pic: A little teaser from 3571

[philso]

Originally Posted by TheThings

(this is the Electrical lead): By running the pwm signal wires next to large motor wires that could potentially have upwards of 40 amps through them, you risk electromagnetic interference across the pwm. For this reason we like to run our pwm cables as far away from our power cables as possible, and where they have to come near each other, we cross them at a 90 degree angle. This prevents the magnetic fields on the power cables from interfering with pwm communication.

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This is standard practice in industry and is described very thoroughly in literature on Electromagnetic Interference.

Originally Posted by Caleb Sykes

Anecdote: I have never had a problem when routing PWM wires and power wires together.

The PWM signals are "digital" and have a large noise margin, by design, and their response to noise is non-linear. Increasing the amount of noise induced on your PWM wires will not cause noticeable degradation in performance until you have used up all of your noise margin. Shifting your wires around may change the coupling enough to start causing a problem. Been there, done that, had to write reports about it, didn't get a T-shirt for it.

Originally Posted by Caleb Sykes

Physics Note: Even if the magnetic field were substantial, routing PWM wires parallel to power wires should not have an appreciable effect on signal, since the magnetic field would only cause a Hall Effect on the signal wires. That is, the magnetic field would not speed up or slow down the electrons, it would just shift the electrons to one side of the wire or the other.

A current in a wire WILL induce a current in a wire that is parallel to it. That is why it is standard practice in industry to avoid running power wiring and signal wiring together, in the same bundle. Please DO route your signal and power wires separately for this reason.

You are correct in thinking that the Hall Effect is insignificant in situations like this. I have never seen any mention of it in any literature on Electromagnetic Interference or in any of the many courses my employers have paid to have me attended on the subject.