Resume from power outage, really only with 24V?



  • Hello, I was starting to confugure my RFF for automatic resume when I have read that this option would work only with a 24VDC power supply....for me this is a big problem because I have 12VDC power suplly and I'm full out of budget for this printer and I don't want to spend more money in it...My question is if there's some way to make the automatic resume to work with 12VDC...But I can't understand a thing...if the power supply disappears at the "light speed", what's the difference between 12VDC or 24VDC if they go immediately off? It doesn't look to me that the board has so "heavy" capacitors to keep enough portion of the power supply to make all the operations to safe stop the print (particullary park the head)....has it?

    Thank you guys!



  • @the_dragonlord said in Resume from power outage, really only with 24V?:

    if the power supply disappears at the "light speed", what's the difference between 12VDC or 24VDC if they go immediately off

    have you ever turned off electronics and noticed that they stay on for a bit? thats the capacitors in the power supply draining.

    the duet will notice the drop in voltage and use its last bit of power to save the state to the sd card.

    there is a bigger margine for the duet to operate on from 24v until there is not enough to operate on.

    from 12v lets say the duet starts its writing at 10v and has to finish before it reaches lets say 5v.

    at 24v there is more room from going to 22v to 5v .

    forget about safe stop of the print head. its all about saving just saving the current position of the g code.



  • @Veti said in Resume from power outage, really only with 24V?:

    @the_dragonlord said in Resume from power outage, really only with 24V?:

    if the power supply disappears at the "light speed", what's the difference between 12VDC or 24VDC if they go immediately off

    have you ever turned off electronics and noticed that they stay on for a bit? thats the capacitors in the power supply draining.

    the duet will notice the drop in voltage and use its last bit of power to save the state to the sd card.

    there is a bigger margine for the duet to operate on from 24v until there is not enough to operate on.

    from 12v lets say the duet starts its writing at 10v and has to finish before it reaches lets say 5v.

    at 24v there is more room from going to 22v to 5v .

    forget about safe stop of the print head. its all about saving just saving the current position of the g code.

    ok, thanks but so for the writing of the gcode maybe 12VDC PS could be enough? In case if I'm not wrong it can be possible to instruct the printer about "what to do" in event of power failure so maybe it would be possible to tell t not to home, right? In case is there some third part hardware that can be combined with the board to increase the life time after a failure? I've seen that there's some boards with a lot of capacitors that can be driven by other boards, is there something alike for the Duet? I already have a UPS connected with the printer so if I'm near the printer I can park it and stop it safely, the trouble is that I'm not home....where I live when they cut off the power usually they do for several hours....



  • @the_dragonlord said in Resume from power outage, really only with 24V?:

    @Veti said in Resume from power outage, really only with 24V?:

    @the_dragonlord said in Resume from power outage, really only with 24V?:

    if the power supply disappears at the "light speed", what's the difference between 12VDC or 24VDC if they go immediately off

    have you ever turned off electronics and noticed that they stay on for a bit? thats the capacitors in the power supply draining.

    the duet will notice the drop in voltage and use its last bit of power to save the state to the sd card.

    there is a bigger margine for the duet to operate on from 24v until there is not enough to operate on.

    from 12v lets say the duet starts its writing at 10v and has to finish before it reaches lets say 5v.

    at 24v there is more room from going to 22v to 5v .

    forget about safe stop of the print head. its all about saving just saving the current position of the g code.

    I've seen that there's some boards with a lot of capacitors that can be driven by other boards, is there something alike for the Duet?

    I meant external circuits with a lot of capacitor connected to the VIN of the board and driven by the board itself in some way (I found circuits like theese for the SKR boards)



  • @the_dragonlord said in Resume from power outage, really only with 24V?:

    ok, thanks but so for the writing of the gcode maybe 12VDC PS could be enough?

    try it.

    is power that unreliable in your area? i never spend any time on this, because a power outage is something that does not happen very often in my area.


  • administrators

    If you don't have a PanelDue or anything else external powered from the Duet's 5V rail then saving the state may work at 12V. If you do have a PanelDue then the chances are not as good.

    Back up your SD card before you test it, because there is a risk that the SD card may become corrupted if the power drops too low while it is still writing.



  • @dc42 said in Resume from power outage, really only with 24V?:

    If you don't have a PanelDue or anything else external powered from the Duet's 5V rail then saving the state may work at 12V. If you do have a PanelDue then the chances are not as good.

    Back up your SD card before you test it, because there is a risk that the SD card may become corrupted if the power drops too low while it is still writing.

    i have a panel due


  • administrators

    The Duet has 200uF capacitance on the input to the 5V regulator, isolated from VIN by a diode. At 12V input, this stores around 12mJ of available energy. At 24V it rises to 55mJ.

    The Duet itself draws around 0.5W, so 12mJ will last about 24ms and 55mJ will last 110ms. 24ms should be enough to save the data unless it is a slow SD card and it has just started an internal wear-levelling operation.

    If you add a PanelDue 7i, that's another 2W or so of energy consumption, so the power will only last for one fifth of the time. With 24V power that still leaves around 20ms. With 12V power it is just 5ms.

    All figures are approximate. Your mileage may vary.



  • @dc42 said in Resume from power outage, really only with 24V?:

    The Duet has 200uF capacitance on the input to the 5V regulator, isolated from VIN by a diode. At 12V input, this stores around 12mJ of available energy. At 24V it rises to 55mJ.

    The Duet itself draws around 0.5W, so 12mJ will last about 24ms and 55mJ will last 110ms. 24ms should be enough to save the data unless it is a slow SD card and it has just started an internal wear-levelling operation.

    If you add a PanelDue 7i, that's another 2W or so of energy consumption, so the power will only last for one fifth of the time. With 24V power that still leaves around 20ms. With 12V power it is just 5ms.

    All figures are approximate. Your mileage may vary.

    is there a way to add some external hardware (capacitors) to improve the save - resume?





  • @Veti said in Resume from power outage, really only with 24V?:

    @the_dragonlord

    dc42
    would something like this work?
    https://www.aliexpress.com/i/32967985788.html

    exactly but it should be interfaceable by the Duet and RRF....when the external board connected to a pin detects a failure the pin goes at low level and RRF starts the failure save procedure....I don't know if this is possible....is it?



  • @the_dragonlord
    If you are just using a bank of capacitors - then its simplest to just have them across VIN. This is because VIN would keep the capacitors charged and they are only used by the Duet when there is no input from the power supply. Based on @dc42 comment. You may get away with just adding a 200uF capacitor - but if it were me I'd think in terms of 1000uF. This is one of those situations were more is better.

    It looks like the BIGTREE mini UPS is just a bank of capacitors with circuitry to detect low power and tell the printer to trigger to save the printer state. Duet already has that circuitry - so it seems that the BIGTREE option is no better than a bank of capacitors (in the Duet context).

    Having "something" detect a power failure and turn on is really only beneficial if that something can provide power (typically a battery bank or generator) for a longer period of time.

    It seems from your description that keeping it simple is what you want.



  • @stuartofmt said in Resume from power outage, really only with 24V?:

    @the_dragonlord
    If you are just using a bank of capacitors - then its simplest to just have them across VIN. This is because VIN would keep the capacitors charged and they are only used by the Duet when there is no input from the power supply. Based on @dc42 comment. You may get away with just adding a 200uF capacitor - but if it were me I'd think in terms of 1000uF. This is one of those situations were more is better.

    It looks like the BIGTREE mini UPS is just a bank of capacitors with circuitry to detect low power and tell the printer to trigger to save the printer state. Duet already has that circuitry - so it seems that the BIGTREE option is no better than a bank of capacitors (in the Duet context).

    Having "something" detect a power failure and turn on is really only beneficial if that something can provide power (typically a battery bank or generator) for a longer period of time.

    It seems from your description that keeping it simple is what you want.

    i want to keep it as simple as possible... how many capacitor do you think I'd need to make an efficient failure saver as it would be if I had a 24vdc power supply? Should them be connected in parallel to each other and in parallel with the VIN? should be needed some other circuitry in case?



  • @the_dragonlord

    @dc42 would likely provide a more informed answer than I in terms of the overall capacitance. But basically - one or more capacitors in parallel with each other (capacitance adds in this situation) and in parallel with VIN - observing the correct polarity.



  • @stuartofmt said in Resume from power outage, really only with 24V?:

    @the_dragonlord

    @dc42 would likely provide a more informed answer than I in terms of the overall capacitance. But basically - one or more capacitors in parallel with each other (capacitance adds in this situation) and in parallel with VIN - observing the correct polarity.

    I supposed this too, lets wait to see if @dc42 has some suggestion for me about this


  • Moderator

    This is basically the same advice given when power resume functionality isn't working as expected, even on 24v power. Add capacitors. So you're on the right path.



  • @Phaedrux said in Resume from power outage, really only with 24V?:

    This is basically the same advice given when power resume functionality isn't working as expected, even on 24v power. Add capacitors. So you're on the right path.

    yesss! now the only thing to know is how many capacitors and what "size" they got to have


  • Moderator

    I think the advice from @stuartofmt with regards to that is good.



  • They are not expensive but I would go for a "brand name" - since quality can vary. Working Voltage is important. Since this is being attached to the output of an already smoothed power supply - a bit more than the highest VIN voltage. May as well go for 35V (fairly common) in case you later upgrade to a 24V Power Supply. So something like a 1000 uF @ 35V.

    Depending where you live -Amazon (or similar) or a local electronics parts supplier.



  • @stuartofmt said in Resume from power outage, really only with 24V?:

    They are not expensive but I would go for a "brand name" - since quality can vary. Working Voltage is important. Since this is being attached to the output of an already smoothed power supply - a bit more than the highest VIN voltage. May as well go for 35V (fairly common) in case you later upgrade to a 24V Power Supply. So something like a 1000 uF @ 35V.

    Depending where you live -Amazon (or similar) or a local electronics parts supplier.

    ok, excellent! I've bought 10 of them from Amazon (10 was the minumu orderable number) How many capacitors should I use? Just one or two or more in parallel to each other?
    I think it's mandatory to add a resistor in series with the capacitor because in the very first moment when you turn on the power supply tha capacitor act almost like a shortcut and with the resistor we are able to compute the charge time with the formula Time=5R*C...in the same time I'm afraid that adding a resistor in series with the capacitor (and so in series with the board) could bring to a partial loss of voltage for the board itself....how about it?

    This is the circuitry i was thinking with C1 surely used and C2 to Cn as optional capacitor to add more "time" to the board and the resistor as optional....is it correct? How about the resistor?

    Thanks20201030_113453.jpg



  • @the_dragonlord I have read this: https://forum.duet3d.com/topic/19150/ups-24v-on-skr-pro-rrf-3/2?_=1604067164270 maybe buying the micro capacitor UPS and using like this could be the easiest way?



  • @the_dragonlord
    As long as you keep the capacitance modest you will not have a problem. It's been years since I was an active elec engineer - but with the aid of an online calculator .... The max current draw at 24V (12V) for a 1000uF capacitor is ~ 3A (1.5A) assuming a rise time from the power supply ~10mS (likely much longer). I.e. the power supply at switch on is not instantaneous at VIN. Your power supply is likely rated at 20A or more.

    Now to the resistor -- if used - it will have to dissipate heat all the time because the rest of the components consume multiple amps. Also - it would cause a voltage drop and diminish the effect you are after (i.e. energy storage as opposed to continuous voltage smoothing). So in this context - not a good idea (unless it's quite small) - and you do not need it (unless maybe you add something like 1F of capacitors 🙄 ).



  • @stuartofmt said in Resume from power outage, really only with 24V?:

    @the_dragonlord
    As long as you keep the capacitance modest you will not have a problem. It's been years since I was an active elec engineer - but with the aid of an online calculator .... The max current draw at 24V (12V) for a 1000uF capacitor is ~ 3A (1.5A) assuming a rise time from the power supply ~10mS (likely much longer). I.e. the power supply at switch on is not instantaneous at VIN. Your power supply is likely rated at 20A or more.

    Now to the resistor -- if used - it will have to dissipate heat all the time because the rest of the components consume multiple amps. Also - it would cause a voltage drop and diminish the effect you are after (i.e. energy storage as opposed to continuous voltage smoothing). So in this context - not a good idea (unless it's quite small) - and you do not need it (unless maybe you add something like 1F of capacitors 🙄 ).

    so you are suggesting me to use only one 1000uF capacitor? Is it enough for a 12vdc powered board to have the time to store the position and raise the Z?


  • administrators

    Unfortunately, to be effective a capacitor across the VIN power rails needs to have a much larger value than the 200uF internal to the Duet, because it needs to power the stepper motors too until they are shut down. The 200uF on the Duet is isolated from VIN by a diode.



  • @dc42 said in Resume from power outage, really only with 24V?:

    Unfortunately, to be effective a capacitor across the VIN power rails needs to have a much larger value than the 200uF internal to the Duet, because it needs to power the stepper motors too until they are shut down. The 200uF on the Duet is isolated from VIN by a diode.

    uh, ok so a 1000uF placed in parallel with the VIN should be enough?


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