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Off-grid

Discussion in 'Plumbing and Central Heating' started by norseman, 11 Oct 2021.

  1. norseman

    norseman

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    It's been a few months since I posted on the subject of running a combi boiler off-grid & although the advice gratefully received didn't solve the problem I thought I would re-visit the situation with an update.

    To refresh memories ... just connecting the inverter to the boiler resulting in the pump running, but no real attempt to ignite & a 'flame failure' code.
    Grounding the earth connection on the inverter's casing to an adjacent earth on a 13A socket produced a couple of attempts to ignite, followed by the same fault code. On both occasions I needed to use the reset facility to restore normal boiler operation after switching back to the mains.
    Yesterday I made the same connection on the inverter to the earth in the boiler's terminal box & ignition actually took place (!) only briefly though, followed by the error code of E168 which is not even listed in the boiler manual. Interestingly in this latest of experiments it was not necessary to reset the boiler as it fired up immediately when switched back to the mains ... so near & yet so far :(

    Thanks for reading folks, any thoughts would be greatly appreciated. Winter is approaching & I want to be independent should the worst happen to the grid.

    Baxi Duo-tec combi
    Mercury IPS600-12 pure sine wave inverter
    110 AH leisure battery
     
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  3. oldbutnotdead

    oldbutnotdead

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    You might do better running the boiler through an inline UPS rather than the freestanding inverter. You could then power the UPS from the inverter setup or the mains, switching supplies while the thing is running if you so desire
     
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  4. norseman

    norseman

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    Thank you for your reply.

    I'm not really au-fait with UPS systems, but if a 4 year old boiler (or maybe it's safety features) has a problem with an alternative power source (inverter) would a UPS be any more successful ?
    I've long since considered a generator for off-grid (professionally wired into the home with a ATS/MTS) but would that power source result in the same problem ?
    Either way if I can't get the boiler to work normally any form of off-grid supply is not worth investing in.
    Your advice is appreciated.
     
  5. SFK

    SFK

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    Norseman,
    Summarising your issue.
    - When on mains 240V volts your boiler pump works and your boiler ignites.
    - When on 12V battery to sine wave inverter your boiler pump works, but your boiler does not ignite.

    So I question, does the ignition process need more 'something' that mains provides, but your inverter does not (for example a good sinewave to charge a highvoltage discharge capacitor).
    I do not know what that 'something' is for a boiler, but typical issues with inverters are:
    - Failure to provide a regular sinwave at any time (but you suggest you have a high quality device)
    - Failure to provide a good Sinewave at high loads
    - Current limited (resulting in issues with sinewave and/or voltage drop)

    So presuming you do not have an oscilloscope I would use a multimeter and during ignition I would test:
    1) Voltage output from Inverter - see if the voltage drops suggesting Inverter cannot cope with a (very short duration requirment) of a high load.
    2) and then current output from Inverter - see what current is being used by boiler during ignition and if it exceeds Inverter spec (although might be a too short a time for multimeter to detect).
    [Current testing with voltmenter has to be undertaken carefully to ensure no damage to the multimeter].

    Note that these same issues might also appear with a UPS as they also typically use an inverter.
    SFK
     
    Last edited: 12 Oct 2021
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  6. MeldrewsMate

    MeldrewsMate

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    This may be of only limited help....
    Several years ago I was called to a house where the Potterton Profile boiler (old technology, pre-condensing) would continuously spark at the pilot, the pilot would be lit, but the main flame solenoid would not energise. After several scratchings of the head and replacement of the main PCB I had to admit defeat. Two days later the occupiers rang to say that they were 'back on the mains' and the boiler was working fine. BACK ON THE MAINS? I didn't know they were off it! It turned out that at the time of my visit their whole street was on a Board supplied (large) diesel generator whilst maintenance was being performed....something they had omitted telling me.:mad::mad::mad::mad:

    The Potty Profile had flame detection via flame rectification, so if your Baxi also detects the flame via FR then it may also be sensitive to a less than perfect sine wave on your off-grid supply. Talk to Baxi about it.
    A solution may be to install a mains filter externally to the boiler or even, as suggested, a UPS. Your 'pure sine wave' inverter may be, in the words of Kim Carnes, as pure as New York snow.
     
  7. bernardgreen

    bernardgreen

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    I think the problem is due to the ignition circuit involving the metal work of the combustion chamber. Hence the spark current flows through the metal work of the combustion chamber to return to the EHT ( Extra High Tension ) voltage source from whence it came.

    If the spark current return the EHT source via Earth wires then the Neutral will be affected by high voltage spikes.
    If there is in-adequate Earthing Bonding to the power source ( 230 V AC generator ) Neutral then the spark may be reduced in size and unable to ignite the gas.

    If the EHT pulse generator feeds an isolation transformer then there is virtually no disturbance to the Neutral and an assured return path for the spark current,

    ignition earthed or not earthed.jpg

    Disturbances on the Neutral may be the reason why RCDs are tripped by a boiler that does not show any Earth leakage problems when tested.
     
  8. SFK

    SFK

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    Bernard,
    I had a quick look at the spark generator.
    https://www.dhsspares.co.uk/product...MIt5SMiPbE8wIV2OFRCh1fywAuEAQYASABEgLqvPD_BwE
    it is 240V @50Hz input.
    Rated at 2.5VA (call that 2.5W) >>> so not using the high currents that I was worrried about
    with a 10Hz output at an unknown voltage (I note that the output sockets are well shielded).
    Seems that it is using a closed circuit.

    Page 45 for a basic curcuit diagram.
    https://mediacdn.baxi.co.uk/-/media...and_service_manual.pdf?v=1&d=20170821T153651Z
     
  9. SFK

    SFK

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    Last edited: 12 Oct 2021
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  11. bernardgreen

    bernardgreen

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    It does look that way with a tag on combustion chamber connected to one of the EHT terminals and thus not relying on a return path via the earthing/ bonding of the combustion chamber
     
  12. SFK

    SFK

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    Image and testing of Baxi spark generator here (sorry not useful to actually solve the inverter issue).
    I notice that he tests it with multimeter on DC rather than AC.
     
    Last edited: 12 Oct 2021
  13. norseman

    norseman

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    The technical help you are both providing is greatly appreciated although much of it goes over my head due to my inability to understand complex electronics. Wiring AC connections & straightforward DC automotive work is about my limit & I admire the level of knowledge you guys possess.
    I'm a reluctant to involve Baxi directly as the boiler is still under a warranty I don't want to risk invalidating. I'm puzzled that my latest attempts (see OP) have generated a fault code that does not appear in the boiler manual ... all the codes are listed with advice to 'contact your installer or service engineer' regarding any code not shown.
    The installer/engineer is local to me, so I'll run the problem past him & he may well find your input helpful.
    Your responses are greatly appreciated, many thanks to you both, I'll update in due course.
     
  14. crappy

    crappy

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    Could it be that the inverter, like mine does, does not see the load as real and stays low voltage? i.e. Below 230v.

    Mine, a VoltMaster, stays at 180V until there is a few 10s of Watts load when it then ramps up the output to 230.
     
  15. norseman

    norseman

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    That's interesting, thank you for the input ... I'll check that out with my m/meter.
     
  16. norseman

    norseman

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    Update on posts #12 & #13.
    A voltage test with my multi-meter reveals that the inverter voltage remains at a constant 230v throughout the test, but as before the burners won't stay alight for more than a few seconds post ignition before reverting to the pump only. It will then try again before having a hissy fit & throwing the fault code E133. Fortunately the reset restores normality after switching back to the grid.

    I did consider a generator to run the home (within the device's capability) but if I can't get the boiler to play ball from an inverter I'm wasting my time/money with a geni.
     
  17. crappy

    crappy

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    Interesting. You could get a cheap 'scope from banggood.com for around £20-30 and see if the frequency or sinwave deviates any.

    I ran my valiant off a 500W VoltMaster inverter a few years ago. Snow downed a tree snapping wires leaving me the only smug one in our area with heat so it's certainly possible.

    Can you temporarily try another inverter off a spare batter?
     
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