question

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Martyn Duerden asked

BMV RS232 interface

Hi all,


I have a fully operational new system but currently without monitoring.

Multiplus 2 48v, BMV 700, automation system


The bmv has a 4 pin serial port on the rear.


5v, Rx, Tx, Gnd.


I have the victron cable 9pin rs232 to the BMV


In the said cable there is circuitry in the 9 pin end, the other end is sealed. see photo.


Questions


1; Are the electronics in the lead converting VE bus signals to RS232?

2; Is the output from the BMV’s Rx, Tx, & Gnd standard RS232 protocol or proprietary and only RS232 after the electronics?

3; Does pin 1 on the BMV need 5v or is it supplying 5v?

4; Is the Gnd common to signal & the 5v line?

Multiplus-IIBMV Battery Monitor48v batterybmv
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2 Answers
wkirby avatar image
wkirby answered ·

1) No, there is no VE.Bus here. It is VE.Direct. That cable is converting VE.Direct (3.3V TTL) to RS232. It is isolated (Si8422 I think).

2) The output from a BMV is standard 3.3V TTL, not RS232. That cable converts TTL (3.3V or 5V) to RS232 (probably a MAX232 on the other side of that PCB???).

3) Pin 1 is supplying 3.3V (I think it is 10mA max). This voltage is needed to supply the BMV's side of the digital isolator (Si8422).

4) GND is common on the BMV side of the interface cable. It is isolated therefore GND is not common on the RS232 side.

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Martyn Duerden avatar image Martyn Duerden commented ·

Thanks for the reply.


Sorry, I did mean VE Direct!

The manual suggests its 5v not 3.3, are you saying VE direct operates as Rx,Tx & Ground? I had assumed it was CAN (Hi/Low) without Ground.


The issue at the moment is when plugged into an RS232 device there is no data stream, any thoughts?


Thanks

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wkirby avatar image wkirby ♦♦ Martyn Duerden commented ·

VE.Direct is TTL serial Rx, Tx and GND. It depends which manual you were reading. BMV's are 3.3V and MPPT's are 5V. The digital isolator is inherently a TTL Voltage level shifter too.

Now, on the 9pin side it's going to need to be powered in some way via the port. If you are expecting anything to come out of it between GND and Rx, then that won't happen on its own. The electronics need powering up on the RS232 side, probably by the DTR (pin 4) or RTS (pin 7) or something like that- difficult to say without seeing it in the flesh.

EDIT: I had another look at your picture, there is a track coming off pin 4 going to that giant capacitor?? That is most likely the pin powering the RS232 side of that converter.

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wkirby avatar image
wkirby answered ·

The BMV just sends a data stream, there is no configuration. You can see the data pulsing out the back of the BMV with just a multimeter over pin 1 (GND) and 3 (Tx).

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Related Resources

Additional resources still need to be added for this topic

MultiPlus-II Product page 

MultiPlus-II Manual

Multiplus-II GX Online Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes