Fleet Maintenance - 45

TRAINING
Bistable relays retain their switched position
even if supply current to the coil fails. This
means bistable relays can prevent the loss of
information on the current switching status.
In addition, with a bistable relay, the vehicle's computer grounds the circuit to engage
the relay. Once the coil is not energized, the
relay is still doing its job and stays connected
even when the contact point
is closed. In order to reset
the relay to an open position,
the current is reversed by the
control circuit which causes
the contacts to open.

relay would stay engaged, and this could create
a parasitic drain on the circuit.
Let's reverse the scenario by replacing a
bistable relay with a conventional relay. The
conventional relay would close the contact
points and complete the circuit, but the
moment the computer removed the ground
from the relay the circuit would open.

Through this scenario, we are not even
considering if the replaced conventional
relay is suppressed or not. If a bistable relay
was replaced by a non-suppressed conventional relay, that could cause damage to the
circuit and continual damage to components until someone realizes the wrong relay
was installed.

»»Fig. 3: Look at the
illustration and the two
relays side-by-side. Now
look closer, can you see the
differences in the schematic?
Image courtesy of K&D Technical Innovations

»»Pictured here are two
similar-looking relays. The
relay on the left is a bistable
relay. It is important to note
that all bistable relays do not
look the same inside. Some
are electronic and some are
mechanical. The bistable relay
shown here is mechanical.
Image courtesy of K&D Technical Innovations

But what happens if there is
no signal to open the relay? It
could become a parasitic drain.
It is important to note that
bistable relays use less current
on the coil side of the relay.
This allows for multiple relays
to be activated and controlled
by a single circuit. This also
puts less strain on the alternator and charging systems
of the vehicle.

The consequences

Imagine what would happen
if a conventional relay was
accidentally replaced with a
bistable relay. If this occurs,
grounding the conventional
relay would close the contacts
and the technician would not
be able to open the circuit. The
VehicleServicePros.com/10122067
December 2019 | VehicleServicePros.com

45


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Fleet Maintenance

Table of Contents for the Digital Edition of Fleet Maintenance

Uptime: Top Industry Trends in 2020 and Beyond
How Active Safety Systems Pave the Way to Vehicle Autonomy
Vehicles: Steps to Understand and Prevent Corrosion
In the Bay: Remote Vehicle Management Enters a New Phase
Shop Operations: How to Prevent, Contain, and Clean Up Shop Spills
Management: A Guide to World-Class Maintenance
Training: What is a Bistable Relay?
Reman, Rebuild, Replace: What's the Difference Between a Supplier and a Supply Partner?
Diagnostics: Four Steps of an Effective Maintenance Program
Fleet Parts & Components
Tools & Equipment
Classifieds
Guest Editorial: Trends in Asset Telematics
Fleet Maintenance - 1
Fleet Maintenance - 2
Fleet Maintenance - 3
Fleet Maintenance - 4
Fleet Maintenance - 5
Fleet Maintenance - 6
Fleet Maintenance - 7
Fleet Maintenance - Uptime: Top Industry Trends in 2020 and Beyond
Fleet Maintenance - 9
Fleet Maintenance - How Active Safety Systems Pave the Way to Vehicle Autonomy
Fleet Maintenance - 11
Fleet Maintenance - 12
Fleet Maintenance - 13
Fleet Maintenance - 14
Fleet Maintenance - 15
Fleet Maintenance - 16
Fleet Maintenance - 17
Fleet Maintenance - 18
Fleet Maintenance - 19
Fleet Maintenance - Vehicles: Steps to Understand and Prevent Corrosion
Fleet Maintenance - 21
Fleet Maintenance - 22
Fleet Maintenance - 23
Fleet Maintenance - 24
Fleet Maintenance - 25
Fleet Maintenance - 26
Fleet Maintenance - 27
Fleet Maintenance - 28
Fleet Maintenance - 29
Fleet Maintenance - In the Bay: Remote Vehicle Management Enters a New Phase
Fleet Maintenance - 31
Fleet Maintenance - 32
Fleet Maintenance - 33
Fleet Maintenance - 34
Fleet Maintenance - 35
Fleet Maintenance - Shop Operations: How to Prevent, Contain, and Clean Up Shop Spills
Fleet Maintenance - 37
Fleet Maintenance - 38
Fleet Maintenance - 39
Fleet Maintenance - 40
Fleet Maintenance - 41
Fleet Maintenance - Management: A Guide to World-Class Maintenance
Fleet Maintenance - 43
Fleet Maintenance - Training: What is a Bistable Relay?
Fleet Maintenance - 45
Fleet Maintenance - Reman, Rebuild, Replace: What's the Difference Between a Supplier and a Supply Partner?
Fleet Maintenance - 47
Fleet Maintenance - Diagnostics: Four Steps of an Effective Maintenance Program
Fleet Maintenance - 49
Fleet Maintenance - 50
Fleet Maintenance - 51
Fleet Maintenance - Fleet Parts & Components
Fleet Maintenance - 53
Fleet Maintenance - 54
Fleet Maintenance - 55
Fleet Maintenance - 56
Fleet Maintenance - 57
Fleet Maintenance - 58
Fleet Maintenance - Tools & Equipment
Fleet Maintenance - 60
Fleet Maintenance - 61
Fleet Maintenance - 62
Fleet Maintenance - Classifieds
Fleet Maintenance - 64
Fleet Maintenance - 65
Fleet Maintenance - Guest Editorial: Trends in Asset Telematics
Fleet Maintenance - 67
Fleet Maintenance - 68
Fleet Maintenance - Insert1
Fleet Maintenance - Insert2
Fleet Maintenance - Cal1
Fleet Maintenance - Cal2
Fleet Maintenance - Cal3
Fleet Maintenance - Cal4
Fleet Maintenance - Cal5
Fleet Maintenance - Cal6
Fleet Maintenance - Cal7
Fleet Maintenance - Cal8
Fleet Maintenance - Cal9
Fleet Maintenance - Cal10
Fleet Maintenance - Cal11
Fleet Maintenance - Cal12
Fleet Maintenance - Cal13
Fleet Maintenance - Cal14
Fleet Maintenance - Cal15
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