|
THE AUTO BLADE FUSE
FAQ FUNCTION:
The standard automotive blade fuse is
an overcurrent circuit protection device, and
should be the weakest link in an electrical
circuit. The fuse function is to protect the
circuit wiring cable insulation from meltng . The fuse should
blow in the event of excessive
current passing through the fuse providing
disconnection to
interrupt
the electricity flow to the consumer.
CURRENT RATING:
Defines the electrical current at
which the fuse should blow.The fuse rating
should be less than the current rating of the
wiring cable so that the fuse blows before the
cable insulation melts. Vehicle blade type
fuses are colour coded according to current
rating.
Voltage Rating : 32 volts d.c.
What causes a fuse to blow?
Faulty consumer drawing excess current for
example, due to a seized motor.
Wiring short circuit
to ground due to loose wiring or damaged cable
insulation, or shorted component..
Incorrect
fuse fitted or used in circuit design specification.
The fuse keeps blowing can I fit a bigger
fuse?
Not recommended. If the circuit has a fault
, the fault should be traced and rectified.
Methods of checking a fuse
Visual check : Turn off power
from circuit . Remove fuse from
holder . Check for broken conductor in fuse.
Test circuit & replace as necessary.
Using a test lamp : Attach test lamp
ground lead to chassis ground, with circuit
switched on and fuse present in circuit, check
power at both terminals of fuse, test should
illuminate at both test points if fuse is good.
If fuse is blown switch off circuit before
renewing fuse.
|Using a multimeter : Set multimeter
to appropriate voltage test range. Ground
negative probe of multimeter to chassis earth
or negative (some vehicles have insulated earth
return systems) , with fuse present in circuit
, and circuit switched on ,check voltage at
both terminals of fuse, Should be the same if
fuse is intact. If fuse is blown switch off
circuit before renewing fuse.
Continuity check using a multimeter : Switch
off circuit. Remove
fuse from circuit, use multimeter set to ohms
range. Apply positive & negative test probes to
either side fuse terminals , should indicate
continuity (0 ohms) on multimeter readout if
fuse is intact.
LED Glow type fuse : if fuse
glows this indicates fuse is blown and needs
replacing following circuit test.
The fuse holder has melted before the
fuse blew :
This fault can occur due to bad connections
between fuse and fuse holder or terminal
connectors causing high resistance and
subsequent heat. Only use good quality
replacement fuses, some economy fuses have
thinner metal blades which can cause contact
and resistance problems. Check the fuse holder
has appropriate rating for the fuse you intend
to use.
How do I select the correct fuse to use when
building a project vehicle eg kit car ?
Voltage rating of the fuse and circuit :
Automotive fuses are generally rated at 32
volts DC or above. allowing use on circuits below that
voltage. Check manufacturers specification . Beware not to confuse voltage rating
with current rating. Interrupt rating:
This is
the current value at rated voltage at which the
fuse should interrupt the circuit when it
blows. A fuse may allow a current many times
higher than its rated current to pass
momentarily to avoid nuisance operation, though
the amount of time the said current passes
through the fuse for will determine if
the fuse blows. Response time :
Response time
or time-current characteristic determines how
quickly a fuse disconnects the circuit in an
overcurrent situation. Fuse manufacturers data
specification should be consulted but as a
guide mini blade fuses have a faster response
time than the standard blade fuses etc.
Temperature:
Electrical circuits are affected by temperature. Characteristics of fuses can change with temperature. See manufacturers datasheets for specification.
|
