Further to my June 17 post, I've done some tests with my own car.
What are the main components that differ an EV from an ICE car?
Now quite
obviously, EVs have a large pack of Lithium-Ion batteries with a 400V or (so
far less common) 800V architecture. Typical battery capacities vary between 40
and 90 kWh but can be higher or lower. A power inverter feeds an AC induction
motor, or a permanent magnet motor – or both in some 4WD/AWD cars. Permanent
magnet motors have become much more common in recent years. The main battery
also takes care of heating and cooling the battery itself, and climate control.
One added benefit for EV owners in cold climates is instant heating of the
cabin, in contrast to ICE vehicles where you must wait for the engine to warm
up first. It certainly makes a
difference in minus 25 Celsius.
Also, the
car has an on-board AC charger which allows the car to be charged from home or
work. The charger includes an AC/DC converter.
A standard
12V auxiliary battery takes care of all none-drivetrain functions and is
charged from the main battery.
So, where
are the potential noise sources with EVs compared to ICE cars? Well obviously,
the inverter is something to consider. The inverter will convert DC from the
battery to AC to run the motor and will also control the energy flow, either to
run the motor or recuperate energy back into the battery.
To be
honest I do not know how much RFI the electric motors themselves could emit,
and if so, which measures could be taken to mitigate the problem. This article may be useful to learn more about
electromagnetic interference.
My test
configuration tries to cover the following:
·
Car
in “Off” position.
·
Car
in “Wake-up” position – 12V systems are active, such as the infotainment system. This usually happens when the
driver approaches the vehicle with the “key” (it’s really more of a remote
control) or mobile phone or unlocks the car. Ventilation systems are also activated,
heater is drawing current from the main battery.
·
Car
in “Idle” position – all systems are active and ready to drive. Typically, when
the “On” button is pressed, or the brake pedal is activated and you can set the
car in D (drive) or R (reverse).
·
Car
moving – accelerating and decelerating.
Please
observe that manufacturers have chosen slightly different approaches to bullet
points 2 and 3.
Test configuration:
Car: VW
ID.5 GTX with 77 kWh net battery capacity, a permanent magnet motor for the
rear wheels (main motor) and an AC induction motor for the front wheels that
only engages during traction loss or full acceleration.
SDR:
SDRPlay RSPdx connected to and powered by a Dell Latitude laptop. IQ files from
HDSDR v. 2.81beta6 recordings are saved to an external SSD.
Antenna:
Wellbrook ALA1530 loop antenna. Powered by an external 12V battery, or from the
car’s auxiliary 12V outlet.
Frequency
range: Obviously RFI can occur anywhere in the frequency range. Since the RSPdx
has a limited range (and the laptop has somewhat limited CPU power), I will concentrate
on the 0 to 8 MHz spectrum. It makes sense also because the original subject
was MW reception in EVs.
External
battery: A 100Ah, 12V Li-Ion battery.
Reference configuration:
SDR, PC and
loop antenna powered from the Li-Ion 12 battery, set up kilometres away from
any potential noise sources, and at least 500 metres from the car (which was
shut down).
Test scheme
The
location was a five-minute drive from the KONG HQ, in a bay without anything
that could produce interference (at the marker):
Test 1: (stationary at the
KONG HQ): Is the in-car 12V power supply noisier than an external battery?
The short
answer is No. But charging does make some noise, particularly at sections above
the MW spectrum.
I first
tested with the external battery, the car in “Off” position and the ALA1530
loop placed around 1 metre away from the car’s rear. I then switched the car to
“Idle”. There was no difference in the RSPdx waterfall.
I then tested
with the internal battery. It will not supply power with the car in “Off”
position, so to use the in-car battery the car needs to be in “Wake-up” position. There was no
difference in the RSPdx waterfall from when I used the external battery.
I also enabled
charging to see what happened. At the KONG HQ, my charging is limited to
10A/2.3 kWh AC. I have no idea if a higher amperage, like 20A/4.6 kWh, would
increase the noise level. Anyway, the MW band was mostly but not entirely unhurt,
while parts of the SW bands were affected.
I didn’t
have the opportunity to test, but I assume that DC fast charging will be an
issue. You would typically sit in an area with lots of infrastructure and
multiple DC chargers from 50 to 300 kW. And with multiple cars charging. Knowing
what passing under a single high-voltage line does to your MW reception, I can’t
imagine how a DC fast charging station can be noise free.
Test 2: (driving from the KONG
HQ to the remote site)
This test
consisted of recording the 0-8 MHz bandwidth while driving from the KONG HQ to
the mobile test area. The 12V battery was placed in the front passenger foot
well, and the Dell laptop and RSPdx on the seat. The ALA1530 was placed where I supposed it
would take the hardest punch – partly on top of the motor and inverter.
So, I drove
ahead, 5-6 minutes, accelerated a bit (when you floor an EV, make sure your
head is on the headrest…) and decelerated to recuperate energy.
The waterfall
was not nice at all. It was obvious that the vicinity of the antenna to the
motor did produce a lot of noise. Deceleration increased the noise a bit, but
not much. Most of the noise was above 1.5 MHz though.
 |
| Figur 1 - Noisy? Ah...yes |
Test 3 (stationary at the
remote site, driving the car away)
At the remote
test side, I set up the loop like what I had done at the KONG HQ (test no. 1).
I then started the car and drove away some 500 metres before I returned. I did
not note any RFI from the car as it drove away from the antenna, and on its
return.
 |
| Figur 2 - Noisy? Noooo..... |
What can we learn?
This test
is no science, it is indeed circumstantial evidence, from a single EV user. I
did not test with an ICE car for comparison. Yet, I feel tempted to draw a few
conclusions.
1. With the antenna some distance away
from the motor and inverter, RFI did not seem to be a big problem. I’d assume
that with the antenna place on the roof, and with proper shielding, MW
reception should be possible.
2. Charging does make RFI. On my car it
did not affect the MW band much, but other cars may have different interference
signatures. At any rate, you usually do not sit in the car while charging.
3. RFI seems to have a very limited
range of distance, regardless of if the car is driving or standing still. This
seems to confirm findings from radio amateurs who have used EVs with V2L (vehicle
to load) capability to power amateur radio stations with 230V power from the
main battery on remote locations. My EV can’t do that.
