Using heater cartridges to heat stage

jml

I want to use heater cartridges to heat my stage. What is the max output current of the stage heater mosfet? Can it support heating two or three 40W heater cartridges in parallel (24V)? Or should I put the heater cartridges in series? The max desired temp of the small stage is 110C.

mrehorstdmd

120W is good for about 250 cm^2 bed area (about 150mm x 150mm). If the bed is larger than that, you will have to wait a long time for it to heat up. Using 3 cartridges will create three hot spots and very uneven heating unless the bed is made of thick aluminum.

Which board are you using?

If the cartridges are rated for 24V and you're using a 24V power supply for the Duet board, connect the cartridges in parallel. It will take 5A total to power the three heaters.

jml

Thanks for the info. My bed is basically that size, how'd you know?

I'm using a recent Duet 2, with 24V power supply like you said. The bed is 3mm aluminum, so I think the heating will be closer to uniform. Glass or some other sheet will be placed on top to print on.

Will 5A be too much for the mosfet or traces? What if I wanted 10A?

mrehorstdmd

According to: https://duet3d.dozuki.com/Wiki/Hardware_Overview
"High Power rating: Each stepper driver is capable of 2.8A motor current, currently limited in software to 2.4A. The bed heater channel is specifically designed for high current (18A)"

The 0.4-0.5W/cm^2 rule of thumb is based on using a heater pad, not cartridges. Heater cartridges are cylindrical, which means very small contact area between the cartridge and a flat plate, which means inefficient heat transfer, which means the cartridge temperature will be quite a bit higher than the plate temperature, or put another way, bed temperature will be quite a bit lower than the cartridge temperature. How will you attach the cartridges to the bed plate in a way that will improve heat transfer, and not be affected by elevated temperatures?

Phaedrux

May I ask, why would you want to do such a thing? Not to dissuade you. Just curious.

dc42

This post is deleted!

Danal

Physically possible per current capacity of Duet. Operationally inadvisable, for numerous reasons, including hotspots. Plenty of excellent alternatives: https://www.google.com/search?q=150+mm+heated+bed Some of them at price points well below three 24V heater cartridges.

Detailed example Under US $10, shipped, 24V 200x200

jml

@danal Thanks for the links. Unfortunately, my bed is not a nice square shape like that. But maybe I will consider reshaping the bed so I can use an off the shelf heating PCB for more uniform heating.

dc42

What shape is the bed?

jml

@dc42 The bed is rectangle shaped. 140 x 100 approx.

dc42

There are at least two companies (Shenzen Ali Brother Technologies, and Keenovo) who will make a silicone heater to your own size, voltage and power specifications. They don't charge very much for this.

jml

@dc42 Oh great, I'll check them out, thanks! Could be useful for other projects as well!