EYE ON ELECTRONICS March 2016_Layout 1 2/17/16 12:23 PM Page 14
Eye On Electronics
More vehicle electronics means more parasitic losses for the
poor battery. Auto start-stop is a killer, too. Possible solutions:
ultracapacitor batteries and resurrection of the 48V system.
A
telematics module such as General Motors’ OnStar is always
drawing at least some power because the on-board has to be
ready to receive a remote command to start the car or report its
location on the owner’s smartphone. The alarm
draws power. Headlamps stay on for a minute
bhoward@motor.com
or two after the driver exits.
More than a few batteries rated for 48 or 60
months give up the ghost inside of two years. It’s
an opportunity to sell a replacement battery more
frequently. The opportunity also carries the risk of
the customer wondering if he was sold substandard goods and one more chance down the road
to vent when reminded of pro-rated replacement
policies. Some people still believe a five-year battery will be replaced free in the 59th month.
OEM suppliers are working hard to reduce
the drain of electrical and electronic components. LED bulbs are replacing incandescents
in taillamps and brake lamps. LEDs raise the
cost of a new car, but the owner may get it back
if he avoids a $50 defective taillamp ticket down
the road. Watch for premium xenon or HID
headlamps to be replaced over time by LEDs
that similarly save energy—enough to make a
modest impact on the vehicle’s fuel economy.
(Don’t hold your
breath waiting for
CFLs lighting the
road ahead of midpriced cars.)
Auto start-stop
saves fuel, as much
as 10% in city driving, but it calls for a
more powerful battery that adds a few
pounds and 20%
more in cost.
If you remember
42V
or 48V electriStart-stop engines improve city fuel economy by up to
10%. But they put extra strain on the vehicle battery cal systems disand require a beefier starter motor.
cussed about 15
Bill
Howard
14
March 2016
years ago, they’re back, at least as a proposal, and
a serious proposal at that. If they come to vehicles, the need for more efficient and lighter systems will trump concerns over arcing and short
circuits. Ultracapacitor battery systems are getting serious consideration. They’re already making inroads onto long-haul trucks, as thousanddollar options to make sure the truck restarts if
the main battery is drained.
What drains a battery when the vehicle isn’t
used? A vehicle left for a week in an airport
parking lot, or the family’s second or third car
left unused in the garage, may well have a dead
battery when the owner goes to start it. If it’s
jump-started and recharged, then goes dead
overnight, it could be that the battery is on its
way out or the vehicle is drawing excess power
when it’s off—parasitic loss.
Every vehicle draws current when the key is
out of the ignition. The service manual should
specify the correct rating. Generally, it should
be no more than 50 milliamps (mA)—onetwentieth of an amp, or half a watt on a 12V system. Not much, though it can add up on an unused vehicle. Sometimes it’s a device that fails to
shut off because of a faulty switch, such as a
trunk or glovebox light, and you can’t see it; or
the dome light that should time out after a
minute and doesn’t, but by that time you’ve
walked away from the vehicle.
You’ll get drain from alarms, telematics systems, proximity keys with radio receivers that
are always on and listening for the key frequency and retained accessory power (RAP) modules. Aftermarket alarms and stereos can draw
large amounts of power when the vehicle is off,
often from an error in installation, such as setting the off-after-x-minutes DIP switch wrong.
Or they may draw power through an alwaysactive standby mode.
Don’t forget accessories in the car: the dashboard GPS, the power inverter in the cargo
area, the USB or cellphone charger. Even if
there’s no device plugged in, the charger itself
may draw power.
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Eye On Electronics
Diagnosing parasitic loss is time-consuming, going circuit by circuit, and you
have to wait for the draw on a circuit to
settle. That could take 10 to 20 minutes.
Open the door and the dome light pops
on. Maybe you can force that off with a
switch. But it may also trigger other
functions that throw off the reading,
such as the fuel pump energizing. Those
power surges may also damage an ammeter or blow its costly proprietary fuse
if the range is set to, say, 200mA rather
than 10 or 20A and you discover something drawing half an amp.
Parasitic drain and no-start issues
can even affect hybrids. Since there’s a
big nickel-metal hydride (NiMH)
propulsion battery doing a lot of the
work, the Prius’ 12V battery is smaller
than the one on some comparably
sized, combustion engine compact cars.
The car’s motor/generator can charge
the main NiMH traction battery, but
the big battery does not charge the 12V
battery, and when that goes dead, the
car won’t start on its own.
There’s also a Prius setup menu item
that lets the owner disable the remote
door unlock if the car is unattended for
long periods; he’d simply use the physical key to get in and start it up. That
would be a useful tool for almost every
car and light truck. Perhaps if the vehicle has telematics, a forgetful owner
could use his smartphone to tell OnStar
or some similar service to shut down
certain applications (the remote key receiver) until the vehicle is started, or until the day he returns from a long trip.
The challenges of keeping the battery
charged have led to a surge in sales of
compact battery chargers/maintainers
from vendors such as Deltran (Battery
Tender), Noco (Genius 26000) and others meant to keep batteries at full charge
but also charge a dead or near-dead battery. They’ve long been popular with
collectors who may not drive a car for a
month or two but want the battery always charged. They cost $25 to $200
and are more compact than traditional
end-user chargers.
In addition to the traditional
red/black alligator clip leads, most also
provide permanent connections via
leads that attach to the battery cable
bolt. It’s a quicker, simpler (and to the
16
March 2016
owner, safer) task to mate the two halves
of the charging cable and its fits-onlyone-way plug ends, then attach the
charger to the wall outlet. There are also
10- and 25-ft. cables that eliminate the
need to string the charger to the vehicle
via a 120V extension cord.
Also growing in popularity are lithium-ion (Li-ion) battery packs the size of
a paperback book, with enough juice to
jump-start a car five, ten or 20 times.
They’re consumer-friendly, with polarity
protection and short circuit protection
(accidentally touch the alligator leads
and no power flows), one or two USB
Vehicles with good batteries can still go
dead sitting one to two weeks from always-on electronics (telematics, door unlock receivers, etc.). Owners should consider a battery charger that’s safe to
leave attached for extended periods.
jacks to charge smartphones, plus an
LED flashlight. For shops, these may be
items that could be sold to customers at
the time of a battery replacement.
The dual 12/42V electrical system was
a hot topic 20 years ago, as automakers
geared up to shift power steering and air
conditioning from belt drive to electric
motors. A 1996 SAE paper envisioned
the system being in use circa 2005. It
died over concerns about shorts and arcing of contacts, while automakers developed motors that worked well at 12V.
Now 42V is back as a proposed
12/48V system, and this time the impetus is for low-emissions hybrid vehicles
ditching high-voltage Li-ion or NiMH
traction motor batteries for leadacid/lead-carbon batteries powering the
motors on mild hybrid vehicles. Alistair
Davidson, speaking for the Advanced
Lead Acid Battery Consortium (ALABC), said, “The low additional cost of
introducing 48V mild-hybrid power-
trains is continuing to attract automakers
because it is the most cost-effective
means of complying with stringent CO2
regulations over the next 10 years.” ALABC contends such vehicles would cut
CO2 emissions by 15% to 20%.
The Kia Optima T-Hybrid concept
combines a 1.7L 4-cylinder engine, a
15-hp electric motor, a 48V lead-carbon battery and an electric supercharger, with more horsepower, torque and
16% less CO2 than a gas-engine Optima. The motor would get the car going
from a standstill.
The Advanced Diesel Electric Powertrain (ADEPT) combines a small
diesel engine and a 48V electric turbine that also captures exhaust waste
for conversion to electricity.
Delphi envisions that all belt-driven
devices except the alternator would be
driven by the 48V system—HVAC
compressor, power steering pump and
coolant pump. Christian Schäfer, Global
Director of Advanced Electrical and
Electronic Architectures at Delphi, said
times have changed in 15 years: “The
main driver is the carbon dioxide
threshold of 95 g/km fleet average in
2021 across the European Union. The
idea is that we have a mild hybrid, so we
don’t need high-voltage on all cars because it is too expensive to implement.”
The starter/alternator could be used for
“e-boost” on front-drive cars.
Long-haul (Class 8) trucks are starting
to use ultracapacitor (or super capacitor)
batteries to supplement the common set
of four 12V lead-acid batteries used for
starting as well as hotel power, or the
needs of the truck when it’s parked away
from shore power (a power line at a
truck stop). Maxwell Technologies, a
main supplier, calls the capacitor batteries ESMs, or engine starting modules.
They provide a jolt of energy for seconds, not minutes or hours, to crank
over the big diesel engines.
The module looks like a truck battery, but it’s packed with capacitors,
which have no significant longevity issues. Kenworth and Peterbilt have begun to use ESMs on some of their
trucks. Cost will be an issue for passenger cars, at least initially. A replacement Maxwell capacitor battery runs
on the high side of $1000.