Uneven Bed Heating

[PikachuPorkChops]

Hello,

I've had my Rostock Max v2 since June and I have always had trouble getting large ABS parts to stick. To combat it I've built an enclosure, and got some bed material called PrintBite which works extremely well for getting prints to stick. Even with all those measures in place I noticed that I'd still get warping on parts of the print that were further out from the center. Printbite only works if it's above a certain temperature threshold.

After purchasing an IR thermometer I discovered that my bed was about 25C cooler at the perimeter than it was in the center. Also, after reading a few forum posts, I discovered that other people were not having any trouble getting their beds hotter than 95C whereas it would take me about half an hour to get to that temp and the printer could barely maintain it.

So that leads me to believe that my PSU is not outputting enough power to heat the bed. I'd rather not drop $60 on a second PSU that I'd use exclusively for the bed. They should supply you with one that actually allows the printer to function properly (or at least as advertised).

I'm wondering what to do here, maybe there are some kind of settings I forgot about? Perhaps I did the wiring wrong? I don't know, but I'm not happy that I've already had to spend quite a bit of money to counter this.

Any help is greatly appreciated.

[Xenocrates]

I would do a few things.

First, get a copper or aluminum heat spreader. Trick laser sells aluminum ones. you can buy 12 inch (actually a little more, at 310MM would be ideal) copper disks online as well. This will help with getting even heat, and also once you are up to temperature, keep it there. It's not a flaw of the Onyx that it can't maintain a totally even temp, that's partially due to the design of the snowflake, and partially due to the design limitations of a PCB heater.

Secondly, check your bed PID max, and if it is not 255, set it to 255. This is an EEPROM setting that can be gotten at either through mattercontrol, or through the LCD and the knob. Use matter control. It's much more convenient to actually set.

Thirdly, check the output voltage of your power supply, and the wiring to it. If it is not 12V's, SeemeCNC may be willing to replace it. However, make sure that if there is a 110/220V select switch, it is in the right place. You may have improperly stripped or improperly installed wires at the screw terminals. There may also be an issue with the solder joints on the Onyx as well.

Fourthly, adding a little bit of heating to the chamber will reduce the work that the Onyx has to do, and is also good for reducing cracking and warping on larger ABS parts. That may be a large part of the issue itself.

Fifthly, Dead-time control may be preferable for your bed. Check some of the posts made recently on the forums about it, I've not played with it myself.

Sixthly, A tea towel on the bed helps substantially with initial heating times. Your heating times are not substantially out of normal. I personally cannot get over 94.4 C on my bed (it can hold a higher temp though) during winter, due the the enviroment my printer is in, and it takes 45~ minutes to reach 80 degrees. And that's with my larger aftermarket PSU. Some places are colder or draftier than is suited for a printer, which is why a heated enclosure is so useful

I wish you the best, and a merry Christmas (or whatever doesn't offend you). I hope the by the turn of the year you have it sorted. Feel free to post questions, or PM them. Preferably post, as I trawl through new posts regularly, and don't always notice a PM quickly, and then others can benefit from the posts later. Others can also throw in as well, of course.

[PikachuPorkChops]

Thanks for the quick response!

1. I was planning to use a MOSFET to connect a more robust PSU that would be dedicated to the Onyx. A heat spreader alone wouldn't help too much in getting the bed temp to get above 95C. I guess I'll get both.

2. My PIDs are all in order.

3. I just checked all the connectors on the Rambo, they're 11.4V. The PSU is set at 115V. The solder joints on the Onyx are all good too.

4. I've been looking into that for a while, but it would involve spending more money I currently don't have The chamber also has an ambient temp of 32C when the hotend and bed are left on for a bit.

5. I will look into dead-time control, but that turbulence only occurs when I reach the limit of the Onyx (~95C). In any case, it seems like a good thing to look into.

6. I've been doing this for a while, it definitely helps reduce warm-up time, but once the towel is removed there's a sharp drop in temp anyways.

It seems I'll need to do a bit more modding to get the printer to where I'd like it to be. I see in your signature you've also switched out the PSU, I'll probably post some sort of mod-log on the forums for personal and public record.

Anyways, thank you for all your suggestions, and for taking the time to respond on a holiday.
Happy non-denominational festivity!

[Xenocrates]

If you're getting a dedicated PSU, may I suggest one that outputs in the 18-24V range? it will need to be beefier, on the order of 20A's on it's own, or 500Ws, but the Rambo is rated to switch it (you will need a larger automotive fuse though), and it will greatly reduce your heatup time. Doing it elegantly would get expensive though, sadly. Adding some heat to the chamber is relatively simple though. A heatlamp, tied to a 5$ relay, and a fairly cheap thermostat will work. Or use this http://growgreenmi.com/ductstat-plug-in ... AsUA8P8HAQ and a heatlamp on it's own, and that will help a good bit.

[PikachuPorkChops]

This was the one I was looking at: http://www.ebay.ca/sch/i.html?_odkw=mea ... u&_sacat=0
But I know a local electronics recycling place that sells 700W used PC PSUs for $40-50. How would it get expensive? I don't think the appropriate FET would exceed $10.

I can't seem to view your image, but a heat lamp is mostly IR, and with the aluminium heat spreader, most of the light would be reflected elsewhere in the enclosure. Unfortunately I also bought a white rostock, meaning that there are very few alternate areas that would efficiently absorb the IR.

Here's my printer, there aren't really any dark surfaces.
[img]http://i.imgur.com/OSmH40b.jpg[/img]

[Xenocrates]

The image was actually a link I clicked the wrong button for. I've gone ahead and fixed that.

The trouble is unless you muck about with adding a current limiting resistor, then you need a 20A PSU for 24V, which is not a voltage supplied by PC power supplies. You can jury rig a pair of server PSU's by disconnecting the DC ground in one, but that's a kludge. And while a FET might work, It's not a solution I prefer. But then, there is an appropriate FET already on the Rambo (The FET's are rated for it, but only barely.) I personally looked at buying a SSR to handle it, and a good SSR for that amperage and voltage is 70$. I didn't want to mix the voltages on the board, and I also wanted to be able to have it fail over to the 12V supply if the 24V was disconnected or failed. A new 24V 21A 500W PSU is around 110$ from mouser, and I'm not certain I want a bargain one, considering the trouble people have with getting the correct voltage out of some of them, and the need for a fairly high wattage, high current part. The way I was looking at doing it was ~230$ for the PSU, the SSR and a form 2 C control relay, plus appropriate plugs, connectors, and switches, and a circuit breaker for it. Not precisely cheap. But considering that it would greatly reduce bed heating times, while also being essentially fail-safe (if the 24V supply falls over, the control relay will trip and isolate the SSR and allow the 12V current to heat the bed as it normally does)

Also, the Melamine is able to absorb IR radiation well enough, as the laser cutter SeemeCNC uses is in the IR spectrum. Not to mention that if you used poly-carbonate walls, it will also absorb IR really well. So well in fact, that it cannot be laser cut well. Acrylic also has a good IR absorption, but not as good as poly.

The printer does look sharp though. I also put LED lights on mine, although mine are installed 60 degrees out of phase with yours, aligned with the towers.

[PikachuPorkChops]

I've been looking around online for this since I got a 3D printer, but I've never been able to find a metric for it. There should be some kind of minimum Watts/cm^2 you want on a heated bed. I'm wondering if just getting a dedicated 24V 15A supply for the bed will be enough to heat it. I'm not sure what ratio of power/size-of-bed I'd need. I've been talking to some people on the IRC about this; they were even the ones to recommend a Seven Switch system (http://reprap.org/wiki/SevenSwitch_1.2).

Using the IR lamp is feasible since I used polycarbonate to make some of the panels.

Anyways I'll continue looking into it. Thank you!

[PikachuPorkChops]

I looked a bit more into the lackluster performance of my bed. The bed is getting 11.4V from the power supply, and I'm reading 1.2 Ohms for the resistance, meaning I'm getting 9.5A and 108W from the bed. The bed is supposed to have only 1 Ohm and be getting 12V from the power supply which would equate to 144W. This means my bed is outputting 25% LESS than it should be. So far I have not found a way to adjust the voltage from the PSU as a means of resolving this.

[Mac The Knife]

These work well,,, and even have a pot on the left side to adjust the output voltage. I believe SeeMeCNC has went away from using the pc powersupplies, and went with this style.
[img]http://ecx.images-amazon.com/images/I/41uyGgXDhEL.jpg[/img]

http://www.amazon.com/Universal-Regulat ... B00D7CWSCG

[PikachuPorkChops]

Obviously the components that SeeMeCNC supplied aren't going to work properly, which is a shame. I guess I'll have to replace both the power supply and the Onyx with something better. Even if I got a power supply that gave 12V consistently, my bed's resistance is still a bit high. I'm looking at some Keenovo silicone beds right now (http://www.ebay.com/itm/Dia-300mm-500W- ... 1456257412). I'll either install one of those, or find a 15 or 18V PSU that I could use for the bed. In the end, I'm just rather disappointed the stock won't work.

I will also probably purchase one of those heat spreaders, but tricklaser has no shipping info on their website, and they probably won't reply to my email until the new year.

Happy holidays to you all!

[nitewatchman]

Before wading in too deep, if you change the power supply to 24VDC and apply it to the Onyx Bed the heat capacity increases to 480 Watts from the 120 Watts you currently have. Last Christmas I removed my Corsair 750W ATX power supply and replaced it with a Meanwell 24VDC 500W power supply. I still supplied 12VDC to everything using a 24VDC to 12VDC converter (no reason then to replace heaters, fans, LED 's, etc.). The bed is switched using a Crydom SSR, this avoids high currents on the RAMBO controller, the switching current is only a few milliamps. While these controllers are excellent, the terminals on the board are not good with large wires and high currents.

My bed with a 1/16" copper spreader (tends to slow heating down) heats from 25C to 70C for PLA in about 1-1/2 to 2 minutes, 25C to 100C for ABS in 4-5 minutes. Before the change, 100C would take 20 to 30 minutes. Bed also keeps up with layer fans running and with copper spreader heat varies maybe 5C across the bed.

Costs vary depending on how hard you shop. The big item is the p/s. Meanwell is a solid name here, used in copies, industrial machines, etc. My costs were as nearly as I recall:

24VDC 500W Power Supply eBay equipment pull) $37.00
D1D40 Crydom Solid State Relay ( new eBay) $20.00
24VDC to 12VDC Converter (new Amazon) $18.00

Fans, terminals, stuff as you feel necessary.

Total for me was about $100. After one year tomorrow no problems, printer runs ALOT.

You need to do what suits you best but for me this is the way to go. Can supply details and photos if it helps.

gary

[PikachuPorkChops]

Hi Gary,

I'm definitely interested, the price is reasonable too. My main reason for not looking into 24V is that I was under the impression the Onyx couldn't handle that, but it seems that it will. Would using a MOSFET in place of a SSR cause any problems?

[nitewatchman]

It has been done and essentially that is all the DC to DC SSR is, an MOSFET packaged with some protection. Biggest problem with SSR's right now is the apparent presence of fakes on the market. This seems to primarily be in the FloTek branding. I know of no Crydom fakes.

My printer has the P/S mounted in the base where the original was and there is plenty of room. I added a IEC socket for a computer type power cord and this has a fuse to protect the wiring to the P/S. I mounted the SSR to an aluminum plate attached to the side of the power supply. I used 1/2" simply because that is what I had - 1/8" or directly to the p/s case would have been fine. In service even when running at 100% during heat up the SSR is not even warm to the touch. The 24VDC to 12VDC converter to mounted next to the SSR and supplies 12VDC To everything else. So 110VAC goes to the p/s and the existing on/off switch goes to the switching terminals on the Power supply. 24VDC from the p/s goes to the converter and 12VDC for the converter connects to the rest of the printer in the same fashion as the original SeeMe p/s and handles every thing else.

A second 24VDC comes from the p/s and connects in series to the SSR and the Onyx bed in a loop. The Rambo output that would normally go to the bed goes to the control terminals on the SSR. Now when the Rambo thinks it is driving the Onyx bed it is in fact on switching the SSR on and off and since the SSR is a high speed device it responds to the PWM applied to control temperature perfectly. My bed will normally overshoot the set point, oscillate two or three cycles and lock in on temperature with about +/1C variance.

Let me look for some example component and I will send you the links. Kinda like fishing, sometimes the are lots of fish biting and sometimes not.

[Jrjones]

I first insulated the underside of my heated bed with Aerogel, which improved my heat up time a little bit and the stability as well.
Most positive thing about the Aerogel was that there is almost no heat transferred to the electronics enclosure through the melamine base.
I recently replaced my power supply with a 360w 12V unit (similar to the ones Seemecnc now supplies with their kits) and I have it adjusted so that when both heaters are on, the heated bed output is 12.2V. Before with the ATX PSU I was reading 11.4V on the heated bed.

It takes 15 minutes to go from 23 deg to 110 deg with a towel on top of the heated bed. It takes about 2 minutes for my hot end to heat up to 235 deg with a 40w heater cartridge.
I use the bed heat up time to fine tune and start slicing the model I am printing.

Aerogel was about $21US for a sample from ebay, and the PSU $35CAD (about $25 US) from Amazon.ca

[PikachuPorkChops]

Nitewatchman: I've got a couple of SSRs kicking around and I've found a 24V 20A PSU on ebay http://www.ebay.ca/itm/Universal-12-24V ... tA5EGZpcug for $70 (I live in Canada)

Jrjones: I upgraded my hotend to use a 40W heater cartridge as well, though it's still the stock hotend. The aerogel "sample" I found on ebay cost $25(!) and I don't see an appreciable advantage it has compared to other --cheaper-- insulators. The PSU that came with mine is rated 450W, which is more than the one you replaced yours with, but I guess the lower voltage is what's affecting the heating. I'll have a look around amazon for PSUs, but I'm planning on using 12V. Thanks for your input!

[Jrjones]

The reason I used Aerogel was because it was the thinnest insulator that could possibly fit under the bed, and I still had to raise the bed by doubling up on the nylon spacers and longer
screws.
Ah, here is the thread Gene started on it: http://forum.seemecnc.com/viewtopic.php?f=36&t=8986

Mind you I bought it back in Feb when the exchange rate wasn't that bad. I was also trying to avoid replacing the psu but I should have asked Seemecnc to keep the crappy ATX when I bought the kit and gone with a proper one from the start.
This is the PSU I bought, https://www.amazon.ca/gp/aw/d/B01734CRT ... UTF8&psc=1
It appears unavailable now, but so far its working well, the fan is quite loud when it turns on, but I dont really hear it over the stepper motors.

I'm also using the stock hot end, but may get the Prometheus to print higher than 250 if that helps avoiding delamination with abs

[nitewatchman]

Nitewatchman: I've got a couple of SSRs kicking around and I've found a 24V 20A PSU on ebay http://www.ebay.ca/itm/Universal-12-24V ... tA5EGZpcug for $70 (I live in Canada)

Looks okay, I would recommend the 24VDCx480W or the next size up. The power supply is adjustable so the output can be lowered slightly to keep the total draw under 480W. Any SSR will work as long as the ampacity is high enough and it is a DC to DC MOSFET unit. If it is a Triac designed for AC it will switch on with the first control pulse and since the voltage never decreases to 0 with the Sine wave it will never switch off.

[PikachuPorkChops]

I'm just about to purchase everything, but I've got one question: How many amps will I need to run the motors and the hotend? I outfitted the hotend with a 40W heater cartridge but everything else is stock. I need to know this in order to get the appropriate converter. I was looking at this one http://www.ebay.ca/itm/New-24V-to-12V-D ... xyVaBSqBfY

Thanks for all the advice

[nitewatchman]

The one you show looks good, I used this converter, http://www.amazon.com/gp/product/B00BWK ... 1_1&sr=8-1. I likely need a lot less than 10A (certainly not 20A) but this one was packaged nicely, plenty of reserve, Amazon Prime and what I could find.

I used a Meanwell 500W power supply, http://www.ebay.com/itm/MW-SP-500-24-Me ... Swv0tVeMfO , essentially the same as you have chosen.

Project on the books for the next week or so is to fuse the 24V outputs from the p/s and the 12V output from the converter with automotive type fuses. I guess that I am just a solution looking for a problem at heart.

PS. Another p/s (located in US - bummer) http://www.ebay.com/itm/MEAN-WELL-SP-50 ... SwjVVVkVpM, I think that the odds are very good that an offer of $30USD would buy this one.

[PikachuPorkChops]

Awesome! I'm ordering now.

The the second p/s you linked will unfortunately cost more than the one I got when you factor in shipping. Also, where can I find shipping cost info for tricklaser? I want to get that heat spreader.

I'll post an update once everything arrives.

[mhackney]

I am compelled to jump in here based not the discussion over in the google delta forums over the last few days. It is VERY important that you understand how your SSR works. They are not all created equally. Last Jan I had a Foster literally catch fire while I was printing. Details in my build thread. The issue is (read the google thread) that there can be a significant voltage drop across some of these SSRs depending on their design. This results in heat generation. A heatsink and fan helps but in my case, did not. Luckily I RARELY print unattended so I was there with a fire extinguisher when it caught fire. I also mount my SSRs OUTSIDE the base unit so it is exposed so I can monitor it visually, can periodically measure it's temperature, etc. The replacement Auberins SSR is really well suited for this application with very low voltage drop. They are affordable at $20 too. I've run mine 6+ hours/day for the last year (nearly every day) with no issues and no noticeable heat produced. It is on a heatsink.

So please do your research and make safe decisions.

As for power supplies, etc. I was one of the pioneers of running a 12V Onyx on 24V. My original Onyx is now years old with no issues. I have several other newer versions and they are all doing fine on 24V.

As for heat dissipators, I was also a pioneer on their use and even manufactured one for a short while. You can actually use 2 layers of thick heavy duty aluminum foil - it works great, and can be cut with a scissors and cost next to nothing if you have the foil already. It has the advantage of heating up quickly too since there is very little extra thermal mass. Just make sure to insulate the Onyx with Kaptan tape where needed and cut out an open area around the power connections. You don't want a short circuit!

[PikachuPorkChops]

That SSR is rated for 100A, 4x more than what I'll be putting through it. I was thinking about getting something less overkill like this. With shipping included, the relay you suggest comes to about $50.

I've got some temperature switches/fuses kicking around. I could stick one of those on the relay so that I don't end up with a fire.

Thanks for the tip about the foil; will try that out.

EDIT: I realize cheaping out on the SSR will be really unsafe, I removed the link in case others read this. I think I will get a MOSFET to drive the board as they are easier to cool, are smaller, and I have more familiarity with them. My question before I purchase one is: are there any issues regarding using FETs to drive the heated bed when compared to an SSR? Aren't they practically identical?