BMW i3 Technical Training Manual page 51

I01￿General￿Vehicle￿Electronics
2.￿Voltage￿Supply
Index
1
2
The￿electrical￿and￿thermal￿conductivity￿of￿the￿carbon￿fibers￿themselves￿is￿extremely￿good.￿However,￿as
soon￿as￿they￿are￿introduced￿into￿the￿resin,￿the￿resin￿defines￿the￿conductivity￿properties.￿The￿electrical
and￿thermal￿conductivity￿is￿then￿extremely￿low￿as￿the￿carbon￿fibers￿are￿encased￿in￿resin.￿The￿carbon
fibers￿are￿not￿covered￿entirely￿in￿resin,￿but￿can￿also￿be￿exposed￿at￿the￿component￿surface.
The￿passenger￿compartment￿made￿from￿carbon￿is￿connected￿to￿the￿aluminium￿frame.￿The￿aluminium
frame￿is￿connected￿to￿ground.￿As￿the￿carbon￿fibers￿establish￿contact￿with￿this￿aluminium￿frame,￿the
passenger￿compartment￿has￿an￿undefined￿potential￿similar￿to￿ground.
If￿the￿insulation￿of￿a￿live￿electrical￿line￿becomes￿damaged￿as￿a￿result￿of￿an￿incident,￿such￿as:
• Accident
• Crushed￿cable
• Improper￿repair
and￿if￿the￿electrical￿conductor￿touches￿the￿carbon￿passenger￿compartment,￿a￿current￿may￿flow
through￿the￿carbon￿fiber￿depending￿on￿the￿circumstances.
With￿a￿vehicle￿voltage￿of￿12 V￿the￿current￿level￿is￿in￿the￿range￿of￿a￿few￿amperes.￿This￿means￿a￿fuse
installed￿for￿the￿protection￿of￿the￿electrical￿line￿would￿not￿activate￿under￿certain￿circumstances.
The￿current￿flow￿through￿the￿carbon￿fibers￿would￿also￿cause￿a￿thermal￿event￿at￿the￿contact￿points￿for
the￿carbon￿fibers.￿Due￿to￿the￿good￿thermal￿conductivity￿this￿thermal￿event￿would￿also￿spread￿to￿other
parts/components￿in￿the￿event￿of￿continued￿current￿flow.￿The￿resulting￿gases￿are￿harmful￿and￿have￿an
unpleasant￿odor.
Exercise￿extreme￿caution￿when￿working￿on￿electrical￿lines.
Lines￿or￿connectors￿which￿are￿not￿insulated￿cannot￿touch￿the￿carbon￿body￿components.
In￿each￿case￿follow￿the￿general￿and￿special￿information￿on￿electrical￿characteristics￿of￿the￿carbon￿body
in￿the￿repair￿instructions￿
Explanation
Carbon￿fiber
Resin
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