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CANBUS cable

5683 Views 9 Replies 5 Participants Last post by  MemphisPapa, 
M
So I have been back and forth with a Chinese company (cough-BestGo-cough) about a charger that won't pick up the message to begin a charge cycle. My BMS is getting the CAN message and I can see the CAN message going to the charger. My BMS support has pointed out that not all CANBUS transceivers are created equal. I suspect that my cheap Chinese charger has a cheap transceiver and is unable to pick up the messages over my dirty cable. I have chopped the stubs to only 8" and have soldered all my wire connections. I have a BT scan tool that is working okay with Torque. All my communication with my BMS is over the CAN which works fine too. I can actually see the message from the charger that shows the communication failure. Does anyone have a special technique to build a solid CANBUS cable that might help resolve my cheap charger issue? Evidently, the charger won't work unless the CAN message is received by the cheap charger transceiver... lesson learnt, buy American.
Thanks.
dh
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S
Hello,

I assume the termination of the bus is done right (120 Ohms etc..)?
Do you have connected the ground to the charger or only CAN low and CAN high?
Do you have a scope to check the quality of the signal?
Are you sure the CAN Message to the charger has the right format (ID, DLC...) and the right data?

One twisted pair of an ethernet cable should work fine, if you don't want to buy a special CAN cable.
Don't route power cables in parallel to the communication wires.

Kind regards,
Tom
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M
I have 120 Ohm termination resistors at the physical ends of the cable. The cable is a shielded twisted pair of stranded 22. The connector at the charger doesn't have a signal ground, so only the high and low are connected. I tried leaving the shielding exposed to clamp in the back of the connector, but it didn't make a difference. I don't have an o-scope , but I suppose it is time to try and find one.
Does anybody have a technique to build the stubs off the main bus cable?
Thanks
dh
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frodus
I know there's some problems with Elcon... Maybe this is similar?

http://lithiumate.elithion.com/php/elcon.php
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S
In my opinion the best solution for the stubs would be a M12 T-Connector like that:
http://www1.lumberg-automation.de/main/common/serie_.asp?lang=eng&cat=3&ser=A11&cat3=_3
But than you need other cabling I think ;).
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S
frodus said:
I know there's some problems with Elcon... Maybe this is similar?

http://lithiumate.elithion.com/php/elcon.php
Click to expand...
"CAN module built before July 2011 cannot handle being on buses that contain more than 2 messages per second!"
-> Sounds bad. Maybe that is the reason why your charge only sends out error messages?
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M
I have an Orion BMS. All the messages on the bus are adjustable. I'll try reducing the messaging. The Torque scanner alone send out about eight though. Not exactly what I would call quality on the charger side for the CAN.


No change after I stopped all but the charger message. I'll find an o-scope, but I suspect a defective charger.
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mizlplix
After two such incidents with Chinese "Manufacturers", I NEVER buy from out of the USA. Period. Or I do without.

Be especially careful on FleaBay too.

Miz
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D
Semper Vivus said:
"CAN module built before July 2011 cannot handle being on buses that contain more than 2 messages per second!"
-> Sounds bad. Maybe that is the reason why your charge only sends out error messages?
Click to expand...
Two messages per second?!
What, did they write the software in interpreted COBOL? 500Kbits/sec is slow. Really slow. A good controller should be able to keep up with the maximum message rate.

CAN bus is used because of its robust signalling. If you have a resistor anywhere on the bus, even the wrong value in the middle with all lines as stubs, it will probably work. Almost all transceivers are acceptably good. The ones with integrated isolators have a bit of a bad reputation, and even those only very occasionally drop a bit. If you have two nodes communicating, look elsewhere for the problem.
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M
2
I found an o-scope. Here are the images (High and Low). I physically cut my CAN cable, stripped the wires, and soldered them all together. I used electrical tape to keep them separate. I did my best to keep the twist going. I also ensured the electrical connection of the shielding. It has been a while since I used on o-scope, but I think this is the expected result.

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