Re: My device stops receiving when powered from battery

At some point the battery would fail. 
It would not be normal to plug infinite nodes into the system without causing a side effect. Every battery has a max current.

The external power worked because CAN Bus signal is differential (A-B) as well as RS-485 is also.
I already saw in a book (Jan Axelson) saying that on RS-485 the common GND must be next to the signals. In OBD-II interface, I see that the GND goes along too.
But I have already tested a RS-485 system without common GND and it worked, I do not know exactly how, it must have some protection mechanism that automatically balances the commons. 


> Sent: Thursday, September 27, 2018 at 7:09 AM
> From: FLJ <[email protected]>
> To: [email protected]
> Subject: [CANLIST] My device stops receiving when powered from battery
>
> Hello everyone,
> 
> as a software developer I'm completely perplexed by my current problem. I
> only have basic HW knowledge and I mostly follow HW diagrams designed by
> others. Until now I guess I was lucky.
> 
> I have an embedded device built upon an STM32 F4 evaluation board and I'm
> using a SN65HVD230 CAN tranceiver from texas instruments with it.
> 
> I have a battery powered system consisting of 3 CAN nodes using NXP TJ1051
> tranceivers, I don't have much detail about the MCUs used.
> 
> The system all alone communicates over CAN correctly as expected.
> 
> If I connect my device to the system's bus, while I power my device from an
> external power supply, everything works fine. I receive all the CAN
> messages I want to from the systems nodes.
> My device is configured in silent mode, I don't want to send anything.
> 
> As soon as I power my device from the same battery as the system, I stop
> receiving CAN messages. My device itself is working when powered from the
> common battery, meaning I can connect with the debugger to it, set
> breakpoints, etc.; only the CAN stops working.
> 
> I've read a lot about common-mode voltage in the past few hours, and about
> splitted termination, but I can't understand what the problem is. I
> would've rather expected or understood if the device wasn't working when
> powered externally, but everything on the same battery should've worked.
> 
> Can anyone help me out please?
> 
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