UPS integration
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If the UPS has a "battery low" output, it might be worth connecting it to an endstop input on the Duet and setting up a trigger to pause when low battery is signalled, to guarantee that the Duet will pause cleanly and save the resume data at that point.
Yes it might be. I'll see how easy it is to do. Better to power down the printer in a controlled and elegant fashion, rather than letting it crash. The resume data is largely irrelevant for me as I don't see how I could re-home Z with a partly printed object on my particular machine. Although maybe if I didn't lift the nozzle when it paused I might be able to resume and salvage something? (assuming the power outage was sufficiently short that the bed didn't cool too much)
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To resume a failed print, you need to re-home the printer. On a Cartesian or CoreXY printer, homing X and Y with a print on the bed should not be a problem. To home Z, you can either use a sufficiently reproducible Z-max endstop, or use the Z probe to home at one edge or corner of the bed if the print does not fill the bed (which is more difficult with a large hot end like the Diamond).
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To resume a failed print, you need to re-home the printer. On a Cartesian or CoreXY printer, homing X and Y with a print on the bed should not be a problem. To home Z, you can either use a sufficiently reproducible Z-max endstop, or use the Z probe to home at one edge or corner of the bed if the print does not fill the bed (which is more difficult with a large hot end like the Diamond).
Ahhh. If homing Z is mandatory to resume a print, that's definitely a no no for me then. As I said, homing at Z min would only be possible on the smallest of prints - the two parallel X rails are about 150mm apart measured at the outside (in y) and the carriage is about wide 150mm wide (in X) with the part cooling fans. So even with a 360mm x 360mm build area, anything larger than about 60mm in either X or Y is going to collide. In fact it's worse than that because if the object was taller than about 150mm, there is even more likelihood that it will collide with the extruder gantry which is even bigger. I could home at Z max but as I said, that's 760 mm away from the nozzle tip, so the bed would have to travel up to 1,520mm and the fastest I can get away with is 10mm\sec or 600mm\minute and I'm not prepared to wait two and half minutes every time I want to home Z. No worries. It's no big deal.
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I'm going to wake this thread up… because it seems odd that none of you discuss running the battery directly on the 12V circuit.
In most of your cases, you have a 12V battery circuit with a charger and an inverter to convert power into and back out of 12V ... at some varying rate of efficiency. Did it not occur to any of you to simply put the 12V battery (gel cel) on the 12V rail?
Now... you need to adjust your power supply "up" to your battery's charge level. Typically gel cels are in the neighbourhood of 13.5 or 13.7 volts. As long as the Duet tolerates that, you're done. A Gel Cel should give you ~30 minutes of run for 350 watts (and cost ~$35) ... a $100 car battery should run the whole thing for 3 or 4 hours ... depending on things.
If you get a larger battery ... you might want to up the power supply to 500W or so.
On some other post our fearless leader said the "low voltage" warning was around 9.8V ... so you'll get 80 or 90 percent of the useful life of a 12V lead-acid cell and you should get a very high efficiency out of the system.
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I've been thinking about pressing an old ups (with new cells) into service to prevent failed prints. I started a thread on it here https://www.duet3d.com/forum/thread.php?id=4634#p40465 I have some delay relays on order, an unusual type which switch the relay after the delay rather than switching it then starting the countdown and then unlatching it. My intention is to use the ups active led output to switch the relay on when the battery comes on, and then connect the other side of the relay to an endstop channel with a pause command triggered by it. If the timer doesn't run out it doesn't get sent so short outages don't pause the printer, if it does then the machine pauses and saves the resume data before the battery reaches the voltage where the ups switches off. This will suit me as one ups can power 3 machines for long enough to achieve this. Although I will have to test all three machines running and pull the power and see how long it can sustain them.
However the idea of just placing batteries in parallel with the psu must be a simpler way of achieving this for one individual printer. Lead acid certainly safer than lithium, but then lithium has some advantages, it would have a BMS so whilst the printer could pause at x voltage and shutdown at y voltage the pack would be disconnected by the BMS at z voltage rather than with a lead acid battery without a similar circuit which would potentially continue to discharge even though the printer was "off" until it was over discharged, as unless you've implemented a relay system for ps on and off, even a printer which has shutdown is still drawing current. So you might render your battery inoperable even if you save a print, not a great improvement, unless you have some way of monitoring and disconnecting the battery (a BMS) which isn't that far off a ups system.
I'm looking forward to experimenting with it.
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My solution on this is a raspberry pi (cheap older model off ebay) and a second usb power adapter. The pi is powered from the ups and the 2nd power adapter is on the mains and feeds into a gpio pin on the pi through some other small board I found that converts usb 5v to pi 3.3v.
When the power drops the normal result is that the generator comes on automatically within 8-10 seconds so the ups's carry everything through. For the times when the generator fails, the pi is counting down (5 minutes i think - set up when had to manually start the gen). When that time runs out the pi executes ssh scripts to shutdown the nas and a desktop.
I haven't investigated how to add the duet to the list of things to shutdown via the network. Pretty sure that is currently do-able, but if the gen is not starting then the failed print is not my biggest problem
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I'm going to wake this thread up… because it seems odd that none of you discuss running the battery directly on the 12V circuit.
In most of your cases, you have a 12V battery circuit with a charger and an inverter to convert power into and back out of 12V ... at some varying rate of efficiency. Did it not occur to any of you to simply put the 12V battery (gel cel) on the 12V rail?
.......................................Nice idea. In my case I'd need to fit 2 batteries to give 24v. That would still leave me with the problem that my bed is 240v AC powered but for 12 or 24v systems it might be a viable way to do it I'd have thought.
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If you are talking about regular 12V car batteries, two of them in series will give you more than 25V - which exceeds the Duet's max voltage rating.
Keep in mind that hooking up a battery in parallel will likely discharge your battery to the voltage level of your PSU. So you loose quite a bit of energy because you do not operate the battery at 100% charge. A car battery is usually almost empty at exactly 12V… (from what I was told).
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That's not the only drawback, once the machine switches to pause, even heaters off, it will continue to discharge the battery unless something cuts the battery off at 11.5v or whatever.
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I wouldn't have thought that any of those are huge problems that can't be dealt with. I'm just thinking that a UPS is essentially a battery running an inverter to give mains voltage. This mains voltage is then stepped down to DC voltage by the printer PSU. From what little I understand, inverters aren't the most efficient devices and there would also be some losses through the PSU itself. So it seems to me to be reasonable to cut out the step up to mains voltage\step do back down to DC aspect and just supply DC directly.
Someone cleverer than I could probably build a circuit that would trickle charge the battery from the printer PSU maybe, then when mains is lost, it switches over to the battery? A bit like a UPS but without the inverter. Just musing…......
Not that it would work for me as my bed is 240V AC.
EDIT. A quick google search shows that one can already buy power supplies with integral DC UPS - might be the way to go for printers with non AC bed heaters?
In fact thinking about it, my 10mm thick insulated aluminium build plate takes forever to cool down so if the power failed once it was up to temperature, I could probably still print for quite a while by just maintaining the DC side of things before the part falls off the bed. Might look into this a bit further.............
EDIT2. How about something like this? https://www.simplypowersupply.com/DC-UPS/AD-155C-Meanwell-24V-155W-DC-UPS.aspx
