Page
21 of 40
Number
PM820010
HVAC: SmartAir eHVAC System
L. Testing the Battery Management System
(BMS)
Overview
The BMS monitors the auxiliary batteries for state of
charge, communicates with the EHVAC system and con-
trols the battery separator solenoid. LED light on the
BMS indicates power to the device and does not provide
diagnostics. Power inputs to the BMS are fuse protected.
When the truck starting battery voltage is above 13.2
volts for at least 15 seconds, the BMS will send an
engage signal to the separator. The separator will close
and allow charging of the aux batteries. When the truck
starting battery voltage falls below 12.5 volts for 15 sec-
onds, the BMS will disengage the separator. The separa-
tor will open and stop the charge of the aux batteries, and
prevent the truck starting batteries from being dis-
charged.
Testing
Before testing the BMS or separator, unplug the BMS for
at least 1 minute to reset the system then reconnect and
attempt to operate the system. If the system does not
operate continue with the following tests.
BMS tab with hole must be connected to the negative
battery terminal on the aux batteries. First, check the aux
battery voltage. Voltage must be above 6 volts for the
device to work. Batteries should be tested and fully
charged before they are installed in the truck for best
results. If not, it can take a considerable amount of time
for the battery state of health indicator to be correct.
Check the LED light on the BMS, it should be flashing
indicating the device has power.
If the aux battery voltage is okay, and the LED is not
flashing, check the connection and 5 amp fuse in the aux
battery sense wire near the BMS.
With aux voltage okay and LED flashing, check for 12
volts from the truck starting batteries. This voltage
passes through a 5 amp fuse in the start battery box and
connects at pin 8 (pos) and 1 (neg) in the 8 pin connector
on the BMS. This voltage, from the truck batteries, is dis-
played on the LED controller (service) screen. It also
powers the output for the engage signal to the separator.
If you do not have 12 volts across pins 8 (pos) and 1
(neg), check the 5 amp fuse and the wiring harness.
With aux voltage okay, LED flashing and 12 volts across
pins 8 and 1, start the truck or connect the start batteries
to a battery charger and bring the voltage above 13.2 for
at least 15 seconds. You should hear a click when the
solenoid pulls in. This would indicate that the BMS has
sent the engage signal from pin 5 (orange wire) of the
BMS to pin 2 on the Terra Power separator, pin 1 is
ground on both devices. This is a 12 volt signal. When
the separator closes, you should see an increase in volt-
age on the aux side of the separator and at the aux bat-
teries. The voltage across both sides of the solenoid will
slowly become the same value, which indicates that the
tractor batteries and auxiliary batteries are tied together
in parallel. If the separator did not close by the BMS,
check the separator. (See below) If the separator checks
okay, recheck the BMS. If the separator closed and does
not allow charge to the aux batteries, the internal con-
tacts of the switch could be defective. Replace the sep-
arator.
If the separator closes and allows charge to the aux bat-
teries, that part of the BMS is working. Now shut off the
truck engine or battery charger and put a load on the
tractor batteries. Examples of a load include the head-
lights and radio. Allow the voltage of the truck batteries to
drop below 12.5 volts for 15 seconds. You should hear a
click when the solenoid disengages. This would indicate
that the BMS has disengaged the signal from pin 5 of the
BMS to pin 2 on the separator. The voltage of the tractor
batteries and the auxiliary batteries should now start to
be different. Turn off the headlights or other loads that
were placed on the batteries. When the separator opens,
it prevents the starting batteries from being drained. If the
separator clicks and does not disengage the internal con-
tacts, the contacts could be welded together. Replace the
separator.
Separator Switch Testing:
NOTE
Power must be present on separator posts to check
separator operation.
Disconnect the Deutsch connector of the Terra Power
separator. Connecting 12 volts to terminals 2 (pos) and 1
(neg) will engage the separator and close the contacts
connecting the start and aux batteries. Disconnecting the
12 volts to terminals 2 (pos) and 1 (neg) will disengage
the separator and open the contacts connecting the start
and aux batteries.
