Heated bed temp with ABS and PEI?

[AlanZ]

I installed a PEI sheet today and it has been challenging to get the bed temperature much over 80 degrees reliably.

I don't currently have an enclosure, and although I can set the bed temp to 90 or 100 to reduce print warping, every time the power supply fan comes on, it sucks the heat down to roughly 80 degrees.

As I am typing this, I have the bed set to 100. It reached 97, and then the fan kicked in and it was back down to 85 within a couple of minutes.

The ABS prints are not sticking very well at 80 degrees, and they warp easily... And I am trying to remedy this.

So, a few things come to mind... In no particular order

Insulate the short space directly below the heated bed, and close up the wiring hole
Insulate the underside of the bottom section top melamine plate.
Make a fan shroud/duct for the power supply so it vents towards the side wall fan instead of straight up towards the heated bed.
Increase power to the Onyx bed... Perhaps with an additional power supply

So anything in particular, or combination of things listed or not, come to mind?

Your thoughts are appreciated.

[teoman]

You seem to be on the right track. The sweet spot for my pei was 115 deg C read from the guesstimator. I do have an aluminium heat spreader between bed and pei.

You can upgrade the wires that will help a little bit.

If you have the newer psu and it has an adjustment knob you could tune it so that it is the correct voltage at the bed terminals when the bed is at full load. (Experts on the components please chime in if the fans will be unhappy if they see 13v when bed is not heating)

A little towel over the bed gets it to temp faster. Check for initial gcode modificatios so the printer screams and shouts at you before it starts the print.

I personally have the bed running via a 20V power supply directly through the Rambo.

But before that get your first layer thickness tuned spot on.

[AlanZ]

What type of power supply are you using? How many watts does the Onyx draw to get to 115? Would a high end notebook power supply, perhaps at 19 volts, do the job?

[JFettig]

I always had good luck with 90c

[Xenocrates]

It is unlikely that a notebook PSU would provide enough power, as at 19V, the bed will draw 17A, or 328W's. Wattage is a function of resistance and voltage (determining the current), rather than it drawing just what it needs. I'm fairly certain laptops don't provide 350W PSU's.

However, I've had good luck between 95C and 105C. Haven't gone any hotter, as right now I can't. I can barely maintain the 95C, which isn't surprising with an ambient of 8C. However, as my PEI is bonded to the AL without a glass layer between it, my actual surface temps are likely closer to Teoman's than you'd think.

[nebbian]

For what it's worth, I run 105 degrees first layer temp, then go down to 100 degrees for subsequent layers. The filament goes down at 0.2 layer height at 250 degrees for the first layer, then 240 degrees and 0.1mm layer height after that. This works exceptionally well for me. The models I print have many short sections, with retractions between sections, on the first layer, and unless i get the temperatures perfect I end up with some sections curling up. This means a failed print unless all sections work perfectly -- and the temps I gave above, work reliably 99% of the time. Another trick is to set the first layer extrusion width to be a lot wider than your nozzle size, I use 0.6mm for a nozzle size of 0.4mm. This wider extrusion width makes the plastic 'squish' into the bed.

Note that the 250 degrees and 240 degree temperatures only work with models that have very thin (0.8mm) walls. If printing something more solid, I go down to 230 degrees or so.

My delta uses a 12V power supply that I tweaked up to 14V, with an automotive 30A relay switching the bed. It takes 5 minutes to go from room temperature to 105 degrees.

Underneath my bed I've got a layer of cardboard, with aluminium tape stuck on, which helps to insulate the bed from the electronics.


I hope this helps you somewhat. First layer issues are super frustrating!

[AlanZ]

Xenocrates,

Thanks for the wattage information. The power supply I have on hand is 170 watts, 20 VoLTE... So not enough.

All: What is a good recommendation for a secondary power supply (and if necessary, a relay)? Amazon links would be appreciated.

[nitewatchman]

My recommendation is to use a 24VDC Primary Supply to run everything.

The p/s would power the bed directly controlled through an SSR and a 24VDC to 12VDC converter would supply everything else (Rambo downstream). This approach uses three major components, has only one power supply and maintains a complete stock configuration from the inputs on the Rambo card on.

[AlanZ]

I like the single power supply approach. Do you have a parts list for all the pieces?

[nitewatchman]

Sample parts:

http://www.ebay.com/itm/MeanWell-SP-500 ... SwLVZV2nGb" onclick="window.open(this.href);return false;

I would offer $50 or wait a bit, mine one year was a Make Offer for $70 - offered $36.63 and it was accepted.

http://www.ebay.com/itm/MW-SP-500-24-Me ... Swv0tVeMfO" onclick="window.open(this.href);return false;

If you are impatient.

http://www.ebay.com/itm/CRYDOM-D1D40-SO ... SwKtlWpWFa" onclick="window.open(this.href);return false;

SSR - Caution some Flotek's have been used in the past with disastrous results. These were generally considered fakes. Remember ohm's law, well another part talks about power lost in watts (SSR gets hot) calculated by the equation w=(I*I)*R. These apparently had very high internal resistance and even with a very large heat sink they would burnout long before their rated output. Unfortunately these then to lock on and run away. It is a good idea to make some provision for a heat sink. I mounted to the side of the power supply attached to a 1/2" plate. Significantly more than required to the 10th power but it was what I had at the time.

http://www.amazon.com/HOSSEN%C2%AE-Conv ... +converter" onclick="window.open(this.href);return false;

24VDC to 12VDC Regulator to supply Rambo and all downstream.

This is what I used. Fuses should be added at the p/s input for protection. The Meanwell is also a protected p/s, if it starts to overload it shuts down or throttles the voltage back controlling the current output.

I can crack the base of my Rostock in a couple of days and get some photos. On mine everything fit within the base with room after removing the ATX p/s.

[teoman]

How many amps is your laptop psu brick?

[AlanZ]

Nitewatchman,

My 24 volt power supply and 24 to 12 volt converter have arrived.

I have ordered a Crydom D1D40, that should arrive in a few days.
What heat sink is a good fit for the D1D40?

[IMBoring25]

The SSR heat sinks are pretty standard. The important part should be the thermal paste on the interface.

[nitewatchman]

Nitewatchman,

My 24 volt power supply and 24 to 12 volt converter have arrived.

I have ordered a Crydom D1D40, that should arrive in a few days.
What heat sink is a good fit for the D1D40?

You can use a commercial finned heat sink or simply attached it to an aluminum plate or sheet. Except for those periods when the SSR is running 100% during heatup, the current draw is actually fairly low. During operation mine is not even warm to touch.

[JFettig]

There are a number of heatsinks on amazon for around $5 http://www.amazon.com/uxcell-Aluminum-S ... r+heatsink" onclick="window.open(this.href);return false;

[AlanZ]

Perfect, thanks!