Hub Dynamos - How do they do that?

John Halliwell said:

There have been several recent posts referring to hub dynamos, I've
seen a few photos of these things, but how do they work?

What's inside the hub

Magnets and a coil. Rotate the magnets around the coil and you get
electricity.

Quoted message said:

and what happens when you switch it off? When it
is off, what is the effect on the rotation of the wheel?

Less drag.

~PB

John Halliwell said:

There have been several recent posts referring to hub dynamos, I've
seen a few photos of these things, but how do they work?

What's inside the hub and what happens when you switch it off? When it
is off, what is the effect on the rotation of the wheel?

Apart from the old barrel dynamos, are there any other alternatives?

Newer barrel generators :-). Which are somewhat better in design than many
older models. I've had no problems with a B&M generator on my oldest bike.

Bottom bracket generator. Not seen one for a while, but expect someone still
sells them. I ran a Sanyo for nearly 20 years. When its bearings failed, I
got the B&M above.

Dis-engageable hub generators. Have some tabs which engage with spokes, then
usually drive a small belt to a generator. Can be disengaged when not
required. Not tried one.

My touring bike has a Shimano £60 hub generator, powering a 3W headlamp.
Lowest hassle of any lighting system I've used; turn on when needed, turn
off when not needed.
Drag when off not detectable in riding. Drag when on is only just felt if I
look for it.

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

Nigel Cliffe said:

John Halliwell said:

There have been several recent posts referring to hub dynamos, I've
seen a few photos of these things, but how do they work?

What's inside the hub and what happens when you switch it off? When it
is off, what is the effect on the rotation of the wheel?

Apart from the old barrel dynamos, are there any other alternatives?

Newer barrel generators :-). Which are somewhat better in design than many
older models. I've had no problems with a B&M generator on my oldest bike.

Bottom bracket generator. Not seen one for a while, but expect someone still
sells them. I ran a Sanyo for nearly 20 years. When its bearings failed, I
got the B&M above.

Dis-engageable hub generators. Have some tabs which engage with spokes, then
usually drive a small belt to a generator. Can be disengaged when not
required. Not tried one.

My touring bike has a Shimano £60 hub generator, powering a 3W headlamp.
Lowest hassle of any lighting system I've used; turn on when needed, turn
off when not needed.
Drag when off not detectable in riding. Drag when on is only just felt if I
look for it.

Go to the B+M Senso lights. Save yourself the work of even sitching
them on and off!

John Halliwell said:

What's inside the hub and what happens when you switch it off? When it
is off, what is the effect on the rotation of the wheel?

You don't really switch them off or on in the usual sense, you either
draw current from them or not. If you draw current there's more drag
than if you don't. With the best hub, the SON, there is not much more
drag than a conventional hub when they're "off", and not much more when
"on". The Shimanos at half the price aren't as good, but they're still
pretty good and there's not particularly perceptible drag on a utility bike.

Quoted message said:

Apart from the old barrel dynamos, are there any other alternatives?

That are as good in terms of fuss-free running? AFAICT No, though you
can get perfectly acceptable barrel dynamos that will do the necessary,
even if not so nicely.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

On Sun, 27 May 2007 23:23:32 +0100 someone who may be John Halliwell
<[email hidden]> wrote this:-

Quoted message said:

What's inside the hub

Much the same as in any dynamo, magnets and coils.

Quoted message said:

and what happens when you switch it off?

There is no external circuit for the electricity to pass along and
so it doesn't.

--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

in message <[email hidden]>, Nigel Cliffe

(') said:

Bottom bracket generator. Not seen one for a while, but expect someone
still sells them.  I ran a Sanyo for nearly 20 years. When its bearings
failed, I got the B&M above.

I ran Sanyo bottom bracket dynamos for years, but note the plural. I found
that the drum of the dynamo wore though in about six months use, leaving
the dynamo scrap because the drum was unrepairable. I never found a
solution for this problem. The bottom bracket generator is a neat idea,
but hub dynamos are much better (and, in the long run, much cheaper)
because they don't wear out.

The drag on a hub dynamo when 'off' is very slightly more than the drag on
a hub without dynamo, but not so you'd notice. The drag on a hub dynamo
when 'on' is *much* less than any other dynamo. If you do any substantial
proportion of your riding at night, a hub dynamo is definitely the way to
go.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; Drivers in the UK kill more people every single year than
;; Al Qaeda have ever killed worldwide in any single year.

On 27/05/2007 23:23, John Halliwell said,

Quoted message said:

There have been several recent posts referring to hub dynamos, I've seen
a few photos of these things, but how do they work?

What's inside the hub and what happens when you switch it off? When it
is off, what is the effect on the rotation of the wheel?

What's inside is basically the same as what's inside a bottle dynamo,
sort of. When you switch it off, the lights go out :-) I have a
Shimano 3N71, which I think is the lowest spec you want to go with
Shimano. Whilst there is some drag with the thing off, this is so
imperceptible as to not even notice it. If you can stretch your budget
to SONs though, they have even less "off" drag, apparently.

Dynohubs do have a load of advantages over bottle dynamos. Quieter, no
way they can slip, lights on at the flick of a switch, lights that can
come on automatically, less drag when they're on.

--
Paul Boyd
http://www.paul-boyd.co.uk/

Paul Boyd said:

Dynohubs do have a load of advantages over bottle dynamos. Quieter, no
way they can slip, lights on at the flick of a switch, lights that can
come on automatically, less drag when they're on.

Less susceptible to damage and knocks too.

Downsides are costing more, 12V not available, and a wheel-build being
part of the process. Though for me the upsides outweigh the down by
quite a margin.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Quoted message said:

Quoted message said:

Dynohubs do have a load of advantages over bottle dynamos. Quieter, no
way they can slip, lights on at the flick of a switch, lights that can
come on automatically, less drag when they're on.

agreed.Note the automatic light sensitive switch with shimanos
If you search this group you will find much previous debate.Drag when
off is of the order of2 or 3 watt which I guess would be like adding
two miles to a hundred miler.So I look with admiation on those long
audaxers who use one.I would be irritated by the thought of even so
small an extra effort if I was pushing the boundaries.
I think I may put mine on my lighter bike to test how it feels at
speed sometime, since I get the impression that it drags more at 20mph
plus but I could be wrong.
For utility and winter riding and all riding well inside my envelope I
think the hub 'dynamo ' is great.
I do not have an expensive light, just a basic type plus a cheap extra
led because 2 is more reliable than one.
TerryJ

Quoted message said:

Peter Clinch twisted the electrons to say:

Quoted message said:

Downsides are costing more, 12V not available, and a wheel-build being
part of the process. Though for me the upsides outweigh the down by
quite a margin.

Do you have a dynamo on your 8 Freight? Obviously, if you do, it's not
going to be a dynohub, so I was curious as to what bottle dynamo you'd
been using? (Since switching from the Grasshopper to a QNT invovled
giving up a SON, and battery lights are proving just as much of a pain as
I suspected they would!)
--
These opinions might not even be mine ...
Let alone connected with my employer ...

Alistair Gunn said:

Do you have a dynamo on your 8 Freight? Obviously, if you do, it's not
going to be a dynohub, so I was curious as to what bottle dynamo you'd
been using?

It's the basic 6V B&M Dymotec 6. Seems to do the business okay, and the
way you can vary the pressure with a wee widget on the unit is a nice
feature that's rendered the all-weather wire brush roller I have in the
backup bits box unnecessary even in slush.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Alistair Gunn said:

Peter Clinch twisted the electrons to say:

Quoted message said:

Downsides are costing more, 12V not available, and a wheel-build being
part of the process. Though for me the upsides outweigh the down by
quite a margin.

Do you have a dynamo on your 8 Freight? Obviously, if you do, it's not
going to be a dynohub,

Not /quite/ obvious though as SON are now doing monohub XS versions
which take a diskbrake

--
/Marten

info(apestaartje)m-gineering(punt)nl

M-gineering said:

Alistair Gunn said:

Peter Clinch twisted the electrons to say:

Quoted message said:

Downsides are costing more, 12V not available, and a wheel-build
being part of the process. Though for me the upsides outweigh the
down by quite a margin.

Do you have a dynamo on your 8 Freight? Obviously, if you do, it's not
going to be a dynohub,

Not /quite/ obvious though as SON are now doing monohub XS versions
which take a diskbrake

Hah! Get thee behind me Satan, you cannot tempt me!

M-gineering said:

Not /quite/ obvious though as SON are now doing monohub XS versions
which take a diskbrake

Or rather, they take a disc brake rotor. Where one actually mounts the
pads and mechs would still be problematical...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

On 28/05/2007 12:44, M-gineering said,

Quoted message said:

Not /quite/ obvious though as SON are now doing monohub XS versions
which take a diskbrake

Do they indeed? (Thinks!!!)

--
Paul Boyd
http://www.paul-boyd.co.uk/

In article <[email hidden]>, Peter Clinch
<[email hidden]> writes

Quoted message said:

You don't really switch them off or on in the usual sense, you either
draw current from them or not. If you draw current there's more drag
than if you don't. With the best hub, the SON, there is not much more
drag than a conventional hub when they're "off", and not much more when
"on". The Shimanos at half the price aren't as good, but they're still
pretty good and there's not particularly perceptible drag on a utility bike.

Thanks to all.

There was me thinking you'd lock the coils and magnets together somehow
to turn it off! Am I right in thinking the 'additional' resistance is
related to the current drawn, if so are there limits (do they come in
various wattages)?

If touring, would it be possible to connect one up to some kind of re-
charge system to provide battery lighting when camping?

--
John

M-gineering twisted the electrons to say:

Quoted message said:

Not /quite/ obvious though as SON are now doing monohub XS versions
which take a diskbrake

I think you'd have problems mounting the required caliper onto an 8
Freight, and I believe said SON monohub is only available for the
HPVelotechnik Scorpion ATM?

Could be interesting to think about mounting (a suitably modified)
example onto a Burrows Ratcatcher though ...
--
These opinions might not even be mine ...
Let alone connected with my employer ...

John Halliwell said:

In article <[email hidden]>, Peter Clinch
<[email hidden]> writes

Quoted message said:

You don't really switch them off or on in the usual sense, you either
draw current from them or not. If you draw current there's more drag
than if you don't. With the best hub, the SON, there is not much
more
drag than a conventional hub when they're "off", and not much more
when "on". The Shimanos at half the price aren't as good, but
they're still pretty good and there's not particularly perceptible
drag on a utility bike.

Thanks to all.

There was me thinking you'd lock the coils and magnets together
somehow to turn it off! Am I right in thinking the 'additional'
resistance is related to the current drawn, if so are there limits
(do they come in various wattages)?

Yes, the pedal resistance comes primarily from the current drawn.

Pretty much every generator(*) conforms to a German specification; this
being 6v and fairly high lighting levels from quite low speeds. They are
constant current devices, limited to 0.5amp, which ensures that a total of
3W of bulbs stays illuminated. (either 3W front alone, or 2.4W front plus
0.6W rear).

Both the Schmidt and the more expensive Shimano can generate a lot more than
6v, whilst still limited to 0.5amp constant current (so won't blow a normal
single light setup).
Both can deliver 12V at higher speeds. So, its possible to wire two bulbs
in series to double the illumination. Usually this is done by manually
switching in a second 3W headlamp at higher speeds. There is a special
Schmidt headlamp for this purpose with a capacitor included which helps its
operation, though any lamp will work if wired correctly.

Alternatively, both SolidLights and Inoled offer LED lamps which
automatically increase the illumination as the voltage rises. Neither of
these suppliers are particularly cheap.

I find a hub with a single 3W bulb is adequate for 20-25kph on unlit rural
roads with no moon. But, its underpowered for 35-40kph.
Twin lamps or the newer LED options give more illumination.

Quoted message said:

If touring, would it be possible to connect one up to some kind of re-
charge system to provide battery lighting when camping?

In principle yes.
In practise it could be a complex circuit as the voltage goes up/down, but
the current stays constant. Further, its AC from the generator, not DC.
I'm sure someone will have done it before.
Might be cheaper/easier to strap a solar recharger to the top of your
luggage and use that instead ?

(* there are some sidewall models which conform to a 12V specification, but
I don't think any hubs do yet).

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

John Halliwell said:

If touring, would it be possible to connect one [dynohub] up to some kind of re-
charge system to provide battery lighting when camping?

Yes, this is possible. Shove the generator's output across a bridge
rectifier. This gives you 0.5A to play with, and a variable voltage from
zero to about 17V at high speed.

Forget about smoothing: The capacitor needs to be chosen on the basis of
the AC frequency, which will be speed dependent.

Use the DC to charge a pack of 4AA NiMH cells.

In reality I find it much less hassle to charge a load of cells before I
leave and take a Maplin fast charger with me. A good long meal at a
carefully chosen table in a cafe charges batteries much quicker than a
whole day of cycling!