Download Motorcycle Electrics

Motorcycle Electrics
By
Jerry Skene
BMWBMW Square Route Rally - 2006
Overview of Seminar
• Volts, Amps, Watts & Ohms
– What they measure and how they are used
(includes Ohm’s law)
• Batteries & charging
• Adding lights and other accessories
• Common tools & supplies
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Volts
• Measure of the electric potential between two
conductors, or the ability to move an electric
charge through a resistance
• Motorcycles use a 12V DC (direct current)
system
• Measured with a voltmeter
• ignition-off voltage is ~ 11.9 volts
• operating voltage is ~13.8 volts
(lowest lethal voltage is ~ 60 volts)
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Amp (Ampere)
• Measure of current flow through a circuit
• Headlight bulb draws ~ 4.5A
• Tail light bulb draws ~ 0.4A, or 400
milliAmps (mA)
• Electrical symbol for current is I
Minimum lethal current through the
human body is 80 – 100 mA
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Watts
• Watt is a unit of electrical power (P)
• Corresponds to the power developed in a
circuit by a current of one ampere flowing
through a potential difference of one volt:
Power = Volts x Current (I)
• a headlight connected to 12V Volts,
drawing 5 Amps consumes 12 x 5 = 60
Watts
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Watts, cont’d
• BMW motorcycle alternators provide the
following electrical power:
/5
180W
R90s
238W
1000cc to `80
250W
recent R/K bikes
400 – 600 W
K bikes (pre-2005)
700W
K LT
840W
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Ohms (Ω)
• A Ohm (Ω) is a unit of electrical resistance
• An ohm is the resistance that produces a
potential difference of one volt when a
current of one ampere is flowing through it.
• A typical 60W high beam bulb has a
resistance of 0.4 Ω.
• 5’ of 18Ga wire has a resistance of 0.03 Ω.
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Ohm’s Law
• Very useful law relating voltage, current
and resistance
• States that Voltage (V) across a circuit is
equal to the current (I) times the
resistance (R): V= IR or I=V/R or R=V/I
• So… the voltage drop across a 5’ length of
18Ga wire (R=0.03Ω) carrying 5A of
current is…. V=0.03 x 5 = 0.15V
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Ohm’s Law
• Use Ohm’s law to calculate the size of
fuse needed to power an 80 watt heated
vest:
P = 80W V = 12V (P=V x I), so I = P/V
or 80/12 = 6.6 Amps
(next larger common fuse size is 7.5A)
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Wire Gauges
• Measured in mm2
or gauge # American Wire Gauge)
• Can use resistance table to determine total resistance of
added wiring
Cross-sectional area
0.5 mm²
(20 AWG)
0.75 mm²
1 mm²
6 mm²
(18 AWG)
(17 AWG)
(10 AWG)
Overload
current rating
3A
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6A
10 A
30 A
Typical Use
instr., turn
signals
headlight
h/l ground
battery
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Batteries & Charging
• Motorcycle batteries are of the Lead Acid design
• There are several variations of Lead Acid:
– Wet Cell (flooded):serviceable, and maintenance free
– Gel Cell
– Absorbed Glass Mat (AGM)
– Gel and AGM require less service than flooded Lead Acid
– Gel Cell and some AGM batteries may require a lower
charging rate
– your motorcycle’s charging system usually dictates the type
of battery you require
– Gel cells have a lower recharge voltage, and can be
damaged by too high a charge rate – best to use a Gel
charger
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Batteries & Charging
• A fully charged battery should read 12.812.9 V
• Sulfation occurs when the voltage drops
below 12.4 V
• Most premature battery failures are
caused by sulfation buildup – a result of
losing charge
• Buy a trickle or smart charger, and use it
frequently.
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Batteries & Charging
•
Common causes of premature failure:
– Battery sits too long between charges. As little as 24 hours in hot weather
and several days in cooler weather.
– Battery is stored without some type of energy input (self discharge).
– "Deep cycling" an engine starting battery. Remember these batteries can't
stand deep discharge.
– Undercharging of a battery: charging a battery to 90% of capacity will allow
the 10% of battery chemistry not reactivated to sulfate the battery
– Heat of 100º F increases internal discharge. As temperatures increase so
does internal discharge. A new fully charged battery left sitting 24 hours a
day at 110º F for 30 days would most likely not start an engine.
– Low electrolyte level - battery plates exposed to air will immediately sulfate.
– Incorrect charging levels and settings. Most cheap battery chargers can do
more harm than good. See the section on battery charging.
– Cold weather is also hard on the battery. The chemistry does not make the
same amount of energy as a warm battery. A deeply discharged battery can
freeze solid in sub zero weather.
– Parasitic drain is a load put on a battery with the key off. This can drain a
battery in a few days
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Adding Lights & Other Accessories
• The most common addition is driving or fog
lights
• Wire these directly to the battery through a fuse
and relay
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Adding Fog Lights
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Replacing your stock brake light
with an LED light
• Recent BMW’s monitor brake light current
• LED’s take much less current: 0.2A vs ~2A
• You must wire a resistor in parallel with the LED light
to fool the computer into thinking you have a stock
brake light
• Ohm’s law says R=V/I = 12/2 = 6Ω, can use 8Ω
• Remember P = V X I, so P = 12 x 1.5 = 18 watts, so
you need a 20W power resistor
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Brighter headlights
• Even a small decrease in voltage to your headlight can
dramatically reduce its light output:
Voltage
10.5V :
11.0V :
11.5V :
12.0V :
12.5V :
12.8V :
13.0V :
13.5V :
14.0V :
14.5V :
Output
510 lumens
597 lumens
695 lumens
803 lumens
923 lumens
1000 lumens ←Rated output voltage
1054 lumens
1198 lumens
1356 lumens ←Rated life voltage
1528 lumens
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Brighter Headlights
• Consider running heavier wires in parallel
with your existing headlight wiring to
minimize voltage drop.
• BMW uses 0.75mm2 (18ga) wire for
headlights, causing ~1.2V drop in voltage
• Adding 12 ga wire in parallel to this will
provide a significant increase in
brightness.
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Tools & Supplies - tools
• Wire cutters
• Long-nose pliers
• Wire strippers
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Tools & Supplies - tools
• Get a Digital Multimeter
– < $8 at Allelectronics.com
• Good crimp tool is an excellent investment
– (try Starkelectronics.com)
• Soldering iron or soldering gun for
heavy gauge wire
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Tools & Supplies - supplies
• Tap connectors are common: be
sure to use the correct size for the
size of wire – too small can
damage original wire, too large
will not make a reliable
connection
• Heat-shrink tubing and a heat-gun
will help make weatherproof
connections
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