# HELP Need A Clear Answer



## speedre9 (Jan 1, 2014)

Since this concerns electrical stuff, I hope this is where I can get an answer.
I am adding a heated bed plate to my 3d printer accessory for my gantry c.n.c. machine. Control software are not an issue, what is are these things.
I have a MK 1 bed plate, a borosilicate glass plate, and a 12v dc 30A power supply. Here is what I need.
What kind of temperature controller and thermistor do I need?
A diagram to wire it all up to the MK 1 bed plate?
I hope someone here can suggest a cheap effective solution to my issues and give me a concise diagram to follow.
I am near my wits end on this issue. HELP !!!anic::angry:


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## rdhem2 (Jan 1, 2014)

Go to e-bay-type in digital temperature controller.  The ones I use are by rex, and usually get them for under $30 for a digital PID, industrial controller.

Next, solid state relays.  Check the amperage to get the size you need.  Specify the input voltage and the control voltage and up to 25amps should be about $6.

Next thermal couples, find the temperature range you need that will work with the controller.  Probably a Type "J" or "K".  Pick the style that will work on your application.  About $8 or less.  A can or enclosure to put the whole mess in with the leads from your element and BINGO.  You are one happy camper.

Wiring diagrams come after you have parts to work with so you know how to wire it.

EDIT:  *Be sure your PID temp controller comes with SSR output.*


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## twstoerzinger (Jan 1, 2014)

I'm not into 3D printing, so I don't know what a MK1 bed is. Is this the part with the resistive heater?
You say that you have a 12 VDC, 30 A power supply, so I am guessing that the heating element is rated 360 watts or less and rated for 12 V operation.
If all the above is true, then I agree with rdhem2 that a PID controller with a SSR (solid state relay) is the way to go. Controllers and SSRs that I have recently bought in this range were a little more expensive than what rdhem2 quotes, but not a lot. You could use either a thermocouple or an RTD (resistive temp device) to measure the temp. If super accuracy is not required, the thermocouple is probably slightly lower cost. The biggest issue with either temp sensor is that it be firmly connected to the heating platen such that the temp sensor quickly responds to heat being added by the heating element.

For those that may not be familiar with PIDs and SSRs, here's a quick and dirty summary.
*PID Controller*
The PID controller (short for proportional, integral, derivative), continuously compares the "process variable" (in this case the temp output of the t-couple) to the "set point" (the temp you want to maintain). The controller comes up with an "error" which is either + or - relative to set point. The controller does some fancy math and spits out an "output" (usually expressed in 0-100% output). The "output" is then passed on to the SSR which actually controls the power current. The desirable feature of the PID controller is that, properly tuned, it can reduce the "error" to zero and hold constant temperature on the process. The PID controller can also be tuned to react to expected process upsets, and to quickly return the error to zero.

*SSR*
Electrical power to the process is typically switched on and off at a certain cycle time, say 10 seconds ( but you can pick other cycle times). So, when the PID says give me 100% power, the SSR remains ON for 10 sec out of 10 sec. When the PID calls for 50% power, the SSR is on for the first 5 sec and off for the next 5 sec. For 10% power, it's on for 1 sec and off for 9 sec. In the old days, this cycling was done by mercury displacement relays, because regular power contactors did not hold up well with constant cycling. With the advent of modern, low-cost, solid state devices, SSRs have replaced mercury relays (good thing because the mercury in the old relays is considered hazardous waste). One thing to keep in mind is that SSRs usually require an aluminum "cooling fin" assembly upon which the SSR is mounted. The SSR is a solid state device, so it gets warm as it operates. Usually you have to buy the cooling thing separate from the SSR, although some smaller SSRs have the cooling fin already attached. Likewise, the control enclosure for the SSR has to have some ventilation or other means to release the heat generated by the SSR.

Keep us posted,
Terry S


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## Rbeckett (Jan 1, 2014)

rdhem2 said:


> Go to e-bay-type in digital temperature controller.  The ones I use are by rex, and usually get them for under $30 for a digital PID, industrial controller.
> 
> Next, solid state relays.  Check the amperage to get the size you need.  Specify the input voltage and the control voltage and up to 25amps should be about $6.
> 
> ...


And make SURE that the controller is for 110 60 cycle AC.  Some are 220 and 50Hz.  I get mine off of Ebay for about 21.00 and the temp sensors too.  No real wiring, just a temp sensor and hook the out put to the mats input and there ya go.  I use one to control my kegerator which I made from a freezer and added the external temp control.  I keep it at 10,5 degrees C which is cold enough to chill sodas and beer just fine...

Bob


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## speedre9 (Jan 4, 2014)

I got a PID with the relay. I asked the same questions on other forums also and got the same general answer. I will use those components to run a stand alone heat source. I'm o.k. with that, later when I eventually upgrade I'll make software driven. But for now it manual.


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## Rbeckett (Jan 4, 2014)

Go to the Homebrewtalk.com site and look up Ebay tempcontroller.  All the diagrams and build instructions are right there and available for immediate use.  That is the blueprint I followed on my Keezor and it wirks better than I could have ever expected and maintains the temp with 1/2 degree centigrade.  I uses an old work two outley electrical box to fit it all together fer heat and cool under the systems control...

Bob


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## speedre9 (Jan 6, 2014)

I did what you suggested and I got a Google search result. But, I don't know what I should look for. The brew site didn't seem to have a search box for the site itself. I'm still needing help on this issue.


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## twstoerzinger (Jan 7, 2014)

speedre9,
Give us a few more details and I think you will get lots of help:
What is the nature of the heating load (sounds  like it is a heated platen). Are there any suddenly applied heat loads,  or is it constant load?
You mentioned using a DC power supply - do you plan to use DC to power the heater?
What is the rating of the load you will be controlling (rated voltage and rated watts or amps)
What make / model PID controller do you have?
What make / model SSR do you have? (if it is a mechanical relay instead of an SSR, then give us the coil voltage and contact ratings for the relay)

Terry S.


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## speedre9 (Jan 7, 2014)

In the documents you will see a rough schematic of how I think it should be done.
 I have included the verbatim texts of instructions for what I have in components, with model numbers, and mfg.'s, and,
 what I think I should do, with my limited understanding of these components.
As stated there are some things I do not have and probably do not need.
Please read, and view them and, make corrections and comments, they are PDF's so anyone can make corrections to them. 
View attachment schematic document.pdf
View attachment HEAT BED SCHEMATIC.pdf


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## twstoerzinger (Jan 9, 2014)

Sorry, but I am still not clear on the electric heater load that you want to control. I did some on-line searching and found several references to a Mark-1 heater for use with 3D printing built by Josef Prusa. See photo. Interesting that an electrical device like this has no label regarding it's electrical ratings.




The only reference I could find to voltage rating was on a site by UltiMachine which stated that they had tested the unit at 12 V and found it to draw 9.9 A on start up. In your first post you mentioned that you have a 12VDC 30 A power supply, so perhaps this is the heater you have and it is rated for 12 V?
I suspect that the heater doesn't care if the power is AC or DC.

So, I am going to go with that you are looking to control a 120 watt heating pad using 12 VDC power, and that the heating pad is bonded to a sheet of borosilicate glass. (Borosilicate I suspect because it has low susceptibility to thermal shocking - think Pyrex). Looks like the dimensions are about 200mm x 200mm or say 62 sq in which gives about 2 w / sq in. Just for reference, you can get "standard" polyimide sheet heaters rated for 115 VAC. They are about .007" thick and are rated for up to 300F. McMaster Carr sells a version rated at 5 w/sq in, but I don't see one of the exact size that you have now. Other vendors also carry these polyimide heaters if the PCB version doesn't pan out.  

*Based on all of that, here are a few comments on the items that you already have.*

*PID Controller*
The model you say you have is a Rex C100FK02-M*AN
From Rex on-line literature, this decodes to a 1/16 DIN, Forward Action, Type K thermocouple, 0-400 C, Relay Contact (output), with a single deviation high alarm. The model you have is a 1/16 DIN size controller. Generally, this size is used when you have 15 or 20 controllers to mount on a single panel (such as a control panel for an extrusion line). This is a compact model to save control panel face area. The only disadvantage is that the smaller sizes don't have as many features as the larger 1/8DIN or 1/4 DIN sizes. One feature your model does not have is an "on board" power supply to run the SSR output. You will have to have a separate DC power supply to run the input to  the SSR.

The model you have is set up for on-off relay output. You will use these relay contacts to make and break the control signal going to the SSR. The controller does not have an "on board" power supply, so you will need a separate DC power source to feed the input to the SSR. The big 12 VDC power supply you have could serve this purpose, but you would want to fuse the lead going to the controller / SSR to protect the SSR and the controller contacts.

The on-line literature I found for the Rex controller is only 2 pages - it is probably abbreviated from what might come in the box. It appears that it will accept input power of 100-240VAC, 24VAC or 24VDC. This is rather typical, but sometimes you have to set a small switch or jumper to configure the proper input power - check the instructions that came with the controller.

Remember that PID controllers like this are capable of controlling a very wide variety of situations, but they have to be properly tuned to match your system. The tuning can be daunting if you have not done it before. Many controllers these days come with an "auto tune" feature that sometimes can do the job. Yours appears to have this feature. To do the auto tune, you put the controller on line and allow it to control the process without any process interruptions for a period of time - like 15 or 20 minutes or until the temperature is stable. Some controllers will terminate auto tune once they feel they have reached stability. Worry about this once you get it ready to run.

*Thermocouple*
You mentioned a thermister in your first post, but the PID controller you have is intended for use with a type K thermocouple. (Larger PID controllers will often accept several types of temp sensor inputs, but the model you have is only capable of type K.) You will need a miniature type of thermocouple that is intended for surface mounting. You will want to thermal-bond the TC to the glass - assuming that the glass temp is the process variable you aim to control. A small piece of high-temp aluminum duct tape should do the job for bonding. You will want to the thermocouple leads to be long enough such that there are no splices - the leads should be terminated directly in the PID controller terminals. The yellow lead is the + lead and goes on terminal 8 on your controller. The red lead is - and goes on term 9. The thermocouple has to be insulated from voltage sources - do not let it touch the 12VDC in the heater pad.

*SSR*
Model number you specify is a Fostek SSR-25 DA. I am guessing that this is a typo and it is a "Fotek?"  The on-line literature I found has lots of Chinese characters, but it breaks down the product code like this:
SSR = single phase SSR
25 = 25 amps rated switching
D= DC input rated 3 to 32 VDC
A= AC output voltage
*This SSR is intended for switching an AC load.* I don't think you can use this model to control a DC load because the SSR needs to pass through "0" volts to shut off. If you are going to supply DC power to the heating plate, I think you will need a DC output rated SSR. I believe the Fotek model would be SSR-25 DD. I see you can get them on ebay for about $6. If you use the existing relay, I think you will need a 12 *VAC* power supply.

I think you will also want a heat sink for the SSR. The SSRs dissipate a fair amount of heat and can be damaged if not cooled. Often, the heat sink is 4X larger in volume than the SSR itself. For some reason, the vendors like to sell the heat sinks separate from the SSRs. You can get the heat sink for $5 or so. You need one that will fit the SSR that you have.

I know this isn't the response you were looking for, but I think you need to sort out some design issues like the DC vs AC power to the heater before you get to the wiring schematic details.
Best regards,
Terry S.


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## speedre9 (Jan 10, 2014)

As you stated " not the response I am looking for". All of what you said is way over my head, too much, too technical.
If you are willing to help me this is what I would need you to focus on. 
One:
With, the components I have, can I, control the temperatures to the MK 1 heat plate.
Two:
Can you provide me with, a diagram of how to wire it up, using, either 12v dc, or straight AC power.
Simply put, without malice or disrespect, don't get technical just write a diagram so I can heat my bed. That's all I need.
I am not trying to be mean or disrespectful in any way shape or form.


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## speedre9 (Jan 11, 2014)

Please accept my thanks to everyone who has added constructive and informative information to me effort. I have decided to abandon this as a project.
I don't have the technical expertise to do it, and I have found that I cannot ask the right questions to get answers I can understand.
Once again I thank you all.


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