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New Induction Heater circuit with no center tap.

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by gary350, Nov 1, 2016.

  1. spec

    spec Well-Known Member Most Helpful Member

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    Hi TCM,

    Do you know, I have been wondering how such relatively small capacitors were used in the power supply of Garry's previous induction heaters, and now you say that commercial induction heaters also use relatively small capacitors. Taking your example, and inserting a 100uF per running amp gives, 150A * 100uF = 15,000uF total, This is a much more manageable value of capacitance, as you imply.

    Such low value capacitors would result in the plus and minus 22V lines being, to a first approximation, 120Hz rectified sine waves, rather than DC with a 1V ripple at 120Hz, as I had intended.

    While a power supply with such a high ripple would be anathema for other applications, say a high power audio amplifier, I can see that it would be OK for an induction heating coil application.

    The high ripple power supply would only produce * 0.707 of the heating effect in the coil of the low ripple power supply, and the capacitors would need to stand the very high ripple voltage (and thus ripple current), but the advantage of much lower value capacitors far outweighs the disadvantages. And the rectifiers and transformer would have a much easier time.:cool:

    spec

    PS: I bet with a high ripple power supply the induction heating coil makes an ominous noise under full steam- like a Frankenstein machine.:D
     
    Last edited: Nov 14, 2016
  2. spec

    spec Well-Known Member Most Helpful Member

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    Further to the high ripple power supply approach, off the top of my head, a good value for the reservoir capacitors would probably be 100,000uF (100mF). At 150A running current, this capacitance value would result in 12V ripple voltage. The 100Kz current pulses would then be filtered, as you and shortbus say, by polypropylene metal film capacitors (and ceramic) as and where necessary.

    100mF, 50V, high-ripple capacitors are available from mainline distributors, like Digikey and Mouser, for around 53 bucks a shot.

    UPDATE: Perhaps use three of 100mF capacitors for each supply line to give a ripple voltage of 4V which would, arguably, give a good cost/perforamce balance.

    spec

    http://www.digikey.com/product-search/en/capacitors/aluminum-capacitors/131081?FV=fc01ac,fc01c8,fc01ce,fc01d1,fc01d2,fc01eb,fc01ee,fc01f2,fc01f7,fc01f8,fc01fa,fc026b,fff40002,fff80009,340124,340127,34036d,3403e1,3403f6,34054f,340550&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25

    https://en.tdk.eu/inf/20/30/db/aec_2013/B41456_B41458.pdf

    http://media.digikey.com/pdf/Data Sheets/United Chemi-Con PDFs/U36D Series.pdf

    http://www.vishay.com/docs/28371/101102phrst.pdf

    http://www.rubycon.co.jp/en/catalog/e_pdfs/aluminum/e_LSQ.pdf

    http://nichicon-us.com/english/products/pdfs/e-lnr.pdf

    http://www.kemet.com/Lists/ProductCatalog/Attachments/391/KEM_A4034_PEH200.pdf

    http://www.cde.com/resources/catalogs/CGS.pdf
     
    Last edited: Nov 15, 2016
  3. spec

    spec Well-Known Member Most Helpful Member

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    Hi SB,

    I now see your reasoning- yes with the high ripple power supply approach MKP capacitors would be good.:)

    spec
     
  4. dave

    Dave New Member

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  5. shortbus=

    shortbus= Well-Known Member

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    Hi spec, this is where I bought mine, price has gone up a small amount since buying but still pretty reasonable.
    https://www.surplussales.com/Capacitors/Polypropylene/Box-Caps/MKP-MKT.html

    They have a pretty good array of others too. https://www.surplussales.com/index/Polypropylene-Polyester-Box-Type-Capacitors.html
     
    • Informative Informative x 1
  6. spec

    spec Well-Known Member Most Helpful Member

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  7. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    With a bit of simple inductive filtering beyond the initial capacitor bank that ripple becomes near irrelevant for high power high current applications.

    In his low voltage system I would put a reasonable sized ~200 - 300 uF per amp electrolytic capacitor bank followed by a properly sized iron core inductor followed by the low ESR poly capacitor bank together as the power supply.
    Once and if he ever gets to a line powered setup the electrolytic capacitor bank could be dropped way back to 20 - 30 uF per running amp. 10x the ripple but when running near 15x the voltage the percentages still play in the end results favor.

    Good front end ripple filtering plus inductive smoothing and HF blocking and stabilization between the switching devices and electrolytics. Solid, stable and easy to work with without a lot of high cost specialty parts. ;)
     
  8. shortbus=

    shortbus= Well-Known Member

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    They do ship internationally. From this page - https://www.surplussales.com/OrderInst.html
    International Customers: Global Express Mail, Express Mail, Priority Mail, First Class Mail (no insurance if order totals less than $20.00 USD), UPS Express, UPS Express Saver and DHL may be used. Please contact us for accurate shipping costs if you are sending payment in advance. Be sure to give complete mailing instructions including address, country, telephone number and details you wish considered for customs. For example, you may want a declaration "For Amateur Radio Use" or a telephone number on the outside of the package. Please give us as many details as possible so that we can expedite your order. E-Mail and Fax orders are welcome and encouraged. Our dedicated machine is monitoring the line 24 hours a day. Worldwide Shipments Made Daily!! 1000’s of International Customers in Over 200 Countries Served
     
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  9. gary350

    gary350 Well-Known Member

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  10. spec

    spec Well-Known Member Most Helpful Member

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    That is a pretty neat schematic Garry.:cool: I suggest dropping the supply lines to 12V, as previously mentioned though. UPDATE 2016_11_22: Also the supply lines need to be regulated.

    spec
     
    Last edited: Nov 22, 2016
  11. gary350

    gary350 Well-Known Member

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    I am thinking 40,000. uf on the +22 vdc side and 40,000.uf on the -22 vdc side. 30,000. uf on each 15 vdc.

    I have several MOT transformers I can use but the primary coil is usually 100 turns on all of those that is 1/2 was is needed for 100% duty cycle. I have some good transformers I can destroy for the EI core then rewind it with the correct primary for 100% duty cycle this EI core is larger for correct primary winding for 100% duty cycle but not sure I really need 100%. I have a 2500 watt EI core I saved from a cooked transformer it will need to be wired 240 vac on the primary. I still have not decided which EI core to use yet. I have a coil winder for my lathe I can wind this transformer in 30 minutes. I use to have a good supply of enamel coated copper wire #16 to #30 sold it all but 3 rolls of #24 each roll is 100 lbs each. #24 will be good for the two 10.5 vac windings that will give me 14.8 vdc my notes says, add 2% for loss. I can use 75 amp wire to get 15.5 vac = 21.9 vdc. I can change any winding by 1/2 or 1 turn or any multiple of that to get any voltage I need. OH wait, I need to read the data sheet again I think I need 6 amps on 1 of the 15 vdc power supplies i can wind 3 coils in parallel to get 6 amps with #24 wire that is 36 turns on the secondary with 240 vac on the primary. Somewhere I read 4 to 6 amps?
     
  12. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    No need for the high capacitor values on the 12 - 15 volt windings being at most they wont see much over an amp average current draw. 1500 - 2000 would be a great plenty there.

    Personally I would put them on their own dedicated power supplies so they are not affected by the power transformers voltage pull down and other possible power instability issues. A pair of 12 - 15 volt 1 - 2 amp wall wart power packs would be more than adequate.
     
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  13. spec

    spec Well-Known Member Most Helpful Member

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    As TCM says, the three 12V power supplies (reduced by me from 15V) do not use much current: 100mA would do, in theory, but I would advise at least one amp for the two supplies for the output transistors and at least 5A (as a contingency for future experiments), for the power supply supplying the driver chip isolated electronics. It is also advisable to have all three supplies regulated. Three terminal regulators would be fine for the two 1A supplies but a separate mains powered power supply would be advisable for the 5A supply (dirt cheap on ebay).

    Afraid I led you astray with the high current requirements for the three 12V (15V) supplies- over caution.:eek:

    May I suggest you try using two MOTs and connect the primaries in series. Then have an identical secondary winding on both transformers, which are connected to the rectifiers as shown by the sketch of post #65.

    2016_11_22_Iss1_ETO_TWIN_MOT_PSU_VER1.jpg
     
    Last edited: Nov 22, 2016
  14. spec

    spec Well-Known Member Most Helpful Member

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    Hi again Gary,

    I have just looked at the ripple current with 40,00uF reservoir capacitors. With a 60Hz transformer, a full wave rectifier, and 100A current drain, a 40,000uF reservoir capacitor would result in a ripple voltage of around 22V. So a 40,000uF reservoir capacitor would do no smoothing at all, to speak of. The other problem is that such a huge ripple voltage would result in a correspondingly huge ripple current which no capacitor could stand.

    So there are two choices it seems:
    (1) have no reservoir capacitors (but still have relatively low-value, high-frequency capacitors to supply/filter the 100KHz current for the inverter).
    (2) have much larger reservoir capacitors. At 100A drain, a 4000,000uF reservoir capacitor would result in a ripple voltage of 2.5V peak to peak. This would be much more manageable as far as reservoir ripple current were concerned.

    The difference between the two approaches is that approach (2) would produce around 37% more heating effect than approach (1)

    Do remember that reservoir capacitors act like batteries and to do any good they have to be high ripple-current, low effective series resistance (ESR) types. That means that the capacitors will be big and quite costly (you can obviously connect capacitors in parallel to make a particular value). Here is an example of the type of capacitor you would need:

    [​IMG]
    http://www.digikey.co.uk/product-search/en/capacitors/aluminum-capacitors/131081?k=&pkeyword=&pv1317=8942&FV=fc01ac,fc01c7,fc01c8,fc01ce,fc01d1,fc01d2,fc01eb,fc01ed,fc01ee,fc01ef,fc01f2,fc01f7,fc01f8,fc01fa,fc01fc,fc01fe,fc026b,fff40002,fff80009,3400b3,3400c2,3400cf,340124,340248,340258,340259,3402fc,3402fe,340391,3403be,3403dc,3405c1,3405d3&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

    spec
     
    Last edited: Nov 22, 2016
  15. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    If line ripple is that much of an issue just use two multi tens of AH 12 volt deep cycle batteries in series for the capacitor bank.

    Personally I don't see DC ripple being much of a realistic concern here. Especially considering that in typical non SMPS systems 1000 uF per running amp is considered a great plenty. Even high power audio amplifiers don't go much over 2000 - 3000 uF per amp on a 50 - 60 Hz power system.

    I think you guys are playing to heavy on ideal power supply theory and not practical reality here given the application.

    Personally I think that if you want to run in the multi KW power levels you need to step up to running off normal line voltage and be done with it. Trying to do so at low voltages just adds too many other component sizing and cost related problems.

    Otherwise for the values of capacitance you think need you either have to step up to using car audio power capacitors (multi Farad with low ESR) stacked in pairs or step up to super caps with multi hundred F ratings and put a bunch of them together.
    But then if you do that you drive your diode bridge peak amp levels into the kilo ampere ranges provided your rewound MOT windings own resistance plus core saturation limits doesn't choke everything off anyway.
     
    Last edited: Nov 22, 2016
  16. gary350

    gary350 Well-Known Member

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    2 MOTs is series r like 2 light bulbs n series. If you put a 100w bulb is series with 75w bulb and run them on 240 vac the 60w bulb burns out. With transformers the load on the secondary determines the load on the primary so both loads need to be identically matched. I will probably start out with 1 MOT on 120 vac to build and test the circuit keep the power low until I know it works like it should.

    In my original mosfet circuit better filter caps improved the output power. Making a separate power supply for each part of the circuit helped too.

    I have no scope but my VOM works to read the DC ripples. On DC it reads DC volts. On AC it reads the AC ripples. If there is no DC ripple there is no reading on AC. The smaller the DC ripple the smaller the AC reading.
     
    Last edited: Nov 22, 2016
  17. spec

    spec Well-Known Member Most Helpful Member

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    But the loads will be matched Gary. The idea was to save you having to rewind the primary of your MOT.

    very wise- I like it. Gently gently is the way forward.:cool:

    .
    Yes, you can use a VOM (Volt Ohm Meter) set to AC, to measure the ripple voltage on reservoir capacitors. It is wise to put a 1uF non polarized capacitor in series with your VOM input lead to block DC from the input of your VOM.
    As a good guide, the peak to peak ripple voltage = AC reading on your VOM multiplied by 2.8.

    spec
     
    Last edited: Nov 22, 2016
  18. shortbus=

    shortbus= Well-Known Member

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    With the problems so far I can't wait for the ones coming with the bootstrap circuits for the ucc21520 when it comes to them.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    I mentioned using batteries earlier on. Four batteries would give +-24V nominal. Another approach would be to use switch mode power supplies, but that would be expensive, unless you used SMPs pulled from scrap equipment

    It is a concern in that full ripple reduces heating effect to 0.707, as stated a few times before.

    I fully agree and with a 100A that would workout to 1F, which would be excellent, but a touch expensive

    That would be even better and gives 2F and 3F for 100A drain.

    That is a sweeping statement TCM and cuts across the very principle of arriving at an optimized design for a particular set of circumstances.

    Of course using a high and non isolated supply would be good from the efficiency point of view, but again as stated before it would be unsafe, but also I think you would have practical difficulties building a coil to match a high voltage, but I have not looked into this in detail.

    Hmm I am not sure about that.

    Not sure of your objective here. I have already stated what capacitors would be needed for a 2.5V ripple current at 100A drain.

    spec
     
  20. spec

    spec Well-Known Member Most Helpful Member

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    I do not see any problems with the bootstrap circuits. Garry has got a handle on that and posted a perfectly reasonable approach and TCM and I have discussed this area with him. This is a normal design process.

    spec
     
  21. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Increase the system operating voltage to compensate. If he's at 22 now take it to 36 and have reserve.

    As far as I know he shouldn't be sticking his fingers or anything else on any of the circuits while they are active any way. :rolleyes:
    As for the induction coil standard air core inductance calculations for the given dimensions and operating frequency will tell exactly what the new turns ratio and sizing will need to be.

    Say he is running a 5" dia 5" high coil with 5 turns at 40 KHz That gives him and inductive impedance of ~ .5 ohms and an effective energy input ~ 1000 watts with his 22 volt input.

    Same coil dimensions but at 60 KHz with 15 turns and a 150 volt input gives him~7.5 ohms and an effective coil energy input of ~ 3000 watts.

    Take the same coil up to 300 volts and drop it back to 40 KHz and it's good for ~18 KW and about the realistic limit he could runoff a 240 VAC 100 amp power circuit factoring in system loses and a bit of circuit overhead.

    The way I see it given the size and capacity of his switching devices he has loads of room to cheat the system with just by changing input voltages which given since he insists on running off crappy rewound MOT's it's way faster and cheaper to do rewinds than go after theoretically optimal capacitor bank design.
     

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