Topic: My Silicone bed/ PCB bed experiences
I wanted to share some of my experiences with different bed options. I currently have a silicon mat from QU-BD. Additionally I have a makerbot replicator PCB bed. My print surface is glass that has been lightly sand blasted.
If you compare the different solutions. The resistance of the heating element is pretty critical.
Standard issue resistor - 3 ohms
Standard replicator pcb bed - 10 ohms
QU-BD Silicone Bed - 1.6 ohms
Please note the resistance was taken with care using a fairly new Fluke 87V. For readings that low I'd be more comfortable with a milliohm meter, but don't have one close by.
Some interesting thing happen with the different beds.
The replicator uses a 24 V power supply. I happen to have an extra old laptop power supply that seemed to do the trick for me. I first tried a relay. I need to put in a diode as a flyback as the relay clacked on and off. Ideally a solid state relay would do the trick.
Using Ohms law I see the following (P=V^2/R)
24V with 10 ohm bed yields 57.6 watts
12 V with 3 ohm resistor 48 watts
12 V with 1.6 ohm resistor 90 watts
I did the math from the reprap bed page. They figure 120 Watts is ideal. http://goo.gl/k5nEa
I think having a second power supply becomes pretty necessary. The 7.5Amp draw of the silicone bed is a bit much for my taste. It seems to me that the ideal way to go is to follow the PCB design, but rebuild it for 12V and 150mmx150mm.
I designed a bed, but got delayed on the production. This is good, because I'm thinking an adjustment of the traces is necessary.
Is there any interest in a group buy on PCB beds with a second power supply input/ solid state relay board?