<p>Yes it is safe to use such relay modules. Note that the printer will use less power than the specified power, when in idle it nearly doesn't use any power at all, the inrush current will be ver low when switching the relay. Furthermore, the relay is capable of handling the current according to its specification. Do note that you are using mains power, which can be dangerous, please make precautions working on mains (pull the plug from the socket) and shield the wires and use proper crimping tools, no solder.</p>
<p>I have done this with 2 printers, one where I cut the 230 V, but the latest one uses a computer 12 V PSU which has a separate wire (I think this is 5 V) which you can short to start the PSU; this is much safer. I used and use OctoPrint with custom shell scripts to turn on the printer and the hot end cooler fan as described in <a href="https://3dprinting.stackexchange.com/a/5812/">this answer</a>.</p>
<p><a href="https://i.sstatic.net/tPLh9.png" rel="nofollow noreferrer" title="OctoPrint menu options"><img src="https://i.sstatic.net/tPLh9.png" alt="enter image description here" title="OctoPrint menu options" /></a></p>

CC BY-SA 4.0
2023-12-07T18:01:07.950Z
2023-12-07T22:39:19.987Z
2023-12-07T22:39:19.987Z
0scar
<p>Prusa says the MK3S+ draws up to 120 W. So let's say 150 W of inrush current.</p>
<p><span class="math-container">$$150 W \div 230 V ≈ 0.65 A$$</span></p>
<p>An order of magnitude less than a typical Raspberry Pi optically isolated relay shield can do.</p>
<p>Is there anything I should be aware of when choosing the board? Anything I'm missing here?</p>

CC BY-SA 4.0
2023-12-07T15:55:50.330Z
I doubt the printer will do that in idle when you turn on the printer, the power will be much less (no heating of the bed or the hot end).
0scar
CC BY-SA 4.0
2023-12-07T16:23:28.827Z
@0scar I also *doubt* it'll be a problem, but I'd much rather *know it won't*. I hope someone here already knows and can share.
Mołot
<prusa-i3><power-supply><raspberry-pi><octopi>
Is it safe to use 230 V AC, 10 A relay shield to turn my Prusa MK3S+ on/off using OctoPrint?
Mołot
# Is it safe to use 230 V AC, 10 A relay shield to turn my Prusa MK3S+ on/off using OctoPrint?

(Asked by: username_0 on 2023-12-07)

Prusa says the MK3S+ draws up to 120 W. So let's say 150 W of inrush current.

$$150 W \div 230 V ≈ 0.65 A$$

An order of magnitude less than a typical Raspberry Pi optically isolated relay shield can do.

Is there anything I should be aware of when choosing the board? Anything I'm missing here?

**Tags:** prusa-i3, power-supply, raspberry-pi, octopi

> **Comments:**
> **username_1**: I doubt the printer will do that in idle when you turn on the printer, the power will be much less (no heating of the bed or the hot end).  
> **username_0**: @username_1 I also *doubt* it'll be a problem, but I'd much rather *know it won't*. I hope someone here already knows and can share.  

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## 1 answers

### Answer by username_1 on 2023-12-07. Score: 1 | Accepted answer

Yes it is safe to use such relay modules. Note that the printer will use less power than the specified power, when in idle it nearly doesn't use any power at all, the inrush current will be ver low when switching the relay. Furthermore, the relay is capable of handling the current according to its specification. Do note that you are using mains power, which can be dangerous, please make precautions working on mains (pull the plug from the socket) and shield the wires and use proper crimping tools, no solder.

I have done this with 2 printers, one where I cut the 230 V, but the latest one uses a computer 12 V PSU which has a separate wire (I think this is 5 V) which you can short to start the PSU; this is much safer. I used and use OctoPrint with custom shell scripts to turn on the printer and the hot end cooler fan as described in [this answer](https://3dprinting.stackexchange.com/a/5812/).

[![enter image description here](https://i.sstatic.net/tPLh9.png "OctoPrint menu options")](https://i.sstatic.net/tPLh9.png "OctoPrint menu options")


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