<p><strong>[edit]</strong>
I just noticed you've mentioned "mains voltage"</p>

<p><strong>DON'T DO THAT</strong></p>

<p>If there is 12V on your heatbed and your power supply gives 12&nbsp;V then you can do it but there will be no control over your heating procedure.</p>

<p>How does it work?</p>

<p>RAMPS is connected to Arduino and then through Arduino to your computer. So applications can say to Arduino - hey, heat it up up to 70°C. So Arduino sends this command to RAMPS and RAMPS is switching on heating, meantime it measures temperature and sends this measurement to Arduino so it knows if your heatbed is already at 70°C or not. Having that knowledge Arduino can decide to still heat it up or rather switch the power of the heatbed off.</p>

<p>If you connect your heatbed directly to your power supply then all of the above controlling sequence will not take place.</p>

<p>Imagine to connect your lightbulb directly to the wall plug. You can do it but then you will not have any chance to switch it on or off. Right? ;)</p>

<p><strong>So in my opinion - don't do that - don't connect your heatbed directly to your power supply.</strong></p>

CC BY-SA 3.0
2016-07-21T19:33:21.650Z
@Ryan Carlyle - how was it possible to double post??? :D
darth pixel
CC BY-SA 3.0
2016-07-22T10:07:35.433Z
Note that if you plug a mains heated bed directly into your (12/24)V power supply, it will barely heat up at all (because its resistance is far too high). I don't think the "don't do that" in all caps is warranted, since it suggests there is some kind of danger.
Tom van der Zanden
CC BY-SA 3.0
2016-07-22T11:41:00.013Z
@TomvanderZanden I did think the same way at the beginning till I realised he mentioned "mains voltage" which suggests using 120/250V but not 12/24V
darth pixel
CC BY-SA 3.0
2016-07-21T19:20:56.920Z
2017-06-21T12:18:44.450Z
2017-06-21T12:18:44.450Z
darth pixel
<p>"Mains voltage" is the alternating current provided by your wall outlets (eg 120v in USA). In order to use a mains voltage heatbed in a 3d printer, you will need to wire up your controller to switch an AC SSR. That way, your low-voltage-DC RAMPS board can control AC current. </p>

<p>If you plug a heatbed directly into a power supply, it will never stop heating, and may burn itself up or even cause a fire. Don't do that. </p>

<p>Because mains voltage has enough voltage to kill you, it should only be used for STATIONARY components, such as the PSU supply wiring and Delta heatbeds. With moving beds, particularly Mendel/i3 style Y-beds, wire fatigue and rubbing can expose the electrical conductors and create a serious safety hazard. </p>

<p>200x200mm is a very reasonable size for a DC bed heater, so there's really no good reason to use an AC heater here. It's more complex and less safe. I recommend getting a different heater. </p>

CC BY-SA 3.0
2016-07-21T19:20:03.250Z
What is an AC SSR?
leeand00
CC BY-SA 3.0
2016-07-21T19:31:58.447Z
basically - solid state relay - element which uses low voltage to switch on/off high voltage
darth pixel
CC BY-SA 3.0
2016-07-21T19:33:47.260Z
"How do I wire an AC SSR with RAMPS" would be an excellent thing to ask in another question.
Ryan Carlyle
CC BY-SA 3.0
2016-07-22T10:04:34.810Z
I wouldn't say a mains voltage bed is less safe than a low-voltage DC one. While AC has the potential to kill you, the current needed for a DC bed is much higher. Therefore you need thicker conductors (which are less flexible and more likely to break due to motion) and higher rated terminals. Considering the majority of printer fires are caused by the high current of a DC bed melting connectors, there's a good case to be made for a mains-power bed, especially considering that earthing mitigates the risk of wiring getting exposed. With RE complexity, a DC heater requires a PSU, AC does not.
Tom van der Zanden
CC BY-SA 3.0
2016-07-23T01:17:44.200Z
@TomvanderZanden In terms of current and under-rated wiring/connectors, yes, I agree absolutely. I'm a strong proponent of 24v systems over 12v for that reason. But anything over 40V puts the equipment in a different class as far as regulatory requirements and safety certifications, simply because it has the ability to kill someone almost instantly on contact. Having all the mains-voltage AC stop at the UL/CE certified PSU is a major testing time+cost advantage for manufacturers. So you're very unlikely to see AC beds on anything but large hobby builds. And those cheap AC SSRs often fail-on!
Ryan Carlyle
CC BY-SA 3.0
2016-07-21T19:16:57.310Z
2016-07-21T19:16:57.310Z
Ryan Carlyle
<p>The heater pad described in your link is designed for 12 VDC or 24 VDC. Therefore, the term Mains Voltage in the description is misleading and probably wrong. Read the voltage and power requirements again and it appears that the heater pad can be connected directly to the RAMPS 1.4 without an external relay or SSR.</p>

CC BY-SA 3.0
2016-08-08T12:48:18.083Z
The pad in question actually has three wires coming off of it; two red ones and one black one.  And it reads 12V on it.
leeand00
CC BY-SA 3.0
2016-08-09T16:00:58.467Z
That is correct. The reason for three wires is so that you can hook it up to either a 12 VDC supply or to a 24 VDC supply. The hookup will be slightly different depending on the supply voltage you use. I cannot tell you exactly which connections to make, but my guess is: for 12 VDC connect the red wires together and to one side of the power and connect the black wire to the other side of the power. Even though the links says you can go directly to the power supply, I still recommend you go through the controller. The description on that link is badly written.
typhonic
CC BY-SA 3.0
2016-07-23T12:12:30.383Z
2016-07-23T12:12:30.383Z
typhonic
<p>I keep thinking it means that I can plug it directly into <a href="http://rads.stackoverflow.com/amzn/click/B007KG0ZYI" rel="nofollow noreferrer">my power supply</a> instead of running it though my RAMPs 1.4; is that correct?</p>

<p>Here is the link to it, <a href="http://www.robotdigg.com/product/209" rel="nofollow noreferrer">200*200mm Square Silicone Heater Pad</a>.</p>

CC BY-SA 3.0
2017-06-21T12:31:44.390Z
As typhonic points out in [his answer](https://3dprinting.stackexchange.com/questions/1536/what-does-uses-mains-voltage-mean-on-this-200200mm-square-silicone-heater-pad#answer-1548), the product description is very confusing, suggesting that 12/24VDC be used, and then that 120/240 VAC can be used. I have written to RobotDigg for clarification
Greenonline
<heated-bed>
What does "Uses Mains Voltage" mean on this 200*200mm Square Silicone Heater Pad?
leeand00
# What does "Uses Mains Voltage" mean on this 200*200mm Square Silicone Heater Pad?

(Asked by: username_0 on 2016-07-21)

I keep thinking it means that I can plug it directly into [my power supply](http://rads.stackoverflow.com/amzn/click/B007KG0ZYI) instead of running it though my RAMPs 1.4; is that correct?

Here is the link to it, [200\*200mm Square Silicone Heater Pad](http://www.robotdigg.com/product/209).

**Tags:** heated-bed

> **Comments:**
> **username_1**: As username_5 points out in [his answer](https://3dprinting.stackexchange.com/questions/1536/what-does-uses-mains-voltage-mean-on-this-200200mm-square-silicone-heater-pad#answer-1548), the product description is very confusing, suggesting that 12/24VDC be used, and then that 120/240 VAC can be used. I have written to RobotDigg for clarification  

---

## 3 answers

### Answer by username_2 on 2016-07-21. Score: 4

**[edit]**
I just noticed you've mentioned "mains voltage"

**DON'T DO THAT**

If there is 12V on your heatbed and your power supply gives 12 V then you can do it but there will be no control over your heating procedure.

How does it work?

RAMPS is connected to Arduino and then through Arduino to your computer. So applications can say to Arduino - hey, heat it up up to 70°C. So Arduino sends this command to RAMPS and RAMPS is switching on heating, meantime it measures temperature and sends this measurement to Arduino so it knows if your heatbed is already at 70°C or not. Having that knowledge Arduino can decide to still heat it up or rather switch the power of the heatbed off.

If you connect your heatbed directly to your power supply then all of the above controlling sequence will not take place.

Imagine to connect your lightbulb directly to the wall plug. You can do it but then you will not have any chance to switch it on or off. Right? ;)

**So in my opinion - don't do that - don't connect your heatbed directly to your power supply.**

> **Comments:**
> **username_2**: @username_4 - how was it possible to double post??? :D  
> **username_3**: Note that if you plug a mains heated bed directly into your (12/24)V power supply, it will barely heat up at all (because its resistance is far too high). I don't think the "don't do that" in all caps is warranted, since it suggests there is some kind of danger.  
> **username_2**: @username_3 I did think the same way at the beginning till I realised he mentioned "mains voltage" which suggests using 120/250V but not 12/24V  

---

### Answer by username_4 on 2016-07-21. Score: 4

"Mains voltage" is the alternating current provided by your wall outlets (eg 120v in USA). In order to use a mains voltage heatbed in a 3d printer, you will need to wire up your controller to switch an AC SSR. That way, your low-voltage-DC RAMPS board can control AC current.

If you plug a heatbed directly into a power supply, it will never stop heating, and may burn itself up or even cause a fire. Don't do that.

Because mains voltage has enough voltage to kill you, it should only be used for STATIONARY components, such as the PSU supply wiring and Delta heatbeds. With moving beds, particularly Mendel/i3 style Y-beds, wire fatigue and rubbing can expose the electrical conductors and create a serious safety hazard.

200x200mm is a very reasonable size for a DC bed heater, so there's really no good reason to use an AC heater here. It's more complex and less safe. I recommend getting a different heater.

> **Comments:**
> **username_0**: What is an AC SSR?  
> **username_2**: basically - solid state relay - element which uses low voltage to switch on/off high voltage  
> **username_4**: "How do I wire an AC SSR with RAMPS" would be an excellent thing to ask in another question.  
> **username_3**: I wouldn't say a mains voltage bed is less safe than a low-voltage DC one. While AC has the potential to kill you, the current needed for a DC bed is much higher. Therefore you need thicker conductors (which are less flexible and more likely to break due to motion) and higher rated terminals. Considering the majority of printer fires are caused by the high current of a DC bed melting connectors, there's a good case to be made for a mains-power bed, especially considering that earthing mitigates the risk of wiring getting exposed. With RE complexity, a DC heater requires a PSU, AC does not.  
> **username_4**: @username_3 In terms of current and under-rated wiring/connectors, yes, I agree absolutely. I'm a strong proponent of 24v systems over 12v for that reason. But anything over 40V puts the equipment in a different class as far as regulatory requirements and safety certifications, simply because it has the ability to kill someone almost instantly on contact. Having all the mains-voltage AC stop at the UL/CE certified PSU is a major testing time+cost advantage for manufacturers. So you're very unlikely to see AC beds on anything but large hobby builds. And those cheap AC SSRs often fail-on!  

---

### Answer by username_5 on 2016-07-23. Score: 3

The heater pad described in your link is designed for 12 VDC or 24 VDC. Therefore, the term Mains Voltage in the description is misleading and probably wrong. Read the voltage and power requirements again and it appears that the heater pad can be connected directly to the RAMPS 1.4 without an external relay or SSR.

> **Comments:**
> **username_0**: The pad in question actually has three wires coming off of it; two red ones and one black one.  And it reads 12V on it.  
> **username_5**: That is correct. The reason for three wires is so that you can hook it up to either a 12 VDC supply or to a 24 VDC supply. The hookup will be slightly different depending on the supply voltage you use. I cannot tell you exactly which connections to make, but my guess is: for 12 VDC connect the red wires together and to one side of the power and connect the black wire to the other side of the power. Even though the links says you can go directly to the power supply, I still recommend you go through the controller. The description on that link is badly written.  

---

