Resume from power failure with 12v PSU + Capacitors

ReVeRb

Re: [Resume from power outage](really only with 24V?)

I recently faced an unpleasant situation like many of you... A 3 day print that ended after 2 and a half days due to a loss of electricity...

So I decided to consult the information on the forum to add capacitors on my 12v setup.

Being on low budget, I acquired 2x 10,000uF 25V, low ESR, Ripple current:2.9A@120Hz-3.335A@10kHz. and will salvage other parts from different electronic part I already recycled/ kept in a box (like the resistor if needed).

I saw this post and inspired myself from it:

https://forum.duet3d.com/topic/19468/resume-from-power-outage-really-only-with-24v/57?_=1658360305205

But, I don't know how to properly install everything(which configuration to be optimal for my setup) to avoid burning my PSU (Chinese 12v 360W, 30A).

Also, I'm in no way an engineer and only have basic technical knowledge of electricity, but capacitors is out of my knowledge so I double checked and the first formula seems to be wrong. Isn't C=Q/V instead of C=Q*V ?

In the post, they talk about the ESR, I have no idea what it represent nor how it work in my case. As I understand it from the reading, if I connect my capacitors in parallel, the low ESR of my capacitors will play a significant role, but I don't understand how to determine if I'm "ok" or not, if I absolutely need a resistor or not and if I do, which kind...

How to I determine the proper resistance value I need to add in series with the capacitor. Anyone have a formula, maybe?

As far as I understand it:

With 2x 10 000uF capacitor. I could store plenty of energy, enough to save on the sdcard, that's for sure, but could I also be able to move the nozzle away (assuming that cooling fan, the bead and nozzle heater are shut down, and maybe even the nozzle fan).

Thank you guys

dc42

@reverb the ripple current and ESR are not critical in this application.

If your PSU also has a voltage adjustment potentiometer and you are not running it close to its maximum rating with everything turned on, then I suggest you also turn up the voltage. Most 12V non-ATX PSUs can be turned up to about 14V.

Nightowl

@dc42
Is that the case with 24V PSUs too?

As you may remember, I'm having some issues with power resume for my CNC machine, so perhaps increasing the power out using the adjustment potentiometer would help my case?

The issue has been diagnosed as there not being enough power left to produce and save the ressurect.g file.

Thanks

ReVeRb

@dc42

Yes, my PSU have a potentiometer to adjust the voltage. As for the maximum rating when everything is turned on, I have no certainty, just a vague idea...

Duet2 board: 12V, 0,5W
Panel Due: ??
Heat bed: 12V, 120W
Heating cartridge for the nozzle: 12V, 70W
stepper(extruder): 600mA max
stepper(x,y,z): 800mA max each.
1 fan: 5V 0.15A

I doubt I'm over 20Amp max... I have plenty of room.

So I could just connect my capacitor in parallel to reach 20 000uF, and install the capacitor apparatus in parallel with the PSU and I should be fine ? I just want to be 1000% sure that I won't create a ShortCircuit to the PSU because I have no idea if the PSU has a SC protection and I'm too low on a budget to buy a replacement.

About the ESR. On the other post, it is mentioned that low ESR cap draw a lot of current from the PSU and the more cap. are connected in parallel, the higher the current draw is... I though the Rippler Current spec was the max current draw of the cap, but apparently no. How to I determine that ? (I just like to validate as much as I can with some formula before I solder anything in place).

How does turning the PSU voltage up will affect the setup? The potential difference will increase, passing from 4V =(10.5V to 6.5v) to 6V = (12.5V to 6.5V), so the delay before everything shut down will increase a bit. On the other hand, that's the reason I bought 2x 10 000uF. I though that it would be well sufficient to add some delay while staying at 12V+/-5% on my PSU...

What is the main advantage of raising the PSU voltage slightly ? How will it affect the 5v supply from the Duet board ? Does anyone tried that 14V supply instead of 12V and if so, how does that affected your bead heater, your heating cartridge, fans, etc.

Thank you guys

dc42

@reverb the stepper drivers will cut out when the VIN voltage drops below about 10V. So with 12V VIN you don't have much margin. With 14V VIN you have around double the margin.

The hot end and bed heater power will increase with the square of the VIN voltage.

ReVeRb

@dc42 Ok, it's been a while, but I finally had the time to build the PCB capacitor bank and install it. It work good and I have approx. 1.5 - 2 sec. before the board shut down.

I'm not sure I understand how to implement it in the firmware, neither how to program it for my needs and limitations...

This is the code provided on the documentation:
M911 S21.0 R23.0 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000"

As far as I understand, I simply copy that line of code info config.g and configure it for my needs?

I have a Delta, with a 12V setup pushing around 13.5V... so it would be:
M911 S12 R13 P"M913 X100 Y100 Z100 M83 G1 Z3 E-5 F1000

Which would raise the nozzle 3mm from it's actual position and retract 5mm all motors(X,Y,Z,E0) at F1000 speed right after it detect a power outage ?

Then it will save the position ?

Does it have to home before it save ? If not, can it just raise the nozzle and retract a bit, then save the position... And when the power is back, I simply home the printer and re-launch the print and it will move where is stopped ?

I don't understand very well how the whole process work all together to be honest and some explanation is welcome!!

Phaedrux

@reverb It saves the last print position whether you have it move or not.
On resume you must home first.

The details are discussed here: https://docs.duet3d.com/en/User_manual/Tuning/Resume