Xantrex XW6048 Reliability

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #32
    Re: Xantrex XW6048 Reliability

    more from up on the mountain.

    "Xanbus has never been based on RS485 hardware. CANbus has its own hardware layer.

    The XW Gateway communicates to the XW system components via Xanbus, and it makes that information available to the outside world through different Comm protocols. One of the options is to access the data through the Gateway's RS485 port which supports the Modbus protocol. To do this the WiPort on the Gateway needs to be removed. "
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #33
    Re: Xantrex XW6048 Reliability
    Dave Sparks wrote: »
    more from up on the mountain.

    "Xanbus has never been based on RS485 hardware. CANbus has its own hardware layer.

    The XW Gateway communicates to the XW system components via Xanbus, and it makes that information available to the outside world through different Comm protocols. One of the options is to access the data through the Gateway's RS485 port which supports the Modbus protocol. To do this the WiPort on the Gateway needs to be removed. "

    Thanks Dave ! Now I see !. (I think I do anyway)
    OK, so what they're saying is that "Xanbus" is still a CAN derivative and MODBUS is a separate method of interfacing with their gateway. I wonder why they went to all that trouble to do the work to make the modbus protocol ? What is it supposed to talk with ?? Supposedly, they did not want anyone to control their devices with the modbus.... Just monitor I guess.

    Maybe it was designed for some special customer ?

    boB
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #34
    Re: Xantrex XW6048 Reliability

    All I am thinking about is that it is Friday. Burnaby said to let you think about it...
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #35
    Re: Xantrex XW6048 Reliability
    Dave Sparks wrote: »
    more from up on the mountain.

    "Xanbus has never been based on RS485 hardware. CANbus has its own hardware layer.

    The XW Gateway communicates to the XW system components via Xanbus, and it makes that information available to the outside world through different Comm protocols. One of the options is to access the data through the Gateway's RS485 port which supports the Modbus protocol. To do this the WiPort on the Gateway needs to be removed. "

    Xanbus would be more reliable if it were based on RS-485 for the physical layer ...
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #36
    Re: Xantrex XW6048 Reliability
    boB wrote: »
    Thanks Dave ! Now I see !. (I think I do anyway)
    OK, so what they're saying is that "Xanbus" is still a CAN derivative and MODBUS is a separate method of interfacing with their gateway. I wonder why they went to all that trouble to do the work to make the modbus protocol ? What is it supposed to talk with ?? Supposedly, they did not want anyone to control their devices with the modbus.... Just monitor I guess.

    Maybe it was designed for some special customer ?

    boB

    CAN Bus is a multi-master bus -- which is a large part of the performance problems. In a single-master bus, the master knows when it's going to talk, so collisions don't happen and there's no arbitration. In a multi-master bus, it's possible for two masters to start talking at the same time. They have to detect the collision, decide which has priority, then the lower priority device has to shut up and listen, and try again when the bus is idle. The more devices on the bus, the greater the probability for collisions.

    Modbus =can= do multi-master, but a message to tell the current master to shut up would have to be sent by a slave so the "master" can turn around and become a slave. My recollection is that SMA's RS-485 / Modbus interface works this way -- a monitoring device starts off as Master, discovers the devices, then turns around and acts as a slave and snoops the bus while something else acts as master and drives the traffic needed for the monitoring device (and the rest of the devices) to get the data it requires.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #37
    Re: Xantrex XW6048 Reliability
    tallgirl wrote: »
    Xanbus would be more reliable if it were based on RS-485 for the physical layer ...

    CANbus physical layer and RS-485 are very similar. Beyond that, I don't really care about CANbus or its protocol very much.

    No need for it ~YET~ anyway.

    boB
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #38
    Re: Xantrex XW6048 Reliability
    boB wrote: »
    CANbus physical layer and RS-485 are very similar. Beyond that, I don't really care about CANbus or its protocol very much.

    No need for it ~YET~ anyway.

    boB

    Well ... they are similar in that they use electricity, but RS-485 reverses the polarity between D+ and D-.

    In my experience, buses based on differential signaling are far more robust than single ended. With UTP wiring, any voltage induced into D+ is also induced into D-, keeping the voltage relationship the same.

    Since CAN bus is single ended, any electromagnetic noise that induces a voltage into the data wire will cause a bit to be added or lost. And power generating gear is a very noisy EM environment. Which, in my half-baked opinion, is why Xanbus is cr@p.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #39
    Re: Xantrex XW6048 Reliability
    tallgirl wrote: »
    Since CAN bus is single ended, any electromagnetic noise that induces a voltage into the data wire will cause a bit to be added or lost. And power generating gear is a very noisy EM environment. Which, in my half-baked opinion, is why Xanbus is cr@p.

    Noise susceptibility to EMI is not always guaranteed. Noise immunity is not always guaranteed either of course for a bus with high CMRR.

    CAN bus CAN be single ended, but CAN bus is first a protocol and not necessarily a physical layer definition. However, CAN bus has from my recollection mainly been implemented as a differential mode signalling system. The usual CAN bus implementations do have a single ended fallback feature as well though, in case one of the HIGH or LOW signals get shorted to a single state. Most of the implementation is left up to the user.

    Single ended communications can be VERY forgiving with noise if designed correctly. Of course, the protocol wants to have some kind of error detection or FEC....

    See...
    http://en.wikipedia.org/wiki/CAN_bus AND ISO 11898-1 (2003)

    Doesn't really matter to me as I said. I'm not making car, truck or vehicle systems and the protocol is not all that inviting to me. It's "OK" I guess. About 11 years ago, at Xantrex, they were talking about Xanbus possibly being like CAN bus. Didn't excite me then either.

    boB
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #40
    Re: Xantrex XW6048 Reliability
    boB wrote: »
    Noise susceptibility to EMI is not always guaranteed. Noise immunity is not always guaranteed either of course for a bus with high CMRR.

    CAN bus CAN be single ended, but CAN bus is first a protocol and not necessarily a physical layer definition. However, CAN bus has from my recollection mainly been implemented as a differential mode signalling system.

    I thought someone posted that Xanbus was single ended? Obviously CAN can be implemented on top of just about anything (IP has been implemented using carrier pigeons, after all ...), but if Xantrex went with a single-ended solution and untwisted telco wiring parts (my recollection, the last time I was face-to-face with a Xantrex system), that would explain a lot. If it really is differential, I'm at a loss, other than CAN bus having issues with excessive traffic and collisions. Which seems to be the problem, based on my experiences (and those of others).
    Doesn't really matter to me as I said. I'm not making car, truck or vehicle systems and the protocol is not all that inviting to me. It's "OK" I guess. About 11 years ago, at Xantrex, they were talking about Xanbus possibly being like CAN bus. Didn't excite me then either.

    boB

    The motor, battery and instrument controllers in my motorcycle (Vectrix VX1) talk among themselves using CAN. That's more than enough extra CAN bus in my life ...
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #41
    Re: Xantrex XW6048 Reliability

    Xanbus is full differential ( by memory )

    Sounds like the issue is simply that devices are overly chatty and don't automatically back off the update rate when the bus utilization gets high, would be very simple to fix , well for me anyways :roll:

    The bus itself is very robust, fully differential and transformer isolated.

    I'm with boB, I didn't like it either and didn't get any brown points for saying so within Xantrex at the time. My reasons were there weren't and still isn't any low cost interfaces to PC's, where RS232 is 5 bucks.

    For all the work and money spent, they should have just used Ethernet but that's not the Xantrex way
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #42
    Re: Xantrex XW6048 Reliability

    SG,

    From what I've seen, "too chatty" is definitely a large part of the problem.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #43
    Re: Xantrex XW6048 Reliability

    Just ran across this app note about RS485 and RS422 that might be of interest to some here.

    http://www.bb-elec.com/bb-elec/literature/tech/485appnote.pdf

    boB
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