Motorcycle Electrics

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Motorcycle Electrics

• By
• Jerry Skene

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Overview of Seminar

• Volts, Amps, Watts Ohms
• What they measure and how they are used (includes
  Ohms 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, contd

• BMW motorcycle alternators provide the following
  electrical power/5 180W R90s
  238W1000cc to 80 250W recent R/K
  bikes 400 600 WK bikes (pre-2005) 700WK
  LT 840W

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Ohms (?)

• A Ohm (?) 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 ?.
• 5 of 18Ga wire has a resistance of 0.03 ?.

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Ohms 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 IV/R or RV/I
• So the voltage drop across a 5 length of 18Ga
  wire (R0.03?) carrying 5A of current is. V0.03
  x 5 0.15V

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Ohms Law

• Use Ohms law to calculate the size of fuse
  needed to power an 80 watt heated vestP 80W
  V 12V (PV x I), so I P/Vor 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 Overload Typical
Use current rating 0.5 mm²
(20 AWG) 3 A instr., turn signals
0.75 mm² (18 AWG) 6 A headlight 1 mm² (17
AWG) 10 A h/l ground 6 mm² (10 AWG) 30
A 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 motorcycles 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 12.8-12.9 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 BMWs monitor brake light current
• LEDs 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
• Ohms law says RV/I 12/2 6?, can use 8?
• 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 Output 10.5V 510 lumens11.0V
597 lumens11.5V 695 lumens12.0V 803
lumens12.5V 923 lumens12.8V 1000 lumens
?Rated output voltage13.0V 1054 lumens13.5V
1198 lumens14.0V 1356 lumens ?Rated life
voltage14.5V 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
• lt 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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? ? ?? Questions ? ? ? ?