Quote:
Originally Posted by Al Skierkiewicz
To back up Alan and Oz, the termination of the CAN bus has more to do with transmission line theory than anything else. A typical twisted pair of #22 wire with approx. 1/3 turn per inch has a stable impedance (above 1 kHz) of about 60 ohms.
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There's a bit more good info here than just how to pick a terminating resistor. While it's always best to keep any wire run as short as possible, there may come a day when you want to use CAN cable runs that are longer than the motor controller pigtails. When you do, try to match those same size and twist count specs as they use. An easy place to find 20-24 AWG pairs with 3-4 twists per foot is in a CAT3 cable; these are mostly easily found as telephone station wire. Matching the diameter is also about not reflecting signals, and the twists serve to reduce the size of the "loop antenna" which causes parallel runs of data cable to radiate signals out, and accept other signals in. (Don't untwist your motor controller CAN cables.) Finally, to minimize reflections, use connectors designed for approximately #22 wire - do not use power connectors like Andersons or Molex.