Forum » Practical Harness Construction - Club Level » Shielded wire

Shielded wire

Practical Harness Construction - Club Level

Discussion and questions related to the course Practical Harness Construction - Club Level


Page 1
Author
108 Views

Could shielded wiring be used to help avoid interrupted signal from say a high output coil? ( Harley coil). I’m not sure if anyone on here is familiar with motogadget products, but I’ve used one of their products called M-button which configures all the handlebar control wires into a single wire back to the M-unit blue (ecu/magical fuse box). I have not seem to have an issue installing this on other bikes, until I tried it on a Harley, from what I’ve gather from other sources. Is that the high output coils will interrupt the signal from the m-button to m-unit, causing the munit to completely shut down. M-unit controlls everything electrical on later model bikes.

Yes, a shielded wire will send the interference to ground, therefore avoiding it to mess with the signal of your button/control unit.

I will suggest a different theory than Frank. Interference from the ignition system is more commonly EMI (magnetic based) rather than electrical. Shielding will not help reduce magnetic interference. OEM's typically take pretty good precautions to minimise EMI effects so if the bike is stock I'm surprised that you have an issue. If some part of the ignition system has been changed however then the chances are higher.

The first thing I would do is confirm it has the OEM specified resistor spark plugs and resistor leads, these two alone make a huge difference to the magnetic flux generated.

If plugs/leads look ok then I would look to see if there is any way to reduce the Hv current loop, if not already fitted you could add a capacitor/supressor/condensor to the coil power supply which will shorten the loop path and check other factors such as the coil secondary is grounded to the cyl head.

Andy Wyatt does a decent job of explaining the theory in this video: https://youtu.be/ZTDsm6b69Lk (relevant bit starts about 6:00).

Thank you Adam! This is an interesting video that I was not aware of. I didn't know OEMs were working that hard to reduce magnetic field into the engine bay.

Everywhere you will read that shielded wire will prevent EMI (electromagnetic interference). I agree that what they can't help with, is magnetic induction. This is the principle that explain why a voltage get induced into a conductor when it is in the presence of a moving magnetic field (the term moving is important, either you need to move the magnetic field, or the conductor inside the field).

When current flows into a wire, it creates a expanding magnetic field, then it stabilize in proportion of the current flow, and when it stop flowing, the magnetic field collapse. Pulsed DC (like in an ignition coil sytem) will create that moving magnetic field. To amplify the strength of the magnetic induction, you can use a metallic core (like the toothed wheel with a reluctor sensor setup), and/or you use a winding of the conductor you want to induce the voltage into (the more conductor that picks up the field, the more voltage getting induced... like a transformer, or an ignition coil primary/secondary).

So my question is, is there really enough magnetic field into a engine bay to induce a enough voltage into a single conductor wire so it can mess with signal from a button (M-Button probably use really low signal I guess...)? I am guessing that close to where the magnetic fields are produced (like the coil winding) there could be enough, but I always thought that besides that, the magnetic field weren't that strong and probably decreased too rapidly to get picked up.

Finally, for the OP, a super easy way to reduce the effect of magnetic induction, is running your wire perpendicular of the magnetic field (less area to pick it up). If you can do that, it would probably solve any problem related to that.