# CAN bus wiring - what size and type?



## Tyn245GL (Oct 12, 2009)

I need to wire my Brusa charger CAN bus to my Lithiumate controller CAN bus. What type of wire/cable should I use? Twisted or not twisted? Will 0.5mm2 be sufficient? Can I use regular UTP Cat.5 data cable?


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## Astronomer (Aug 7, 2008)

It should be twisted and shielded. Ground the shield at only one end to avoid ground loop interference. 20AWG or larger diameter will be adequate. You can actually buy CAN-Bus wire. It's designed to be 120-Ohm at the nominal baud rate, but adherence to that impedance specification pretty much goes out the window at the connection points since 120-Ohm connections aren't ever used by equipment that employs CAN-Bus. Consequently, pretty much any shielded, twisted pair wire 20AWG or larger will do.


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## Qer (May 7, 2008)

Astronomer said:


> It's designed to be 120-Ohm at the nominal baud rate, but adherence to that impedance specification pretty much goes out the window at the connection points since 120-Ohm connections aren't ever used by equipment that employs CAN-Bus.


Uhm... Not sure if I misunderstand you here, but the devices on the bus SHOULDN'T terminate the bus. There should only be two terminations on the bus, one in each end, and the devices themselves should be high impedance loads. Pretty much like old time coax Ethernet (but 50 Ohm termination).

ww1.microchip.com/downloads/en/AppNotes/00228a.pdf

See page 2, figure 3, for an example.


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## Elithion (Oct 6, 2009)

Tyn245GL said:


> I need to wire my Brusa charger CAN bus to my Lithiumate controller CAN bus.


See the Brusa to Elithion wiring diagram.



Tyn245GL said:


> What type of wire/cable should I use? Twisted or not twisted? Will 0.5mm2 be sufficient? Can I use regular UTP Cat.5 data cable?


Please see the controller installation instructions. It tells you what type of wire to use, and specifically about the CAN bus wiring. 



Tyn245GL said:


> Can I use regular UTP Cat.5 data cable?


That is not stranded wire. The instructions specifically say stranded wire.


Please do take advantage of the free Lithiumate tech support forum. If you bought from Evolve, please take advantage of their free tech support (phone or email).



Qer said:


> Uhm... Not sure if I misunderstand you here, but the devices on the bus SHOULDN'T terminate the bus.


Oh? Why not? As long as there are exactly 2 terminations, and they are at the end of the bus, who cares if the termination is physically inside the device or hanging loose on the wires? The CAN termination in the Lithiumate BMS can be turned on or off. The Brusa has no termination. 

For more info on building a Li-Ion pack, including on the CAN bus, see chapter 6 of the Li-Ion BMS book.


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## Qer (May 7, 2008)

Elithion said:


> Oh? Why not? As long as there are exactly 2 terminations, and they are at the end of the bus, who cares if the termination is physically inside the device or hanging loose on the wires? The CAN termination in the Lithiumate BMS can be turned on or off.


Yep, but the terminators should always be at the ends. Astronomers post gave me the feeling he that he meant that ALL devices should be 120 Ohm, which would bring complete havoc to the bus.

That the termination sometimes is bundled with a device is just a special case of the general rule.


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