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3dguy

Heated Bed Build and a question about the Z Stage.

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I am finally getting back to building my heated bed upgrade since I first enquired about it in September of 2013, I got a bit derailed for awhile. I believe I have all the parts I need:

a MK1 PCB with 16" leads

a 9.5" x 9.5" x 1/4" Aluminum Plate (may be a bit thick)

a 9.5" x 9.5" x 3/16" Ceramic Glass Plate

Ceramic Fiber Board for thermal insulation between PCB and aluminum

a 4.7k resistor (on Ultimaker Board already)

a 100K Axial Thermistor

a Fotek SSR-40 DA Relay

a 12V 16A Brick power supply

a 4 pin female power receptical

Surface Mount LEDs for the PCB

Surface Mount Resistor for PCB (still en route)

Clips to hold glass in place.

Is this everything I need?

If you don't mind, I have a few questions about the wiring connection for a heated bed.

What gauge wire to use for the thermistor, is 20 or 22 gauge good?

How do I wire the PCB to the Relay, Power Supply, Ultimaker Board and the 4 Pin female power connector?

I have not done any wiring since 1982, I am just a tad rusty.

Is there a recommended max weight limit for the z stage?

I am not sure if my parts will be to heavy and I am thinking about getting a new stage made, if it is not cost prohibitive.

I have uploaded a few pictures of the parts and the relay diagram:

4.7K Resistor On Board And MK112V DC Power supplyLEDs And ThermistorPTFE Tubing For thermistorRelay And Power ConnectorPS 4 PIN Female Wiring DiagramHot Bed ConnectorTemp-3 ConnectorSSR PCB Diode and Power Connections to UM1 2)12V DC RelaySSR RelayHeated Bed heating And LED testMicro AdjustersNew Dioder LED BracketsNew Heated Bed On current Z Stage

 

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In principle your part list look ok apart from the SSR-relay. If I read your posted schematic it shows that it expects AC current and it looks like that you want to use it with a 12V DC power. That will not work, the triac that is used will not turn off. It will turn on all right but it will not turn off until the moment the input voltage drops to 0 (the zero crossing). That is the problem with these solid state relays there are so many types that it quickly becomes confusing.

 

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Thanks, that part was confusing. The description on Amazon wasn't clear to me. I found the correct relay for sale at Radio Shack and will pick it up hopefully Sunday. Now I know what poles gr5 and others were referring to in some of their posts, 30, 87, 85, 86. When my relay was labeled 1, 2, 3, 4 I was lost.

 

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Ok, so now the diagram is starting to make sense. Let me see if I have this right.

1) Solder one of the leads from the MK1 to one of the power supply's 4 PIN Female Connectors (+) pins.

PS 4 PIN Female Wiring Diagram

2) Solder the other lead from the MK1 to the #87 pole of the 12V DC 40A Relay.

3) Solder a connection to the corresponding (-) lead of the power supply's 4 PIN Female Connector.

4) Solder that negative lead to the #30 pole of the relay.

5) Solder a lead to the #85 pole of the relay.

6) Solder a lead to the #86 pole of the relay.

7) Connect the free ends of the leads from the #85 and #86 poles to the Hot Bed Connector on the UM-Board. (Does it matter which lead goes to which screw on the Hot Bed Connector?)

 

Hot Bed Connector

8) Solder or use a 3 PIN connector to connect the two leads from the thermistor to the Outer two connectors on the "Temp-3" connector on the UM-Board.

Temp-3 Connector

9) Make sure the bottom of the MK1 PCB is insulated from the aluminum base plate. I think I will do this with both Kapton Tape and Ceramic Fiberboard.

Does that sound correct?

 

 

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@3DGuy

For me it is difficult to translate text into schematics but for your point 7, yes it does matter. Check the wiki

http://wiki.ultimaker.com/Heated_Bed

And you can see which terminal is positive and which is negative. The fly back diode in that schematic should block. So the top of the schematic is the 19V and the bottom is the switched ground.

 

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Three things:

- You should tie the same polarity pins on the power supply together. So tie P1 and P2 together and P3 and P4 together. The reason is that you are going to have fairly high current in the circuit. That is the reason the PS has two pins for each polarity. Each lead in the PS cable and connecter pin should only carry half the current.

- Which relay from Radio Shack are you using? If it is a normal electromechanical relay, the polarity of the connections to the HOT BED connector won't matter. However if it is a SSR, the polarity must be correct. On the HOT_BED connector, the terminal on the side towards the outside of the board is +. The terminal next to the HEATER2 terminal is -

- Here is the difficult part, since you are using a thermistor, you will need to solder a 4.7k resistor to the control board in the R4 position.

 

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The fly back diode in that schematic should block. So the top of the schematic is the 19V and the bottom is the switched ground.

 

Thanks, I'll take a look at the wiki again.

 

Three things:

- You should tie the same polarity pins on the power supply together. So tie P1 and P2 together and P3 and P4 together. The reason is that you are going to have fairly high current in the circuit. That is the reason the PS has two pins for each polarity. Each lead in the PS cable and connecter pin should only carry half the current.

- Which relay from Radio Shack are you using? If it is a normal electromechanical relay, the polarity of the connections to the HOT BED connector won't matter. However if it is a SSR, the polarity must be correct. On the HOT_BED connector, the terminal on the side towards the outside of the board is +. The terminal next to the HEATER2 terminal is -

- Here is the difficult part, since you are using a thermistor, you will need to solder a 4.7k resistor to the control board in the R4 position.

 

So I should solder a Jumper Wire connecting the two + and another Jumper Wire to the two - and then solder a wire to one of the + and one of the -, that should not be to bad.

Actually the 4.7K resistor was the easy part I did that several days ago. The hardest part about it was de-soldering the through holes for the resistor, it took several attempts as the solder wick did not work, I had to use a solder sucker.

4.7K Resistor On Board And MK1

 

**** WARNING - DANGER WILL ROBINSON *****

I scanned radioshack.com and there are NO suitable relays for this purpose!!!!!!

 

It is this relay, it will not come up with a normal search. Radio Shack's search is horrible.

http://www.radioshack.com/product/index.jsp?productId=3020762

 

 

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Unfortunately, that relay is 12VDC. The HEAT BED connection outputs about 19.5VDC. Most likely you will find that the relay heats up from the extra power. It might burn out at some point.

If you want to use a SSR, I went with this one but @ $30 it isn't cheap:

http://www.phidgets.com/products.php?category=9&product_id=3950_0

Just note that both the input and output are polarized so you need to be careful with connecting it.

 

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My 20 cent solution for the time being would be:

For the 12V relay you could add a 47Ohm 1 watt resistor in series to bring the voltage down to about 12V. I just checked the spec on the link and it says 12-14V coil current. So if I take the middle of that I calculate with 13V. So you need to drop 19.5-13=6.5V. The spec also mentions the current the relay draws. It is 133mA. So you can calculate the resistance you need by 6.5/0.133= 48.8 Ohm. Well the now match it with available values and you get 47Ohm. So the relay will get about 13.2V on the coil which is still according to the spec. Make sure to buy a 1W version since it will dissipate about 0.133*0.133*47=0.83W.

Personally I don't like those kind of relays but it will work. Since the relays need to switch quite some power and also regularly they do weir out.

 

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anon4321,

Thanks for the link to Phidgets for the 3950 SSR. I went ahead and ordered one with the optional heat-sink, shipping was almost as much as the relay, I am impatient and want it in the next 2 days so I can try to build the heated bed while I'm off.

I couldn't resist buying the HELLA 965400031 Black 24V 30 Amp Mini ISO SPST Relay with Bracket from Amazon either, I got it for free and only had to pay for overnight shipping, $3.99, I figured it couldn't hurt to have a backup.

 

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To absolve myself, please note that YOU DO THIS AT YOUR OWN RISK AND I CANNOT BE HELD LIABLE FOR ANY DAMAGE, INJURY, FIRE AND/OR DEATH.

The big issue with the SSR is that both the input and load sides are polarized.

You should make all connections EXCEPT those to the relay and then verify that polarity using a meter and that the relay connections will be positive to positive and negative to negative. The hardest one is the HEAT BED terminal on the controller. The outer most post is + and the post next to the other connectors is -.

The diode is required if the load is inductive and protects the SSR load side from inductive kick back voltage that occurs when the load is switched off. The heat bed is mostly resistive and probably only marginally inductive depending on its construction.

I used the diode as cheap insurance for the $30 relay.

Again, verify ALL POLARITIES before connecting to the SSR but this is how mine is connected:

SSR Heated Bed Connection

 

Here is the SSR in IRL. Note that my PS also had two positive and two negative leads/pins due to the current. The two + are tired together at the SSR terminal. The two - and one lead to the bed are tied together by the wire nut. The remaining lead from the bed is attached to the other load terminal. The diode is reversed biased across the SSR so that it doesn't conduct when the polarity is correct !

 

The input side simply goes straight to the heat bed terminal with, of course, the correct polarity.

 

 

 

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Actually, now that I look at it. I don't think the diode is connected optimally. It really should be across the bed leads (in reverse polarity, the marked side going to the more +). The way I have it protects the relay but not the PS..

It really should have the marked side connected to the lead going to the - on the load side of the relay and the unmarked side connected to your P3/P4 (-).

Like this -

SSR Heated Bed Connection 2

 

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To absolve myself, please note that YOU DO THIS AT YOUR OWN RISK AND I CANNOT BE HELD LIABLE FOR ANY DAMAGE, INJURY, FIRE AND/OR DEATH.

 

Thanks for the information. I take all responsibility. I have put together small electronics kits before but never anything with a power supply over a 9 volt battery, and never anything with relays and a diode like the one that came with the relay. I just want to try my best not to fry my electronics and get the heated bed going.

 

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