AM (MW) Band And Electric Vehicles: Should We Worry? (Pt. 2)

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.

Are car manufacturers telling the truth? Is MW reception impossible in an EV?

Hard to say. I think MW reception is possible, provided enough shielding and clever location of the antenna. My guess is that many EV manufacturers have dismissed MW as an obsolete media platform just like CD players. Although I’m a keen MW DX-er myself, I think they’re right.

The lack of AM reception is a US, or North American issue. Lawmakers in Europe will never engage themselves. FM and DAB will be the choices for terrestrial broadcasting for the foreseeable future.