Electric motors and inverters are hell on AM radios. They create a lot of electromagnetic interference (EMI). Even though automakers want to get rid of AM radios in their EVs, EMI expert Joanna McLellan says they can fix the problem easily and cheaply. At times this gets technical but you’ll still get the gist of what she is saying.
Any product sold in the US is supposed to pass FCC part 15 prior to being offered for sale. I don’t get it. The 3rd party certification on the product in the system is supposed to catch it. How are the vehicles being sold ? In the EU, the CE mark covers this.
This is crazy!
Every electronic product has the FCC notice that none of us read. This should apply to cars too!
The motors drivers should have snubber networks to recirculate the currents in the small area to prevent the radiation.
Joanna is spot on. The schools teach theory and it takes getting your finger burned to really the learn the practical aspects. Joanna gives the speed of light as 1ns/ft. That is is the speed of light in a vacuum or air. In a circuit the speed is typically about 2/3 of the speed in vacuum which exacerbates the problem.
I am currently teaching a class where I work where I am exposing the recent graduates practical aspects of electronics. I have been told by several of the attendees “thank you, All I had in school was theory.”
A tool that Joanna didn’t mention that should be one of the fundamental ones to find the source of the EMI is a spectrum analyzers. Most will display the FCC limits; all will show the peaks of the frequencies that are escaping.
Thank you for having this interview.
Lance, is AM radio reception in Europe affected by EVs?
My brother’s comments: “We used to get interference from the Impulse generator and the easy solution is to place a small capacitor across the input terminals of the CRO. To make things work better you make up a voltage divider with a resistor in the incoming line and a capacitor between the lines. No trouble!
The assumption that the interference will disrupt mobile radios is no more problematic than hearing crackles from lightning. Because digital communications has error correction on the data when it is transmitted and received There should be no problems with SMS type messages. Because if there is a disruption of the number of digits being sent and the number being received, the message is simply sent again till there is agreement between send and receive.
It would be interesting for you to go for a drive in the big T and take an AM radio with you and see if it is capable of receiving the local radio station.
I saw a Police vehicle fitted with a radio transmitter that effectively turned off a car engine simply by interfering with the cars electronics. Heaps better than road spikes.
If you drive a petrol engined car under the bus bars in an Aluminium Refinery the magnetic field is so strong that all the metal cores in the cars electronics saturate and your ignition coils do not work. This is why they use Diesels in the refinery. ( once you saturate a magnetic core it effectively has no core )
When I was below the bus bar I could place a 12” shifter horizontally against a metal cabinet and the shifter would not drop to the floor but simply stand horizontally out from the metal door, only touching at one end. Magic hey!
The other thing about the lady’s talk was she used the capacitance of the windings of the motor to the steel stator. This is slightly incorrect as the troublesome part of the impulse wave , the front of the wave, which has a frequency of about 1 MHz and will not go through the windings , but around them via some other stray capacitance.
I have seen this happen to 11kV transformers when we were testing them. The front spike sails through then the lower frequency wave comes via the windings. Typically a 150kV impulse applied to the HV side, will produce a 15kV spike on the 240 volt side.
So things are not completely simple , but solvable.”
Not all products in the United States must meet FCC part 15 requirements. The automotive, agricultural and industrial equipment industries are self-certifying. These industries set their own limits without oversight by any governmental or private organization.
If harmful interference is experienced coming from a device produced by one of these self-certifying industries, people and organizations can file a complaint with the FCC.
Joanna, I really enjoyed this discussion and hope you continue to share your knowledge on Autoline (and with the automobile manufacturers). I started down the path of electrical engineering in the ’90s, and got as far as an electronics technician degree before switching to Radiology (which is also heavily Physics based). I found it interesting that back then, my Computer Program requirement included having to program a very basic computer packed in an aluminum attaché case with a numeric keypad and a small LED readout, whereas by the time I was taking the same titled class for Radiology, the class was essentially a Microsoft commercial, showing how to use Word, Outlook, and Accel!
My father was an electrical engineer trained in the Air Force based in Alaska during the cold war. He took what he was working on to the grave with him, so we don’t know what classified work he was involved in, but these discussions would have been right up his alley.
Sounds like we need to get some of his friends out of retirement to start re-teaching some of the old school electronics values. I am forwarding a link to the show to some of his buddies that I still talk to, but they are a dying breed.
I believe this would be a great show to have an included transcript, like you do for Autoline. I realize you don’t normally have that feature for the longer length shows, but there was so much helpful info. Maybe just an outline of the topics and Joanna’s answers?