Heating bed

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bjorn
Posts: 102
Joined: Fri Aug 10, 2018 6:00 pm

Re: Heating bed

Post by bjorn » Sun Mar 03, 2019 4:06 pm

bjorn wrote:
Tue Feb 26, 2019 8:28 am
Adding adittional heat is possible. Bump the voltage fed to the bed to say 48V and it should perform quite well, not much room to add 48V supply inside and I doubt using a boost converter and drawing an extra 30W is good for the original power supply.
DO NOT increase the voltage to either bed or hot end; the original wiring just can't handle much more, and ribbon to print head and wires to limit switches doesn't have any temperature rating so likely 60C.

I've looked at using 24V supply when making the change to Duet Maestro, but I'm not gonna do that without replacing ribbon to print head and FPC to bed, the adittional current is just too much.

(Yes, we can increase the voltage to reduce the current, but then the resistance in the heater elements has to increase as well and without magic beans that basically calls for a new bed/extruder)

Update: 70C in 20 minutes is about as far as I'm willing to push this thing.
Last edited by bjorn on Wed Mar 06, 2019 1:21 am, edited 1 time in total.

bjorn
Posts: 102
Joined: Fri Aug 10, 2018 6:00 pm

Re: Heating bed

Post by bjorn » Tue Mar 05, 2019 7:52 am

At the end of an ~8hour print bed temp showed 82% (of 90C target = 73.8C) - with no adittional insulation or anything out of the ordinary. Ambient temp +19C.

Not sure if this is because I seated the FPC cable on the motherboard properly or just the only time I've looked at the printer at the end of such a long print. Will try to measure the voltage drop to the bed again before throwing out the original electronics to see if it changed after re-seating the cable on the mainboard.

bjorn
Posts: 102
Joined: Fri Aug 10, 2018 6:00 pm

Re: Heating bed

Post by bjorn » Wed Mar 06, 2019 4:07 pm

Little change in voltage drop after FPC being seated properly.

Monitored the current draw when trying 24V, started off at 1.72A and dropped steadily towards 1.40A after 10 minutes as the bed reached 65C. Unsure if the PCB alone has so much of a PTC effect, or if what I thought was a 0R bridge is in fact a PTC. Will need to repeat measurements with a wired meter and bring out the scope to be sure the electronics arent doing any PWM stuff.

If it does have or act like a PTC then using 24V with the original FPC may not be so bad (I tried with a proper wire this first time).

Confirmed 18.5 ohm at 75C and 14.4 ohm at 20C. The biggest influence on how fast the themperature rise seems to be the speed of the fan below, with off being ideal. Its easy enough to disconnect from the original board, the 3pin connector behind the rainbow ribbon cable. Not sure if this is by design or just a side effect of using the PCB as a heater.

tiertini
Posts: 4
Joined: Thu Feb 28, 2019 8:15 pm

Re: Heating bed

Post by tiertini » Sun Mar 10, 2019 10:48 am

@bjorn encountering the same problems after buying the printer with the TAG "able to print ABS" which I believed in and
they fooled me as well. I am waiting on my RMA to send the printer back and refund the money.

Did you find anything more? Are you able to print ABS with only 70°C bed temp?

bjorn
Posts: 102
Joined: Fri Aug 10, 2018 6:00 pm

Re: Heating bed

Post by bjorn » Mon Mar 11, 2019 7:33 am

I have printed about 3-4kg of ABS so far, but anything that that has a large-ish surface area is likely to warp. I recently printed a Pi case, and it took 3-4 attempts, ended up adding "mouse ears" to the model before printing.

Smaller parts usually printer quite well, just a shame that the raft is more often than not bigger than the part I need. But I'm working on replacing the motherboard and use a slicer that can actually procduce raftless prints that work.

I recently tried adding some thin fiberglass insulation just because I had it appart, and seems to have had a negative impact, possibly related to the PTC effect I was seeing. More investegation required, but I also think I'll receive the aluminum bed with a 230V heater one of these days so might not get around to it.

I did have a chat with my local vendor (who has to deal with much stronger consumer protection rigths than Tiertime) and explained what the marketing material said, and what my experience and expectations were - they decided they wanted to send me a replacement printer first to see if it could do what it says on the box, and refund my purchase if not. That was in January, and I'm still waiting for the new printer. With everything I've seen replacing the electronics, I view it as highly unlikely that any printer will reach 90C without modifications - and I have big reservations about the rigidity of the whole Z/X assembly with the bed coming close to 90C.

bjorn
Posts: 102
Joined: Fri Aug 10, 2018 6:00 pm

Re: Heating bed

Post by bjorn » Mon Mar 18, 2019 6:42 pm

bjorn wrote:
Wed Mar 06, 2019 4:07 pm
Confirmed 18.5 ohm at 75C and 14.4 ohm at 20C. The biggest influence on how fast the themperature rise seems to be the speed of the fan below, with off being ideal. Its easy enough to disconnect from the original board, the 3pin connector behind the rainbow ribbon cable. Not sure if this is by design or just a side effect of using the PCB as a heater.
This is just slightly more than the temperature coefficient for plain copper so there isn't much to do about it, but even if its just 0.393% pr degree it halves the available power after 80 degrees to less than 10W when supplying 14V as I measured on mine. 10W is less than the lost heat.

So final conclusion is that it will be very difficult to increase the temperature without insulating the whole enclosure to reduce heat loss, rewiring and increasing the supply voltage for the bed, or just plain out replacing it. I've been running mine at 24V and if left long enough it will hit 80C without insulation, but thats the temperature the ABS holding the whole bed assembly start to soften so I'm not going to push it past that. That also confirms its never been designed to hit the ABS target temperature in my book.

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