High reported C-Bus voltages

Discussion in 'C-Bus Wired Hardware' started by more-solutions, Feb 28, 2017.

  1. more-solutions

    more-solutions

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    I have one C-Bus switch reporting a network voltage of 41.1v.

    Since there's nothing on the network that should be able to provide that voltage, and since nothing else is showing anything that high (next highest is 37.1v, so still high but presumably within tolerance of the measurement capabilities of the units?), I'm assuming this is a unit fault.

    But is there something I should be worrying about here? For example, can failing powered units generate excessive voltages? The 37.1v is coming from a 4-channel Pro dimmer (ie a powered unit).

    Mark
     
    more-solutions, Feb 28, 2017
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  2. more-solutions

    tobex

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    There are capacitors in each of the CBUS modules and that may pump up the voltage. I would remove one of the power supply modules to see what happens.

    As a precaution, test the resulting network voltage when you power down each of the power sources and determine whether or not one power supply creates an unusually large drop when removed, compared to all of the others. In other words, systematically remove each power supply from the grid one at a time.
     
    tobex, Mar 1, 2017
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  3. more-solutions

    Wonkey

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    If you have the old white box PSU they can fail with a high voltage check the O/C voltage it should be less than 42V if its more then replace it with anew din rail unit.
    C-bus voltage should be 36V and soon drops as more units are added.
    I would check with a good digital meter the voltage at the unit in question and the PSU in a loaded state.
    Some PIR's are known to report high voltage and is nothing to worry about.
    I presume this install is not a new one given the fact that you have a 4 channel pro dimmer, hence is there another issue you have not mentioned causing you to investigate the voltage.
     
    Wonkey, Mar 2, 2017
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  4. more-solutions

    more-solutions

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    The installation is 10-12 years old, all DIN rail except dimmers. Very few power supplies (none on this network as far as I can remember), mostly powered relay units and dimmers.

    The switch was showing in error, so a diagnostic scan followed which showed the high voltage. It was intermittently impossible to load in TK but settled.

    I'm thinking replacing the switch would be a good first step as they're cheap (E2000 range). If the replacement shows a high voltage then investigate further. Does that sound sensible?
     
    more-solutions, Mar 2, 2017
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  5. more-solutions

    Wonkey

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    I would check the voltage with a multimeter with the key input connected and disconnected.
    you should see little voltage change, if this is the case and MM agrees with the scan then you have a psu problem.
    I expect from experience your multi meter will read a lot lower due to the fact you mentioned you had problems scanning the key input and therefore I presume you have poor comms.

    What other problems are you experiencing on this network

    Try the Key input on another network and see how it responds before buying a new one.
    Comms issues on networks that have been working are normally due to some physical change, building work causing cable damage, water from a storm, spare cables that is connected at one end and just insulated with tape at the far end, and has become damp.
    Post as much info as you can so the community can help and remember to answer the questions, because it takes everyone on a journey to helping you solve the problem.
    Colin
     
    Wonkey, Mar 3, 2017
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  6. more-solutions

    more-solutions

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    If possible I will try to get some voltage readings. (I'm not based on site so it has to tie in with a site visit, also it's an occupied area that isn't always easy to gain access to.)

    I'm certainly keen to investigate it properly but it might not be possible. Replacing the switch may be the only option I get (albeit that I can then still test the old switch back in the office).

    I am on site tomorrow and will see if I can get any useful diagnostic info then.
     
    more-solutions, Mar 6, 2017
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  7. more-solutions

    more-solutions

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    Update from site:

    I didn't get to check this last week but today have investigated with a meter, which reported a more normal 34v.

    We swapped out the switch, and the new switch is similarly reporting 34.1v via TK, so I think that points to an issue in the switch.

    Thanks for the info and advice, everyone!
     
    more-solutions, Mar 14, 2017
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