January 4, 2012
Description
It's no secret to owners of Emaker Huxleys that the heated bed has a design flaw. Many owners, including myself, have experience multiple failures of the heated bed.
http://www.emakershop.com/forum?vasthtmlaction=viewtopic&t=276
IMHO, it's not if but when the bed will fail. I decided to design my own replacement bed for the Emaker Huxleys despite already ordering the ReprapPro Huxley's PCB bed.
Reason being that the PCB bed is not a drop-in replacement for the Emaker Huxleys. Changes to the Y-axis is required and the thermistor tables are different too.
This bed is designed to be a drop-in replacement and has a larger build area that will allow actual printing of the promised 140mm x 140mm area.
One of the problem when coming up with the design is determining the resistor to use. Indeed there seems to be no guide to this. For my case, I used my rusty electronics knowledge and some guesswork.
First, determine the power wattage for the bed. 90-100W seems like a safe bet, and since the Emaker Huxley's power adapter is only rated to 120W (19V). It's best to give some allowance. Obviously, if your bed is huge or uses a thicker aluminum, you have to compensate for that.
So current, I = 90W / 19V = 4.74A
Resistance, R = 19V / 4.74A = 4ohms
I decided to use 6 x 15W resistors to spread the heat more evenly, but I believe 4 x 25W will work too. So roughly 4ohms / 6 = 0.66ohms each.
http://singapore.rs-online.com/web/p/products/107-3560/
I also got some high-temp hook up wires.
http://singapore.rs-online.com/web/p/products/177-0952/
You can use back the original thermistors that came with the kit but just for reference, it's this one.
http://singapore.rs-online.com/web/p/products/528-8592/
License:
Creative Commons - Attribution - Share Alike