I'm hoping for a few years.

[Brucey]

if you want to get the hub 'just so' then adjust it so that there is a little play when the QR is less than half-tight, but then disappears when the QR is fully tight. That should do it.

BTW the bearings may be making a noise but then so might the generator itself. If the windings, poles, or magnets are not 100% secure you will get a noise and the movement might even cause the windings to go open circuit eventually.

cheers

[edocaster]

Checked for grease inside and there was plenty there. Re-adjusted the bearings. This can be tricky with hub dynamo's because of the magnetic friction. Apart from feeling for a little slack with the hub out the dropouts, I'm satisfied when the hub nearly stops, then rocks quickly between a couple of poles.

I recorded an improved rotation time in the wheel build stand of ten seconds (up from five), then a further ten of the wheel just rocking like a pendulum (there was little rocking before). Any further slack can be adjusted out tightening the QR skewer.

I must say that the bearings sound louder than anything I've had before, but that must be expected at this level and I can't argue with the price (£13), if the thing works - I'm hoping for a few years.

I'm not sure how important rotation times are, but that does sound a little disappointing. The secondhand T665 (equivalent to a 3N72 I believe) hub I bought gives 25 to 30 seconds unloaded, and 15 seconds with lights on - although that's with a good hard initial spin. With the lights on, a lot of the initial speed does scrub off in the first 5 seconds though.

However, this is a fully built wheel, with a fairly heavy rim+tyre, so that could just be momentum.

It'd be a massive shame if the 3N30 and similar hubs have markedly more unloaded friction (why?), as that would add another compromise to a budget option.

[Brucey]

....It'd be a massive shame if the 3N30 and similar hubs have markedly more unloaded friction (why?), as that would add another compromise to a budget option.

well all the test data shows about double the lights-off drag vs the more expensive ones. That is why they are cheaper. They are still stacks better than the older Nexus models though. And the lights-on drag is comparable.

Lights off this costs you maybe 0.5kph or less @ 30kph or so. Peanuts really. The extra drag is about 1/20th or less of what typically goes into the tyres, for example.

cheers

[bivvy]

How did you get along with this hub? I'm thinking of getting the disc version of it

http://www.rosebikes.co.uk/article/shim ... _info_tabs

shimano tech docs say this has the same internals as the DH-3N31

[CREPELLO]

It's been fine. Certainly for the money, it couldn't be beaten. I don't notice any drag, although spinning the wheel by hand produces noticably more friction than a higher spec Shimano dyno hub. And it only powers a 1W B&M Fly.

As for durability, it hasn't had a particularly hard life, although it is on the 'daily'. So it has spent a fair amount of time out in the rain. As yet I haven't noticed any bearing issues. But I have re-greased and checked the bearing tension.

The only thing for me is this particular hub does look distinctly utilitarian. Although it's only on my daily, the bike a rather nice CB Dalesman which I have come to really like, so this hub is getting replaced by a more fetching DH-3N72 which I have spare. But nothing to do with performance.