MACS Monthly Newsletter - 2022 - APR3

from HV Positive to HV Negative, or even 12-volt systems
or ground is detected. If even a small amount
of current is flowing from the HV Battery when it
shouldn't be, the HV system will not close the Main
Contactor and warning lamps are illuminated.
" High Volage Isolation " trouble codes indicate a
this isolation protection. Something as
failure of
" simple " as an orange wire with scuffed insulation
can generate an isolation code in the rain. Special
meters, PPE and training are required to diagnose
these issues.
We don't want to CAUSE " isolation " issues. It can
come down to something as simple as coolant and
water. Previous MACS articles should help in selecting
the proper coolant to use for the vehicle in your
bay.
ALWAYS USE COOLANT APPROVED FOR THE VEHICLE.
If in doubt, use OE coolant. I gave up trying
to stock and identify proper and approved coolants
and just purchase OE coolant for anything but DexCool.
You may find this of interest. Here in Canada,
aftermarket " approved " pre-mixed coolant is sometimes
TWICE the shop cost when compared to the
OE pre-mixed coolant from the dealer.
NEVER use plain water in a High Voltage cooling
system. The corrosion protection and non-conductive
properties of the specified coolant are required
to inhibit corrosion of the HV components.
Speaking of water,
if you are using concentrate,
pay strict attention to recommended concentration
ratios and the type of water specified by the manufacturer.
Failure
to follow manufacturer's recommendations
for liquid coolant can lead to a vehicle developing
isolation codes and diagnostic headaches.
Battery thermal management
When it comes to Hybrid and EV battery longevity,
thermal management is everything. It doesn't matter
if the battery is of the older NiMh chemistry or Li-ion
or whatever improved battery type comes down the
road, every type of battery charges best at a certain
temperature or discharges best at a certain temperature.
There
is even research showing that while charging,
some battery types charge best at a certain percentage
of charge at a certain temperature! I'll make
up some numbers for example to make the point
April 2022
3
Battery facts...
* Batteries heat up when they are charged
slowly.
* Batteries heat up when they are charged
quickly.
* Batteries heat up when they discharge
during use.
* Batteries heat up when they are charged
during use.
* Batteries function best at a certain temperature.
*
Batteries can be damaged when used
heavily at low temperature.
* Batteries can be damaged if allowed to
reach high temperature.
MACS Service Reports
Figure 4: 2008 Toyota Prius High Voltage battery cooling
air inlet.
(SOC=State of Charge) ...Using a Level 2 charger,
Battery " X " charges most efficiently and safely from
20% SOC to 80% SOC at 35°C. When the SOC rises
above 80%, Battery " X " charges most efficiently and
safely at 60°C. This is just an example with made-up
numbers, but this is the type of thing some engineers
are discovering and developing as technology
advances. Charging algorithms have been around
for a long time (12v charger/maintainers).
Mike Bailey
MACS Monthly Newsletter - 2022

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