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Wrong CAN termination resistor?

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DarioP
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Wrong CAN termination resistor?

Hi,

I noted that in all the available schematics --> https://vesc-project.com/node/311 the termination resistor of the CAN bus is 220 Ohms, however it should be 120 Ohms.

Am I missing something or has it been overlooked?

Thank you

 

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frank
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220 is totally fine. If you have 4 units it will drop to 55hm ( 220Ohm/4). That is already very low.  With 120Ohm you could only couple 2 units.

DarioP
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Thank you for your clarifying answer.

I was thinking about the high-speed CAN where the bus is terminated at both ends and the nodes have no resistance, but now I understand that VESC implements the low-speed CAN, where each node is comes with its own termination resistor and where the total resistance should not be lower than 100 Ohms.

Cheers

frank
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It is a general problem of CAN. If you place no termination resistors, people forget to place the resistors on the cable and run into trouble. If you place them, you might need to de-solder some resistors. In most setups we don't have that many CAN devices (bike, skate, monowheel, rc car etc.)  and with 220OHm the systems work. Once you surpass a certain number of CAN devices ( quadcopter, complex robot etc.)  you have to de-solder some termination resistors. People building such complex systems typically are skilled enough to do that job.