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HT Oven Build Question

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by steve in sc, Oct 7, 2019.

  1. steve in sc

    steve in sc

    20
    Feb 14, 2014
    I think I’ll stick with my drawing unless someone sees a glaring error with it.
     
  2. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Your schematic will work fine.
     
    steve in sc likes this.
  3. tony santovenia

    tony santovenia

    31
    Sep 20, 2018
    hey guys, in an attempt to not start another post for ht oven builds, I will ask my question here
    as silly as it sounds, i have minimal experience with electrical wiring etc, I will have an electrician friend of mine look over what im wiring up or help me...
    my dilemma is figuring out what to buy as far as switches/lights/in line fuses. its all a bit confusing to me and there are so many choices when i go online to get what I need.
    im following dan comeos schematic that I posted earlier here... however I cant figure out those parts to buy...
    my build is exactly that build, 240v 3000W 12.5 amps... 2 38.4ohm elements (I already made them) in parallel.

    more specifically.. what are those inline fuses in the schematic? exactly what do I buy? ... and the main power switch.. the "elements on" light ... and where the lines from the spots 1,2,3,4 on the pid intersect with the lines from the relays and the main leads (how do you splice these or connect them together.. do I need to buy something for this?)

    I already have my PID, 2 SSR's and thermocouple picked out (Inkbird ITC106VH SSR output relay alarm..... 2 Inkbird SSR-40DA (3-32v DC to 24-380V AC ........ and Yeeco +K Type thermocouple 0-1300C)

    can anyone help me identify exactly what I need to buy ?
     
  4. tony santovenia

    tony santovenia

    31
    Sep 20, 2018
    once again this is the exact schematic im talking about and it matches my build
    [​IMG]
     
  5. steve in sc

    steve in sc

    20
    Feb 14, 2014
    Howdy! I am by no means an expert but I can tell you what I'm doing and using. I finished up wiring my control box today and will wind my element tomorrow and get it all sorted out to be isolated through the side of the oven case so it can be mated with the element feeds on my build. Mind you, my build is 120vac and right at 1400-1500 watts. I have a single SSR and only a DPST mains switch as well as an element on/off switch. The control input wires to the SSR are 12vdc from the PID. That in mind, I am using a 12vdc led lamp as well as the element cut off switch I picked up from a local auto parts store. It should work perfectly. I decided to add a light after the element cut off switch in my above schematic and wired it in between the positive and negative input controls to the SSR coming from the PID and after the element cut off switch. The only thing to keep in mind with that is to hook up the positive dc from the PID controller wire to the cathode leg of the led. If not, the led will not light up when the element cut off switch is engaged to the ON position. As far as the inline fuses... As long as you get fuses rated for the voltage and current you are pulling in the circuits, you're good. Ask your electrician friend for an opinion once you hammer it down. I used a 20A in the mains feed and a 1A in the current feed to the PID for my build as the PID does not draw much of anything as far as current is concerned. Hope your build goes well! Sounds like you're well on your way. When mine is done, I will post a more refined schematic and details of the build.

    Cheers!
    Steve.
     
    tony santovenia likes this.
  6. steve in sc

    steve in sc

    20
    Feb 14, 2014
    Evening All,

    So today I tightened up and sorted all the wiring and double checked everything. I am still waiting for two ceramic standoffs and two split bolts for the element lead connections because I just want to make sure they cant touch the case if the brick inside shifts for any reason. I drilled holes large enough to keep a buffer with the steel case but I just want to be double sure there is no fault to case ground. In the mean time, I wanted to do a test fire and see how the element may expand and shrink over a heat and cool cycle. I wanted to do three cycles but had to drive to Charleston and back so I didn't have time but for one cycle. I don't smoke anymore but I do vape and have used kanthal to make vape coils and learned a long time ago to do several burn in cycles on a newly wound coil and then adjust individual coils for peak performance and even heating. I can't imagine its any different with a kiln element. I had the control box sideways and set several inches away from the case so I could monitor everything as well as take some current flow readings on the element leads while the PID was allowing the SSR to pass full current cycles during heating which ended up being slightly over 11 amps (perfect buffer on a 15 amp circuit). Surprisingly, the 120V oven heated to over 900 F in under 8 minutes. The PID started to taper off my 1000 F setting and it was another two min to reach 1000 F. I thought it would take longer at the voltage and wattage I built it to and that was nice surprise. I let it soak for about 10 min and then stopped the cycle and observed the cool down. It all went well except for one thing I was a bit surprised about. The cabinet sides both got to about 130-140 degrees on a very short 10 minute full heat cycle and then remained quite warm, (over 125 F during cool down). The top, bottom, and back of the oven case stayed just barely above ambient temperature. The majority of the element coils are on each side. Since my design has the control box mounted on the right side of the case frame and the fact that the left side of the control box is open, I've decided to make a design change and close that side of the control box with a steel plate as well as install standoffs to move it at least an inch away from the side of the case. No need to allow all that heat inside the control box to shorten the life of the SSR and PID. I may even sandwich some kaowool there to assist in keeping the control box components as cool as possible while working. My little two brick never gets quite that hot on the outside. Maybe 90-100 F but definitely not 140+ and no idea how much higher it would go on a longer heat cycle! I should have the rest of the parts I need sometime next week so in the meantime, I'll work on the design change. Once I have this lil guy done, I'll post a refined schematic with the little changes I made to the wiring as well as some photos. As a side note, I followed the guidelines from DanCom's kanthal calculator and came up with 29.63 feet at the coil diameter I wound and the gage of wire used. To my surprise, the resistance was too high at almost 11.8 ohms when done. I very carefully measured the length before cutting it and winding the coil. I ended up having to cut off about 20" or so to get it at my target which was 9.6 ohms. I ended up with 9.4 ohms and I can live with that. I'm not sure if it's an anomaly with the wire I bought or just a space/time continuum issue here in Darlington SC :) Anyway, I think I will do another calculation with DanCom's .xls file for a shorter element and wind it with some of the remaining wire I have so I can experiment and hammer that math down for future coil windings, maybe even two or three different lengths... I don't know the "inside baseball" math but can guess that the change does not take a linear path with kanthal the longer you go, probably a complicated logarithmic curve involving math even Martians don't understand. Either way, I'll reverse engineer a test coil or three if necessary to get the correct resistance according to the math of the calculator and see what comes of it as far as correct length on that sample of kanthal I bought. No bets on any different suppliers though. I hope all this info will possibly help someone tinkering with a HT oven build someday.

    Cheers!
    Steve.
     
  7. Backyard

    Backyard

    98
    Jul 19, 2019
    Resistive ohms are linear. Double the length, double the ohms. Half the length, half the ohms, etc

    Either you miss measured the length, the wires ohm is different than you thought, the diameter of the wire is inconsistent or you did the math wrong.

     
  8. Backyard

    Backyard

    98
    Jul 19, 2019
    For others, when wireing it up for 120 volts, what is the point of a 20 amp main fuse. You have no electronics or anything sensitive to protect that the circuit breaker is not capable of doing.

    If you are plugging it into a standard US 120 volt outlet, then it is already protected by the 15 or 20 amp breaker.

    For the 208/240 volt setups, sure as many outlets of those voltages can have anything from a 20 amp all the way to 50 amps or more sized breaker powering them.

    Also most breakers are only rated for Continuously supplying 80% of its rating. Therefore a 20 amp breaker can continuously supply 16 amps. Above that you hit the time temperature curve and potentially can pop the breaker. Many won't as the oven will likely cycle on and off with enough off time to allow the breaker to cool.

    Something to keep in mind
     
  9. steve in sc

    steve in sc

    20
    Feb 14, 2014
    I was very careful measuring the length. Did it twice with sharpie marks every two feet to be sure. Did sound engineer work for years back in the 90's and thought the impedance measurements would be linear with kanthal too. I ended up with less than the calculated 29.63 feet of wire. Used a caliper to measure a test wind for the diameter and used an online calculator from DanCom to get the correct length. I would wager that its inconsistent thickness. Won't know till I do some test coils.
     
  10. steve in sc

    steve in sc

    20
    Feb 14, 2014
    I built the oven circuit based on several amalgamations of schematics I was able to find that were tested builds. Most I find online are 220 circuits and I wont need that until I get a dedicated 220 circuit ran to my work area. It is basically a fail safe for a dead short in the current feed within the oven. I could be wrong but as I understand the way resistance works in a circuit, the closest protective device will fail prior to the main breaker of any circuit. A dead short will heat up and blow a fast acting 20A ceramic fuse in the oven long before creating enough feedback in the wiring all the way back to the main CB panel to heat up the CB and pop it, (mind you though, we are talking about milliseconds as electricity moves at around 186,000 miles per second). If fuses weren't needed in 120V circuits due to the reasoning of having a main CB already rated to protect a device, no devices would have fuses installed to protect them. I appreciate your information and understand your reasoning completely. I put it in there as a safety device for the possibility of a dead short in the oven itself which could happen within an SSR or a chaffed wire in the control case. I imagine it could also happen with an element too where it terminates and connects to the feed wires.

    Cheers!
    Steve.
     
  11. Backyard

    Backyard

    98
    Jul 19, 2019
    The current is consistent throughout the circuit. The current measured at the plug, switch, etc is the same as the breaker. It will also be the same all the way back to the nearest transformer. It is the voltage that take a hit and drops at each resistive point

    Fast acting fuses are not needed except on sensitive equipment. And then they are almost always less then the breaker rating. Using a 20 amp fuse on a (almost) purely resistive circuit that is also plugging into an outlet protected by a 20 amp breaker is redundant.

    How many fuses have you seen in a toaster, hair dryer, electric oven or clothsc dryer, coffee maker etc. The only ones I've seen are thermal fuses not current fuses.

    It's not really going to hurt anything to have them but they are not needed either

     
    steve in sc likes this.
  12. Backyard

    Backyard

    98
    Jul 19, 2019
    Are you measuring the wire in impedance? Are you expecting there to be any significant amount of reactance on the circuit?

    I would just measure the wire as you would DC with just a simple ohm reading.

    Sorry if my last few posts look like I'm busting your balls, but I'm not trying to come off negative or anything. Just trying to get a few things straight. There are others that will likely read this later as a guide to build one and we need to make sure there is good information here

     
  13. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    If you want to thermally isolate the control box from the cabinet don't use a steel side plate. Install a piece if Ins-board between them.1" or 3/4", whichever is the best fit.

    The cabinet will get warm to hot on most HT ovens. The better ones have a 1" blanket of Ins-wool wrapped around the bricks. Another trick is to wrap the outside with ab high temp insulation wrap like the stuff you wrap a hot water heater with. Don't wrap the control box, though. It needs to stick out so it can get convection cooling. If you don't haver a fan in the control box, adding a small computer type pancake fan is a good idea. Place it in the center of the back or side panel. Also, there should be plenty of 1/4" ventilation holes in the controller box back. Put a double row spaced about 3/4" apart at the top, and another double row at the bottom of the back panel.
     
    steve in sc and Backyard like this.
  14. steve in sc

    steve in sc

    20
    Feb 14, 2014
    Don't sweat it at all. At 51 years old and 24 active duty AF, I can handle it. I appreciate all the input as well. Never built one of these guys before and I want it to work so I don't have to rebuild it other than replacing an element when it will eventually fail. I measured the 16 ga kanthal exactly that way. I was just perplexed that the calculator was not right... Or was it the wire being inconsistent somehow? I really don't know. I just know with a resistive circuit, the math says what it says and the length from the calculator was not right for the correct resistance. Hoping all this discussion will help someone in the future to double check every step.

    Cheers!
    Steve.
     
  15. steve in sc

    steve in sc

    20
    Feb 14, 2014
    Wrapping the bricks is exactly what I'll do when I build a 220 oven. What is Ins-board? You'll have to pardon my ignorance on that jargon. I'll catch on one phrase at a time. :) Oh, and the fan is part of my modifications as the build has gone along. Once its all done, I'll wrap it up with a good schematic and build details as well as photos.

    Cheers!
    Steve.
     
    Backyard likes this.
  16. Backyard

    Backyard

    98
    Jul 19, 2019
    Its been a while since I have purchased any but I remember there being several different alloys used in heater wire. All being called nichrome or kanthal wire though. I'm not familiar with this calculator you used but does it take into account the different resistance of each version/alloy

    ?
     
  17. steve in sc

    steve in sc

    20
    Feb 14, 2014
    Kanthal A1 is what I used. I don't have the invoice near me now but in my wrap up I will post all the pertinent information about where I got what I used. The calculator is from jtknives page. Its put together by DanCom and is a downloadable excel file. I saved it so I wouldn't' have to go looking for a calculator when I need it again. The only user input variables are: Desired Watts, Input Voltage, # of elements, and coil diameter. The calculator gives output data for 16, 18, and 20 AWG wire. I wouldn't use it for nichrome wire.

    Cheers!
    Steve.
     
  18. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Ins-board is a fiber insulation board. It is what they line the forges with at NC Tool and Forge Co. It is made by tge same company as Ins-wool.
    High Temp Tools and Refractory carries everything you will need to build forges and all refractory supplies fro ovens and such.
    www.hightemptools.com
     
    steve in sc likes this.
  19. tony santovenia

    tony santovenia

    31
    Sep 20, 2018
    Hey steve, I had the same exact problem with dancoms kanthal calculator. I think it has something to do with the "diameter of coil" input. ... either ur supposed to put the outside diameter desired, the technical diameter of the coil (measured from the middle of the wire to the middle of the wire not outside to outside), or the diameter of the rod ur using to wind/inside diameter of coil) i used the technical diameter of the wanted coil which ended up giving me the same issue, nothing that i couldnt snip and stretch tho
     
    steve in sc likes this.
  20. Backyard

    Backyard

    98
    Jul 19, 2019
    one trick I did with mine was to add a large diode (and a switch to disable it) across the contacts on the contactor I used. this basically runs the coil at half the watts on the off cycle by still letting though half the wave form. this would help stabilize the temperature a little better by not letting it drop as much during the off cycle. I imagine it would work for those using an SSR. if yours doesn't fluctuate much between the on and off cycles (mine bounced about 10* f and less with the diode) then you will not likely benefit from this
     

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