silicon rubber heater bed -120 Deg celsius in 1 minute (Page 3 of 4)

Im finding this thread pretty interesting seems the standard heater takes its time to get to temperature. can someone post some pictures of how they are mounting the new heater?

How long does that take to heat up?

Setting the extruder to 200C and the bed to 100C, starting them at the same time: it takes only about a minute longer for the bed to reach 100C after the extruder has reached 200C. 

I almost don't know what to do with myself now.  I used to be able to go make myself a sandwich, eat it, and come back and still wait for a few minutes to start my print.

The sheets shaved another 5 min off my heating time...also discovered my thermistor was cracked in half oops...it was working before so idk...glad I have a couple backups.

Has anyone considered using one of those silicone sheets to print on? Obviously they can handle higher temps. Just lay one on the print bed potentially with some sort of adhesive.

I hadn't considered printing directly on to silicone baking sheet.  I'm pretty happy with the smooth bottom layer from printing on to glass.

you can see the heat element thru the silicon pad with a good light... you don't need x-ray

A word of caution on using solid state relays to control your bed heater.  If they are SCR or TRIAC based (very likely) they are designed to handle AC current only, and once you turn them on, will not shut down if you are using DC current.  In other words, as your controller turns them on, the heating element will begin to heat, and when it reachs temperature, and the controller tries to turn them off, they will continue to heat until power is removed from them.

I (finally) spent some time on this yesterday, and was very pleased with the results. My method so far:

• Upgraded power supply to 12V 12 amp (linked earlier in the thread).

• Replaced power terminals on electronics to larger screw terminal (highly recommended, no more slipping out).

• Replaced bed connector on electronics to screw terminal (should be safer and more reliable).

• Soldered on jumper leads as discussed in other thread.

• Bought a connector compatible with stock thermistor plug and crimped/soldered it onto the silicone mat thermistor wires.

• Copied and pasted thermistor table (for this thermistor) into firmware found googling and uploaded firmware

• Ran bed PID autotune, recorded numbers and set the firmware with PID bed heating and these values

I am using the standard inbuilt mosfet, with the jumper leads and new terminals to prevent it gettng too hot. I googled the part number and it was rated plenty high for this application. So far it hasn't even gotten too hot to touch, even at full load. With my cooled electronics cover in place, this should be 100% reliable and safe. No solid state relay or extra wiring needed!

With the new terminals for the bed, I can swap the electrical connections for the new and old heater/thermistor in about a minute.

Leaving the thermistor setting at 6 in the firmware was very inaccurate. Firmware was reporting about 40-50 degrees BELOW what recorded IR temperature ie. 50 vs 90. Thermistor table from internet was much better, about 10 degrees off at lower temps but within a few around 100.

Band bang control with the new bed was no good. Since it heats so quickly, a 5 second cycle had it shooting above the target and then dropping below in the next cycle. Reducing the cycle to three seconds was better, but switching to PID was improved again and highly recommended.

I've yet to finalise the physical mounting of the bed, but am planning to have a thin metal plate underneath it with holes for the bed height screws, and a recess for the thicker part where the wires feed in to the silicone. I might even use the standard aluminium plate for this.

One thing I want is glass to print on, but I will get it cut 150 x 170 so that it extends over the mat 10mm at the front and back. I'm planning on printing some nice quick release clips so that I still have the full printing area but the glass panels can be swapped out easily.

I'll do a full write up with pics when it's sorted but in the mean time here is a teaser image of the heating up in Repetier. New power supply for both, standard setup for the lower line, silicone bed sitting on top of standard bed with cast iron soldering helper on top to add a bit of thermal mass. As you can see it goes from low 30s to 100 in under 2 minutes!

"A word of caution on using solid state relays to control your bed heater.  If they are SCR or TRIAC based (very likely) they are designed to handle AC current only, and once you turn them on, will not shut down if you are using DC current.  In other words, as your controller turns them on, the heating element will begin to heat, and when it reachs temperature, and the controller tries to turn them off, they will continue to heat until power is removed from them."  I was sold and bought a DC-DC SSR, I am not sure of its specific tech, but once I had it wired in correctly I haven't had a single problem. I would prefer the most simplified solution so...

I don't get close to 2 min heating times so, I will just do what Lawsy has done and use the on-board Mosfet for switching...It's a great idea to increase the capacity of those traces,  I have seen it suggested several times on RepRap forums as well so it is a very good fix to a common issue.

Question for Lawsy. The jumpers mentioned in your post. Did you add the jumpers between the adjacent +12V and -V pads for the bed connector? Want to be sure before doing it.