3 Phase Kiln Retrofit....from 1PH to 3PH

Discussion in 'Furnaces and their construction' started by BattyZ, Oct 17, 2021.

Page 1 of 2
  1. BattyZ

    BattyZ Silver Banner Member

    First off, I realize I am going the opposite way then, like, everyone on this. I have a kiln that the elements were very much worn out so I pulled them. My shop has 208V 3PH and I would very much like to take advantage of that.

    My idea is closely related to this one:
    https://www.joppaglass.com/elements...S/3_ph_230VAC_30A_folder/3_ph_230VAC_30A.html
    [​IMG]

    From the other posts about resistive wire I believe 3 lB of Kanthal A-1 should give me enough to pump 9-12KW.
    https://euclids.com/collections/element-wire/products/1lb-kanthal-a-1-wire-14g

    Temp control would be with the Omega controller I already have, thermocouple and this contactor:
    https://www.ebay.com/itm/323925771176?hash=item4b6b7b03a8:g:trAAAOSw0VxdiQj6

    Really styling this after Kelly's 8KW furnace with just an additional element. The goal is to be able to melt aluminum and maybe copper/brass in a timely manner all-electric using the power I do have to my advantage.
     
    BattyZ, Oct 17, 2021
    #1
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Power looks fine to me. The max surface loading of the coils should be in range. At 208 vs 240 probably a little shorter element length than mine for the high end of your range but that's simple ohm's law calc. What are the internal dimensions of the kiln? Will it be strictly melting or heat treat too?

    Best,
    Kelly
     
    Al2O3, Oct 17, 2021
    #2
  3. Smoking Shoe

    Smoking Shoe Silver

    I put 14 gauge and 10500 watts into my Kanthal spreadsheet using 3 coils at 208V
    Amps/coil at cold start = 16.83
    Resistance length per coil = 66 feet ... not including lead in length
    Surface load = 3.4w/cm^2 (close to the low limit per Kanthal 6 being right in the middle)
    Coil diameter should be between 8mm and 19mm ........ Pick one that gives good coil spacing to fit your inner diameter.
    The last part of the sheet depends a lot on the interior dimensions of the kiln.
    Kanthal.jpg
     
    Smoking Shoe, Oct 17, 2021
    #3
  4. BattyZ

    BattyZ Silver Banner Member

    Ideally I would do both with it. I still have another 240v kiln running at 208. Priority is melting though.

    Thanks for those calcs Smoking Shoe! I can get more info tomorrow as far as real world geometry.

    Appreciate the help guys.
     
    BattyZ, Oct 18, 2021
    #4
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Might be interesting to take note of how the original kiln elements were laid out. Getting uniform temp can take some doing. For heat treating it can be beneficial to have multiple coils that can be fired independently.....and top is usually hotter than bottom. For melting it's not much of an issue.

    For T5 aluminum I just load and turn it on. If I want finer control, I bring the furnace to temperature, then load it, and use one of two coils to maintain temp. It really just depends on the degree of precision required. T6 aluminum is a little touchy but most steels, not a problem.

    Best,
    Kelly
     
    Al2O3, Oct 18, 2021
    #5
  6. BattyZ

    BattyZ Silver Banner Member

    You bring up a great point. In my OP I list the 3P contactor for controlling all of them. I also have thought about ordering 3 of these...
    https://www.omega.com/en-us/control-monitoring/relays/solid-state-relays/ssrl240-660/p/SSRL240DC50

    I could have them all wired to the same source signal but have inline toggle switches to heat with only one or two elements like you mentioned.

    Going to pull the trigger on getting 3 lbs of 14 ga Kanthal inbound so I can get started on coiling them.
     
    BattyZ, Oct 19, 2021
    #6
  7. BattyZ

    BattyZ Silver Banner Member

    "Next day" as promised. lol I know this kiln is not the best of shape but should work for my needs.

    20211022_160952.jpg 20211022_161002.jpg
    20211022_161018.jpg 20211022_161036.jpg

    3lbs, 300 some ft of Kanthal A1 14 ga has been ordered. Hopefully, I can get a contactor ordered today as well.
     
    BattyZ, Oct 25, 2021
    #7
  8. BattyZ

    BattyZ Silver Banner Member

    OMEGA ENGINEERING SSR3PH600AC25, contactor order has been placed! 16 amps per channel via the excel spreadsheet so 25 amps per channel should cover me. In addition to this; will have 1 switch for the auxiliary on the contactor for a safety. Will also have 3, 30 amp, switches for per channel control, also acting as a redundant safety.
     
    BattyZ, Oct 25, 2021
    #8
  9. Smoking Shoe

    Smoking Shoe Silver

    Looks like 56 inches around the kiln?
    For 3 coils at 10500 watts (in the middle of your desired range) this is close to the ideal coil diameter per the Kaanthal documents:
    coil length.jpg
    Numbers outlined in RED are the relevant ones. The coil diameter for the ideal coil spacing is kind of large compared to what I've seen in most kilns so you may have to reduce the diameter to fit the slots you have - or enlarge them.
    The numbers are also for ONE wrap around the inside of the kiln for each coil.
    For a longer coil to wrap around the inside twice:
    coil 2.jpg
    This gives a much smaller diameter coil but may be hard to wind that tight.

    Note: the K factor for coil winding diameter has not been tested in the real world. It is more of a 'fudge factor' based on prior experience with similar material.

    One more try to upload the spread sheet..................
    Change the file extension to ***.xls from ***.txt
    This site doesn't allow the Excel extensions.
     

    Attached Files:

    Smoking Shoe, Oct 25, 2021
    #9
  10. BattyZ

    BattyZ Silver Banner Member

    THis is what I am going to go for. Do you think I would be fine with wrapping them around a 1/2 bar?

    The excel file worked for me! Thanks!
     
    BattyZ, Oct 25, 2021
    #10
  11. Smoking Shoe

    Smoking Shoe Silver

    You attribute skills to me that may not be congruent with fact. ;)

    I resort to Excel files because my calculator punching skills need improvement to be called "poor".
    Per my spread sheet a 1/2 ;inch bar should put you right on the ideal coil spacing per my Kanthal manual.
     
    Smoking Shoe, Oct 25, 2021
    #11
  12. BattyZ

    BattyZ Silver Banner Member

    Hey, the less human interaction the less room for human error!
     
    BattyZ, Oct 26, 2021
    #12
  13. BattyZ

    BattyZ Silver Banner Member

    Parts are rolling in! 20211101_101518.jpg
     
    BattyZ, Nov 2, 2021
    #13
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Make sure you double or triple up the resistive wire leading out of the kiln to the conductor connection.

    How big are the melts you're anticipating? Unless you're planning on say ~60lbs of Al, the majority of your first heat time will be to bring the kiln mass to temp. I'm just going to guess a 60-90 minutes for modest melt mass and a small fraction of that for a second melt say <30min. My furnace gets some benefit from the coil being very close to the crucible because the radiative heat transfer is a function of that path length, so sometimes you see longer times from small crucibles in big kilns.......but either way, in the big picture it's just a few minutes.

    Is that inline with what you had seen on your previous electric melts?

    You can always bring the kiln to temp before you load it. Since you have 3ph you may be paying more but my residential electricity is $.09/kw-hr So your rig would be in the vicinity of $1/hr to operate. Cheap and clean.

    It also depends on how hot you run the kiln. I set my controller at 1800F. If you load it with your melt cold, what you will find is the melt will lag the kiln temp by a couple hundred degrees so you'll always reach pour temp before set point (not so in my low mass furnace). You can preheat empty to higher temps but may still have similar phenomena when you open it to load.

    What size crucible will you use and just typical tongs and shank for handling?

    Best,
    Kelly
     
    Al2O3, Nov 14, 2021
    #14
  15. BattyZ

    BattyZ Silver Banner Member

    Update!

    Made a jig, super complex, way fancy, never to be replicated again!

    20211115_172038.jpg 20211115_172019.jpg
    It was actually a spare machined part with a hole that I welded to a rectangular tube that, get this, already had the right size hole! This is why I trip over things all the time, for moments like this. lol Did have to buy a $7 1/2 in rod so that was a bit of a letdown. Anywho, the system worked well for the first element. Stretched it and did a test fit.
    20211115_212742.jpg 20211116_131229.jpg 20211116_132216.jpg

    At .5 inch ID it was a bit of a literal push to get the coil into place. Will be curious to see how this holds up because my old elements seem to vibrate initially on power up. If it becomes an issue I am sure there are various ways to hold the element in place.
    For the connections going outside, I have this MC order on its way.

    hitempcons.PNG
    Should cover my bases. Triple stranded out of the furnace to the MG wire via ceramic nut. MGwire to the terminal blocks. Regular conductor to the solid-state relays and safety switches.
     
    BattyZ, Nov 16, 2021
    #15
  16. BattyZ

    BattyZ Silver Banner Member

    My answer is yes. If the system proves reliable and steady. I will eventually work my way up to an A60. For the instant future, I will be well below that.

    Honestly, this sounds great to me. This is right in line with my propane furnace times, maybe a little bit slower. I will take slower and steadier on a casting day though.

    Yep and yep. This was the vision from the beginning. Excited to test out the number crunching...which leads me to my next, maybe final, hurdle with this rebuild. How to measure 3 phase power usage. Seems to be loads of power meters for single-phase but the 3 phase options are triple the price. No pun intended. Any ideas out here guys?
     
    BattyZ, Nov 16, 2021
    #16
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Might be a little more than that but expect 3-4 hrs with A60.

    Measure one leg and P = V x I x 1.73 x PF

    Power Factor of .8 is typical for induction motors but I'd expect in the 90s for purely resistive load.

    Best,
    Kelly
     
    Al2O3, Nov 16, 2021
    #17
  18. Peedee

    Peedee Silver

    We found a place selling cheap re-furbed utility meters. Not sure if that is an option (it is clumbsy as you have can't reset the index)
     
    Peedee, Nov 16, 2021
    #18
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Moved from another thread......

    Don't count on that. Unfortunately, it's not a linear world. You can put heat into small melts faster for the same reason very small melts lose heat very rapidly. Accepting true induction heating of ferrous alloys, but for crucible heating.

    We discussed it a little in your build thread, but a big factor is your furnace volume and therefore thermal mass of it's walls are increasing as a cube (^3). The other significant factor can be the distance from the wall/coil to the crucible. Small gaps are best because it increases the rate of radiative heat transfer and greatly amplifies the smaller amount of air in the gap. I think this is why people with large kilns still report long melt times when the have a small crucible inside.

    The good news is you don't have to raise the temp of the entire furnace mass because there is a temp gradient across the wall (typically 2000f at ID and 200F at OD for IFB kilns), and each successive inch is larger in volume/mass. The better the insulating value of wall material, the steeper the temp gradient across the wall, and even lower percentage of furnace mass that must be heated. This can be a pretty straight forward calculation of the energy required to heat your furnace alone, but you're going to know shortly......after you flip the switch.

    My 10" bore low mass furnace is very high performing for all these reasons. -Third time is a charm I guess. It's 8kw. In round numbers, from cold start it will melt an A10 as full as I can charge it with aluminum in 30 min. The same furnace in dense castable (about 80lbs of it IIRC), was 90 min. The same furnace in IFB was about 60 min. The dense castable furnace would quickly melt a second charge.

    One other thing you need to be careful of with electrics (or any furnace for that matter) is adding large (cold) pieces to the melt. It can freeze the heal. I only mention it because without hot vent gas it can be harder to preheat extra charge in an electric.

    Best,
    Kelly
     
    Al2O3, Nov 28, 2021
    #19
  20. BattyZ

    BattyZ Silver Banner Member

    So if a guy put another IFB(or other) liner with element grooves one could see better radiative heat transfer? What about an insert cast out of pumpable ceramic to hold the elements? This option looking like your low-mass furnace. Would need to wind new elements. Maybe a Mk II idea. Might as well go low mass in general if I was to go that far.
     
    BattyZ, Nov 28, 2021
    #20
Page 1 of 2

Share This Page