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From: (Jobst Brandt)
Subject: Re: Sturmey-Archer Dynohub
Date: 23 Jan 1997 17:30:07 GMT

Frank Krygowski writes:

> Among my other wierdnesses (such as riding bicycles), I enjoy
> tinkering with bicycle generators, and I enjoy old & odd technology.
> So I was quite pleased when my favorite LBS said "Oh, by the way,
> I've got a Sturmey-Archer Dynohub still in the box, with headlight
> and everything.  I think it's from at least the mid '60s."

> The box is now in my basement.  (And the hub is stamped "1255",
> which makes me wonder if he was 10 years off.)

No, most SA stuff is super ancient.  There are plenty of 3-speed hubs
in use with older date marks.

> At this point, I'm interested in any tips or info on the device.
> I have the original instruction booklet (including "don't remove
> the armature without a keeper ring", whatever that looks like).
> But I'm somewhat curious about spokes, in view of two factors:

This is a serious misnomer.  It should read: DO NOT DISASSEMBLE
without reading the manual.  The stator must not be removed from the
20-pole magnet without at the same time pushing in an iron plug of the
same diameter.  The magnet will demagnetize itself instantly if the
magnetic return path (the stator or "keeper") is broken even for a
nanosecond.  This continuity cannot be over emphasized.  All 20 poles
must be in close proximity to a continuous magnetic return path at all
times.  Most Dyno Hubs have been disassembled by unwitting mechanics
and their magnets are "flat" producing negligible power ever after.

I built a magnetizer for re-energizing these magnets, having never
found a hub that was not improperly disassembled.  I have one unit
here and gave one to Wheelsmith, back when we thought this might be a
good idea.  I gave up on it when I found the hub produced too little
power for my desires even though it was remagnetized higher than
originally.  I compared it to a new one that Wheelsmith had in the
box, similar to the one you found.  There are good hubs in Europe,
such as the Sachs hub and others.

> 1) The steel flanges are quite thin, about 0.075".  I'd expect this
> would give problems at the spoke bend.  Back up washers?  Other
> tricks?  BTW, spoke hole diameter seems to be about 0.108".

Yes, that's also a problem.  I drilled out the axle so I could use a
QR skewer and mounted a white light to the front with a red light to
the rear, right on the hub body, so I could be seen.  I didn't try to
light my way with it.

> 2) The low side spoke holes are very unusual, being double keyhole
> in shape - looking sort of like the planet Saturn.  I suppose these
> are just for convenience in lacing?  Push the spoke head through the
> large center hole, then shift to the proper side slot?  Any
> precautions necessary?  Seems backup washers, if necessary, would
> negate any benefits.

Yes, that is necessary because spoke insertion is otherwise
impossible with a blank wall of the large side opposite this flange.

> Also, 3) As a longshot: if I end up using this on my commuter, I'd
> like a quick release axle in place of the existing solid one.  Any
> chance of doing this?  The booklet says "The cone on the dynamo side
> is fixed at Works and should not be removed."  Sounds grim to me.

That's no problem if you can (magnetically) correctly disassemble it.

Jobst Brandt      <>

Subject: Re: S-A Dynohub - worth fixing up?
Message-ID: <weja8.19644$>
Date: Wed, 13 Feb 2002 01:23:40 GMT

Bill Putnam writes:

> I have Sturmey Dynohubs on several of my bikes.  I find that the
> Dynohub with a suitable halogen bulb from Reflectalite works well.
> The light output is not as great as a standard generator system, but
> for urban riding I find it is adequate.  I also wear reflective
> clothing and have reflective tape covering many parts of my bike,
> along with a rear VL 700 Vistalite LED taillight and two "belt
> beacons" on my belt.  This set up makes me quite visible, but is not
> adequate for lighting the road to see potholes etc.

> I use the voltage regulator from Reflectalite and get the following
> voltage/speed:

> Speed (mph)Volts  Watts  Lumens
> 8          4.0     0.8    7.4
> 10         4.8     1.1    15.3
> 12         5.2     1.3    21.1
> 14         5.5     1.5    26.4
> 16         5.8     1.7    32.6
> 18         6.0     1.8    37.3

and goes on to warn of not removing the armature from the magnet lest
it demagnetize itself, a characteristic of alnico magnets.

I was also interested in the benefits of this hub and found none that
had not been demagnetized although at the time there were many around
in bicycle shops (when Raleigh three speeds were popular).

I built a magnetizer that works well using four large capacitors
totaling 37000mF and charged to 150V.  Winding six turns onto a core
for the magnet to slip over was the main effort because the turns must
reside in the gaps of the magnet, that looks like a series of joined
horse shoes, to affect suitable magnetization.

Jobst Brandt  <>  Palo Alto CA

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