Hard to get bed to 90 degrees on Plus

[lewisd]

I've got a Printrbot Plus Metal, and I'm finding it takes a LONG time, like half an hour, to get the bed to 90 degrees. This is even in an enclosed wooden box not much bigger than the printer, with my homemade ventilation system turned off, so no airflow.
Is that normal?

[PxT]

Those beds are slow to heat up because they're huge, but 30 minutes seems excessive. What kind of power supply are you using? You can try insulating the underside of the bed so that less heat escapes — or more accurately so that less cool air can flow under the bed and steal your precious heat. People have used cork, cardboard, and various other things. There was an official solution for sale at one point but I think it's gone from the site now - a sheet of mylar-like material that went underneath to reflect the heat back towards the bed.

[lewisd]

It gets up to 70-80 degrees (from ambient 20-30) pretty quickly, but that last 10 degrees takes a good 10-15 minutes.

It's the power supply that came with the printer. Seems like a pretty heavy duty ATX supply. Would using a power supply that's rated higher on one of the 12v rails help any, or is the current limited by the Printrboard or the wiring?

The mylar sheet you mention, was that attached to the underside of the bed itself, between the rails?

[Mooselake]

Is the bed heater set to PID in the MP's firmware? If so, is there an equivalent of the extruder's autotune?

This phone's not made for walking^^^^^^^googling...

Kirk

[PxT]

[Mooselake]

Fast rise to within 10°, then slow to the setpoint sounds like the tuning's off if it was a hotend.

However, not sure why that massive bed would be set for PID, bang-bang would be just fine.

Kirk

[Mooselake]

Mussellake, the clam vacation hot spot

[PxT]

Ah, you're right. Bang-bang is the default for the bed on the stock firmware. Ignore my earlier comment.

[Mooselake]

Well, trying to autotune the bed would be a good test, particularly if it succeeds. So would setting it to, say, 80° and seeing if it goes fast to 70 and then creeps up the last 10 degrees.

In the old demontek underpowered supply days a piece of cardboard over the bed would insulate it and make it heat up noticably faster. FWIW the cardboard under my heated bed has been there since about 2013, and been up to over 110C without problems

Kirk