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Thread: Evohome Hot water problems

  1. #51
    Automated Home Legend paulockenden's Avatar
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    There's something odd about the CS92A and particularly the comms side and the way it interacts with the controller because several times now people have reported here suddenly getting errors on multiple (radiator) zones as a result of low battery in the CS92A.

    If that had happened once I might consider it to be fluke or user error but I can think of at least three reports, possibly more.

    The CS92A shouldn't affect radiator comms at all, but it does.

    It does, however, suggest that the problem might lie in the controller rather than the CS92A itself. Or perhaps a bit of both.

  2. #52
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    Mine is a strap on sensor. Installed 5.25 years ago but as reported no real issues. However, there have to be problems as too many other people report such.

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    Quote Originally Posted by paulockenden View Post
    There's something odd about the CS92A and particularly the comms side and the way it interacts with the controller because several times now people have reported here suddenly getting errors on multiple (radiator) zones as a result of low battery in the CS92A.

    If that had happened once I might consider it to be fluke or user error but I can think of at least three reports, possibly more.

    The CS92A shouldn't affect radiator comms at all, but it does.

    It does, however, suggest that the problem might lie in the controller rather than the CS92A itself. Or perhaps a bit of both.
    I am using an arduino/CC1101 to monitor the messages and simply don't see messages from the CS92A when it stops working. If the issue was controller related, I would have expected the messages to continue to be sent by the CS92A?

  4. #54
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    Quote Originally Posted by paulockenden View Post
    There's something odd about the CS92A and particularly the comms side and the way it interacts with the controller because several times now people have reported here suddenly getting errors on multiple (radiator) zones as a result of low battery in the CS92A.
    I've never had a low battery alert from my CS92A because I always start having a lot of problems with the sensor long before the batteries get low enough to trigger a low battery alert. I don't even know what voltage the alert is sent at...
    If that had happened once I might consider it to be fluke or user error but I can think of at least three reports, possibly more.

    The CS92A shouldn't affect radiator comms at all, but it does.

    It does, however, suggest that the problem might lie in the controller rather than the CS92A itself. Or perhaps a bit of both.
    If the effect is real the only explanation I can think of is when the voltage gets to a certain low threshold the radio in it starts going crazy and sending out lots of broadcasts, colliding with other devices.

    We know that when the CS92A powers on / boots up it immediately sends a temperature reading. We also know that the spec for comms on this frequency range state that each device must transmit with a very low duty cycle - less than 1% of air time from memory - to keep collisions at a minimum.

    As part of that it's required that each device keep track of how much air time it has used recently (in the last minute ?) and refuse to send any further packets if it has exceeded its allocation for that time period, and not transmit again until the next time period - we know the HGI80 does this for example - if you send it too many commands in too short a time period it will refuse to send some over the air to adhere to the limits.

    However imagine that the battery voltage is teetering around a threshold where the device shuts down and powers on again - every time it powers on it probably forgets how often it has sent recently, sends a temperature broadcast, as part of sending that broadcast the power drain on the low voltage high resistance cells drops the voltage below the threshold and it shuts down again. When it shuts down the voltage rises again and it boots up again. Repeat ad nauseam and you are suddenly sending a continuous storm of broadcast messages without regard to air time limits. This would absolutely cause problems with all other Evohome devices at the property and is essentially a form of denial of service "attack".

    If this is really what happens it would be easy to prove it with something that could monitor the over the air messages. Just a theory, but it's at least plausible. It could be something as simple as insufficient hysteresis in the power management / reset control of the SoC which decides at what voltage the device shuts down or boots up. If the hysteresis is too small in relation to the impedance of the depleted batteries and the load drawn by the transmitter it would cause an oscillation that resulted in continuous reboots.
    Last edited by DBMandrake; 31st January 2020 at 05:01 PM.

  5. #55
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    And another 3+ hour outage of the hot water sensor tonight resulting in an error on the screen and no hot water reheat. Take the battery out and put it back in - instant temperature reading. Getting a bit boring....

    Trying to resist the urge to rip the CS92A apart before my NanoCUL arrives..
    Last edited by DBMandrake; 1st February 2020 at 06:22 PM.

  6. #56
    Automated Home Legend paulockenden's Avatar
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    Probably a silly/annoying question but have you tried another battery?

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    Quote Originally Posted by paulockenden View Post
    Probably a silly/annoying question but have you tried another battery?
    You must have missed the posts where I said I swapped in brand new Energizer Lithium Ultimate a couple of days ago...

    If anything it made things worse, although I suspect the physical disturbance of the battery contacts is the reason, not because there's anything wrong with the new batteries. (which there isn't)
    Last edited by DBMandrake; 1st February 2020 at 10:56 PM.

  8. #58
    Automated Home Legend paulockenden's Avatar
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    Ah, sorry, too many things to read.

    It’s just that sometimes you're so close to something you overlook the obvious. I’ve done that FAR too many times.

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    I know, you shouldn't need to do this, but, do you want to try soldering a double battery holder directly to the PCB and see if that helps.

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    Quote Originally Posted by bruce_miranda View Post
    I know, you shouldn't need to do this, but, do you want to try soldering a double battery holder directly to the PCB and see if that helps.
    It's certainly something I'm willing to try at some point further down the line, and would certainly rule out or implicate the battery connections depending on the result.

    But first I'd like to try to capture some over the air traffic while it's misbehaving, so I don't want to touch it any further until I can do that. It seems to be playing up semi-regularly at the moment (even when I don't get an overt fault warning, I see from my graphs that almost every day updates are erratic and sometimes very delayed) so that seems like a good time to do some traffic sniffing and gather some hard data.

    I have a spare Raspberry Pi 2 which I could set up as a dedicated 24/7 monitor with the NanoCUL, that would allow me to correlate logs from that with my temperature graphs and fault log... the only question is where to position it in the house. It's currently in the TV cabinet which is not a good place to ensure good reception as there is too much interference and too many other wireless devices near it.

    However if I put it elsewhere the Pi itself would need to be on wireless, and the close proximity of its wireless transmitter might interfere with reception, so still trying to decide how and where it set it up.
    Last edited by DBMandrake; 2nd February 2020 at 09:18 AM.

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