# CAN Bus wiring with BMS



## sourcefinder (Dec 17, 2010)

Hi,

I use 160 cells LiFePo 100 Ah on two Orion BMS Units.
In this case both units communicate via a CAN Bus.
Each unit has two CAN Bus Systems, CAN1 and CAN2.
I set up one unit as master and one as slave.
They are connected like shown on the attached drawing.
CAN1 is terminated inside the bms units, CAN2 has no termination, so I need the 120 Ohm resistor.

Everything works right, but when the units are online for a while, they produce a CAN message error. The time when this occurs is different, sometimes after some hours, sometimes after some days.

Anyway, when the error occurs the bms stops balancing (but all other operations are ok and I can connect it also with the can adapter) and I want to balance cells as long as the vehicle is in winter storage....

Anyone of you and idea how to make the CAN Bus more stable?
Is it important to make the wires in a special length?
Or do you think I should check the soldeirng points?

Thank you,
Best Regards
Hermann


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## CKidder (Dec 12, 2009)

After looking at your attachment I am surprised it worked at all. I think you might be misunderstanding how canbus works. For each canbus port you have a high and a low pin. They are usually referred to as CANH and CANL. Between these two pins must be termination at both sides of the bus. Otherwise, all devices on the bus have their CANH pins connected together and their CANL pins connected together. You probably want to just use CAN1 H and L on both units. Since they are both terminated you have the proper amount of termination on the bus. That is, you do so long as nothing else on the bus is almost terminated. 

But, if you still have problems after that then try to make sure that your H and L bus lines are twisted together and kept as far away from power wires as possible.


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## sourcefinder (Dec 17, 2010)

Hi CKidder,

Thanks for your reply.

The units have to be connected via CAN2 from the master-unit and CAN1 from the slave unit. The CAN1 from master unit is used to transfer battery data to the display. 

All CAN1 ports are terminated inside the bms units.
All CAN2 ports are not terminated and need the 120 ohm resistor.

This is what I have done like it is shown in the drawing.....

Thank you,
Best Regards
Hermann


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## peterguy (Jun 18, 2012)

Hi Hermann,

each CAN Network needs two Termination resistors, not only one.

A simple way to check the Termination of the Network is to take a multimeter and measure the resistance between the CAN lines (CAN High and CAN Low). The measured value should be around 60 Ohms.

Which Baudrate do you have configured for the CAN Busses? The faster it is the less robust your Network will be. If possible I would always try to avoid 1MBit.

Regards,
Peter


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## peterguy (Jun 18, 2012)

Ah, and one other important thing is that the wires must be twisted pairs!


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## frodus (Apr 12, 2008)

As mentioned previously, the Orion BMS has a termination resistor inside the device on CAN1. He only needs to provide one more termination resistor.

http://www.orionbms.com/manuals/pdf/bms_series_manual.pdf

The 2 wires for CAN need to be twisted pair, and be twisted right up to the Orion. The termination resistor goes right at the CAN2 terminal. Keep Baud at 500K or below and don't put on a CAN bus with anything else, just those 2 units.

Hermann,
Did you configure per that manual?


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