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| Cheap Digital temperature controller for heat blanket http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=19892 |
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| Author: | Fred Tellier [ Wed Dec 03, 2008 7:53 pm ] |
| Post subject: | Cheap Digital temperature controller for heat blanket |
Hi I finally completed my bender and forms and have done 2 trial bends on the unmatched sides I picked up a while back on Ebay. Being a retired industrial controls electrician I felt that the blanket needed better control. I did a search on ebay for cheap ( paid $35.00 ) controllers that could handle 5 amps which more than the amp reading I get with the controller John Hall included with the blanket, set at about 80%, which seems to give plenty on heat. The only thing that is strange when the unit is in deg F mode the set point display on the front panel is 32 degrees too low, the math for this display must be off, but the unit controls fine in F at the set point entered, just the display is out. It comes with a K type thermocouple which reacts to slow for my liking so I cut off the sensor unit and twisted to wires together and it real quick and accurate. You can do this as the entire wire is thermocouple wire and as long as the ends of both wires come together it is a thermocouple at that point. This will also make it easy to place the thermocouple in the bending sandwich. If you think that is a little Mickey Mouse I can assure you that we used this method in the paint ovens at work and we had 100's of these made up this way. These controllers are quite simple to program as you will only use the on/off control, so no PID loop tuning is needed. The blanket will hold within a few degrees of the set point as long as you leave it turned on. The seller has a few more if anyone is interested http://cgi.ebay.com/Dual-Digital-F-C-PID-Temperature-Control-Controller_W0QQitemZ120337160869QQcmdZViewItemQQptZBI_Automation_Components?hash=item120337160869&_trksid=p3911.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318 Fred Tellier |
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| Author: | Brad Way [ Sat Dec 20, 2008 10:03 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Fred...I used a similar controller for my setup and am fairly pleased with the control. However, please tell me more about the thermocouple issue? I have been thinking about getting a different thermocouple because it seems my heat is more up and down than I would like. Thanks! |
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| Author: | bluescreek [ Sat Dec 20, 2008 10:20 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Your control is interesting. I am always amazed and builder ingenuity john |
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| Author: | npalen [ Sat Dec 20, 2008 11:35 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Fred--I use a leaf type thermocouple which seems to be fairly responsive. Is there anything to be gained by removing it? Nelson |
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| Author: | Pat Foster [ Sun Dec 21, 2008 10:26 am ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Great info, Fred! Is the display error present in C mode? Thanks, Pat |
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| Author: | Alan [ Mon Dec 22, 2008 10:57 am ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Fred, Thanks for the link! I got one and installed last night in the bender I got from John Hall (pictures attached). The thermocouple was very slow to respond, so I did as you suggested and cut it off and twisted the wires together. It now responds much faster, but the temperature is off by about 80 degrees at bending temperatures (I had already removed the thermometer probe when I took the picture, so the variance isn't as great in the picture). It can be used as is, once the correct setting is determined, but I would like to get a thermocouple that will read correctly. Any suggestions? One change I made was to add a relay to eliminate the need for the router speed controller. My heating blanket is 8.5A, so I used a 125V 10A relay that I got from Radio Shack (part number 275-217). The output relay from the controller operates the 10A relay and 120V from the power cord is wired to the contacts of the 10A relay. The other side of the contacts goes to the timer, which is wired to the outlet. Again, thanks for the link. Alan |
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| Author: | npalen [ Mon Dec 22, 2008 12:01 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I set up my Fox-type sometime back with one of these controllers and have had good luck with it also. It's quite interesting to watch the PID (P rogrammable-I ntegral-D erivitive) do it's thing when homing in on the temperature setting. It's like it's almost human! (Probably smarter than some of us humans) I also run a Variac in the power circuit so that I can regulate the power input up to about 130VAC. Now if someone could direct me to a FAILSAFE method of bending highly figured maple to a 1" radius cutaway......... I have good lunch money waiting for you. Nelson |
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| Author: | Shane Neifer [ Mon Dec 22, 2008 12:19 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Hey, all of the EBAY controllers that are listed seem to be 3A versions, will they work? (I am thinking not....but am hoping for some help here!) Thanks Shane |
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| Author: | npalen [ Mon Dec 22, 2008 6:55 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
http://cgi.ebay.com/LCD-Display-Precision-Thermometer-Thermocouple-K-Type_W0QQitemZ180314992418QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item180314992418&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50 This might be an option for someone not wanting automatic control. Shane--I would guess that 3 amp relay output is fairly typical for these units and probably not enough to drive a heat blanket, depending on blanket size/load rating. I think most folks use an auxilary relay like Alan mentions above to handle the load. I used a solid state relay not they they're any better. Nelson |
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| Author: | Alan [ Mon Dec 22, 2008 8:22 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Nelson....I might try one of those. I could use an accurate thermometer...hope that one is. I compared the readings of the two digital thermometers I have and they differ by 25-30 degrees F at bending temps. |
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| Author: | Shane Neifer [ Mon Dec 22, 2008 9:04 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Thanks Nelson, but now I am even more confused. I "get" things fairly quickly but I usually need to be shown. I take it that that link is just a digital thermometer, or is something more? And if I wanted to get one of these 3 Amp units so it will keep the temperature where I want it (relative at least) can I get a relay to do that and what would that look like? I like learning so I would like to try and put one of these together but I am hoping that some one can show us how  ?Thanks! Shane |
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| Author: | npalen [ Mon Dec 22, 2008 9:59 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
http://www.luthiersforum.com/forum/viewtopic.php?f=10102&t=12108&hilit=temperature+controller This might be of some help. |
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| Author: | Mike OMelia [ Mon Dec 22, 2008 10:46 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Alan wrote: Fred, Thanks for the link! I got one and installed last night in the bender I got from John Hall (pictures attached). The thermocouple was very slow to respond, so I did as you suggested and cut it off and twisted the wires together. It now responds much faster, but the temperature is off by about 80 degrees at bending temperatures (I had already removed the thermometer probe when I took the picture, so the variance isn't as great in the picture). It can be used as is, once the correct setting is determined, but I would like to get a thermocouple that will read correctly. Any suggestions? One change I made was to add a relay to eliminate the need for the router speed controller. My heating blanket is 8.5A, so I used a 125V 10A relay that I got from Radio Shack (part number 275-217). The output relay from the controller operates the 10A relay and 120V from the power cord is wired to the contacts of the 10A relay. The other side of the contacts goes to the timer, which is wired to the outlet. Again, thanks for the link. Alan Alan, could you please post a parts list and wiring diagram? THanks! Mike |
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| Author: | Fred Tellier [ Tue Dec 23, 2008 8:40 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Hi everyone I just got home from visiting my mother in law in Maryville Tn and was surprised to see the replies on this post. I have used the controller 4 times with the speed controller that John Hall supplied with my blanket and if you keep the controller at or below 3/4 setting the amps are around 4 checked with a digital amprobe ( I'm a retired electrician with all the good tools still ) I found this setting provided plenty of heat. Also most of there controllers are rated a 3 or 4 amps at 240 volts so they will handle more at 120 volts. As for the thermo couples they consist of two wires of different metals and where they touch together is the actual thermocouple point so the wires can be cut off and twisted together at the temperature reading end. This reduces the amount of metal that must respond to a temperature change so they will respond much quicker. If anyone is concerned about the contacts over heating it is easy to add a higher amp relay. |
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| Author: | Alan [ Wed Dec 24, 2008 12:39 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Mike, The controller I used is the one on EBay that Fred mentioned (XMTD-718T). I'm sure that others would work, but you would need to verify the connections on the controller (120V, and relay contacts). This is being used in the on-off mode; when the temp exceeds the setting on the controller, the relay opens, removing power from the blanket. When the temp falls below the setting, the relay closes, connecting power to the blanket. Since the relay output is rated at 5A and the blanket is 8.5A, I added a 120V/10A secondary relay (Radio Shack part number 275-217). The timer was the timer that came with the bender that I got from John Hall. Here is what I did: First, I drilled a 3/4" hole in the side of the bender and screwed in a cable clamp for the power cord. It was a nice tight fit, so no need to use the nut on the cable clamp (see "cable clamp" picture attached). I then removed the small piece of birch ply on the front of the bender and replaced it with a larger piece to mount the controller, timer, and outlet (see attached "front" picture). Wiring: The thermocouple connects to terminal 1 and 2 on the controller (Blue lead on terminal 1, red lead on terminal 2). The black (hot) lead from the 120v power cord connects to controller terminal 12. The white (neutral) lead from the 120V power cord connects to controller terminal 11. A jumper between the controller terminal 12 and terminal 9. Connect controller terminal 8 to pin 8 on the Radio Shack relay. Connect pin 7 on the Radio Shack relay to terminal 11 on the controller. Connect pin 5 on the Radio Shack relay to terminal 9 on the controller. Connect pin 3 on the Radio Shack relay to the input of the timer. Connect the output of the timer to the gold (hot) terminal on the outlet. Connect Pin 11 on the controller to the silver (neutral) terminal on the outlet. I also attached a drawing of the wiring diagram. Again, thanks to Fred for the link and helping me to get it hooked up. Hope this helps. Alan |
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| Author: | Dave Fifield [ Fri Jan 02, 2009 9:14 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I want to thank all of you for the information posted in this thread. Most helpful!! It got me fired up to convert my Fox Style Bending Machine over to a temperature controlled rig. I found some different PID controllers on eBay (bit cheaper than the ones cited above). I made two channels, one for each blanket - either two big blankets in a sandwich or (what I have right now) a big blanket and a smaller extra blanket for doing cutaway bends. I cut the front panel out of some smokey acrylic sheet using my laser - didn't have to drill a single hole!  I put a couple of 15 minute clockwork timers and some 1KW dimmers in series with the blankets, but I found (after I had it up and running, of course!) that the dimmers really aren't needed at all. Also, I put the two solid-state relays on a substantial heatsink (from a local electronics surplus store) on the back panel, but found the heatsink really isn't necessary either! A simple sheet of aluminum for the back panel would have sufficed. I didn't use the K-type thermocouples that came with the PID controllers - they were too chunky for my liking. I splashed out on a couple of Fluke thermocouples (they sell them as spares for their multimeters). These are much thinner/sleeker probes, and covered with Teflon. Here's a few pictures of my converted rig. Right click on them to see/download the high resolution version:    I put a plywood bottom on the unit after taking these photos, so it's safe from prying fingers. The auto-tune function on these PID controllers works beautifully. Like Nelson said above, it's interesting to watch them do their stuff! All in all I'm very pleased with this modification. Thanks again to all of you for pointing me in the right direction. Oh, so now my old LMII manual controller is not going to be used ever again (by me). Anyone interested in it? I'll let it go cheap. PM me if you're interested.  Cheers, Dave F. |
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| Author: | Alan [ Fri Jan 02, 2009 9:41 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Very nice Dave! I ordered another K-type thermocouple off eBay that looked less clunky. I haven't received it yet, so don't know if it is any more accurate than the one that came with my controller. I appreciate the tip on the Fluke thermocouple. I may have to check that out. |
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| Author: | Fred Tellier [ Sat Jan 03, 2009 5:38 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Actually a thermocouple is the contact point where the + and - thermocouple wires come together, I spent a large part of my working days as a controls electrician in a Chrysler auto plant, we made up the couples for the paint ovens from bulk thermocouple wire twisted together at the reading end and crimped into a stacon ring connector that was screwed to the oven wall. I just cut the end off of the thermocouple that was included with the controller and twisted the wires together, it works real well and is dirt cheap as there is enough wire on the supplied couple to make 2. The fluke meter temperature probes are also a good idea, if I knew I would start building guitars and need temperature control I would have brought a couple of them home when I retired, and even some thermocouple wire, we had miles of it. One needs to realize that the closest contact point to the controller of the wires is the actual thermocouple, so this is where the readings are taken. |
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| Author: | Dave Fifield [ Sat Jan 03, 2009 7:47 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
By chunky, I meant that the wire, including its outer sleeve, was too thick to put put in the SS/heating blanket/wood/SS side-bending sandwich for my liking. For grins, I disassembled the crimped bolt thingy that was on the end of the thermocouple that came with the PID controller. Inside, it's a normal small brazed thermocouple joint, so if you're happy with the thickness of the wire/sleeve, then you could use the thermocouple that comes with the PID controller for your side-bending sandwich.  Fred - Is just twisting the thermocouple wires together and crimping them good enough for a long-term solution? I would be worried about the possibility of galvanic corrosion at the joint. Wouldn't the two dissimilar metals in the thermocouple wires create a difference voltage that will eventually lead to corrosion? The two wires of a thermocouple are normally brazed together to prevent air/moisture from entering as far as I can tell. Perhaps the galvanic difference voltage is too small to worry about? I'd be interested to hear what your experience tells you about this factor. Cheers, Dave F. |
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| Author: | Andy Birko [ Sun Jan 04, 2009 9:11 am ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
npalen wrote: PID (P rogrammable-I ntegral-D erivitive) do it's thing when homing in on the temperature setting. The "P" actually stands for proportional. One thing I do regret is not doing better in my controls class. |
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| Author: | Fred Tellier [ Sun Jan 04, 2009 1:45 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I also pulled back the outer braiding and just used the wire insulation and the twisted ends between the blanket and the slat. We used the twisted ends in crimped connectors on all applications where the walls of the oven temperature was needed. In some areas we were at 600 plus degrees and there was failure when the wire actually broke due to stress caused by heat and vibration. We were required to change these out as required by the ISO standard, in areas where the actual air temperature was measures we used the wand type Thermocouples that were exposed to the air flow. In regard to the PID loop values I feel there is no need to use them as on off control is plenty accurate enough for our needs. I get a range of 3 to 5 degrees around the set point, and with a PID properly tuned for the application we could cut that probably only in half. The idea of the PID is to smooth out the variations around the set point, the preset values given in the programming instructions are a good point to start. We had a very expensive program to assist in loop calibration and often spent a lot of time tuning loops on new equipment. Fred |
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| Author: | Barry Daniels [ Fri Jan 09, 2009 4:06 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I am putting together the parts to build one of these heat controllers. The insulation on the supplied thermocouple is really tough glass fiber that resists all my cutting tools. Any secret tricks to cutting this stuff? |
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| Author: | Dave Fifield [ Fri Jan 09, 2009 5:43 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
Barry, I cut the glassfiber strands with an ordinary pair of sharp scissors! Perhaps yours is made of tougher stuff? Dave F. |
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| Author: | Barry Daniels [ Sun Jan 11, 2009 7:53 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I think its the same thermocouple as shown in the photo. The glass fibers were tough and a little bit slippery so they just slid out of the sciccors as they were closed. I ended up using a pair of razor sharp snips that worked pretty well. My next and larger hurdle is figuring how to connect the controller. I made the mistake of getting a different unit that the one you guys used. Would one of you be willing to look at the manual (if I can link it up here) and helping me on this? |
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| Author: | Fred Tellier [ Mon Jan 12, 2009 7:58 pm ] |
| Post subject: | Re: Cheap Digital temperature controller for heat blanket |
I would be happy to help, post the manual and terminal block diagram. Fred |
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