Before we can print we need to apply the Kapton tape on the heated board, but first we need to see if it works. I soldered a DC connector to the heated table's wire so the power brick can be reattached easily.
When strapping cables to the bars, I used some tubing in between to not damage the wires against the sharp threads. My idea is to later on print out a bracket to mount it correctly to the bar.
Measure the resistance to check for any short circuits, it should in theory be 8.8 ohm, but due to the 5% tolerance mine read 9.5 ohm. Set the power brick to 17v and plug it in. After a while it should start to heat up the board.
I used a professional surface temperature probe from Testo. The heat is quite accurate and spread evenly over the whole surface. I got approx. 57c all over except over the resistors where I got about 60c.
If your table doesn't get hot enough or too hot, check what voltage you have selected or even better, use a multimeter to measure the voltage in the DC connector.
I found a useful page converting Watt to Celsius (yes, I'm sceptical to the conversion formula, but it somehow seems to be in the ballpark). Use this formula to get your Watt: U*U / R, for example in my case 17*17 = 289, 289/9.5 = 30.42W and this will give me 57.7c according to the conversion site.
Applying Kapton tape was no easy task. It wrinkles easily and capture a lot of air bubbles. I got quite frustrated and Googled to see how other was doing it. I stumbled upon an extremely good solution that "zaggo" came up with. Before you start you should clean the surface with Acetone or similar.
You need a small bowl with water, some dish soap, a scraper (or similar), a scissor and Kapton tape.
Mix some dish soap into the water and stir a bit.
As you can see I have already started and applied the first strip of Kapton, perfectly without any wrinkles or bubbles.
Start to apply the water-soap solution on the surface where you want to put the Kapton tape. Don't be afraid to apply to much of the solution (but try to keep it on the plate :)
I'm going to overlap the Kapton a little bit, so That's why we have the solution on the Kapton strip as well.
Now, apply a strip of Kapton over the water solution. It will not stick to the surface yet, allowing you to easily move it around to put it in place.
I positioned mine with a 0.5mm overlap and dried up the exceeding water solution around the new Kapton tape.
Use a scraper (in my case a cork handle) to push out the water. I used some paper to dry it up at the ends. Then just leave it to dry for a while and it will stick to the surface like a glove :)
Repeat the process over again until you finished the whole surface.
No wrinkles, no bubbles, just easy...
Your trick for kapton tape is awesome!!! It works really fine!!! I'm following your blog because I'm assembling my orca v0.30 from Mendel Parts and I discovered alot of missing information in your blog! I have one question, I have a pair of power supply one of 70W and one 90W which is for the printing bed and which for the gen6 controller board? thank you!
ReplyDeleteShort Answer:
ReplyDeleteI use one 70W for the control board and another 70W for the heated board. Your power bricks is not "injecting" 70W or 90W, it can DELIVER 70W or 90W.
My Heated board only consumes 30W to give 57 Celsius so any brick would do fine in my case.
Long answer (the theory behind it):
How much power (W) you are going to need is decided by the resistance (Ohm) and Voltage (V) in your heated board.
The resistors are mounted and fixed so the only thing you can change is the Voltage. First you need to decide what temperature you want and from there calculate the power needed. From that you can then calculate what Voltage you should select to get that power.
Example:
My total resistance is 9.5 Ohm (due to 5% tolerance).
My resistors Max Watt allowance is 15W each, giving maximum 60W (I can produce maximum 60W with them).
The temperature I want to have is 55 Celsius.
So to get 55 Celsius I need about 30W (according to the calculator on http://www.conversion-website.com/energy/Celsius_heat_unit_IT_to_watt_hour.html). To produce 30W with the resistance I have mounted (9.5 Ohm) we need a voltage (V) of 16.9V. We get this by taking the square root out of Ohm x W, 9.5 x 30 = 285. SQR(285) = 16.88.
The closest Voltage I can select is 17V. Done!
If you get trouble to calculate your Watt/Voltage, let me know your total resistance and what Voltages you can set your power brick to.
On the back side of my brick there is a table of Voltage and Ampere that can be delivered. To convert them into Watt you multiply Voltage and Ampere. This is the MAXIMUM Watt it can deliver at the given voltage without being damaged.