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Old 3rd February 2009, 23:53   #1
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Default Suggestions to shield wiring from magnetic fields

I have setup a standalone ECU on a custom build of mine. Now it involves a custom wiring harness with a lot of wires. For fueling, ignition, charging, misc inputs and outputs. The build is fairly small in size, so cabling space is limited, so a lot of wiring is bundled up together.

I faced a peculiar problem today. There is serial communication cable that I hook up to my laptop to access the ECU. With the engine off, it connects perfectly, lets me run diagnostics, setup, make changes etc. However, when I'm running the software with the engine running, after a while the communication is invariably lost. This happens after 2-3000 rpm. This issue never occurred when we ran the engine on the test bench. Where we had a lot of space to route the cabling.

I spoke to tech support for my ECU and they are pretty sure it needs EMF shielding of some sort due to magnetic fields causing noise in the communications cable or the USB-Serial converter. I would like to now what sort of DIY magnetic shielding I can do for the wires locally. I see a lot of options on the internet but I'm not sure I would have access to them here, financially or otherwise.

Also, if noise due to magnetic fields is such an issue, how can I be sure it's not affecting my signals to actuators or my signals from my sensor pickups?
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Old 4th February 2009, 00:01   #2
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Use a pseudo coaxial cable routing. Wind one wire around the cables and ground that single wire. This will act like a shield.

Also it is a wise idea to not have higher current/power cables near to these digital lines as they create havoc.
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Old 4th February 2009, 00:12   #3
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HDD and some electronic components come in static shielding bags. Will those work?
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Old 4th February 2009, 08:56   #4
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Did you tried using ferrite cores ? You can find these ferrite cores from old branded PC, cables etc. Google gives a clear view of how these cores look

ferrite core - Google Image Search

Using coxial as vid6639 said is a must.
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Old 4th February 2009, 09:01   #5
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Quote:
Originally Posted by ported_head View Post
HDD and some electronic components come in static shielding bags. Will those work?
Not really, those are used to protect against static discharge not EMI.
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Old 4th February 2009, 09:33   #6
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Usually aftermarket ignition system tend to interfere with standalone ECU & probably the root cause for EMI interference. A proper grounding along with shielded cable is essential for such kind of setup, you can also try installing noise filtering capacitors to some vital input signals being fed to ECU from various sensors.
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