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Building a PID-type blanket temperature controller
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Author:  Tim Mullin [ Tue Apr 11, 2017 12:35 pm ]
Post subject:  Building a PID-type blanket temperature controller

Several folks have seen pictures of my temperature controller and asked if I would provide more details on the parts required and the construction. I don't claim to have been innovative in any way -- I've simply taken the same PID used by LMI as the base for their temperature controller and designed my unit around that. A few notes before I get into details:
1. Don't expect to build a unit comparable to the LMI product at a fraction of the price. The LMI controller is actually pretty good value, so unless you are comfortable with electronics assembly and prepared to do some sourcing of parts, I would recommend going to LMI to purchase their unit.
2. If you don't understand my basic wiring diagram, you should probably ask yourself if you have the competence to attempt this build. You're dealing with control of 120VAC, so it's not a place to mess around if you don't have some knowledge in this area.
3. Wire size is important. The heat blanket side of the control needs to handle 10 amps of current, so wire used should be at least 16AWG. This large guage of wire will not connect easily to the connections on the PID, so you must use smaller diameter wire for the controller circuit that is fused at 1 amp -- I used 22AWG.
4. I already had a separate mechanical timer as a fail-safe switch between my controller and blanket, seen in one of the pictures. Some PIDs have a timer function built in, so you may prefer that. Whatever you do, be aware that you should NEVER leave a blanket unattended in use. Not only can you easily scorch a side if things don't go right, you can also lose your shop (and possibly your house) to fire.

Now, the parts required. I've attached a pdf file in a followup post listing all the parts, the supplier I used, and their online price (late 2016) without shipping. Some were sourced in Canada (where I live) and others from the US. I used a PID from Auber Instruments -- it's the same model as used by LMI. I also found a box from Auber -- if you use the same box, be aware it's a tight squeeze, especially with the hardware holding the box panels. Plan and cut carefully! The PID accepts connections from a K-type thermocouple -- a special panel connector facilitates this connection. The PID also has output for a Solid State Relay (SSR), allowing you to switch the 10amp load to the blanket

You'll need a wiring diagram to guide your parts layout and assembly. Mine is attached to a followup post -- consult the parts list for the spec on the various components. Be sure to observe polarity on the SSR and K-type thermocouple connections. Also observe the proper connection of the Live and Neutral feeds for the 120VAC. And finally, note that large gauge wire used for the blanket circuit is indicated on my wiring diagram with a heavier line -- use at least 16AWG wire for these connections. Wire colour makes no difference electrically, but can be helpful to confirm your connections are correct. For my 120VAC connections, I used conventional black, white and green for Live, Neutral and Ground wires, respectively. For the low voltage DC connections to the thermocouple and the SSR, I used red and black for positive and negative terminals, respectively.

Once you've worked out the physical layout of components on the front and rear panels, use masking tape and a pencil to draw the outline of the cut outs. Components available from large suppliers like Digi-key usually have helpful technical documents that specify the exact dimensions of cutouts for various panel types. You'll see in the pictures, I simply drilled a series of holes through the aluminium, then used files to enlarge and shape the holes as required. I fould that fit of some components was less secure than I liked, so I simply added a drop of epoxy inside to make sure the components couldn't shift.

As much as possible, I used insulated crimp connectors. Those used for higher current connections (the blanket circuit) were made doubly secure with a solder connection. The 120VAC panel sockets and fuse connectors were soldered.

It's important to note the bolt added to the bottom of the box as a common ground connection -- the green wires.

A sequence of photos follows to illustrate the various stages of construction:
physical layoput.jpg

front panel layout.jpg

front cut outs.jpg

front cut outs complete.jpg

wiring complete.jpg

front view.jpg

rear view.jpg

with blanket and timer.jpg

Finally, make sure you read the instruction manual for the PID to understand calibration process and correct use. If you're using the SYL-2362 PID, you can also refer to Robbie O'Brien's Youtube video describing its use in the LMI unit:

Author:  Tim Mullin [ Tue Apr 11, 2017 12:37 pm ]
Post subject:  Re: Building a PID-type blanket temperature controller

In this followup post, I've attached a copy of the parts list:
Parts list.pdf

and the wiring diagram:
Wiring temp controller.pdf

Author:  Anthony Armijo [ Mon Apr 24, 2017 10:11 pm ]
Post subject:  Re: Building a PID-type blanket temperature controller

Thanks for all the information that you posted. You definitely went all out with helping us. Much appreciated.

Author:  James Orr [ Mon May 27, 2019 5:46 pm ]
Post subject:  Re: Building a PID-type blanket temperature controller

Tim, thanks for posting this tutorial. Even though I ordered the parts two years ago, I finally put it together yesterday. It was definitely satisfying when it fired right up out of the gate.

I wanted to share a few things I found helpful in the spirit that others may as well.

Most challenging part of the project? Cutting out the chassis. I don’t know if they used hardened steel or what, but I went through an entire pack of cut-off wheels in my Dremel and it took forever. I ended up adding quite a few beauty marks to the faceplates, so I gave them a dusting with Rustoleum texture coat and some satin black spray paint. If you have a jigsaw with a metal cutting blade, that's the way to go.

I wasn't familiar with the reading the schematic when it came to the power plugs, so I looked a few things up to make sure the prongs were wired correctly. gaah

L = Load. These are the black wires.

N = Neutral. These are the white wires, and also the wider prongs on the plug (to help you orient yourself when wiring it up). White wire conforms to standards, but I used red because it’s what I had.

I used Tim’s wiring shot and schematic to double check my work as I went. I’d reference it after making each connection, then mark/trace the wires in highlighter on my print-outs.

It's a little hard to see how the fuse holders are wired in Tim's wiring pic, so I’ll include a close up shot of that section in mine just in case it helps someone out. FWIW, the 10 amp fuse is on top in my controller and also in Tim's.

Author:  Tim Mullin [ Mon May 27, 2019 9:08 pm ]
Post subject:  Building a PID-type blanket temperature controller

Very pleased it worked out well for you, James, and that the tutorial didn’t lead you astray.

Not surprised you had difficulty cutting the panels with a Dremel. They’re made from aluminum and guaranteed the mess up any high-speed cutter. On mine, I simply used an HSS bit in my drill press and hogged out each cutout, then finessed with files. Whatever works.

Makes no difference how you wire the connectors on the fuse holders.

Well done!

Sent from my iPad using Tapatalk

Author:  James Orr [ Sun Jul 14, 2019 8:31 pm ]
Post subject:  Re: Building a PID-type blanket temperature controller

This is definitely a pleasure to use. Thanks again, Tim. Image

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Author:  Barry Daniels [ Mon Jul 15, 2019 8:30 am ]
Post subject:  Re: Building a PID-type blanket temperature controller

Aluminum clogs up cutting wheels making them totally ineffective. Best to use a toothed cutting tool.

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