Bed Heating Issues

[griffinbryan]

Hi,

I just finished my Rostock MX V2 build last night and today I went thru the calibration. Everything with the build & calibration went very smoothly up until I got to the temperature tuning. The extruder temp kept over shooting the target and failing the PID Autotune. So, I mounted the PEEK fan on the extruder by wedging it in and with the fan I was able to get the extruder to autotune. The bed has been a whole different set of issues....

First, when trying to run the temp autotune on the bed it times out every time, even when I preheat it before running the routine. I finlly just gave up on this and decided to try a print anyway. Well, the bed never would get to printing temperature. I tried insulating it with towels and was able to get the temp up to about 95 deg. and started a print but the bed could not maintain that temp and the part came loose after a few layers. I purchased some .030" PEI to use on the bed before I started the build so I went ahead and applied it to the glass with the 3M transfer tape that was being talked about in the PEI thread. With the PEI on the bed, the last print attempt got to about 55% completion before the temperature dropped too low and the part came loose again. It looks like the highest temp the bed can maintain is somewhere between 65 and 73 (ish) degrees.

I have the Onyx wired with 14 AWG. So I THINK the problem is the power being supplied to the bed from the Viotek PSU...? The voltage at the RAMBO reads 11.78 V with heat on and the bed disconnected. With the bed connected it drops to 10.44 V. The current draw under load is initially about 13.25 A and slowly drops while the bed is heating. One extra piece of info... I have some LED lighting mounted to the extruder being supplied with a 12V tap from the PSU. I noticed the lights flicker in sync with the power being supplied to the bed. It's really noticable when the PID loop is actively maintaining temperature.

So any ideas why the bed isn't getting enough juice? Do I have a lame PSU?

[Jimustanguitar]

You're sure that the thermistors aren't crossed?

[griffinbryan]

You're sure that the thermistors aren't crossed?

Pretty sure. The extruder temp control works great so I assume I've got the thermistors wired correctly.

I checked the temp at the center of the bed with a thermocouple and it was within a couple degrees of the temp displayed on the LCD. The temp on the outer areas is about 16 degrees hotter. I'm trying a print on the perimeter with a bed temp of 81 degrees. 91% so far and still sticking but I do see some curling in the corners.

[Eaglezsoar]

You're sure that the thermistors aren't crossed?

Pretty sure. The extruder temp control works great so I assume I've got the thermistors wired correctly.

I checked the temp at the center of the bed with a thermocouple and it was within a couple degrees of the temp displayed on the LCD. The temp on the outer areas is about 16 degrees hotter. I'm trying a print on the perimeter with a bed temp of 81 degrees. 91% so far and still sticking but I do see some curling in the corners.

There are other users who have had a similar problem and decided to run the Onyx at 24v by purchasing a 24v supply and a solid state relay.
Type in your browser site: seemecnc.com 24V and it will find some of the topics that deal with it. That is how I run my Onyx and is quite effective.
The 24v power supply we use is one that can supply 30 amps but 20 amps would probably work.

[geneb]

If you're trying to reach high temperatures (north of 90 degrees), you'll need to look into a 24 volt supply.

That being said, I print ABS at 80C and I've yet to have an issue. I don't understand this incessant drive to insanely high bed temperatures.

g.

[Tinyhead]

That being said, I print ABS at 80C and I've yet to have an issue. I don't understand this incessant drive to insanely high bed temperatures.

If only we could all get our ABS to stick at 80C! I can only get my bed up to around the 90 mark (after a good long wait... and even then, if I so much as fart in the room, the temp will drop about 5 degrees). I used a heating pad to get the bed up to 110C and the ABS stuck, but as soon as it cooled back down to around 90 the parts just popped off. Other than 2 small fan holders, I have yet to produce a successful ABS print.

I'm guessing the stock power supplies are right on the edge of effectiveness when it comes to heating the bed. I wonder if a larger supply could get another 10 degrees out of the bed or something. I know on my machine, when the bed is heating, my LEDs flicker quite a bit at the voltage drop.

[Eaglezsoar]

That being said, I print ABS at 80C and I've yet to have an issue. I don't understand this incessant drive to insanely high bed temperatures.

If only we could all get our ABS to stick at 80C! I can only get my bed up to around the 90 mark (after a good long wait... and even then, if I so much as fart in the room, the temp will drop about 5 degrees). I used a heating pad to get the bed up to 110C and the ABS stuck, but as soon as it cooled back down to around 90 the parts just popped off. Other than 2 small fan holders, I have yet to produce a successful ABS print.

I'm guessing the stock power supplies are right on the edge of effectiveness when it comes to heating the bed. I wonder if a larger supply could get another 10 degrees out of the bed or something. I know on my machine, when the bed is heating, my LEDs flicker quite a bit at the voltage drop.

Using the Aqua Net Extra Super Hold hairspray I run my bed at 80c all the time and the parts are stuck so well it is difficult to get them off the glass until it cools down.

[griffinbryan]

I've attached a shot of my second ABS print at 72%...

I re-leveled my bed after applying the PEI (which I failed to do before the first print), and for now my work around for the bed heating issue is to print 60mm off center where my surface temp is reading about 82C. The bed thermister is still only reading 71.5C.

I think I will upgrade to a more robust PSU in the near future. The LED flickering seems to indicate that my current PSU is having trouble keeping up with the current demand. Has anyone else tried this with success?

[Eaglezsoar]

I've attached a shot of my second ABS print at 72%...

I re-leveled my bed after applying the PEI (which I failed to do before the first print), and for now my work around for the bed heating issue is to print 60mm off center where my surface temp is reading about 82C. The bed thermister is still only reading 71.5C.

I think I will upgrade to a more robust PSU in the near future. The LED flickering seems to indicate that my current PSU is having trouble keeping up with the current demand. Has anyone else tried this with success?

Some users have converted their Onyx to run on 24v and there are many topics about this on the forum.
Here is just one you may want to read: http://forum.seemecnc.com/viewtopic.php?f=54&t=1792

[Lanty]

Sorry to hear some people are having issues with their heat bed.

My Max v2 gets up to 90 in about 15 min or so and holds the temp fine once it gets there. I have an small towel that I throw over the bed as it's heating up to help insulate it. I boiled some acetone at 110 the other day with no problem and my basement is pretty cool. I've been printing ABS (225 nozzle 90 bed) and have had minimal curl, When I do get edges curling up I have noticed the glass was a bit dirty, so probably more my fault vs. temp issues.

[Shizuma]

It very likely could be the PSU, the PSU that comes with the kit is junk, I had nothing but problems with being able to get the printer up to proper temps for ABS with that PSU, I had to lower the bed to 85C and put a towel on it to get to that temp with the hotend at 220C and the PSU sounds like it's going to die any min the voltage drop is so severe, I put a high quality 550 watt ATX PSU in my V1 and no problems at all, I can get the bed temp up to 100C with no problems at all now with the hotend at 225C.

I really think that it's a hit or miss thing with that PSU too because some people have no problems at all, and other like myself have tons of problems, that's unfortunately the problem with cheap PSU's, they are very inconsistent.

[griffinbryan]

Thanks for the input, Shizuma. What was the make and model of your new PSU?

I have been experimenting with PLA the last couple days and have gotten much more consistent results than ABS. Except for higher heat applications this is my material of choice for now. With the stock glass plate at 60C and purple glue stick it sticks like, uh... glue.

[Shizuma]

The specific PSU I got was the Thermaltake SMART Series SP-550PCBUS 550W ATX, though just a bit of warning with that one, all the wire are black, so it's not quite as easy as getting 6 yellow, and 6 black wires for the 12v and the green and black for the power on switch and calling it a day, you need a ATX pin out chart/multimeter with that specific one. Really so long as you get any decent quality PSU with enough power you should be good. Really I would look for any PSU that's 80 plus certified and check the 12V rail specs, the stock 450 watt PSU only has 22A on the 12V rail, the 550 watt one I got has 42A on the 12v rail, you also want to make sure the PSU is a single 12V rail type, not multiple rails.

Another thing that's good to do is to load the 5v rail, a lot of ATX PSU's have issues with the 12v rail giving consistent voltage without a proper load on the 5v rail, I loaded mine with 2x 10ohm, 10 watt sandblock resistors in parallel attached to the back vent of the PSU so they get airflow to keep them from getting too hot.

I haven't even tried PLA with mine, just ABS because a lot of stuff I print i'm concerned with the lower temp at which PLA parts can warp, so being able to get high bed temps was important for me, the stock PSU the kit came with I only ended up running the printer for a week with before I decided to replace it.