RF/EMI Test Setup for EV Shop???.......... - Page 1
Forum section: electronics / projects

author: Smokey
author_rank: Super Contributor
timestamp: March 27, 2025, 06:46:58 am
content: I'm looking to put together some EMI test gear for a shop that works with Electric Vehicle Conversions.The idea here is that this test setup would help troubleshoot noise issues primarily in low voltage cabling for communications busses like CANBus and other high speed data busses in the vehicles that connect various components. It's one thing to say "do proper grounding and keep stuff separate" but without some means of measuring the effects you are kind of shooting in the dark and that's frustrating. They occasionally also have to troubleshoot other shops work and it would be nice to zero in on noise issues directly with a measurement. While I've occasionally played one on TV, I'm not really an RF guy, and they certainly aren't. It's not for CISPR compliance, it's just troubleshooting. So a bunch of high end Keysight stuff would probably be overkill. But it probably does deserve something better than a TinySA.The main EMI offenders are:1) Inverter/Motor: 3-15kHz switching at many hundreds of amps (750A Peak, 225kW even through it's not typically running that hard)2) DC/DC Converter: Unknown switching frequency. Bucking battery voltage up to 400V down to 12V for all the 12V stuff. 1.5kW.3) OBC Charger (not fast charging): Unknown switching frequency. 6.6kW4) Various pumps and compressors in the 20A range.Stuff to get:1) Spectrum Analyzer2) Clamp on RF Current Probe3) Near Field Probes4) ?I figure a SSA3021X Plus will be fine for the spectrum analyzer part of this. If for some reason it needed to go for a ride in the car, they can power if from a mobile power pack or something. Tell me if I'm wrong here.Question: What RF Current Probe would you recommend for this type of stuff? A clamp on type is greatly preferred, but I'm not sure exactly what frequency range would be optimal, or if it really even matters for this usage. Would this 250MHz be fine or should I look at the 500MHz?Tekbox TBCP2-250 :https://emcsupplies.com/collections/current-monitoring-probes/products/tbcp2-32mm-snap-on-rf-current-monitoring-probe-up-to-750-mhz?variant=37926266765496What else am I missing? Are there any other special considerations for the setup given the EMI situation of a 200kW motor/inverter?

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 27, 2025, 11:02:00 am
content: You would probably find an active current probe more useful than a RF current transformer. Something like a Tek A622 (I'm sure cheaper options exist). I'm assuming you'll often be needing to sniff for RFI on power distribution, and passive current transformers will saturate with just one or two amps of current, making them fairly useless for power distribution. An option with built-in AC coupling might be useful too (since you probably don't want the low frequency currents to eat up the dynamic range of your scope/SA).A rogowski coil might also be worth considering, especially if you want to probe in places where a bulky current probe wouldn't fit (like busbar and such).Some basic differential probes would certainly come in handy as well, something similar to the Tek P5200 (lots of cheaper clones of these exists, I think there might be some eevblog-branded ones?).

author: Smokey
author_rank: Super Contributor
timestamp: March 27, 2025, 06:53:23 pm
content: I already set them up with the high current stuff. Both rogowski and hall probes up to a couple thousand amps. But only at lower frequency.This inquiry here is specifically about EMI on data cables.

author: Kasper
author_rank: Frequent Contributor
timestamp: March 28, 2025, 05:33:22 am
content: This worked for me on a much lower power project. Having a few sizes was particularly helpful. Was fine with FFT on Rigol DS1054Z but a lower end Siglent SA was a nice upgrade.EEVblog #1178 - Build a $10 DIY EMC ProbeYouTube · EEVblogFeb 7, 2019

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 28, 2025, 07:28:47 am
content: A modestly priced professional grade hand held analyzer is a much better option than a main powered SA. I have an earlier model of these TTi units:https://www.aimtti.com/product-category/spectrum-analyzersI don't know about probes, you would need to source them elsewhere or make your own. FWIW it is easy to make a pickup loop on the end of a piece of coax and search with that, or for E field pickup a short piece of insulated wire around 6 inches long.SJ

author: Smokey
author_rank: Super Contributor
timestamp: March 28, 2025, 08:55:48 am
content: I only really added near field probes since they are cheap, and yes a coax loop works fine. But I know where the noise is coming from. It's the inverter and motor.If I was to make an analogy, it would probably be like trying to have a conversation in the middle of a rock concert. 200kW high frequency switching is going to be everywhere.

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 28, 2025, 11:40:13 am
content: Quote from: Smokey on March 27, 2025, 06:53:23 pmIf you're limiting yourself to observing EMI on "victims" (i.e. data/signal cables), then passive current transformers should be ok (but I would make sure it can tolerate at least an amp without saturating).Might be worth getting some very small ones for probing individual wires in bundles. In the past I made DIY clamp-on probes by winding a few turns of wire or coax through aclamp-on cable ferrite like this.I typically don't find "near field probes" useful for troubleshooting EMI, unless you invest in a means to position them in a very repeatable manner. That means not just waving them around by hand, but giving each their own holder (like a Noga indicator holder). Electric field probes in particular are difficult to get consistent readings from, as they depend much more on cabling/grounding.