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"
the other based on a Saracen Tufftrax 29. Both of these have hydraulic
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-cutoff 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 disintegrated 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
universal motorcycle rear brake-light switches (manufactured by Honnoh
but available via ebay
etc.). 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 motor cutoff 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
image to expand it in a new browser window
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 cutoff 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 a delay of up to one full wheel rotation (
m with 29" wheels).
throttle also has only about 4 power levels, and so its action is too
crude to allow it to be used to compensate. 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).
Lighting and ancillary
In view of the preceding discussions in this and the parent article,
the following circuit was devised (click on the image
it in a new tab).
The circuit includes the following features:
Battery Isolator switch
It was mentioned in the e-bike battery article
the charger has the effect of switching the battery output back on.
This is unnacceptable, and the solution is to provide a 100A switch on
the power control box. The actual current requirement is more like 10A,
but a vehicle-battery fire-safety switch can give a good low-resistance
connection for the motor.
Note that the motor gets an unlimited
the battery, but all of the other circuits are protected by fuses.
These are standard automotive fuses, except for the one in the input
to the 12V switch-mode converter, which was provided as a
component on the circuit board.
50V analog meter
| An issue that arose
isolator switch is
that, although the contacts were made from good quality copper, the
supplied nuts on the connecting studs were found to be passivated
with a yellowish colour that might have given the casual observer the
impression that they were brass. A test with a magnet
their true composition. The problem here is that any connecting
lug is trapped between the nuts, and does not make direct connection to
the high conductivity stud. Hence, with the original nuts done up
tightly, the overall
on-resistance of the switch was found to be about 0.1 Ω,
would have caused a voltage drop of about 0.8 V with the motor
output (max. current of around 8 A). Most of this loss can be
avoided by replacing the nuts with copper or brass items (both M6 and
0BA nuts will fit on the type of switch shown). Any shakeproof or
spring washers used should, of course, also be brass or copper.
(on the rider's control console): By carefully dismantling an
analog voltmeter, it is possible to add a third terminal that bypasses
the series resistor.
A 2200μF 6.3V electrolytic capacitor can then be
directly accross the coil. This damps the movement to give a
settling time of a little more than 1s, which prevents the delicate
device from being destroyed by shocks and vibration.
The actual battery voltage is vastly
more informative than the battery status-bar, since it can also
indicate switch and connector problems (this might prove important if
still using the supplied mounting-plate connector). For a battery
constructed by connecting
10-cell Li-ion (graphite anode) stacks in parallel, the relationship
status and voltage is, to a good approximation, as follows:
12V switch-mode DC-DC converter.
University - Li Batteries
Note that compasses and
meter movements need to be kept well apart. Even using an Alpkit hoop handlebar
required separation is not easy to achieve.
console): A 3.75 milli Ω shunt is placed in series with the
motor feed inside the PCU box. A 20A fsd ammeter (i.e., a 75mV fsd
analog meter calibrated 0-20A) is connected across this shunt and mounted on
the console. A small switch on the PCU box gives the choice of reading
the total battery current ('All') or the current drawn by the motor on its own.
Note that a galvanometer with a 3.75mΩ
resistor across it is naturally damped by this near short-circuit.
A 10A output down
converter permits the use of motorcycle indicators and flasher unit,
a car or truck day-running light (DRL or 'side light'), and it allows
the provision of a cigar socket. Note that the bike battery pack
already has a USB connector for cellphone charging, but car accessories
of current consumption up to the fuse rating can use the 12V socket.
All of the bike lights and indicators are LEDs,
and this requires a special LED (low current) flasher.
The 12V converter used by the author
came in an
aluminium box, which was intended to act as a heat sink for the power
transistors. It is a simple matter to open the box and remove the
circuit board. The transistors can then be mounted on the back of a
finned heat sink (white thermal grease required), with the fins open to
the air on the outside of the power control box. A little architectural
silicone between the heat sink and the power box will keep the rain out.
Brake lights and Kill Switch.
The brake switches activate a TIP127 PNP Darlington transistor.
This already has an on-chip resistor between base and emitter and, with
of about 1000, all it takes is a single resistor and about 1mA of
base current to turn it hard on. The collector is connected
directly to the stop light.
allow the motor cutoff function to be disabled during off-road use, in
case a red panel LED will light every time the corresponding brake is
This warns the rider to restore the kill function once back on public
The tail-light was
bought from a
Chinese supplier via ebay and is branded Wuxing, type WD101. It is
designed for e-bikes and scooters
using 36V batteries. It has a total of 7 high-brightness LEDs,
connected as one string of 4 and one of 3, with series resistors to
limit the current. The stop light should always be brighter than the
tail light, and so the string of 4 LEDs is the stop light. The addition
of a 1N4004 diode enables the tail light to supplement the
brightness of the stop light in the event that the tail light is not
already in use.
One issue I found with the tail light
unit was that
it was built using white LEDs. This meant that the red colour, as seen
through the clear-red outer cover, was not as highly saturated as it
should have been. This, incidentally, is an issue that can only get
worse with age, as the sun bleaches the filter. The solution
to replace all of the LEDs with red high-brightness types.
the stand uses the brake-switch kill function to disable the motor when
is down and the power is on, and a flashing red warning LED signals
condition. Flashing of the LED is accomplished by using the
turn-indicator unit. A current of anything more that about 4mA is
sufficient to operate a flasher unit intended for LED indicators.
Adapting a side-stand to incorporate a
safety switch was an engineering project in
its own right (see side
), but well worth the effort. Failure to retract
is immediately obvious when pulling away, particularly if a twist
& go throttle is used during initial acceleration.
Note that for modern motorcycles,
engine cutoff is
activated when the side
down. So far (July 2020) no manufacturer has seen fit to produce a
retro-fit pedal bike side-stand with a switch to plug into an e-bike
wiring harness. This situation needs to be rectified.
Illumination of the road ahead is provided by two 6-LED ultra-high
brightness units intended for use as
motorcycle headlights or fog lights. These are unbranded,
operation from 9 to 85V,
and are again bought from a Chinese supplier. They each have a
switch-mode power converter, which means that the current goes down as
the voltage goes up. The nominal power rating of each lamp is 10W,
nominal current of 278mA at 36V. The luminous output of a high
brightness LED can be up to 9 times that of a tungsten lamp of the same
power, and these are easily in the upper range of that statistic. The
two lights are both the same, the difference between dip and full being
in the adjustment of the handlebar clamp in each case. Note that a
switch on the console, 'cont dip' (i.e., continuous), allows the dipped
beam to remain on
when full-beam is selected. The ability to turn-off this latter feature
allows battery charge to be conserved when necessary.
A motorcycle handlebar switch provides
and main-beam selection, but also has a horn button. In the UK however,
most pedestrians and motorists find the use of an electric horn
offensive, and that will be especially true if the person making the
noise is a pedal cyclist. A bicycle should preferably have an amusingly
old-fashioned audible-warning device, such as a mechanical bell or a
rubber-bulb horn. This makes the horn button redundant, but a couple of
diodes turns it into a headlamp flasher. A
slight operational inconsistency lies in the fact that the tail-light
will also flash if 'cont dip' is selected in the daytime, but the
inclusion of an extra diode to prevent that does not seem worthwhile.
Also, we can take a leaf out of the computer program-developer's book
by saying that 'this is not a bug, it's a feature'.
One additional safety lighting feature
provision of a day-running light (DRL). Such lights are a particularly
good idea in winter or when the weather is overcast. I bought a set of
4 of these, unbranded Chinese 2-LED units with DOT compliance,
rated for 10 to 30V operation. Checking on a bench PSU showed that
limiting is via a resistor. The maximum voltage of 30V is not
enough for the 36V supply (it is intended for 24V trucks), and so the
single unit used is fed from the 12V
supply. The current drawn with an input of 12.6V was measured at
58mA, giving a power consumption of 0.73W. One bad feature of
these lights is that the positive wire is black and the negative wire
is white, so I marked them with red and blue H20 Hellerman sleeves
to avoid confusion. On one occasion of accidentally connecting one
backwards to a PSU however, it didn't work but it was undanaged.
Current practice with new motorcycles
is for the lights to be on all of the time while riding. This is not a
legal requirement for e-bikes however, and it will reduce the range.
The low-power DRL facility allows lights to be used without significant
reduction; but the first line of defence must always be to wear
The front turn-indicators are mounted on an O-ring sealed ABS box in
front of the handlebar mounting point. The box external dimensions are
160 × 45
mm, and the depth is 55 mm. The width is just sufficient to place the
centres of the indicator lenses 240 mm apart, which is reasonably
compliant with UK minimum indicator separation regulations for
motorcycles.This box also contains the brake-light
switches and has a DRL unit on its front. A 6-core cable is required to
front box to the rider's console, with IP68 cable glands at each end to
keep-out the water.
The rear turn-indicators are mounted on
the same type of box as the front ones, and this is attached to the
tail-light mounting plate on
a luggage rack. Rear indicators only need to be ≥180
mm apart to comply with the UK motorcycle regulations, and this allows
the use of smaller lamp units. The rear box also carries the
and is connected to the console via a 5-core cable and two
There are, incidentally, retro-fit
updating classic motorbikes. One such kit puts the indicator
straps that can go around the fork legs or on either side of the
headlight. The problem here is that the centres of the
might not then be 240mm apart, in which case the arrangement will be
illegal (although the garage carrying out the MOT (Government
roadworthiness) inspection might not know that). For those who do not
want to delve too deeply into the bike electrical system, a supply for
the flasher relay can simply be obtained from the DRL feed.
The console is an O-ring sealed box mounted on the handlebars. It has a
transparent front so that the ammeter and voltmeter can be mounted on a
panel inside, with white LEDs to illuminate the dials in the dark. The
toggle switches are also secured on an internal panel by means of thin
nuts, but protrude through the clear front and have a waterproof rubber
boot over the toggle. The switch
convention is 'up for on' (in keeping with military and engineering
Enables dipped beam to stay on when full beam is selected.
(day-running lights), front and rear.
No cutoff, front
still be used when the front brake is applied).
No cutoff, rear
(rear brake can be used for speed control on loose or wet surfaces)
Side stand down
Flashes when the stand leg is down and power is on. Drive
motor is disabled.
No front cutoff
when F brake lever is pulled).
No rear cutoff
R brake lever is pulled).
Indicator LEDs are 6V
bezel types, also mounted on the panel inside the waterproof box. They are provided with extra padding
resistance to establish a running current of about 10 mA.
Cables leading to the console from the power control unit (PCU), the
tail unit, and the front indicator unit all have in-line
connectors. This allows the modules to be separated for service. The
handlebar switch (Indicators, Main / Dip, Flash) does not need such a connector because it can be split
and removed from the handlebar by removing two screws.
TBC . . . . .
Road Vehicles Lighting Regulations 1989
schedule 7. Original (as made), unrevised. For motorcycles:
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 the MOT test, but compliance is advisable).
Mini-B series connectors
. IP66 in-line with 1 m
cable attached. Panel mount versions also available.
Honnoh Brake Light switch:
The switch can be secured by means of an M12×1.75 nut, but
the thread actually appears to be a special 7/16" × 15tpi
(11.1 × 1.7mm) size. This is not a standard UNC thread.
E-bikes do not have regenerative braking. One reason for that is that a
mid-drive pedal-assist motor cannot be used as a generator in a
freewheel system. In order to work as energy recovery devices, any
motors must be constantly locked to the wheel rotation while the bike
is in motion. Best
2-wheel transportation practice also dictates
that the drive torque should be applied to the rear wheel, while most
of the braking torque should be applied at the front wheel. Taking
these issues into consideration leads to the conclusion that a
generator large enough to provide a significant braking effect is best
fitted to the front wheel. This generator, furthermore, should have
very low drag when not loaded. The type of generator that fits the bill
is, of course, a large direct drive (gearless) brushless hub motor.
Such motors are admittedly, somewhat heavy (2.6 to 7 kg), but they are
A major problem with fitting a large
front hub motor, in addition to the normal 250 W mid-drive system,
would lie in convincing the authorities that the regenerative braking
system cannot be
used to power the bike. Indeed, if the bike is also capable of off-road
use, it would be ridiculous not to use the front motor to obtain a
drive system. The inevitable custom electronic system would then,
unfortunately, present a formidable, possibly insurmountable, challenge
in the matter of obtaining Vehicle