Trying to keep from burning something up or worse (@Team_3D_Fab might be of help too)
I’ve been getting my Mendel90 working, slowly and my 200x300mm PCB heatbed just doesn’t have the “oomph” to maintain 100 degrees C. I haven’t built an enclosure yet (which can help the bed retain heat) but reading through the specs for my heatbed I found this info:
- Resistance between 1 and 1.3 ohm for the 12V (110 - 144 Watts)
- Resistance between 4.5 and 5 ohm for the 24V (115 - 128 Watts)
- Running 24V on a 12V setting will heatup the heatbed to 100 degree Celsius in only 2 minutes (while consuming 443 - 576 Watts!!!)
Which sounds good and all, but my PSU is only 360 watts so I fear it could try to draw too much current and burn up my PSU.
Here’s the relevant pads on the board:
I had hooked it up in 24v mode to pads 2 and 3. I will re-wire it to +24 on pads 2 and 3 and ground on pad 1.
So my first question is - I should treat this as a parallel resistance problem, right? I have resistances from pad 2 to 1 and from pad 3 to 1.
If that’s the case, I get:
1/Rt=1/1.2 + 1/1.2
giving a total resistance of 0.6 ohms. Which at 24v is 40 amps or 960 watts. If I’m good so far I can adjust my firmware to keep the heatbed driver throttled to about 20% to give me about 200 watts.
Unless I’m doing my math wrong.