MK42 bed clones finally available?

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Aziraphale
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Re: MK42 bed clones finally available?

Post by Aziraphale » Tue Sep 26, 2017 11:20 pm

Mine arrived earlier this month, almost exactly a month after I ordered. So they are getting there, they're just being slow as balls.

Mine arrived with all six screws and standoffs, but the standoffs were expecting to screw into tapped holes in the bed frame which my Chinese i3 frame clone doesn't have, but thanks to previous posts in this thread I had already bought some female-female standoffs and screws to go into them from under the bed frame, so I just used those instead.

I also found that the screws that go in from the top of the bed didn't screw down quite flush with the bed surface, so I've ended up with slight bulges in the PEI sheet where the screws are located. That doesn't seem to have caused any issues so far, though. All of my printing with this new bed has been extremely good. Parts stick to the PEI wonderfully - ABS and PLA both without any glue or anything else, just a 6mm brim (PETG needs a gluestick layer to prevent it sticking too well to PEI, remember!).

Oh, and my bed's electrical resistance between the two wire terminals on the bed is 0.8 ohms. That's a theoretical 15A at 12V, but in practice I only see 13.5A, so my (12 AWG) wiring & MOSFET must add another 0.15 ohms or so. Given that the bed takes over 15 minutes to heat to 95°C, more like 30 mins for 100°C and over 100°C is basically impossible, I'm now looking into options for running a higher voltage just for the bed. I've ordered a 30A boost converter from AliExpress which will let me take the bed up to about 16V and 20A, but I'm not sure that my 12V supply has enough capacity left for 30A of draw from the boost converter. So I may end up replacing the 12V supply with either an 18V or a 24V supply, using a buck converter to get my 12V rail back (for the electronics, fans, hotend, LED strips, etc) and then PWMing the 18-24V to whatever effective voltage I want to use on the bed. I have an external bed MOSFET, so I have a lot of freedom like that. I'll also be running my TMC2100 drivers at either 24 or 35V for maximum silence (through a separate boost converter, since they're lower power).

Which begs the question: is there anything wrong with running a Mk42 bed at a higher voltage (and thus higher current and higher power)? I can't think of any problems with doing so as long as the overall temperature is controlled, which it will be, but I might be missing something! So please, if I'm missing something there please do ruin my plans :p I'd rather find out now rather than after breaking a bed!

slippyr4
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Re: MK42 bed clones finally available?

Post by slippyr4 » Wed Sep 27, 2017 8:42 am

You might find it doesn’t regulate temperature very well even with PID tuning; the thermistor is on the back and the heater on the front of the bed separated by the GRP which is an insulator.

Marlin has an option to limit the duty cycle on the bed. You are probably going to need that: your 0.8 ohm at 24 V is 700 Watts.
Self-built Prusa i3 MK2 clone
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Aziraphale
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Location: Wiltshire, UK

Re: MK42 bed clones finally available?

Post by Aziraphale » Wed Sep 27, 2017 10:28 am

I'm pretty sure the Mk42 has the PCB traces on both sides of the board. I could be wrong, but I seem to recall noting that as a difference between my old MK3 bed and the new Mk42.

And yes, I'm using a Smoothieboard but that has the same PWM option for heaters including the bed. The default config comes with an example line for "a 12V bed on 24V supply", so I'd be using that value but tweaked a little to get the equivalent of 16-18V instead of 12V.

I guess I can try it and see :) Was just hoping someone had experience doing that already!

Vertigo
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Re: MK42 bed clones finally available?

Post by Vertigo » Thu Sep 28, 2017 3:52 pm

Aziraphale wrote:
Tue Sep 26, 2017 11:20 pm
Given that the bed takes over 15 minutes to heat to 95°C, more like 30 mins for 100°C and over 100°C is basically impossible,
I would have assumed there to be no difference in this regard between the original bed, and the clone? THing is, my original Mk42 heats up to 90C quite fast. I never timed it, but its not much longer than it takes the nozzle to heat up. >100C is also absolutely possible, I never tried to see how high it got, but I did set 115C at one point, and I doubt that was the limit (it was still pulsing).

I havent measured my PSU voltage yet, maybe mine is set for a slightly higher voltage. I certainly hope this clone bed, if/when it ever arrives, wont double my heat up times. Its one of the things I love about my MK2S.

slippyr4
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Re: MK42 bed clones finally available?

Post by slippyr4 » Thu Sep 28, 2017 4:15 pm

I have one of the d3di (the indigogo campaign that so many people haven’t received their boards) and also one of the autotronix boards from Norway.

Despite being made from the same open source designs, they are different resistances and hence different powers.

The difference is almost certainly down to the thickness of plating on the board. Whilst the layouts themselves are open source, there’s more to PCB manufacture than just the layout.
Self-built Prusa i3 MK2 clone
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slippyr4
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Re: MK42 bed clones finally available?

Post by slippyr4 » Thu Sep 28, 2017 4:16 pm

Aziraphale wrote:
Wed Sep 27, 2017 10:28 am
I'm pretty sure the Mk42 has the PCB traces on both sides of the board.
No, it’s single sided with traces on the top. There is silk screen on both sides though, which on the bottom marks the proper location of the thermistor.
Self-built Prusa i3 MK2 clone
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MaxRink
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Re: MK42 bed clones finally available?

Post by MaxRink » Fri Sep 29, 2017 11:08 am

slippyr4 wrote:
Thu Sep 28, 2017 4:15 pm
I have one of the d3di (the indigogo campaign that so many people haven’t received their boards) and also one of the autotronix boards from Norway.

Despite being made from the same open source designs, they are different resistances and hence different powers.

The difference is almost certainly down to the thickness of plating on the board. Whilst the layouts themselves are open source, there’s more to PCB manufacture than just the layout.
Which one is better?

slippyr4
Posts: 224
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Re: MK42 bed clones finally available?

Post by slippyr4 » Fri Sep 29, 2017 11:35 am

The d3di one is higher power but is so warped it’s completely unusable.

The autotronix one is lower power but flat, so that’s what I am using day to day.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

Aziraphale
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Joined: Mon Aug 21, 2017 11:21 am
Location: Wiltshire, UK

Re: MK42 bed clones finally available?

Post by Aziraphale » Fri Sep 29, 2017 1:07 pm

slippyr4 wrote:
Thu Sep 28, 2017 4:16 pm
Aziraphale wrote:
Wed Sep 27, 2017 10:28 am
I'm pretty sure the Mk42 has the PCB traces on both sides of the board.
No, it’s single sided with traces on the top. There is silk screen on both sides though, which on the bottom marks the proper location of the thermistor.
Looks like Orballo changed things up a bit, then. I just checked my bed and it definitely has traces on the bottom, and not much silkscreen on the bottom, either (definitely no markings for where to put the thermistor - I just guessed and taped it between the two central screw holes).

I wonder if that's why mine takes longer to heat up? The resistance will be higher, presumably, but if it was much lower I'd end up with crazy current flowing at 12V - 13A already sounds quite high, given that I doubt the official Mk2 comes with a particularly beefy power supply.

I think I'll try to Amazon Prime a 24V PSU for delivery tomorrow and have a play over the weekend.

Top side:
IMG_20170929_113412.jpg
IMG_20170929_113412.jpg (1.24 MiB) Viewed 2026 times
Bottom side (look carefully - it's the same pattern as the top, but hard to see in photos):
IMG_20170929_113438.jpg
IMG_20170929_113438.jpg (962.12 KiB) Viewed 2026 times

slippyr4
Posts: 224
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Re: MK42 bed clones finally available?

Post by slippyr4 » Fri Sep 29, 2017 1:21 pm

That’s odd. Is the bottom connected? What does it look like at the connector area, underneath?

Might be that it’s two 1.6mm FR4 boards laminated.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

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