Convert MK2 to 24 volt?  

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wirlybird
(@wirlybird)
Reputable Member

Hi all,

I have an MK2 that is original electronics (all 12v) except I run the stock heat bed from a separate mosfet.  I would like to convert to 24v.

I have a Meanwell 24v power supply that is unused I can use.

How involved is this?  My reason is I have a 24v hotend I want to test and the MK2 would be a good test platform.

Changing fans to 24v is easy but what else is going to be needed?  Is the heat bed going to need to be changed?

 

Thanks for any info on this.  I search for info but didn't really find anything specific to doing an overall conversion on an MK2.

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Posted : 10/09/2020 4:10 pm
clemens.m
(@clemens-m)
Reputable Member

Don´t do that with the original heatbed (MK42 Prusa). I don´t know the exact numbers but I can give you an idea: I think the original MK42 has about 160W driven at 12V. That means there is a current of 160W/12V = 0,9 Ohms.

O.k. now we take the 24V powersupply and connect that to the MK42 heatbed (it has 0,9 Ohms no matter how much voltage is put on it). So let´s do a short calculation: R = 0,9 Ohms = U [v] / I [A] ==> I = U / R = 24 / 0,9 = 26,6 A. So connecting the Heatbed to 24V will drive a current of 26,6A and that means an electrical power of P = U * I = 24 * 26,6 = ~640W. I am not sure if that is a good idea for the heatbed, maybe not that easy to handle for the PID-regulator and I am sure your power supply will not be able to provide this power - that is 4 times the power of the heatbed driven by 12V.

If you would like to move from 12V to 24V you need a different heatbed - and without some modifications you don´t find an original Prusa Heatbed for 24V which can be assembled to the original carrier of the Y-axis.

Best regards, Clemens

This post was modified 2 months ago 2 times by clemens.m
Posted : 10/09/2020 4:36 pm
wirlybird
(@wirlybird)
Reputable Member

@clemens-m

Thanks.

What if I ran a separate mosfet for the hotend heater, like I have for the bed?  I'd just need to source 24v for the hotend and everything else can stay 12v.

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Posted : 10/09/2020 4:42 pm
clemens.m
(@clemens-m)
Reputable Member

@wirlybird

That is possible but be careful - wrong wirering - and you have a destroyed microcontroller board. So you should be used in things like that.

Best regards, Clemens

Posted : 10/09/2020 4:44 pm
wirlybird
(@wirlybird)
Reputable Member

@clemens-m

Wiring the external mosfet to run the heater is no problem.  I did it for the heat bed and it works great.  Takes the strain off of the main board to heat the bed.
Just need to source 24v to the mosfet.

This post was modified 2 months ago by wirlybird
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Posted : 10/09/2020 4:53 pm
wirlybird
(@wirlybird)
Reputable Member

So I found several DC-DC 12v to 24v step up converters on Amazon.

One I am looking at is 10A/240W.

Would this be sufficient to power a E3D v6 style 40 or 50w heater?

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Posted : 10/09/2020 5:13 pm
clemens.m
(@clemens-m)
Reputable Member

@wirlybird

One question: What is getting better if you are using a 24V extruder instead of 12V extruder. The original extruder in the MK2 has 12V and about 40W power. As you wrote the 24V extruder is nearly similar in provided power. So it is not heating faster or more accurate or something else (in my opinion - am I wrong?)

Best regards, Clemens

Posted : 10/09/2020 5:22 pm
wirlybird
(@wirlybird)
Reputable Member

@clemens-m

Good question and I'll clarify!

My stock setup works fine but I am testing a different hotend setup and it is only available in 24v.  The MK2 is my best option for testing as it is an E3D style mount..
My other printer that I could use runs a volcano so too much adapting to get lengths ok and everything else I have run thermocouple instead of thermistors so they won't work.

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Posted : 10/09/2020 5:31 pm
clemens.m
(@clemens-m)
Reputable Member
Posted by: @clemens-m

Don´t do that with the original heatbed (MK42 Prusa). I don´t know the exact numbers but I can give you an idea: I think the original MK42 has about 160W driven at 12V. That means there is a current of 160W/12V = 0,9 Ohms.

Sorry I was calculating on a sheet of paper and when I posted I was not fully concentrated: Current I =160W / 12U = 13,3A. ==> So resistance is R=U/I = 12V / 13,3A = 0,9 Ohm.

Rest is ok

Best regards, Clemens

Posted : 10/09/2020 6:26 pm
clemens.m
(@clemens-m)
Reputable Member

@wirlybird

Find out if the heater cartridges for 12V and 24V are the same dimension - could also be a way.

Best regards, Clemens

Posted : 10/09/2020 6:27 pm
wirlybird
(@wirlybird)
Reputable Member

Ok so let's circle back to the begging on converting the MK2 to 24v.
I have the bed on an external mosfet now with 12v from the power supply bypassing the Rambo.
What if I took a 24v line from the "new" power supply and stepped it down to 12v and fed it to the external mosfet?  This should then supply the Rambo with 24v and the bed with 12v.
I think the only thing to change to 24v is the two fans.

What do you think?!

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Posted : 10/09/2020 9:26 pm
clemens.m
(@clemens-m)
Reputable Member

@wirlybird

Sorry I am out. I know what is to do on an Arduino Mega 2560 and a Ramps board if you want to change input voltage from 12V to 24V. I never had a look to the Rambo Board. But I am sure there is something similar - sure there is somewhere a voltage regulator which is doing 12V down to 5V (or something like that). BUT I HAVE NO KNOWLEDGE ABOUT THAT ON THE RAMBO BOARD. Be careful and think twice (at least) !!!

Best regards, Clemens

Posted : 10/09/2020 9:55 pm
wirlybird
(@wirlybird)
Reputable Member

@clemens-m

That's ok.  I wasn't implying doing it on the board.

No worries, I think I found a solution.

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Posted : 10/09/2020 10:13 pm
nikolai.r
(@nikolai-r)
Noble Member
Posted by: @wirlybird

How involved is this?  My reason is I have a 24v hotend I want to test and the MK2 would be a good test platform.

In this case the easiest approach is to swap the heater on your 24V extruder to 12V heater. Or use an external mosfet switch for that. Rebuilding the printer for that sounds like bringing the mountain to Muhammad 🙂

This post was modified 2 months ago by nikolai.r
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Posted : 11/09/2020 7:03 pm
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