Herse's ingenious generator lighting system explained
René Herse generator (dynamo) lighting system was challenging
to figure out because only the headlight remained and traces of
the wires still inside the frame. It was a mystery to me exactly
how the wires were routed from the generator on the seatstay through
the frame, fork and front rack to the headlight.
generator and lever
Since it wasn't with the bike, I also had no idea how the generator
attached to the brazed-on threaded post for it on the inside of
the seatstay, or how the lever above's cable was routed to move
the generator against and away from the wheel to turn the lights
on and off. (The lever only pulls the cable up, which is not how
the generator moves [it only moves in and out].)
purchased multiple generators before I finally found the correct
Soubitez "N" model, which hangs beneath the seatstay
(most USA-issue generators stand above the seatstay). So that
I could attach the cable to the generator, I then made a small
aluminum plate with a cable anchor bolt on it to attach to the
bottom of the generator (the generator seems made for this modification).
through trial and error, I discovered the only possible way to
route the cable to turn the generator on/off correctly. You can
see all of this in this photo if you click to enlarge it. Look
closely to see the cable anchor plate I made and the elegantly
simple way the cable routes to change its direction of pull to
move the generator in and out.
For the wiring, there are two wires attached to the generator
that runs against the rear wheel creating the electricity. One
wire leaves the generator and attaches to the taillight, which
is mounted right next to the generator on this bike. The headlight,
however, is attached to the front rack.
power to the headlight
To power the headlight, there are second and third wires. These
two wires are almost entirely hidden inside the frame, fork steerer
and components to protect them from damage and ensure you never
lose your lighting due to a cut wire or electrical short. How
René Herse routed and connected the electricity from these
wires is ingenious.
The second wire leaves the generator and goes into a hole in the
seatstay. It only runs a short way before exiting the stay and
entering the rear fender's rolled over edge. It travels inside
the fender to the bottom of the fender, where it turns left and
enters the chainstay. From there it goes forward into the bottom
bracket shell and continues all the way up the down tube, ending
at the head tube.
on the illustration on the left to open a full-size diagram, my
version of a René Herse illustration of how the internal
wiring works. It will help in understanding the following
second wire can't continue from the top of the down tube because
the fork is in the way, and the fork has to be able to turn from
side to side for steering. So, René Herse made a contact
between where the wire stops at the head tube and the fork.
copper ring inside the head tube
To keep constant contact so electricity always makes it to the
headlight, René Herse attached a copper ring around the
inside of the head tube (photo).
small square hole you see in the copper ring and the cylindrically
shaped piece in the hole is the end of the second wire, the one
traveling from the generator all the way to this point at the
top end of the down tube.
carbon brush inside the fork steerer
In this photo you can see the carbon brush that makes the electrical
connection between the copper ring and the third and final wire,
which is attached to the headlight. The electrical connection
between the stationary copper ring and the fork is made via this
small sprung carbon brush that protrudes from the fork steerer.
A spring keeps the carbon brush in contact with the ring in the
head tube transfering the electricity from the rear end of the
bike to the front end.
the copper ring and carbon brush assembly are insulated from the
frame and fork (or else an electrical short would occur). In this
photo of the carbon brush protruding from the fork steerer, you
can just see a black shadow around part of the brush. It's some
type of nylon or rubber that's insulating the brush assembly from
the steerer. I can't see what insulates the copper ring from the
head tube and/or exactly how the copper ring is held in place.
The ring seems permanently attached, so perhaps it was bonded
to the head tube with epoxy?
that's needed to get the electricity from the connection inside
the fork, is the third wire that travels from the copper brush
spring inside the fork, down into the front fender, then into
the front rack's hollow tubing and all the way to the headlight!
A fun detail is that the headlight is attached to its support
arm on the rack with a chainring bolt.
most amazing, once I attached the parts and connected what new
electrical wire was needed to the old ones protruding from the
frame, the 40 year old lights came to life; a testament to René
Herse's brilliant design (pun intended).