Why would you need a UPS for a 3d printer?
Let me describe the scenario…
You have spent a lot of time on your 3d printer, adding this and that mod, improving the quality and repeatability of your prints. So now you can slice a model and print it knowing that it will be as good as it can be.
Ok, now for the big one. The 100 hour print,the one you keep putting off knowing it will tie up your printer for over 4 days – but it will be worth it.
You slice it and download the file to SD card, no computer crashing will stop this print! Wow – how big is that file! No matter it fits onto the card.
You have the filament – still in it’s original wrapping.
Everything is set.
You insert the SD card, preheat the machine, load the filament. Then you select the file and hit print.
After a short warm up the printer nozzle moves slowly across the print bed and within seconds the filament is starting to be extruded. You breathe a sigh of relief, you shouldn’t as you have levelled the machine and checked it yesterday but still…
You watch as the bed starts getting covered with filament, now the second layer. The Z motors move and the nozzle continues it’s merry dance across the bed. You smile, the first since you started the job.
Walking away you know you have to go out and won’t be back for hours.
Later that night you return to the house, you smell the familiar odour of the printer , but no noise.
Creasing your brow you walk into the room where the printer sites still.
The screen shows the start screen, the nozzle rests at the last place it deposited filament on your model.
Unbelieving, you shut your eyes and then open them, as if that will magically start the printer again and time was just playing a practical joke. But no when you open your eyes the nozzle is still where it was, the screen mockingly shows still shows that you have no print jobs on the go.
NO… this cannot be happening, your mind start s racing – what could have gone wrong?
You have done all of the mods to make it reliable, you have improved the cooling, the stability, the hot end – WHAT NOW?
Looking over at your clock and seeing it flashing, it dawns on you what has happened – a power cut. You don’t know how long but a power cut. This stopped your print dead.
On waking up there is no automatic resume, there is no get going again only the removal of what has been printed and clean off the nozzle.
A deep breath and a sigh leaves your body as you pull the bed towards you to remove what has been printed, if it of any consolation – it looks good, a snort of derision and a shake of the head, why did I not think of that?
Oh well only four days to go….
I am sure plenty of you know this feeling only too well, if this hasn’t happened to you then good. It has happened to me a couple of times and …. GRR.
What can you do to stop it?
Well you can add yet another mod to your printer, this time an external one.
Adding a UPS for a 3d printer ( Uninterruptable Power Supply) will allow the printer to keep going until the battery goes flat. So if you have very occasional power dips or power cuts you can add a small one, or if you have power cuts of an hour you need to calculate the worst case scenario and buy a UPS to suit.
How do you do that?
Ups’s are sold typically in VA units, your printer is rated in watts.
Some would say they are the same, but the UPS industry has used the VA units at a phase angle – don’t worry if you are not technical – working it back to power is quite easy.
All you do is multiply the VA rating by 0.6 and you get the true watts of the UPS.
Note: this multiplier is an industry standard for small UPS’s.
So taking a 700VA ups we can multiply this by 0.6 to get 420 watts. This is the true maximum power of the UPS.
Looking at your printer specifications should give you some indication of how much power it consumes. If not I will make some assumptions.
The typical 3d printer works off of a 12v power supply. The heated bed consumes about 12A, the nozzle a little less at 6A. The remaining electronics and motors consume about 2.5A, with the motor currents being the majority of that.
Noting that the nozzle and bed and motors can be on at the same time we need to find the maximum current taken by the printer , so we add the currents together
12+6+2.5 = 20.5A
Don’t be scared by this figure, it is at a low voltage and when scaled up to the mains voltage it will be a lot smaller.
To find the power of the printer you multiply the current by the voltage – so we have :
20.5* 12 = 246Watts
This is the power at the low voltage.
To find the power at the mains voltage we have to assume a power supply conversion factor of 0.8, so the power is divided by 0.8
246/0.8 = 307.5Watts
This is the peak power when the motors are going and the bed is heating and the nozzle is heating, this is not the continuous power being consumed.
Once the bed is heated and the nozzle is up to temperature you will typically have a on/off cycle of about 15%, so the maximum power is only on for 15% of the time.
So we can see that the 700VA ups will power the 3d printer as the 420 watts are above the power requirement of the printer of 307watts.
So how long will it last?
To guestimate this we need to know how large the battery is inside the UPS.
So on an APC 700Va unit the battery is a 12V 7Ah unit, which is typical of this size unit.
Calculating the printer average power, we said before that the on/off time is about 15% so we can multiply the peak power by 0.15 to get the average power:
307*0.15 = 46.05 watts av.
To get the current from this we divide by the voltage (240v)
46.05/240 = 0.1918A
If we round this to 0.2A we won’t be too far out and make the calculations easy.
As the UPS is creating 240v we need to scale the current by the efficiency of the unit in converting and te scaling factor from the low voltage to the high voltage.
240/12 = 20 scaling factor
Eff = 80% or 0.8
So the 7Ah is multiplied by the efficiency
7*0.8 = 5.6Ah
And divided by the scaling
5.6/20 = 0.28Ah
So we can see that the UPS should last – in peak condition – over an hour.
In reality you will be lucky to get half an hour out of it.
The reason for this is that the peak power will be taken at certain times and this loading will reduce the battery capacity quickly. So I would bank on this size of UPS to last about 20 minutes.
Note : what you can do to make this unit last longer is to increase the Ah of the battery. Going up to a 14Ah battery will improve the operation time by 2 etc.
Just bear in mind that the battery will take longer to charge as well and the software included with the UPS, if used, will get confused, unless you can alter the parameters.
Expect the battery to last up to 2 years before requiring replacement.
Another tip is to have the battery outside the unit so that it stays cooler, heat kills batteries.
Confused – overloaded with technical? What would I recommend?
My recommendation for the Anet A8 is to buy a UPS of at least 700VA, ideally 1kVA, and see if you can get a large battery for it.
Do youthink it is worth adding a UPS for a 3d printer, if so what size are you going to use, Leave a comment in the box below sharing your experiences.
Thanks for reading