Automotive Engineering - December 2023 - BET-19

Some contactors have the ability to
send a signal reporting their status so
operators know if a contactor has failed
to open or failed to close. This is a feature
that is worth the extra cost. In the event
that the circuit is exposed to higher
power than specified, the energy may
cause the contacts to weld together. This
means the circuit remains live and connected
to the battery. In turn, this may
lead to situations that damage the test
system or pose danger to people.
Other examples include underspecifying
the size of the cables and connectors. In the
event of an overcurrent, the cables and
connectors could melt and start a fire.
Melted connectors are not uncommon in
battery test systems. Even bolted connections
require careful implementation. If the
connections are not tightened to the proper
torque spec, heat points could eventually
melt the cables or cause high resistance
points which could skew test results.
Overlooking Safety Features
Many engineers never think about putting
e-stops in the system. If a battery
starts going into a thermal event, the
operator needs an e-stop to be able to
immediately shut down the system.
Another way to handle battery thermal
events is with a temperature sensor. The
sensor signals that the battery temperature
is going up at a certain rate, and
control software shuts down the system
automatically. It would be a mistake to
leave out either of these safety features.
Another important safety consideration
is equalizing the voltage before connecting
to a battery. Failure to equalize could
create a significant arc, which wears contacts
and could be an electrical hazard.
Potentially, it could cause equipment damage,
personal injury, or component failure.
The ability to equalize voltage can be
achieved in two different ways. Some
systems pre-charge the instrument to a
voltage approximately equal to the battery
voltage. Another approach is precharge
resistance. There is a contactor on
the negative line and two contactors on
the positive line. On one positive contactor,
the circuit has a resistor that slows the
current inrush. Otherwise, a sudden inrush
could damage system components. After
the voltage has a chance to equalize at a
slow rate, the system closes the second
Many components must be integrated successfully to build a battery test system. (Image: EA
Elektro-Automatik).
positive contactor and opens the connector
with the pre-charge resistor.
A pre-charge approach requires the system
to measure the voltage on the device
under test, match that voltage in the test
system, and then close the main contactors.
Some companies make this a manual
process. A technician uses a multimeter to
measure the battery before they connect it.
Then the technician sets the power supply
voltage and turns on the output. After that,
the technician goes back to the battery to
re-measure. When the voltage is equal,
they flip a switch to close the contactors. If
technicians skip a step, or if they don't notice
that the voltage is off by a digit, they
could damage the test system.
Details matter when it comes to safety.
For instance, the engineer who is integrating
the system may not label the
connections clearly. A technician might
connect the negative to the positive and
the positive to the negative. If the voltage
is -110 volts on the battery and +110
volts on the test system, then the total
error is 220 volts. Such a significant level

Automotive Engineering - December 2023

Table of Contents for the Digital Edition of Automotive Engineering - December 2023