MACS Monthly Newsletter - 2021 - MAR9

power (i.e., charger power) to heat the battery
and not use HV Battery Pack power, thereby
reducing the impact on vehicle range while
providing a warmer interior temperature.
6. The vehicle On-Board Charging Module
(OBCM) will determine how quickly an HV
Battery Pack will charge with the HV Cabin
Heater powered ON, if Level 2 Charging is being used. Example: If an electric vehicle utilizes a 6kW Cabin Heater and an OBCM with a
rating of 3.3kW, then the HV Battery Pack will
have minimal (if any) charging while the HV
Cabin Heater is set to HIGH heat setting. In
fact, the HV Battery Pack can undergo stateof-charge (SOC) depletion during charging
when loads exceed the maximum OBCM kW
output, and S/W may inhibit high cabin temps
when loads exceed the OBCM or if the vehicle
is not connected to a charger. If the OBCM is
rated at 7.2kW, the HV Battery Pack will receive charging current, albeit low, but a higher
power OBCM can provide higher load currents
to charge the battery and operate other loads.
OEMs may have specific strategies to control
the rate of HV Cabin Heat during HV Battery
Pack charging (i.e. lower Cabin Heater heating rate) to ensure that the battery charging
results in minimum charging rate (although
it will be much slower) while still providing
cabin heat at a lower level.
7. If Level 3 charging is utilized, then heating the cabin at full power while charging the
battery at high rates can easily be achieved
without significant impact to battery charging
time.
Power systems on a BEV are highly integrated.
HV Battery Pack SOC, OBCM rating, and HV Cabin Heater temp setting effects total charging time.
If additional vehicle loads are powered on during
charging or lower ambient temperatures, this will
also add to charging time. This needs to be considered when a customer has passenger compartment
heating complaints or vehicle range complaints. n

Some Final Thoughts on the Cabin Heater

Although there is much more that could have
been covered in this article, there are other considerations when working with HV Cabin Heater systems:
1. Measuring the resistance of the PTC heating elements, in most applications, will not be
possible. Since the electronic circuits are at the
front end of the Cabin Heater circuit, there is
no repeatable method of measuring resistance
without (destructive) disassembly of the heater.
2. Cabin Heaters can be a source of causing
HV Isolation Faults. Although this article did
not review the process of Isolation Fault testing, OEM service information (DTCs and testing procedures) will provide guidance on the
testing. HV Isolation Faults are safety faults
and can cause a loss of propulsion.
3. When the Cabin Heater system is being utilized at a high-power level (cold weather), it
can significantly reduce vehicle range. Here
is a link to an excellent article with data provided by FleetCarma that discusses this issue:
https://www.greencarreports.com/news/1089160_
nissan-leaf-chevy-volt-range-loss-in-winter-newdata-from-canada
4. Owners/operators of BEVs should consider
using the 12V heated seats on a higher setting
in lieu of using a high setting on the Cabin
Heater to reduce the electrical load on the HV
Battery Pack. This will increase vehicle electric
range.
5. The optimal process of using the HV Cabin
Heater to warm the interior in cold weather
is to connect the vehicle to a charging station
(Level 2 / 220Vac or Level 3 / DC Fast Charging at 50kW - 100kW) while warming the interior. One method of achieving this is to program the vehicle to " precondition " the interior
with heat 30 minutes before using the vehicle
(using vehicle instrument controls or smart
phone app). The vehicle will utilize utility

MACS Service Reports is published monthly by the Mobile Air Conditioning Society
Worldwide. It is distributed to members of MACS Worldwide and is intended for
the educational use of members of the automotive air conditioning service and
repair industry. Suggestions for articles will be considered for publication, however,
MACS Worldwide reserves the right to choose and edit all submissions.

Editors:
Elvis Hoffpauir, Steve Schaeber
Production Designer:
Laina Forcey
Manager of Service Training:
Steve Schaeber
Mobile Air Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsw.org * Website: www.macsw.org

Unless otherwise noted, all photos/art by author.

January 2021

MACS Service Reports

https://www.greencarreports.com/news/1089160_nissan-leaf-chevy-volt-range-loss-in-winter-new-data-from-canada https://www.greencarreports.com/news/1089160_nissan-leaf-chevy-volt-range-loss-in-winter-new-data-from-canada https://www.greencarreports.com/news/1089160_nissan-leaf-chevy-volt-range-loss-in-winter-new-data-from-canada http://www.macsw.org

MACS Monthly Newsletter - 2021

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