As I pressed print, the heated bed started to heat up but after about an hour it still had only reached 108 degrees. I got my meter and tried reading voltages and resistance of the bed. Resistance seemed OK. Voltage was hard to figure if it was right or not.
I sent an email asking how long it normally takes for the bed to heat up and got the answer if you cover the bed about 15 mins about 30 mins if you don’t, and a suggestion “cover the heated bed with something while it was heating up”. This was some sound advice so I got some artists board and covered the bed. The time was reduced to about 12 minutes but I could only just make it to 110 degrees.
So I tried printing again. The 110 degrees lasted for seconds as soon as it started to print the temperature dropped to around 90-95 degrees.
I have learned the hard way that if the temperature of the bed drops below about 105 then the item being printed does not stick well and that is what happened with my first print. It was only a cube but as it printed the bottom side of the cube the piece started to move. But the extruder just keeps pushing out the filament. This trial and error went on for a while.
The voltage of the bed was reporting 10.9 volts and I was not sure if this was normal or if there was voltage drop somewhere. I tightened up the terminal block connection to the bed.
Then I checked the connector to the power supply that came with the kit. It had been made by hand and it looked like one of the wires might be loose. Ah, yes it came out in my hand. The whole thing is run off a PC power supply so was easily remedied. I went to the local computer store and got a connector for the power supply. This helped but it was not the main issue.
I separated the PTCs away from each other, afraid that the temperature of one was triggering the other and causing it to be a high resistance. I started to look to see what other improvements I could make.
1) I went to Ikea and got some thin cork normally used for place mat settings, and placed it under the heated bed.
2) I noticed the fan on the extruder heat sink was blowing air. I saw that in the example prints there was something that attaches to the heat sink to divert the air. This is what I was going to print.
I managed to print something, but right before it finished it started to unstick from the bed. But it was usable though. I could now reach 115 degrees and the temperature was still dropping but not as drastically as before. I fiddled with the settings again.
3) I looked at the board and noticed the heat sink on the main FET did not have heat sink compound; maybe it was getting hot and causing a voltage drop. I tried pointing a fan at the FET and finally things were working better based on the display. I was staying above 105 degrees. I did some further investigations. Other people had similar issues.
4) It was suggested that the PTC was changed to one with a higher value. I added an in-line fuse.
5) Change the FET to a higher rated part (I used IRFB743) and as I changed the part I added a smear of heat sink compound.
6) I also started to look for a terminal block that had a bigger gate and more pressure on the wires when tightened.
7) I reattached the thermistor under the heated bed so that it was in maximum contact with the heated bed.
I started it all up and now my heated bed was going to 115 degrees and dropping to 110 after the first layer (This is the correct operation). But more importantly it was maintaining 110 degrees.
Looked like the original parts in my equipment were on the verge of its parameters and that is why it is not working perfectly.
Now that I was pleased with operation I dressed the wires so that they did not resemble a bundle of wires.
It took a while but I now my prints are coming out pretty good.