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Induction Heater - Series Resonant - uC/PLL Tuning [ReactorForge]

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Move Thread LAN_403
Josh Campbell
Tue Jun 19 2012, 03:51AM Print
Josh Campbell Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
7749246452 640ffd139b N

************************************************** **********

Github Repository: https://github.com/ThingEngineer/ReactorForge

************************************************** **********


Photos: Flickr - Induction Heater (updated as I progress)

Goal: Replace dirty coal forge and heat producing propane forge in my brothers blacksmith shop for work on smaller items.


Primary Requirements:
  • Heat .5 inch square carbon steel to 2200-2400 °F DONE
  • Easy and safe to use by non technical users Easy DONE, working on safe
  • Draw under 30 Amps at 120V Update: 60A at 240V DONE
  • Water cooled work coil DONE
  • Water or air cooled electronics DONE
  • Thermal readout of water temperature, power supply, and inverter DONE
  • Mains current usage readout DONE
  • Auto shutdown and warning for an over temperature condition DONE
  • Operate in the 30-100KHz range DONE
  • Fully automatic - No user tuning required DONE
  • Working coil changeable by user without opening case DONE
  • Foot switch operation DONE


Secondary Requirements:
  • Heat .5 inch square carbon steel to 2600–2800 °F DONE
  • Thermal display (LED or LCD) DONE
  • Built in power control for operating at less than 100% powerDONE
  • Multiple resonant tank frequencies via capacitor or working coil inductor changes without system recalibration DONE
  • EMI filtering DONE
  • Unity power factor DONE (.97 to .99)


Type: uP/PLL tuned inverter coupled to a series resonant tank via a toroidal coupling transformer, .5-1.5 uH work coil

Resources:
  • All the other great IHs on this site of course!


************************************************** **********
************************************************** **********

Progress: (See Flickr gallery for full-size photos, and more photos not shown here.)

  • 12/29/2017
    Another video, this one goes over the basic functionality of the machine. Not how to use it but more how it works on a high-level. I'll be making videos of each component/system and how they specifically work individually, this is more a walkthrough of how they all work together. (And don't worry, I'll get a microphone before making those videos.)

    Have a great weekend everyone!

    Here is the link if the embeded video doesn't work.
    https://youtu.be/q-JiucZY7mM



  • 12/29/2017 Here is a video update from today.

    24

    I ran into an issue with the IGBT drivers. And rather than trying to patch the prototype boards up AGAIN I think it's time to get some real boards made for the ReactorForge.


  • 12/16/2017
    Wow, jump forward in time again and here we are. I have been busy over the years but I have never given up or complete stopped work on the ReactorForge. I am making an active effort to continue this project now.


    Cooling1
    I've got it hooked up to a decent chiller now. No more pond pump and the 5-gallon bucket with a small computer fan radiator. Although that worked quite well.


    Cooling2

    Cooling3
    I also set the whole thing up on a rolling metal cart from Sam's Club. This was perfect, lots of room on the bottom for the chiller, a small area for spare coils and a shallow top for the induction heater to sit.


    I'm now working on the new firmware. If you follow the GitHub (click watch) you'll see the progress.
    IMG 3029


    Since the scope of this project has gotten quite large I needed a bit more room than one forum thread so I have also been posting updates on the blog and on Patreon. But I will continue to update this thread and be active on here as well. Thank you all for your input and help over the years!


  • 6/13/2014
    It's been a while since my last update here but I've been busy with this project and my day job. Since the last update, my brother has quit his day job, built a big new shop and is now full time making tools using an updated induction heater model as his sole heat source (no coal or gas forge).

    In an effort to give back to the open source community I have organized the older project files into a repository on GitHub that I am making publicly available under the project name ReactorForge. This repository includes all schematics and code for my first 2 induction heaters (the second of which has been in operation full time for over a year). Over the coming weeks I will be organizing and releasing the information for the new version seen in the video below. This will be the last update to this thread as it has been focused on the older model. The newest prototype is much different and I will be starting a new thread to cover it.

    The video below is of the mark III beta prototype (code name: CriticalMass) in operation.



  • 2/15/2012
    My brothers company he started, Argyll Hammer is doing well on eBay and he's starting to get customer orders now. He just posted this one today on his Facebook page:
    "Big order, 40 pairs of tongs going to the guys at Trackers Earth, a wilderness survival/outdoor skills school in Oregon. They will be doing some blacksmithing classes soon now too and needed tools."
    1360957197 5258 FT1630 Tong Order

    The pressure is on to get the next version up and running. Just working on the case and refining the coupling transformer.


  • 01/2013:
    I updated this thread so that the newest updates are on top and the old ones are on bottom since it was getting so long. I'll remember to do that in the future since it was a pain inverting the list items.


    I've added a cooling solution to the IH to eliminate the need for running hoses to and from it before use.

    I also added a small high CFM fan with a push button switch powered from the 12V cooling fan supply to pull away fumes when heating a work piece. This came as a request from my brother who was surprised this was not an add on feature for commercial units.
    Pump 1/2HP 650GPH

    Radiator for 4 x 120mm

    High RPM 12V Fan 120mm x 4

    12V Power Supply

    8373051351 C4bb74ec1e N 8374124792 93f346d8cd N 8373051957 48031bd4ef N 8373052245 Ca8aaa0a73 N 8373052709 3608b50b9a N 8374126156 F5a75e0011 N


    What's next? Well not much for this unit. I've been working on the next one which is an LCLR tank topology vs this series resonant version. The entire unit is more robust and much simpler. I've eliminated the PLL drive and am driving each of 4 individual gate drivers with a high frequency PWM (64MHz base F) power stage controller. This has eliminated the touch analog circuitry, and most important allowed me to phase shift the full-bridge for perfectly smooth power control from 0 to 100%.

    I'll be compiling that project in it's own topic most likely since it is vastly different from this one. I'll also circle back and update the schematics and code for this one. The field testing and heavy use my brother has put on the unit has reviled much and yielded beneficial changes.


    On another note, my brother sold his Habañero Chile Grande - Link2
    Not because it didn't work as intended but because it was more expensive and vastly less convenient to use than the IH. He also went part time on his day job and is now making more selling custom tools than he is in his career position. So the pressure is on to get a more reliable, higher power unit going! Not to mention a backup.


  • 8/18/2012:
    My brother made a video of his shop progress and did a big portion of it on the IH, it was cool seeing it used by someone besides myself when I was not there to baby it which was really the biggest goal.

    When he is talking he is addressing some online blacksmith community. A quick warning, he is a big dork which is not the same as us nerds and geeks. :)

    update: I think he deleted the video.


    Work in progress UPDATE: COMPLETE:
    A few of the items I'm working on right now:
    • The next tank setup which will eliminate case heating by reducing inductance and raise tank efficiency.

    • A new control board with lots of upgrades including a micro-controller that will do the phase locking (on its own, no FPGA, working on a breadboard now with a small LV test tank, just needs some more tweaking). This is big not because there is an issue with the PLL, that thing works like a champ. But because it will allow me to have a tunable range with no center frequency, basically a PLL that can set it's own tunable range each time it runs allowing the user to switch coils out without retuning the PLL circuit. I know I could accomplish this to some degree using a varactor (C1) and two digitally set potentiometers (R1,R2) on the PLL but that's adding more failure points to an already touchy circuit in my opinion.

    • I'm also redesigning the IGBT driver to be more like a commercial driver with isolated DC/DC converters for each transistor, fault sensing and protection to detect over-current and short-circuit conditions, adjustable blocking time, desaturation protection and better common mode rejection... to name a few.



  • 9/16/2012: So exciting day today, finally got the IH set up in my brother shop for some real life tests and heavy use. After using it for only a few minutes I think he was ready to git rid of his $1500 propane forge he just bought.

    There was a lot more I wanted to work on such as better current limiting, current readout on the LCD, program timed cycles, temperature sensing and safety cutoffs, etc. Although the unit can run at a 20KW (.99PF) at 100% duty cycle indefinitely with no over heating as long as the water is running even with no work piece in the coil. Much more over 20KW and the coupling coil heats up above 130F so that will be the first thing that gets upgraded. I'm going to let him keep this one and build a new one with a new board and better tank setup and see how far I can go. He would like to be able to melt about 5-10lbs of material for making his own steel, seems easily do able.

    Anyway here are a few pics and videos, nothing really technical just the results of a semi-permanent setup in the shop. I left the case off to allow some tweaking if needed and because there is a bit of inductive heating in the case where the tank is close to the metal, a cleaner tank setup will probably solve that. Copper stock on order!

    Messing with a 1/2 bar at 10-20KW (10 cold, 18-20 hot)


    Pulling apart a 1/2" bar with an induction heater at about 12 KW


    7994441669 0e7efa447a N7994447810 4ae9674535 N7994436908 C716fc300b N

    More in the Flickr album of course...


9-12-2011: Here is the current schematic for the control board and a few photos of the first prototype board, good bye noisy breadboard!
1347557083 5258 FT141053 Controller


  • 7979818578 5eb28bae42 N7979820813 5ab3f3fd45 N7979820253 Ca7fdaee36 N

    The small breadboard on the side was for testing an active filter/amplifier for mains current sensing (which is a pure sine wave with Fo embedded in it) that is currently using a ratiometric hall effect sensor: ACS756SCA-100B. There were a few other tweaks and additions I made after the board was fabricated as with most prototypes, but the schematic is updated.


    Also it now supports small controlled fusion reactions. ;)
    7979817156 97d42a6e5b M7979816361 Ec636276bb M



  • 8/24/2012: Ok it's been a while since my last update, these things take time to create and well time is money. I received the hall effect sensors (Allegro's ACS758ECB-200B-PSS-T) and have those hooked up to monitor mains current so I can implement current limiting and power factor correction. These are very easy to use, the output is ratiometric to Vcc so it remains accurate in a noisy environment and with temperature fluctuations.
    7852879222 F22b123bb4 N

    The main reason for current monitoring was to be able to implement some form of current limiting. At the moment I am using a simple zero point detector circuit to signal to the uController the beginning of an AC cycle. A time delay is then imposed before reading the current with an ADC channel to ensure that the reading is taken at the peak of each cycle.

    2mS Scale
    Top trace: Top half of the 20V-peak AC on the low voltage power supply
    Bottom trace: 5V squared representation of the mains AC inverted
    7853259536 73467e2332 N

    So using falling edge detection to fire an interupt in the uController we can now measure the current at any phase angle on the positive current slop.

    1mS Scale
    Top trace: Top half of the 20V-peak AC on the low voltage power supply
    Bottom trace: 5V test pulse generated 4mS after the beginning of the positive going AC slope putting the test pulse roughly at the peak of the half cycle
    7851532628 2eafe1922d N

    Shown below is the 240VAC waveform along with the mains current waveform. Since we are using a rectifier and a filter capacitor we have this horrible non-linier current wave form. To measure the peak current we need to sample it at exactly 2mS into the positive half cycle. We can not simply cut off the bottom of the current waveform and smooth it with a low pass filter since the waveform is non-linier. Doing so would give us an average current reading, but I am interested in the peak current. This is where some reading up on Power Factor would be good if you do not already understand the benefits of having a unity power factor.

    Power factor on Wikipedia
    Power Factor Basics <-- very good one

    2mS Scale
    7851522952 E5c6791417 N


    There was a problem with measuring the current at a set phase angle, depending on the load the current waveform can shift or change shape entirely as seen below.

    2uS Scale
    120VAC waveform along with the mains current waveform. This is a better power factor than running on 240V at higher power levels but still below .80.
    7851526324 3604ca7c84 N


    So I need to measure the current at any point from 0-90 or 0-4mS from the positive slop trigger point. I decided to run the ADC continuously after triggered by the falling edge of the inverted square AC waveform, keeping track of two values. 1: the highest current value read since the beginning of this phase and 2: the average current value since the beginning of this phase. The ADC keeps running until the average level begins to drop, a 5 amp drop was a good point to avoid prematurely stoping the ADC due to fluctuation. This means the zero point detector is no longer needed for current reading, but I still have something else in mind that will require it later... active power factor correction.


    Power factor is a big deal when you are drawing a lot of current. Say running at 240VAC your peak current is 100A but your current wave form is non-linear, you have a lot of wasted power or KVAR. If your power factor is .75 then then your true power or KW is only 18,000, the KVAR is 6,000, and the total KVA is 24,000. Your machine is making use of 18,000 watts of power or 75A but your breaker, rectifier, and filter cap all need to be able to handle 24,000 watts or 100A. If you could bring your power factor closer to unity or 1 then your reactive power (KVAR) to true power (KW) would be zero and the current used in the system would equal the current supplied to the system. So no energy would be wasted as reactive power.

    There are many ways to go about correcting power factor depending on if you have an inductive, capacitive, or non-linear voltage to current phase relationship. The method I had chosen, although it would require a fairly large inductor was a buck-boost type which to put it simply uses a switch to short the rectifier output across an inductor. The inductor holds a charge that is then released back into the filter capacitor through a diode. The switching rate is varied to force the capacitor to draw charging current in phase with the AC mains. Not a terribly complex idea and not complex to implement. But it does require another switch either MOSFET or IGBT since the switching rate is still fairly low which means another driver. And it requires a large inductor to store energy and a diode to direct the flow of that energy. It will also require uProcessor time to read the current waveform and adjust the pulse rate to correct as needed, or a stand alone buck-boost power factor correction chip which will require another handful of passive components. In short I'm trying to keep this project simple and cost effective but still with incorporate some valuable features like power factor correction.

    This lead me to start at the root of the problem (which is why it has been a while since my last update). What causes bad power factors. A lightbulb which presents a purely resistive load on the AC mains has a perfect power factor of .98 to 1. (Some stray inductance here and there, and probably a very small amount in the filament coil.) But nearly perfect by any measure. So what is causing my big amp sucking DC power supply to have such a crap current waveform. The rectifier itself doesn't draw any current or affect current draw of the load, hook one up to AC and you get 120Hz out. Hook a light bulb up to that and you still get a power factor of 1.

    AC Mains
    7851525746 990fa42587 M

    Rectifier output (Inverter input) No Load / Load
    7851524516 6833c9744f M7854837954 0c5c735716 M

    Hook a filter capacitor up to that same circuit and bam, the power factor drops to about .70. This is because the capacitor does not re-charge in phase with the voltage. Rather the current begins to rise early in the phase and peaks just before the peak of the voltage so the current leads the voltage. Any capacitive reactance causes current to lead voltage. We could counter act that capacitive reactance with inductive reactance, similar to what is happening in the tank circuit at resonance. But we have the same problem here as we did trying to read the current at the peak of the waveform, depending on the load that the IH is drawing the effect of capacitive reactance varies because there are other factors involved besides a simple XL/XC circuit, so we would need to vary the inductance. Again requiring the need to read the complex waveform and adjust.

    Let's go back to the light bulb hooked up to the AC mains through a rectifier with no filter capacitor. Why can't I do that with the induction heater? Rather than a feeding a fixed DC voltage of 340V (240 x √2) to the IGBTs and getting a consistent square wave output of pulsed 340V we feed 120Hz 340V peak into the IGBT inverter and the output is a 120Hz envelope containing the resonant high frequency component. Well I say I can do that. There can be issues with under voltage IGBT's turning on from an off state but since we are pulsing them at a frequency much higher than the frequency of the input voltage this effect is non-existant or does not affect IH operation at least.

    Power Factor reading on a Kill-a-Watt meter (While running on 120V about 10A)
    7851523948 11b1816b51 N

    240VAC mains input and current waveforms
    7851528528 8c65d9f177 N

    Same as above but zoomed in on the high frequency resonant component of the current waveform
    7851527114 Ba71e63f4b N

    Inverter drive Fo and mains current waveform
    7854836434 1f38708811 N7851530732 Db8318b747 N

    Inverter output showing the resonant component Fo inside of the 120Hz envelope
    7854836734 5b861ff080 M7854837002 4aeffd4874 M7854837284 5469de40fc M7854837550 6b2cfbfd0d M

    Another feature I added was soft starting and stopping of the inverter Fo by ramping the PWM output feeding the VCO from 15V (Max VCO Fo) down until a resonant lock is achieved, and when the stoping the IH the VCO is ramped up from it's current setting back to VCO max be for disabling the PLL VCO using pin 5 of the PLL. This gives a nice smooth start and stop of the inverter with no bucking or large in-rush current.



    So far I have not been able to find any negative side effects in running the inverter like this, only one big positive. Which is 25% less current draw while still maintaining the same output power both by measurement and by results.

    1/2 Bar white hot and sparking in 10 seconds from cold. Melted in half at about 12 seconds.
    7851534184 Eca64e503d N7851534560 8583ecfe7a N

    In this video I pulse the IH on and off to keep the metal from just melting and falling off but keep it hot enough to burn it away. I am going to add a code to allow the user to change the maximum current so pulsing to do this type of heating will not be necessary.
    Melting 1/2 carbon steel


    Time for some fun:

    Penny Fire:
    Zinc has a fairly low ignition temperature, seen here is the zinc oxide left behind from a penny fire! I had a vacuum ventilating to outdoors for this. I would have taken a picture of the fire but I was to busy making sure it was contained. It was a brilliant white (similar to burning magnesium) with a ting of green. Out of the fire spewed long strands of smokey blue zinc oxide.
    7851565254 31c3943c24 N

    Another way to use the work coil
    7851567028 02e967a55c N

    Quickie furnace cement crucible
    7851567664 43ff2d2a40 M7851568290 8a0b8cd43c M7851569204 68d0ef9064 M

    Molten zinc in a crucible and the effect of the magnetic field on the zinc.


    Molten Al, Cu, Zn alloy
    7851576668 B9f1e3a704 M7851577284 3a455a708b M7851577688 738290644c M

    Cooled Al,Cu,Zn alloy
    7851578888 Ea1cdab187 N7851579452 564d6d8331 N
    Alloy: 75% Al - 20% Cu - 5% Zn : This ended up being a very interesting alloy, with a dark sheen and heavy feel, very brital even though it was cooled slowly and has a beautiful crystalline structure.
    Alloys of Al Cu and Zn are very common and among some of the hardest and lightest known to man. With a little precipitation hardening this one would be much less brittle but it has much more copper than most alloys of this type to be useful for much.



  • 8/9/2012: I've migrated away from the MOSFETs to IGBT's using a simple driver setup, TC4421A/22A's driving a P0585NL gate transformer which is controlling the gates of 4 x 30W discreet MOSFETs which are in turn driving a custom wound 1:1:1:1:1 gate transformer that can handle about 30 watts to drive the IGBTs directly. I chose to go ahead and do this before working on the current limiting for two reasons. One because IGBT's will be used in the final design so it has to happen anyway and two because I'm waiting on some single IGBT blocks for the current limiting circuit. I'm not going to use SCR's like originally planned. I'm either going to detune the tank or use an IGBT to PWM the the DC bus output between the rectifier and filter cap.

    Water block construction:
    7749243612 2a199c950b N
    7749244508 Ae65259056 N

    IGBT setup on water block with the 3 Phase rectifier, filter cap, snubber cap, and bus connections:
    7749246452 640ffd139b N
    New IGBT inverter mounted:
    7749250216 Efe7809a29 N
    IGBT driver test setup
    7749504346 F729fc78cc N

    Currently I'm running two 580V 3.75uF Eurofarad tank capacitors with a .864uH work coil for an uploaded Fo of 62.5Khz. Unloaded this setup pulls 50A when feed with 120VAC single phase and 125A when feed with 240VAC single phase. With 200A IGBT's I won't be trying it on 3 phase.

    Videos:
    Testing 1/4" square on 120V peaking at about 35A Sparkling white hot in about 25 sec

    1/4" square bar @ 25KVA
    1/2" round bar @ 25KVA


  • 7/30/2012: Over the weekend I got the resonant control working with the micro controller and PLL and changed to a larger coil (4 uH) which lowered the resonant frequency to around 41KHz. I still need to do some work on the coupling transformer, I don't have an issue with the wires heating just the toroid cores.
    7677066066 92316b3986 N
    7677101238 1d4c410f85 N


  • 7-30-2012: I had a noisy ground issues that was causing the uProcessor to reset when the unit hit about 12 amps of current draw from the mains but solved it last night when I rearranged the test setup so that the control lines were all leading away from the tank. I also removed the variac and hooked directly to a 30A circuit breaker through 6AWG wire. With this setup the unit draws about 20A with a cold work piece and 30 to 32 past curie.
    Something else interesting is that I no longer seem to have a problem with the toroids in the coupling transformer heating up. This was after a 5 minute run at 3000VA. Will take a closer look at this later.
    7686149102 044b33eb8b N

    The next addition to the unit (after I complete the current sensing circuit and code) will be to replace the MOSFETs with IGBT bricks (200 or 400A). My brothers original power requirements were a bit limiting but he now has available a 240V 60A circuit so I can up this to a 15KW unit.
    7686150814 23f30fb47a N


  • 7/25/12: So it's been a while since my last update, I tend get caught up in the process and don't make time to document my progress. Once it's complete I'll have a nice summary of the whole project. Since the last update I made and stuffed an inverter board. This board was initially just for testing so I could complete the control logic and work with the basic signals that are present in this type of IH. Well I wasn't happy with it. I had trace heating at higher power levels and and melted solder resulted in a flash over from tank output to ground taking out a few components near it's path. I redesigned the inverter board routing the HV manually on larger bus lines, seperated the HV from LV control, and added some latch up protection on the now larger TO-220 drivers (from SOIC-8). I also made the inverter ground and LV ground connection optional and clearly defined. All signals look beautiful and I can safely run at 15Amps (off of 120V mains using the voltage doubler power supply) for long periods using the now water cooled MOSFETs. Even with the cooling water around 90-95 degrees F the FETs hover around 115-130 degrees when pulling 15A at resonance.

    Flash over:
    7584767618 2d0e389852 N

    New inverter board, water block for bridge and MOSFETs, coupling tx (trying different toroids and wire), tank setup (removed loop intended for current balancing an MMC), terminal strip for connections.
    7603867314 6ff17d308b N

    Test setup with Inverter logic drive in, Inverter current out, and tank voltage out. Will get some cleaner pics up as well as all the scope tracings.
    7643786282 365941fe51 N

    New Inverter (V2.1):

    1343240967 5258 FT141053 Inverter 1343240967 5258 FT141053 Inverter Pcb

    Updated eagle project files for the inverter: ]ih-inverter.zip[/file]

    As always there are more pics in the Flicker album not shown here. Since these pictures I have removed one of the tank capacitors and raised the work coil inductance slightly, the resonance frequency is still around 65KHz. More to come soon on the PLL/uController resonance lock.


  • 7/2/12: Completed initial schematic and board design for the Inverter Power Supply, Low Voltage Power Supply, & Inverter. All control logic will remain on a breadboard until I work out how I want to control resonance, manage power, and what needs monitoring. I'll make the boards on the 5th and stuff them on on the 6th when the last of the components arrive. That leaves the weekend for the fun part, putting it all together and making it work!
    Images and Eagle project files:]ih-power-inverter.zip[/file]
    1341266246 5258 FT0 Inverer Power Supply 1341266246 5258 FT0 Inverter 1341266246 5258 FT0 Inverter Pcb 1341266246 5258 FT0 Low Voltage Power Supply 1341266246 5258 FT0 Low Voltage Power Supply Pcb


  • 6/28/12: Bonded tank cap mounts to the tank cooling pipes and mounted the caps. A little No-Ox on the copper plates between the caps to keep the connection clean. The brackets are made from 1/16" rigid coper and are short to allow the capacitors to dissipate heat via the cooling water running through the pipes just below them.
    7464506952 68239b3a72 Z7464512822 511a699522 Z


  • 6/27/12: Assembled the first coupling transformer (will use litz wire when it arrives), and capacitor mounting brackets for the Eurofarad tank caps. Working on a phase monitoring set up to possibly eliminate the PLL. Basically I'm using a comparator to turn the wave form of a current transformer (at the output of the inverter going to the coupling transformer) into a square wave, changing states at the zero cross points. This is fed into one port of the uP. Another comparator set up connected across the tank capacitor sends a similar square wave to the uP, this one shows the phase of the voltage across the capacitor. Since we know that the current and voltage are in phase in the tank at resonance we can use these inputs to determine if we are at resonance and if not which way to tune. The comparators outputs are shown in the photo below, I on top and E on bottom. I'm not sure yet if I want to generate the inverter driver frequency with a uP interrupt or a VCO of some type, we'll see. I'll have schematics and results up here as soon as I complete them.
    7461683856 1573534faa Z7461678510 375b50ac8f Z7462015922 Bbeaeb9961 Z


  • 6/23/12 - 6/25/12: Built the PLL/uProcessor circuit on a bread board to test and work out a final schematic design for the resonant frequency range needed. (Currently 45-100KHz) - Received lots of toroids, caps, and other fun stuff, most of the parts that I don't have in stock are here now.
    7461969614 9d097a6d29 Z



  • 6/20/12: Received rectifiers (1000V 50A) and caps for HV supply. Wired up the HV multiplier power supply for testing. AC IN:DC OUT = about 1:2.85 so 120VAC in yields about 340VDC out.
    7417489192 B8fed05571 Z


  • 6/16/12 - 6/18/12: Obtained the remaining copper parts needed to assemble the tank. Cleaned out an old ATX computer case and modified to work as a case for the Induction heater. Fabricated and mounted working coil and internal plumbing for tank capacitor mounting, coupling transformer mounting, and water cooling. Most of the parts will be arriving this week form Digikey, Mouser, Newark, OnlineComponents, AliExpress, and of course eBay
    7398211550 Af35637367 Z7398193588 7bf3ea5484 Z
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Dr. ISOTOP
Tue Jun 19 2012, 04:54AM
Dr. ISOTOP Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
How are you planning to control power? Bus voltage control, phase shifting the legs, detuning, pulse-skipping?
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Josh Campbell
Tue Jun 19 2012, 05:30PM
Josh Campbell Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
I'll most likely adjust the phase angle before the HV bridge rectifier using large Eupec PowerBlock SCR's:

1340125246 5258 FT140297 Phase Angle


1340125368 5258 FT140297 Img 2639


Other options I will want to try are making a fully-controled SCR bridge rectifier in place of the standard one. Or making a variable tap coupling transformer.
Did you ever incorporate any type of power control into yours, have any suggestions or pointers?
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Dr. ISOTOP
Tue Jun 19 2012, 08:33PM
Dr. ISOTOP Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
2bytes wrote ...

I'll most likely adjust the phase angle before the HV bridge rectifier using large Eupec PowerBlock SCR's:

1340125246 5258 FT140297 Phase Angle


1340125368 5258 FT140297 Img 2639


Other options I will want to try are making a fully-controled SCR bridge rectifier in place of the standard one. Or making a variable tap coupling transformer.
Did you ever incorporate any type of power control into yours, have any suggestions or pointers?

I had a 4-tap transformer to control power for different work piece materials, and I detuned the driver for finer control. Its not good for the bridge, but I was using watercooled CM400's, which dealt with it fine.
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Dr. Dark Current
Sat Jul 14 2012, 10:11AM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Remember to use an inductor if you are controlling a capacitive load with a SCR.
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Josh Campbell
Wed Jul 25 2012, 07:32PM
Josh Campbell Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
Dr. Dark Current wrote ...

Remember to use an inductor if you are controlling a capacitive load with a SCR.
Definitely! But thank you for the reminder, sometimes I'm only reminded of subtle things like this AFTER catastrophic component failure. I would like to actually cancel out any reactance using a boost type converter and correct the power factor to 1 so the SCR's would only see a resistive load. But this is obviously not a major requirement in order for the IH to work properly so it will probably be the very last thing I do, if I do it at al, for now denting above resonance works just fine.
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Josh Campbell
Thu Aug 09 2012, 11:30PM
Josh Campbell Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
I was really looking for a reason to use these SCRs in something but I don't think I want to use them just for the sake of using them when driving an IGBT is so much easier and more flexible. I am going to test using an IGBT to PWM the DC bus before the filter cap, will update with results soon. I do need to do some type of current limiting for sure since when connected to 240V it pulls about 125 amps with no work piece to load it, which is about twice what my brother has available where this is going.

Check out the new vids, nothing new really (glowing stuff) but it does show the working PLL/uP tuning in use. I'll get some videos of the scope and the IH together while in use to show that part a little better. One button operation is really nice, rather not say how many MOSFETs I blew tuning it manually during testing. :)

Videos:
Testing 1/4" square on 120V peaking at about 35A (Sparkling white hot in about 25 sec)
1/4" square bar @ 25KVA
1/2" round bar @ 25KVA
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Gabriel35
Fri Aug 10 2012, 12:21PM
Gabriel35 Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Pretty Impressive!!!
I hope that someday I can reach something like that!!!
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Josh Campbell
Fri Aug 10 2012, 11:19PM
Josh Campbell Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
Gabriel35 wrote ...

Pretty Impressive!!!
I hope that someday I can reach something like that!!!

Appreciate it Gabriel, once I finish the closed loop hall effect current sensing/limiting portion I'll get the rest of the schematics and pcb layouts up along with descriptions and walk throughs. And after I refine the Atmel code I'll post it up here as well. So far I've made the prototype boards but once I get a revised "final" version I'll have some made and probably post the rest of them up here just to offset the cost of ordering multiples. As of now it will have a low voltage ps board and then all the control and driver circuitry on another board. With a possibility of having the driver circuitry on it's own board as well, we'll see, there's not much to that part now that I'm using IGBT's.
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Jrz126
Sat Aug 11 2012, 07:05PM
Jrz126 Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Looks great.

Where'd you get the ferrite cores for the coupling transformer? What material is it?



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