SD4 Heatbed Installation (Page 3 of 3)

beware... my link is just for the example. if you read the comment , you will see that it's not the best quality...

if i were you, i will search for something of 60A or more (seem that SSR are a bit overrated when they come from china..) instead of 40A.

this one seem ok ( http://www.amazon.com/Hoymk-Amr-60dd-Ac … amp;sr=1-2 ) but it come from china.. so expect long delivery...

If at first you don't succeed...  Disappointed with my first attempt I replaced the heatbed again - this time with much better results.  I decided I liked the original idea of the SD design (heat pad on back with aluminum to spread the heat) but felt it needed a little boosting to improve the heatup time and to keep it flat.
I purchased 0.25" thick piece of Alcoa cast aluminum off eBay for $18 (2X the thickness of the stock and ground flat to sub-mil accuracy) and after drilling and tapping all the holes attached a 8"x8" 300W silicon heatpad (also from eBay for $20).  Next, I added a layer of aluminum foil to help reflect the heat upward followed by a piece of 0.25" thick felt for insulation.  Finally, I printed a fixture to hold the glass plate in place.:



I wired the heatpad directly to my 50A PSU mounted on the back of the unit:

And now the money shot - 10C delta from max to min *across the entire platform* (most of the area was <5C delta).  Pretty pleased with this:

It heats up to 100C in 12 minutes (Actual - RH thinks it reached temperature in <5minutes).  Maybe once I tune the PID, this will improve, but even this is almost half my previous bed.

[Note: the cool spot in the middle is caused by a chip of glass missing from the back side that came off with a print creating an airgap between the glass and the bed there. A pristine plate should not have that.]

Very Nice!... but no unattended printing!!

Hmmm.  I suppose I'm playing with fire here (perhaps quite literally) but there is no way I'm going to sit around watching paint dry^H^H^H^H^H models print.  I do keep tabs via the webcams and have a fire alarm in the equipment closet where I keep the printer.  Maybe I should design a redundant and independent temp sensor.  Something that cuts power if the extruder exceeds 290 or the heatbed exceeds 120.  In fact, I'll go search - I bets someone's already done it.

Not saying this is a solution, but what would you guys suggest to use for the short time you absolutely can't look after the print?
What kind of sensor should be used?

And this thread got me wondering again if a MK2 heatbed is better or even as good as a heat pad...
It seemed like an MK2 is better at heat distribution, but now the thermal images show otherwise?

I'm going to pick up one of these
http://www.amazon.com/Flame-Defender-12 … e+defender

A thread about alternative heatpads is a great place to talk about fire safety, but I'm sorry for taking it so far off topic.