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Power transient freezes Lochinvar Knight controller

Llaves Member Posts: 6
Some small fraction of the time when my backup generator shuts down, there's some sort of power transient that freezes the controller on my Knight KB80 boiler. This is not repeatable, so I can't perform any kind of testing. In addition, the transient is minor enough that nothing else in the house notices it, including $10 clock radios that will reset if you look at them cross-eyed. All the clocks on the appliances are fine too. When I say the controller freezes, I mean it won't respond to anything, including the buttons on the front panel. The only way to reset the controller is to power cycle the boiler. Has anyone else observed this problem,, which strikes me as indicating that the controller power supply doesn't have adequate filtering (which really isn't much for a low current 5V power supply). I've reported this to Lochinvar but gotten no response.

(In case you might be wondering why I've seen this enough to notice, I have off-grid solar and the backup generator automatically starts  when the batteries get low, which can be as much as once or twice a week when the weather gets crappy and the sun is low in the sky.)

The best I've come up with for now is to check the boiler when the generator stops. If I'm going to be away for a couple of days, I plug the boiler into a timer which power cycles the boiler once a day to make sure it's never out for too long. I've got a circuit sketched out to detect the condition and power cycle the boiler, just haven't gotten around to wiring it up.


  • NYplumber
    NYplumber Member Posts: 503

    Have you considered a computer ups?
  • Llaves
    Llaves Member Posts: 6
    UPS is not the answer

    I've considered a UPS, but ruled it out. My current power is essentially a giant UPS - 45KWH worth of batteries and a very high quality inverter that produces a close enough approximation to a true sine wave that it's harmonics are lower than those from your power company. A consumer grade UPS would either involve a fast switch between direct AC to inverted AC, or else it would rectify the AC to charge a battery, then invert the power to provide AC. If the former, the glitch is likely to be larger than my existing system, which actually controls the generator shutdown, so it first syncs the inverter phase to match the input AC before switching from the generator to the inverter power. If the latter, it's likely to be a square wave inverter, and who knows how the boiler would respond to that. (And it's also a very power inefficient way to operate, with losses rectifying, charging, drawing from the battery, then inverting. )

    I'm pretty surprised that Lochinvar has never responded to my reports (which I know they received). If this problem occurs to someone more litigious than I am, and they suffer losses (think frozen and burst pipes), that's a lawsuit waiting to happen, as well as bad publicity. The problem might be a bad power supply on my unit, but they've ever offered to swap power supplies to check. Or it might a bad design decision to omit a $0.25 capacitor in the power supply.

    The low-voltage board provides enough signals to determine the frozen state (I think). If so, it only takes a couple of dollars of parts and an afternoon to solder up a solution. When I it bothers me enough, I'll go that route.
  • icesailor
    icesailor Member Posts: 7,265

    I'm no expert on any of this and you sound like you know far more about the subject that I will ever know in the rest of my lifetime.

    However, I have an antique stereo component system that I brought to Florida with me. So I can play my antique LP records, tapes and CD's. Plus, listen to my satellite radio, When I connected it up, I needed a power strip to connect all the components. The first one I found was the large UPS back-up for my old computer I had in my office. So I connected it up because it had LOTS of places to plug in.

    Florida Power from FPL. really sucks where I live. I know full well what you are saying about $10.00 clock radios resetting over the least fluctuations. My Microwave Oven is worse. However, since connecting the stereo system, I used to hear this Clicking on occasion. A relay in the tuner or inside the UPS, I never knew what. One day, I realized that the UPS was recognizing all these bumps on the lines. That it would be picking up voltage fluctuations that I couldn't even see on the TV or any other appliance.

    I'd be trying a decent battery back-up UPS on just the boiler. It doesn't need to be the whole house, just the boiler. If you're off grid, you usually get all kinds of strange fluctuations. Its worth a try and not all that expensive. When I lived in Massachusetts, we used to get lots of bumps. The UPS was always clicking over something to do with street voltage. And the batteries were always up to snuff. Your problem probably has more to do with frequency control than voltage problems. Power utilities spend millions on frequency control. I doubt that your power system has. And those wall hung beer cooler boilers are just a laptop computer on a wall. Without the battery. I can pull the AC plug out of my laptop and it switches without a skip. Older laptops would crash.

    Something to consider, possibly.
  • SWEI
    SWEI Member Posts: 7,356
    What kind of inverter, specifically?

    have you put a 'scope on it to see what the waveform looks like at the boiler input terminals?  I have seen some pretty strange stuff come from the interaction with power supplies.  I'd be inclined to try a power conditioner (a real one, with pounds of iron and copper) just to see what happens.
  • Llaves
    Llaves Member Posts: 6
    It's an Outback VFX3524

    As noted, this is an off-grid power system, not some cheapie inverter you plug into your car to power your laptop. I've got a dual inverter setup providing 240V. Each inverter will provide 2800VA continuous load and 4800VA surge, with 2% harmonic distortion (lower than the spec for your power company). Voltage regulation is +/- 2%.  Each unit is 60 pounds, more than half of which is the massive transformer inside the unit.  I have not hooked up a scope or power analyzer to verify the unit is in spec.

    But all this is largely irrelevant because the problem does not occur when the inverter is running, it occurs when the power switches from the backup generator to inverter power. (Oddly enough, it never occurs switching TO the generator, even though the same phase sync issues are involved.) As noted earlier, the inverter controls the switchover, so it first syncs to the phase of the generator, then switches. It's also telling that NOTHING else in the entire house has ever shown a problem during this switchover. Anything else seeing this glitch either filters it out or copes with it. Not the boiler controller. Even if the glitch is so big that it would pass through the power supply, the controller should contain a watchdog timer to reset itself rather than freeze. And it freezes so hard that it won't even read the switches on the control panel.
  • SWEI
    SWEI Member Posts: 7,356
    Percentage of THD

    does not really describe what happens with nonlinear loads.

    Look for a used Oneac CL or CP  series unit on eBay.  They sell for pennies on the dollar.
  • Jamie Hall
    Jamie Hall Member Posts: 21,096
    A true

    computer/high fidelity grade UPS is the answer to this one.  True, there is an efficiency loss -- but the connected load (your Lochinvar) never sees anything except the sine wave produced by the UPS.  The UPS takes whatever is coming into it and charges a battery -- filtered DC.  The output from the battery (still DC) is inverted, crystal controlled at 60 hz, and delivered to the load.

    Cheap?  No.  Sorry about that.

    Effective?  Yeah...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SWEI
    SWEI Member Posts: 7,356
    Double conversion UPS

    is what you just described.  Good ones come with proper output filtering (aka power conditioning) onboard.
  • icesailor
    icesailor Member Posts: 7,265

    Cheap at twice the price. If it works.