Large heat bed dual heater question

(mtkim_SW) #1

I have a tronxy x5sa printer.

Part of the common issues is the large heat bed is, taking forever to get to PLA temps.
Not all prints are going to use the 300+ x 300+ build area. So, my idea is to get a smaller silicone 12v heater and using that to print for smaller builds while just using a single thermistor, while having the option to print larger builds.
The main purpose is to lower the power used.
I know I can change it to 24v, but there is the added cost of getting the parts to do so, plus the overall power draw for smaller prints.
My question is, is there a way in the config to have it change which heater to used in the context of switching?

I can wire in a relay and a switch, but I want a more elegant solution.


Imported from wikidot


You could have two beds connected to two different big MOSFETs, but it’s not clear to me what you are trying to do. You want to have two heated beds that you swap between? If your bed cannot heat up fast enough, or stay at the set point, then I would suggest insulating the bottom of the bed.

(Mikekim_SW) #3

Points -

  1. Limit power draw for smaller prints
  2. option to use larger heater for larger prints

smaller heater 120 x 120 12v heater
Larger heater 315 x 315 12v/14v heater
Larger heater will be run with 24v, through a separate mosfet circuit.

Smaller heater will sit on the bottom the larger one, covered with cork board.

My question is, is there a way to switch between the heaters in the config file?


Yes, there are several ways to accomplish what you are trying to do, and some of those ways don’t involve the config at all. You could just have the wires run from one of the big MOSFETs to a plug (or terminal block) external to the Smoothie and plug in either bed. Or you could simply change the pin assignment in the config from MOSFET 1 (e.g. pin 2.5) to MOSFET 2 (e.g pin 2.7), then you would be controlling the second bed (again assuming you have enough big MOSFETs on the Smoothie because if you are running at 12V you cannot plug a 40W hotend into a small MOSFET because it will pull too much current.).
Or you could get more complicated and connect each to a big MOSFET and create a new module and name it bed2 (or whatever), and have your program access that bed instead of the first one. Or you if you have only 2 big MOSFETs and one is being used up by the hotend and the other by bed1, you could use an external MOSFET and control that via a Smoothie small MOSFET and externally control the bed. Many ways.

Before you stack two heater elements together, then try and run a 12V element with a 24V PS (not a great idea even with PMW) and use an external MOSFET, I encourage you to think more about the problem. What you are proposing is a very inelegant solution to the problem of “I want to save a few bucks on my electric bill”. I’m not trying to be argumentative with you, I’m just trying to get you to think about it, because your power consumption cannot be that high—your stock PS is only 360W. My advice is to insulate the bed and that will help a lot and don’t not burn down your house trying to literally save a few cents.

(Mikekim_SW) #5

Supplies I have on hand

4x HA210N06 external mosfets.
24v 420watt power supply
3x 24v to 12v buc converters

My 330x330 bed on a 12v circuit, it can only get to 50*~60*. The bed has previsions to change it to 24v
My 120x120 bed only consumes only 120watts.
Where I’m at, power costs 150% more than the national average per kwh