Heated Bed Build and a question about the Z Stage.

[anon4321 16]

It's close. The diode should be used to protect the relay on the load side, reverse biased.

With an electromechanical relay, you would need something to protect the MOSFET from inductive kickback from the relay's coil. SSRs don't have this problem. Also, I don't have access to the schematics but I believe the UM1 board has that protection diode on the board on all three heater connections.

See D1, D2 and D3 in my sample pic -

Not that it matters electrically but you are low side switching which means more of the positive side is always connected. I prefer to use high side switching as in the attached pic because it interrupts the + side earlier. This means in the off state, most of the circuit is at ground level. With low side switching, most of the circuit is at the PS voltage. This would lead to a higher chance of a problem if some part of the circuit is grounded by accident even in the off state.

 

[3dguy 0]

I didn't even see those, diodes they are really tucked away under those Darlington transistors.

Thanks for the further explanation about low side and high side. I will go with your original setup. I almost had it put together last night accept I ran out of 14 gauge wire. I appreciate the tip on the silicone wire, that stuff is a lot easier to work with then 14 gauge auto wire.

Can the diode be insulated or have heat shrink applied to it or PTFE tubing without effecting its operation? I have like 24' 8" of PTFE 1/32" ID left. The diode seems like it could be a shock hazard or worse with it's exposed leads.

I soldered the tiny surface mount LEDs to the PCB now just waiting for the surface mount thick film 1k resistor to arrive so that the LEDs do not get fried. It is the last piece I need to finish the PCB, hoping it arrives today. I ordered two new fans the same day I ordered the resistor, the fans came from China and got here snail-mail before the resistor which is only coming from Texas, also snail-mail.

 

[anon4321 16]

You can insulate the diode. It probably isn't really used as it is for blocking inductive kickback (http://www.falstad.com/circuit/e-inductkick.html) and the bed isn't inductive or only parasitically inductive.

Note that without the LED, the polarity of the connection to the bed doesn't matter. However, it will when the LED is added,

Also note that the PWM output for the fan on the UM print head is actually ~19.5 volts. The UM1 does use a 12V fan which is apparently OK with the higher voltage. However, in my experience, other 12V fans do NOT tolerate the higher voltage and immediately go "POOF".

 

[3dguy 0]

Note that without the LED, the polarity of the connection to the bed doesn't matter. However, it will when the LED is added,

Also note that the PWM output for the fan on the UM print head is actually ~19.5 volts. The UM1 does use a 12V fan which is apparently OK with the higher voltage. However, in my experience, other 12V fans do NOT tolerate the higher voltage and immediately go "POOF".

The PCB has a spot for 2 LEDs, one for either polarity, I soldered both on so 1 of the two should work either way, at least according to the manufacturer, but I know they won't work without the resistor so I really hope it arrives today.

The new fans I ordered are from the same manufacturer as the original fan and they have nearly the same ratings so I hope the new ones work. The stock fan is 12v .10A and the new fans are 12v .14A.

 

[3dguy 0]

Okay, I have the electronics hooked up per the wiring diagram, the SSR is in place with a heat-sink. I just have to muster up the courage to plug in the power and turn the printer on. I must say I am just a little nervous.

 

[3dguy 0]

 

Success! :-P

 

Thanks for all the help. So far everything is working like a charm. The bed heats up and the LED works to signal the bed is on, and shuts off when the bed is off. I can't test it out yet as far as printing, I have to wait until next week when my new aluminum bed is finished being milled.

 

I also need to remove the screws and springs for the bed level system and drill new holes for my new system with microadjusters where the bed rests on the head of the adjuster in a small recess in the bottom of the aluminum.

 

 

[anon4321 16]

Yeah, there is that moment where you hold your breath and power it up and hope you don't see smoke!

BTW, since your are using an SSR capable of switching on and off quickly, you can set the bed heating algorithm into PID instead of the default bang-bang mode. Then once you get the full bed assembled, you can use the PID autotune to derive the P, I and D values. In this mode, the power to the bed is more closely modulated which you will see as the LED flashing quickly.

To do so, you need to recompile the firmware.

Get the firmware here https://github.com/Ultimaker/Marlin using the download zip button on the middle-bottom right and unpack.

Get the Arduino 1.0.5 IDE here: http://arduino.cc/en/Main/Software and install

In the location you unpacked the firmware source, open marlin.pde. In windows .pde is associated to the Arduino IDE.

In Tools -> Board, select "Arduino Mega 2560 or Mega ADK"

In the tabs, find configuration.h

Find this line:

#define TEMP_SENSOR_BED 0

change to:

#define TEMP_SENSOR_BED 1

Find this line:

//#define PIDTEMPBED

Changed to:

#define PIDTEMPBED

With the printer connected and powered on and Cura closed, click File -> Upload and the IDE will build then flash the new firmware.

Once your bed is completely assembled, you need to tune the PID parameters for the bed "system". You can play around with this without your Alu surface but you will need to redo this as the values will change with the thermal mass of the Alu.

To run the PID autotune,

Open Cura

Click File -> Preferences

Select the Pronterface UI for the printing window type and click OK.

Now go to File -> Print.

Once the connection is established, use the text box at the bottom right to send this command:

M303 E-1 S70 C8

(Note the S value is the target temp, adjust it to be the temp you believe you will use the most).

The bed will go through several heating cycles and output three values as the PID is "dialed-in"

Record the last set as the output instructs.

Now to "burn" those values into the FW, find these lines:

#define DEFAULT_bedKp 10.00

#define DEFAULT_bedKi .023

#define DEFAULT_bedKd 305.4

Replace the values you recorded from the autotune run.

Make sure Cura is closed and click File -> Upload in the Arduino IDE.

Enjoy the blinky goodness of the hyperaccurate and almost certainly overkill of running the bed in PID mode.

More info about PID and autotune here: http://reprap.org/wiki/PID_Tuning

 

[anon4321 16]

Those levelers look very nice.

 

[3dguy 0]

Yeah, there is that moment where you hold your breath and power it up and hope you don't see smoke!

BTW, since your are using an SSR capable of switching on and off quickly, you can set the bed heating algorithm into PID instead of the default bang-bang mode. Then once you get the full bed assembled, you can use the PID autotune to derive the P, I and D values. In this mode, the power to the bed is more closely modulated which you will see as the LED flashing quickly.

 

Just turning the UM on to upgrade the firmware was bad enough, when it came time to plug in the power for the heated bed, I was ready to run for the extinguisher .

 

Those levelers look very nice.

 

I wanted to get micro adjusters since I first got my UM in 2012. These were actually not overly expensive.

My setup is going to be a little different. My aluminum plate is actually going to be the baseplate and then a thermal barrier of 1/16" Ceramic Fiber Board which can withstand temperatures well above 1300 degrees F sustained, then the PCB Heater, then Clear Ceramic Glass is the print surface.

I am drawing up an aluminum Z Stage that I would like to get made if it will not be overly expensive. The problem is that where I live the humidity changes constantly and I have to re-level my bed after every print often times. Adjusting the leveling screws on the fly as it is printing.

Thanks for the links and extra information for the PID control. I will definitely have to take advantage of that.

 

[3dguy 0]

Thanks again anon4321!

I finally got my new setup going with my new bed levelers and the aluminum bed sitting on them in small recesses on the bottom of the plate, then a 1/16" piece of ceramic fiber board (going to replace it with a .093" piece of PTFE cut to size, the fiber board sheds a fine white dust I don't like), then the MK-1 PCB Heater then a 3/16" piece of Clear Ceramic Glass held in place by silver medium binder clips (I would like to find a better solution.) It is so nice to be able to print several prints without having to make constant big bed leveling adjustments. I just finished designing and printing 8 press on brackets for my Ikea Dioder LED lights and they work very well, though I think I will do a slight redesign and push them in 1" towards the inside of the printer (getting some minor shadows from the edge of the top.)

 

It is so easy to remove prints now. No more having to scrape and sand Blue Tape off of my ABS Prints!

 

I just have one more major upgrade to do and that is finish building my new all aluminum Z-Stage. I am almost finished with the design, I am just waiting for my new Trapezoidal Flange Mount Nut and the two new Drylin R Flange Linear Bearings to arrive so I can finalize the position of the mounting holes and have the new stage cut out (not the cheapest of upgrades, I wish I knew how to do millwork myself.) I should have the upgrade done in the next few weeks. My parts should all be here by June 26th. I can't wait to try it out when it is done, my current heated setup is almost 3/4" taller than the acrylic bed was and my new design should make it even thinner than the current UM-1 stage design by a decent amount.