Lighting & Electrics
Improving e-bike ergonomics and safety by
adding standard motorcycle lighting equipment and other electrics.
Commercially produced e-bikes are required to have motor kill switches,
which operate when the brake levers are pulled. For those who build
their own e-bikes however, this functionality is optional, and also
sometimes difficult to implement. The Bafang BBS01 and 02 mid-drive
kits, for example, are supplied with replacement brake levers that have
switches; but those levers only work with cable-operated brakes. For
those who have hydraulic brakes, there are magnetically-operated
switches that can be bought separately; but the parts attach to the
brake levers using adhesive pads, and many levers have no flat surfaces
on which to stick things. Also, the resulting open magnetic
circuit has a large compass-safe distance (>0.5 m), which
mounting a compass on the handlebars. Finally, there are hydraulic
brake systems designed for the e-bike market, with switches
built-into the levers (such as the Tektro Auriga E-comp); but having to
replace the brakes on an existing bike is expensive and requires
considerable work, and
the switches are also usually magnetic.
Given the difficulties, the lazy
solution to the kill switch problem is
simply not to use them. They are designed to be open-circuit until the
brake is applied, and so it is not necessary to plug them in to the
motor wiring harness. There are then however, many situations in which
it takes the motor controller several tenths of a second to realise
that power output should cease; and in those instances, the unwanted
energy must be dissipated in the brakes. This effect is not necessarily
serious, but it does imply a
degradation of stopping distance, unnecessary brake-pad wear, and a
small extra drain on the battery.
As stated in the parent article
the author has two e-bikes; one based on a Forme Sterndale with 27.5" wheels, and
the other based on a Saracen 29". Both of these have hydraulic brakes,
with levers that lack anywhere to put
stick-on magnetic switches. It was my firm intention however to fit
switches somehow; not only for the motor-kill function, but because,
apart from legislative inertia, it is hard to think of a reason for
excusing e-bikes from having brake lights.
The Saracen 29 has Tektro
Auriga brakes that have an M4 reach adjustment screw on the
It can also be observed that some Tektro levers, such as the Orion SL and Auriga Pro
have a reach adjustment screw with a large knurled head; which suggests
that a longer screw might be used without interfering with the rider's
natural hand position. I therefore fitted longer screws with locknuts,
the point being that the protruding part might be then used for
attachment of some kind of linkage, and rode the bike like
that for a while to see if there was any ergonomic downside. I found
that I was completely unaware of the non-standard screws, and so
started to consider how I might make use of them.
My first thought was to try to
or pull-operated switches to the brake lever bodies. There is however
nowhere obvious to attach anything; except perhaps for a tapered region
next to the
hydraulic hose connection, and a simple clamp attached at that point is
unlikely to grip
reliably. It goes without saying of course, that after a long career
in engineering, I have a strong aversion to sticky pads (perhaps they
have improved, but all of the
ones I have ever used fell off after a year or so). It
seemed therefore, that I would need to develop complicated mouldings to
fit around the brake-lever bodies and give mounting points for
waterproof micro switches, and that I would probably need to disconnect
the hydraulic hoses in the process of fitting them. In such
circumstances, it is best to wait and see if a simpler idea comes along.
This work took place at a time when I
had already ridden for many miles without kill switches. This meant
that I was unaware of how much benefit they might give in
practice; and while I definitely wanted them, my principal
interest was in upgrading the e-bike electrics to be like that of a
conventional motorbike. It had therefore been my intention to add a
waterproof ABS box of 160 × 45 × 56 mm beneath the
handlebars, orientated so as to allow the mounting of traffic
compliant with the
statutory minimum separation of 240 mm. I mounted the box on an
attached to the handlebar stem by means of extended clamp bolts and
spacers. I also put a 30° bend in the bracket, to make the
the box vertical relative to the road. It was while doing this work
that I realised that by positioning the indicator stems to be as far
possible, there was enough room behind them to allow the fitting of
motorcycle rear brake-light switches. These are simple spring-loaded
mechanical pull-switches, mounted by means of an M12 plastic nut, and
supplied with a pull-spring that can be bent to fit a wide variety of
I must confess that, had I come up with
solution in the absence of any intention to fit indicators, it would
have seemed complicated and inelegant and I would probably not have
it. With the indicator box present however, it became immediately
straightforward, robust and cheap. The arrangement is shown below, with
the lid of the box removed to show the switches inside. This,
incidentally, is the
original test configuration, with the switches in parallel connected
directly to one of the Bafang kill-switch ports (the brake light
circuit has yet to fitted). The kill function is activated
by shorting the blue and black wires in the Higo Mini B3 cable (which
was taken from one of the Bafang-supplied brake switches). The red wire
(Hall sensor B+ 5V) is not used, but must be insulated.
click on an
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The supplied pull-springs are simply
bent around the extended reach adjustment screws on the brake levers
and adjusted until the switch is slightly pulled-out (but not yet
closed) with the lever at rest. Motor cut-off then occurs before the
brake pads are engaged. The ends of the springs are formed into loops
using brass inserts taken from a small electrical connecting block.
This ensures that there are no sharp wire-ends for fingers to find
accidentally in the dark. The original M3 zinc-plated steel grubs
screws of the connector block have been replaced with stainless A4
Allen-socket screws to prevent corrosion. The loops formed are
just large enough to permit the springs to be removed without using
I first tested the arrangement using a
bike stand, and noted that while the shut-off of motor power was
immediate on pulling a brake lever, there was a delay of about 1 second
before power was restored after the lever was released. I wondered if
this might noticeably reduce bike acceleration after braking, but the
effect was not apparent while cycling on ordinary roads. The
reason for that is
probably that I did the workshop test while holding the throttle open,
whereas the throttle is allowed to spring-back during normal
braking. Hence there is always a delay in getting going again in
practical situations, and the electronic delay is naturally obscured.
What was really noticeable about the
implementation of the motor-kill function however, was the effect on
braking in response to the actions of other road users. Without kill
switches, there is always a heart-in-mouth moment
when suddenly required to brake while travelling at speed. This, of
course, is because the brakes are inefficient until the motor output
ceases. You can get-used to this, and after a while might not even be
consciously aware of it; but it is very noticeable when the transient
sensation of impending disaster is taken away. There is also a general
improvement in the responsiveness of the braking system, and this gives
a greatly increased feeling of confidence in riding the bike. I quickly
came to regard kill
switches as essential when using public roads, and I realise that I
might have avoided
considerable stress had I fitted them from the outset.
I am however not convinced of the
benefit of kill switches when riding off road. In that case, the speed
is anyway very low, and the brakes can be used to give a subtle
modulation of the motor output that cannot be achieved otherwise. The
motor controller requires information from the back
wheel Hall sensor in order calculate the rider's power requirement, and
this necessarily involves an average delay of half a wheel rotation.
throttle only has about 4 power levels, and so its action is simply too
crude. Controlling the motor by loading it with
the brake until the system catches-up provides the solution, but not if
pulling the lever causes the motor to shut down for a whole second. In
my first foray onto a rough surface, I lost balance and nearly fell-off
at about 2 mph
because of this; and I would say that the off-road capability was badly
compromised. The short term solution, of course, is to
unplug the motor-kill connector; but ultimately the system used on a
mountain bike needs an easily accessible
switch and a warning light (the latter to remind the rider to restore
function when going back onto the public roads).
Amp safety isolation keyswitch.
V meter with damping. On front console - actual battery voltage.
Brake light and kill-switch circuit - diode operates tail light as
additional brake light in daytime, transistor pulls-down the kill line.
Switch to allow kill function to be disabled off-road + red warning light.
stand motor kill function and red warning light. Side stands are
hideously dangerous. No power until the stand is up. Can use the switch
from a bafang brake lever.
36 V 10 W LED headlights and tail light. Choice of Dip + Main on full, or
alternate Dip / Main to conserve batt.
light (DRL) - often a good idea to use bike
lights in the daytime, particularly in winter.
British pedestrians and motorists are angered by the use of a horn. - Fit a bell. Use the m/c horn button as
a headlight flasher.
12 V switch mode converter, cigar socket, 12 V LED m/c flashers.
Removable handles, either side of console, to
allow bike to be turned upside-down for puncture repair.
Road Vehicles Lighting Regulations 1989
schedule 7. Original (as made), unrevised.
Dist. between front indicators is 240 mm or greater.
Dist. between rear indicators is 180 mm or greater.
Regs are not clear on how this distance is to be measured - it
meant 'bulb to bulb' in 1989. At least 240 mm between middles of
front indicatior lenses should therefore be OK (also,
≤ 250 W e-bikes
don't have to pass MOT, but compliance is advisable).
Mini-B series connectors
. IP66 in-line with 1 m
cable attached. Panel mount versions also available.