[Idea] New Heatbed with more "zones"

Hi Developers,

what do you think about a new heatbed design with more than just one heat area?

Why we heat up every time a big area also if we would just print a small thing?
The heatbed heat's all the time and consume many power all over his lifetime!

My idea:
Design a heatbed with more area's like my attached example scheme.



Actually we need 4 wires. Two for heatbed power and two for thermistor.
We can make it work with this for wires also but need some parts more.
Maybe a small microcontroller which communicates with the main controller via two wires like "serial, SPI, TWI, I2C or something like this" and three driver transistors.
The drivers can be smaller, because we have not 100% power on one of them.
The microcontroller can control the temperature self and heat just the size which is requested from the main controller.
Actually we use about 130 Watts for a 20 x 20 cm heatbed.
Please think global! There are lot of 3D printers all over the world. So we can save some noticeable CO2 with this.

Sure, the hardware is a little bit more complex but a 3D printer too.

Taner

Edited 2 time(s). Last edit at 10/27/2015 06:57AM by db1nto.

I think you are looking in the wrong place if your goal is to reduce carbon emissions.

Would this help heating up faster? Putting the whole energy in to only heat up the blue area should help heat up the bed much faster for small prints, right?

Rather than a microcontroller, you could just have 2 switches... wire the power for the outer panels in parallel to the inner panel, with one switch in series with each outer panel. Before printing, you switch on the appropriate switch(es) depending on the size of the object.

This does assume that the outer panels heat at about the same rate as the inner panel, since the inner panel's thermistor is all that is used to control the bed temperature. I'd guess that this would be near enough, since that's essentially what happens when you have one large panel with one thermistor. But I vaguely recall that dc42 (or someone else) had a scheme for wiring thermistors in series to get an average across them all. If you went for this option, you'd want double-pole switches, so that only the in-use panel thermistors were wired into the averaging circuit.

Rather than concentric panels (which I think would be hard to source), you could have a mosaic of (e.g.) 25 identical small panels. Having several identical panels would mean that they would behave (more or less) the same as the one in the middle which has a thermistor and does the temperature control. These could be wired up in concentric rings to the two switches to give the same functionality as the concentric design.

Or the small panels could be wired up in a matrix with up to 25 switches, so that any individual panel could be connected to the heated bed supply. In this model, there's no particular requirement for the small panels to be square (they could be rectangular), nor that they be similar in shape to size of the bed.

Of course, there's no reason why your printer controller couldn't control these panels via relays... it would add no workload to the controller whilst printing, since it would just turn on the appropriate panels before printing. I think Marlin has some functionality for switching GPIO pins? Certainly Octoprint does. If you want to automate the panel selection, I'd guess that you'd scan the G-code file to find the XY limits of the object being printed, thereby identifying which panel(s) need to be turned on.


@JustAnotherOne: This wouldn't help heat the blue area faster. Assuming the power supply is adequate, the heating rate is controlled by the voltage of the supply and the resistance of the pad. To put more energy into the same pad, you would have to increase the voltage.

@DRobs86: Whilst this won't save the planet, it may save something on your power bill. A 300x300 heater draws 350W when on. I don't know what the duty cycle might be... that would depend mostly on ambient temperature and insulation. Arbitrarily, I'll assume 50%. If you print 6 hours per day, that's (more or less) 1kWh = 27 cents for me. If you can cut the heater down to 200x200 it costs 9/25 = 36% (10c), and 100x100 is 1/25 = 4% (1c). You'd possibly save $50 per year, depending on how much printing you do, and how many of those prints were medium or small size.

Frank

Good all around analysis Frank. First let me say that 27 cents per kWh is steep! Ouch.

Secondly I'm not sure that we don't want some of that extra heat though, particularly 28th abs. Don't we want the air around the print to stay a little warmer than ambient air? For instance, it's probably non ideal to print an 6x6 object on a 6x6 heater. The edges of the print would be subjected to a greater temperature differential than if the same object were printed on an 8x8 heated bed. This could cause some curling.