MK42 bed clones finally available?

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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 3:14 pm

I obviously can't see under my printer too well, but from what I can see, especially the underside of the two solder pads (below), doesn't show any sign of there being any vias connecting the two sides. I also can't see any vias from looking at the photo I took of the top side before I mounted the bed on the printer (full resolution photo attached).

So as far as I can tell, they've just put pointless tracks on the bottom side?!

I can say that the top and the bottom are definitely not identical - different silkscreen for a start, although it looks like there's still copper on the bottom side of the solder pad area - so I'm really not sure what they're doing :)

I've now ordered a 24V 25A(!) power supply for delivery tomorrow, so we'll see what I can do with that. I'll replace my 12V PSU with it, so I'll need ~3A at 24V for my hotend, motors, fans, LEDs, etc. (via a 300W/7-or-9A [depending on which I choose to use] buck converter), but that still leaves 20A at 24V that I can PWM into the bed. I really am sick of having to wait quarter of an hour for the bed to heat up!

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Aziraphale
Posts: 29
Joined: Mon Aug 21, 2017 11:21 am
Location: Wiltshire, UK

Re: MK42 bed clones finally available?

Post by Aziraphale » Thu Oct 05, 2017 3:31 pm

I got my new 24V PSU set up on Sunday - and it's a bloody loud thing. I think I'll have to wire an external potentiometer inline with the fan's power cable so I can turn the fan speed down a lot, because even after it had been heating the bed for a while it was still blowing out cold air, so it's clearly not getting that hot. (Alternatively I might try using an NTC thermistor inline with the fan, so that it speeds up as things get warmer, but I don't know how practical that would be. I'd have to get the NTC's value and the value of any additional resistors just right to produce a good temperature-vs-speed range. These things are supposed to have temperature-controlled fans by default, but the cheaper ones very rarely live up to that promise...)

Anyway, last night after work I finally had the spoons to configure the Smoothieware config and get it all tested out and wow, what a difference it makes!

I gradually ramped the Smoothieware bed max_pwm value up from 64 (out of 255; they recommend 64 for when driving a 12V heater with 24V). A value of 64 gave me 5.5A at 24V (equivalent to 11A at 12V, or 132W, which is actually a little less than the 13.5A/162W that I was getting with straight 12V), so I tried 80 (7.1A, 170W), 100 (9.3A, 223W), 128 (50% PWM; 11.3A, 271W) and then finally settled on 145 (13.9A, 334W).

So that's now dumping a touch over twice as much power into the bed as I was getting before, and now, instead of taking over 15 minutes to reach 95C, it's now heating to that temperature in four minutes which is soooo much better! I tried raising the temperature to 110C and then 120C and both of those increments happened in about 30 seconds each - good going, considering it struggled to hit 100 before!

So overall I'm very happy with that. I have a nice big print bed - a flat print bed, even - with a real PEI sheet that actually works (unlike the stuff that's sold on Amazon), and it heats to ABS temperatures in under 5 minutes, barely taking longer than the hotend does.

And with 14A from the bed, plus about 3A into the buck converter down to 12V, that's only 68% load on the PSU, so hopefully my questionable, no-name supply won't die too quickly! <insert link to Tom's video on having to repair these cheap PSUs because they die so easily>

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

Post by slippyr4 » Thu Oct 05, 2017 3:50 pm

does yours say that it's thermal controlled on the case?

mine did, but it wasn't. Theres supposed to be a thermal switch inside, glued to the inside of one of the toriods, which switches the fan on and off. Mine just had a jumped soldered in place instead, so i added a thermal switch. I also replaced the fan with a scythe one and it's a lot quieter, and actually the fan doesn't run that often anyway. well worth the "fix"
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
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Aziraphale
Posts: 29
Joined: Mon Aug 21, 2017 11:21 am
Location: Wiltshire, UK

Re: MK42 bed clones finally available?

Post by Aziraphale » Thu Oct 05, 2017 10:01 pm

That's encouraging, thanks. I've got next week off work, so I'll certainly take a look :) What did you mean by a thermal switch, though?

I've also found a couple of sites that suggest circuits combining an NTC thermistor, an op-amp and a transistor (and some other bits) to control the fan, so if that circuit you talk about doesn't exist, I can add something in there. I'm not sure but I might even have op-amps in my electronics collection; I definitely have transistors. No NTCs, though (unless standard 3D printer thermistors are NTC? I've not checked!). I might bring my DigiKey order forward a bit for that, since China's on holiday and I don't think I can wait for China delivery with this fan :P

This 24V 25A PSU from Amazon (no real brand, besides maybe "AC-DC" stylised to look a bit like Meanwell's "MW") doesn't say it has the thermal control of the fan, but the 12V 33A PSU that I bought from E3D did say that the fan was thermally-controlled, but I never heard it change speed, so either it wasn't thermally-controlled, or its only control was to kick it into a super-loud mode at full load that I never experienced (it had a label saying, essentially, "don't worry if the fan isn't spinning, it'll only turn on at higher loads", so I suspect it just didn't have control).

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: MK42 bed clones finally available?

Post by slippyr4 » Thu Oct 05, 2017 10:20 pm

Mine (like many) has engraved on the case “this power supply is built-in on off control circuit” which is a lie.

You could come up with a complex circuit for variable fan control but it’s be hard to make it work well, and what is the point? If you fit a quiet fan and a simple thermal switch then it’s either silent (when the printer isn’t working hard) or quietish (when the printer is working hard).

My MK2S clone runs the fan about one third of the time when printing ABS with the bed at 100, and the fan rarely runs at all with PLA and the bed at 60.

The fan I used was a gelid FN-SX06-38 which is nice and quiet and quite cheap.

The thermal switch is a KSD9700. They are available NC or NO - you want NO and the trigger temperature 35 or 45 degrees would be fine.

Feel free to post a photo of the board in your PSU and I can say if it is like mine.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
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chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: MK42 bed clones finally available?

Post by chumm » Fri Oct 06, 2017 12:14 am

This is great info, thanks! My 24v runs like a jet engine full time and it's really awful, just ordered the fan and switch to mod it. I don't suppose you've found a quiet 30mm 24v fan?

Fuzzylogic
Posts: 6
Joined: Fri Oct 06, 2017 12:26 am

Re: MK42 bed clones finally available?

Post by Fuzzylogic » Fri Oct 06, 2017 12:49 am

The tracks on the bottom side are not connected to anything, but i think they are there to prevent warping of the board.

I experimented with making a MK42 board myself, and first tried a copper plane at the bottom, traces on the top, but that board was not perfectly flat. And heating it up made things worse. It was also not directly etched from 32um copper clad. So the resistance was 0.7 Ohm. Unusable.

2nd attempt, i had a 2 boards made with 18um copper on the top and bottom. Resistance was to high (2 Ohm) , But once i connected both sides in parallel, it worked fine.

3rd attempt, 32um copper top/bottom. Measured resistance 1 Ohm. Perfect.

Final version on the left, first(green) version on the right.
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Aziraphale wrote:
Fri Sep 29, 2017 3:14 pm
I obviously can't see under my printer too well, but from what I can see, especially the underside of the two solder pads (below), doesn't show any sign of there being any vias connecting the two sides. I also can't see any vias from looking at the photo I took of the top side before I mounted the bed on the printer (full resolution photo attached).

So as far as I can tell, they've just put pointless tracks on the bottom side?!

Aziraphale
Posts: 29
Joined: Mon Aug 21, 2017 11:21 am
Location: Wiltshire, UK

Re: MK42 bed clones finally available?

Post by Aziraphale » Fri Oct 06, 2017 12:39 pm

slippyr4 wrote:
Thu Oct 05, 2017 10:20 pm
Mine (like many) has engraved on the case “this power supply is built-in on off control circuit” which is a lie.

The fan I used was a gelid FN-SX06-38 which is nice and quiet and quite cheap.

The thermal switch is a KSD9700. They are available NC or NO - you want NO and the trigger temperature 35 or 45 degrees would be fine.

Feel free to post a photo of the board in your PSU and I can say if it is like mine.
Thanks, I've found those switches on Amazon so I'll grab a few of those - I want to mod my old 12V PSU as well as the new 24V one.

Here's an imgur album of photos of my 12V PSU from E3D. Too many photos to post in this thread directly :) I've found a few NTCs inside but no sign of a thermal switch and no sign of one being replaced with a jumper, either, as far as I can tell. There is a missing "ZNR1" component in photo #5, but from what I can tell that's just supposed to be a MOV. Best of luck figuring things out for that - I'd be very grateful if you can find where a thermal switch needs to be connected, though!

I'll get photos of the inside of the 24V fan later. It's all installed on the back of my printer's enclosure at the moment, so gaining access to remove the case won't be trivial. Hopefully I can at least leave it in place and functional while I take photos and figure out how to mod it - I'd rather not have my printer out of action for ages.
chumm wrote:
Fri Oct 06, 2017 12:14 am
I don't suppose you've found a quiet 30mm 24v fan?
Nope, I haven't, sorry. Here's a DigiKey search for 12V 30mm fans sorted with quietest first, but they don't have any 24V fans in that size.

What's this for? My PSUs both use 60mm fans (DigiKey search for 60mm 12V fans sorted quietest first, and for 24V 60mm fans) and there are plenty of options there. If it's for a hotend heatsink cooling fan, e.g. to replace the E3D v6 fan, you're probably better off looking for a 40mm-to-30mm fan adapter model to print, then getting a 24V 40mm fan which are also very common. I'll probably end up swapping to a quiet 40mm fan for my hotend soon, but right now the PSU is by far the top priority!

Of course, keep in mind that a lot of very quiet fans don't actually move much air around, so keep an eye on the CFM figures as well :)
Fuzzylogic wrote:
Fri Oct 06, 2017 12:49 am
The tracks on the bottom side are not connected to anything, but i think they are there to prevent warping of the board.
That's super interesting, thanks for posting that. It's curious that Orballo have those traces on the bottom of the bed while Prusa don't.

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: MK42 bed clones finally available?

Post by slippyr4 » Fri Oct 06, 2017 1:13 pm

The copper wound toroid next to the yellow transformer is where the switch would be. Is there something glued in to the hole in the middle of it? hard to tell in your photos. there's lots of thermal glue there though.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
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Vertigo
Posts: 22
Joined: Mon Jul 31, 2017 9:00 am

Re: MK42 bed clones finally available?

Post by Vertigo » Fri Oct 06, 2017 2:02 pm

I just got a tracking number for my orballo MK42. Took ~3 weeks.

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