Emergency Planning - Power Cuts?

Discussion in 'BigBox General Chat' started by Jasons_BigBox, Mar 19, 2017.

  1. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Evenin' all,

    A few days ago, we had a short power cut. It only lasted a minute or so and the printer wasn't on at the time but it got me thinking about what to do.

    In general, the machine will fail safe but I'm a little worried about the hot end without the heatsink fan running. With no cooling (but also no heating), we'll be looking at the heat from the block being dissipated to the air around but also travelling up the heatsink.

    The question is, can the heat in the block raise the temperature of the heatsink to a point where it can damage the surrounding parts, the fan moulding and the printed part that the hot end fits into? If I know about it, it wouldn't be too hard to remove the heatsink locating grub screws and lower the hot end onto the bed.

    Any suggestions?


    Cheers

    Jason
     
  2. Kanedias

    Kanedias Well-Known Member

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    I had the power cut out a few times mid print - prompting me to buy a UPS - and it caused no noticeable effect on the printer, including the part cooling fan shroud which I reprinted in PLA after the original got damaged.
     
  3. Dr Jeep

    Dr Jeep Well-Known Member

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    I've done it with a daemon on linux called apcaccess and some scripting against the octoprint API to shut the printer down safely and record the last complete layer before the battery runs flat. Pretty sure I posted a guide somewhere here but my google foo is failing me right now.
     
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  4. Dr Jeep

    Dr Jeep Well-Known Member

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  5. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    I've not got octoprint or a ups unfortunately.

    Thinking again, I have several lipo batteries at hand (I fly r/c planes). I'm going to look into making up a connector to attach to the heat sink fan. I might need a voltage regulator to drop to 5/6v (not sure of the fan rating) but I have a few of those too.

    It's been a long day...... my first thought was to use a variable voltage supply I have...... THAT RUNS OFF MAINS POWER...... numpty.....
     
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  6. A Dragon In A Pie Costume

    A Dragon In A Pie Costume Well-Known Member

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    you could program a print from layer function, or something and have it keep track of its layer in EEPROM or write on the sd what gcode line it's on, then only home x/y and start printing hoping the z axis hasn't moved or have the option to align it
     
  7. A Dragon In A Pie Costume

    A Dragon In A Pie Costume Well-Known Member

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    you knownwhat? I'm gonna try to get working on that and submit to the official marlin repo
     
  8. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Sounds a good idea.

    I'm really just concerned that the printer may be damaged without any cooling. I suppose a large spanner held against the hot end would act like a heatsink and draw some of the heat away.
     
  9. Dr Jeep

    Dr Jeep Well-Known Member

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    I'd recommend careful consideration, the EEPROM on the Atmel chips like the ones used on the Rumba have a pretty lousy endurance. 100k writes to a single address from what I recall.

    Given the length of your average gcode file...if you write the position for every line without some sort of wear levelling (which you'd have to code in yourself as the atmel has none by default) then you could burn out those memory cells in one print !

    Worse than that, not sure if it specifically affects this atmel chip but others I have used seem to have had an issue with flash corruption on power fails during write operations. Not seen it well documented but I found you can blow addresses other than the ones you are writing to if the power goes mid write. What this means in reality is writing to the eeprom every layer could randomly corrupt the printer config if the power goes at the wrong moment (though not the memory space where the firmware is held, that's isolated from these writes).

    SD card would be a better option, though most of those aren't that great for endurance, but it is at least easily replaceable.
     
  10. dc42

    dc42 Well-Known Member

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    We included a power monitor in the Duet WiFi and Duet Ethernet hardware so that we can implement this. When the power starts to drop, we'll write the file position to EEPROM and attempt to park the motors using the remaining energy in the power supply capacitors. But bear in mind that with the bed heater off, the print is quite likely to detach from the bed in many cases, so it's not as useful as it sounds.
     
  11. A Dragon In A Pie Costume

    A Dragon In A Pie Costume Well-Known Member

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    ewww duet :p

    thought about that, maybe use the x rods to hold it down?
     
  12. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    I think David is on to something here. Depending on the bed, what you are printing and filament, and if you usually experience prints popping loose by them self.

    The best bet would not to have a power outage :p

    Get a big UPS and hope it can sustain the print as long as the outage.

    E.g. this UPS will give 6 minutes backup at half load so with some quick and dirty math about 40% efficiency for its battery.

    I think I remember my BigBox used >150W and that would give you 13 minutes backup when the battery is new and will degrade the next 5-10 years to 0 minutes :confused: before replacing the batteries.

    Go for a bigger UPS and I think we could easily reach 30 minutes backup, it's all about money.

    Edit, forgot link: https://www.powerwalker.com/?lang=en&page=product&item=10120073
     
    #12 Stian Indal Haugseth, Mar 29, 2017
    Last edited: Mar 29, 2017

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