Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 61249 times)

Offline petespaco

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #320 on: February 19, 2021, 07:05:09 PM »

The capacitors:
BM brand.
0.33 mfd  630VAC, ((1200VDC)
Type MKP

Regarding the uncommented post about the video about "Induction Heating 101":
You will be paying at least USD$1000 and probably more to get one of those running by the time you get a water coolant system running.
If you shop around, you can find some of them for as (apparently) cheap as USd$600, but then they want USD$300 plus for shipping!  And that's without a water cooler.

I am not saying that you shouldn't do it.  I know several guys who HAVE gone that way and they are generally pretty satisfied.
One HUGE caveat though---  Those things are always billed as "15KW" machines, although their maximum input power is only about 7.5KW.
But of course, as they say in China, "if you can cheat, cheat".  I am surprised that no one has taken them to task on that issue.
All that said, however, they do a good job, and generally seem to be pretty robust.

In my opinion, here's THE best guy to watch if you want to learn more about that unit:
(EJ of the Anvil):
https://www.youtube.com/channel/UCRRCSJ1ZNe3Sa-PmfsJsPzA

Pete Stanaitis
---------------




Offline hightemp1

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #321 on: February 20, 2021, 04:58:43 PM »

The capacitors:
BM brand.
0.33 mfd  630VAC, ((1200VDC)
Type MKP

Regarding the uncommented post about the video about "Induction Heating 101":
You will be paying at least USD$1000 and probably more to get one of those running by the time you get a water coolant system running.
If you shop around, you can find some of them for as (apparently) cheap as USd$600, but then they want USD$300 plus for shipping!  And that's without a water cooler.

I am not saying that you shouldn't do it.  I know several guys who HAVE gone that way and they are generally pretty satisfied.
One HUGE caveat though---  Those things are always billed as "15KW" machines, although their maximum input power is only about 7.5KW.
But of course, as they say in China, "if you can cheat, cheat".  I am surprised that no one has taken them to task on that issue.
All that said, however, they do a good job, and generally seem to be pretty robust.

In my opinion, here's THE best guy to watch if you want to learn more about that unit:
(EJ of the Anvil):
https://www.youtube.com/channel/UCRRCSJ1ZNe3Sa-PmfsJsPzA

Pete Stanaitis
---------------

Thanks for cap specs: found a pack of 10 for about $10.  Ok to add all 10 to the "turbo board"? Good place to add caps on turbo board may be parallel with water tubes since the twelve caps on main board end there?

Very good video Pete, but currently I am less interested in how to use heaters and more in how they work.  Here's one from the boomer on theory and DIY zvs boards.  The program he uses for troubleshooting circuits looks interesting, at least for those who know how to use it. 

"THE BOOMER" waxing-out on induction zvs control circuit.
/>
Got me thinking about DIYing a bigger board.  Our 2.5Kw boards are pretty simple with common parts.  Other than the 6 mosfets and 12 special caps(about $25 total retail), I could probably have cobbled together everything else and slapped something silly together like everybody else.  Also wondering if this basic zvs design is scaleable up to 10kW -anyone here using 7.5kW or above?  China is out with a new 5kW unit and I suspect 6kw shortly.  Maybe at 10kW there is a better design since DC power supplies for ZVS get more expensive?

 Topic: What happens when L and C are not matched?  (Read 1221 times)
https://highvoltageforum.net/index.php?topic=638.msg4193#msg4193

Check out this massive crucible  8)

https://books.google.com/books?id=aCgDAAAAMBAJ&pg=PA24&dq=popular+science+induction+furnace&hl=en&sa=X&ved=2ahUKEwjq7Z-0wvfuAhWqd98KHek-AcMQ6AEwBHoECAIQAg#v=onepage&q=popular%20science%20induction%20furnace&f=false



« Last Edit: February 22, 2021, 04:26:09 AM by hightemp1 »

Offline Mads Barnkob

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #322 on: February 20, 2021, 07:42:56 PM »
There has been people building large scaled up ZVS induction heaters before. Its now 10 years since Rogerinohio did it and I would guess that the Chinese manufacturers just copied his ideas on how to scale it: https://4hv.org/e107_plugins/forum/forum_viewtopic.php?id=129196
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
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Offline hightemp1

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #323 on: February 27, 2021, 04:50:48 AM »
Not sure if anyone has posted pics of board yet so here are some pictures of the 2.5kw version I received with the two fans removed:

A magnifying glass (not pictured) showed that solder on one of the power diodes did not make it through to the back side of board?

Any tips on making a beefier turbo board? How bout 10 more caps, 2 more mosfets with matching diodes, resistors, etc. Making deeper traces somehow and overload protection for mosfets?


UPDATE: Mads, thanks for that link.  Very good stuff though appears site is no longer active.  I wound up on your website and if you don't mind I'd like to post your advice and tips on ZVS induction heater design:

"Considerations
The MOSFETs used need a voltage rating about 4 times higher than the supply voltage and a on-resistance below 150 mΩ. In ZVS operation the switches see a voltage that is π times input voltage, so 4 times rating of input voltage leaves some head room for playing it safe.

If supply voltage gets over 40 VDC, consider using resistors between 470R-800R for the gates. Supply voltage needs to be minimum 12 VDC, lower than 470R gate resistors can be used in that case, if supply voltage dips under 10 VDC, there is a risk of MOSFETs failing from overheating by working only in the linear region or short circuit if one of them stops switching.

Supply voltage should not exceed 60 VDC, as this is very close to 200 VDC across the MOSFET. The internal construction of MOSFETs with a higher voltage rating makes them unsuitable for use in a self oscillating circuit like this Royer oscillator.

A MMC is made from 27 capacitors to avoid excessive heating in a single capacitor. The capacitors will still heat as massive current flows between the tank and work coil. To get a good result, a large tank capacitance is needed, if a capacitance lower than 4 uF is used, results might be disappointing. It is strongly advised to use a capacitor with made from polypropylene (MKP) or similar that can handle large RMS currents, it might even be necessary to water cool the capacitor too. A MMC as the one I use here can only withstand short run times and will even then heat up.

The value of the inductors are advised to be between 45 to 200 uH and depending on core material the number of turns varies a lot, use a LCR meter to check the values.

Water cooling of the work coil is a must! Even at just small runs with moderate power input as the ones I have conducted, the work coil would take damage from heat."

(6)IRPF260N mosfets
(12)0.33 mfd  630VAC, ((1200VDC) Type MKP
« Last Edit: March 20, 2021, 02:29:02 AM by hightemp1 »

Offline petespaco

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #324 on: February 28, 2021, 04:33:46 PM »
Quote
Any tips on making a beefier turbo board? How bout 10 more caps, 2 more mosfets with matching diodes, resistors, etc. Making deeper traces somehow and overload protection for mosfets?

The best "tip" I have is this:
Simply look around on the internet for sellers of the 4000 and 5000 watt units to see what they have done.
Places like Ebay, Amazon, Aliexpress and Banggood.
To increase power, they usually simply add pairs of Mosfets and duplicate the driver circuits, adding more capacitance and thicker traces as they go.  Some manufacturers/sellers have also added protection circuitry, too.
But, of course, you have to find bigger power supplies to match all that output.  5000 watts at 50 volts is 100 amps, right?

Pete Stanaitis
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Offline hightemp1

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But, of course, you have to find bigger power supplies to match all that output.  5000 watts at 50 volts is 100 amps, right?

Pete Stanaitis
---------------

Regarding bigger power supplies.  I think two of the common 3kW servers in series gives 100 volts @ 60 amps, not 100 amps, (parallel conncetion may be much safer) though you probably could wire PS in parallel.  Update: I think two 3kw PS in series @ 100 volts posses a serious electrocution risk since DC would be floated.  Not sure, but regulations i think require proper grounding for anything over 50 volts.

Yes, another obstacle, but more volts may be less of a problem than more amps with ZVS design.

Point is, I am not looking to get 5kW out of present board.  The TURBO add-on board option is maybe only a 10-30% boast so we can take full advantage of our 3kW power supplies?  A 2.5kw to 3kw over-clock gives 25% more power (500 more watts, or 10 extra amps @ 50 volts) to our work loads. 

Yes, for sizes of 4kW to 20kW heater/furnaces one would not modify this board, but would either start from scratch or buy expensive new. 

« Last Edit: March 15, 2021, 10:41:18 AM by hightemp1 »

Offline petespaco

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Quote
I think two of the common 3kW servers in series gives 100 volts @ 60 amps, not 100 amps,
100 volts is NOT an option for these things.  The supplies would need  to be in configured in  parallel. 

I'd work on coil design to maximize power TRANSFER.
Maybe even consider a cobalt crucuble, since cobalt's curie point is MUCH higher than that of iron bearing steels.

Pete Stanaitis
---------------

Offline hightemp1

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Quote
I think two of the common 3kW servers in series gives 100 volts @ 60 amps, not 100 amps,
100 volts is NOT an option for these things.  The supplies would need  to be in configured in  parallel. 

I'd work on coil design to maximize power TRANSFER.
Maybe even consider a cobalt crucuble, since cobalt's curie point is MUCH higher than that of iron bearing steels.

Pete Stanaitis
---------------

Mads did three 750W power supplies in series for 2.25kW?  I read ZVS circuits work better with more volts and have trouble handling more current?  I think MADS said Mosfets peak out somewhere in these higher kW ranges, but china appears to be using them at least for the 4-5kW units.  Ok, so they are using dual 3kW PSs at 50 volts, as you say, then traces must be huge and more expensive mosfets, caps - either way components get pricier I suppose.
Update: I think two 3kw PS in series @ 100 volts posses a serious electrocution risk since DC would be floated.  Requlations require proper grounding for anything over 50 volts.Floating DC ground at any voltage posses risk.

Thinking coil only MOD might only give 5% max boast, if that.  I know thinner means more power, have you tried the 2 or 3kg skinny crucibles designed for those induction desktop gold/silver melters?  If I remember correctly, BadPeter could melt over 3 pounds with the 1800W unit though it took about an hour.

Cobalt currie point definately makes it an interesting unknown wildcard, but lots of power is going to have to go into a dense heavy metal, and resitance is not as good as graphite.  Sure its been done before but can find no literature and can find no crucibles.   Melting point of cobalt is actually about 25 degrees less than iron so maybe works with copper alloys esp. brass using a barrier coating.  Cobalt is so dam expensive but if you get 5 times more melts then ?   Crucible expense is a problem. 

But to your point - can cobalt give us more power?  There is a Russian You-Tuber who also thinks it is worth investigaing, and maybe has the resources to do test.  I guess time will tell us if Cobalt can give a power lift and/or compete with graphite.

Update: Pete, I think Dave says below that when increasing power for a given coil shape, voltage and current should increase proportionately.  With proposed turbo board, maybe most of increased power would be attributed to amperage increase only since voltage is fixed on PS.  So maybe coil shape should idealy change?  Also, as previously mentioned, I'd like to somehow get frequency closer to 20kHz or even 10kHz.  Adding 10 extra similar caps and a longer, wider coil should get me fairly close?

CHECK OUT THIS DESIGN:
/>
Picked up some good tips, no; but, you guys all need to give him some pointers, I think.

Disclaimer: I am an electronics knob.  Do not follow what I do.


« Last Edit: March 10, 2021, 05:18:34 PM by hightemp1 »

Offline davekni

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Such ZVS oscillators can run with more voltage or more current.  My little Jacob's ladder runs at 170V (but under 2kW).  IGBTs work well at higher voltages.  I've seen one running on rectified 220V line for an induction cooking appliance prototype (using SiC FETs).  For normal induction heating, the work coils need lower voltage at higher current.  For a given work coil, current and voltage need to increase together.  That is generally below line voltage, even here at 120Vrms.  (And isolation from line is needed for safety.)

Using two additional low-threshold-voltage FETs for gate drive (instead of pull-up resistors and diodes) can dramatically reduce gate drive power while simultaneously speeding up gate drive:
https://highvoltageforum.net/index.php?topic=1439.msg11002#msg11002
I've made several ZVS oscillators with variations of the above circuit.  So far none at 5kW, as I don't have any use for such, nor a sufficiently-large DC supply.
David Knierim

Offline hightemp1

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Such ZVS oscillators can run with more voltage or more current.  My little Jacob's ladder runs at 170V (but under 2kW).  IGBTs work well at higher voltages.  I've seen one running on rectified 220V line for an induction cooking appliance prototype (using SiC FETs).  For normal induction heating, the work coils need lower voltage at higher current.  For a given work coil, current and voltage need to increase together.  That is generally below line voltage, even here at 120Vrms.  (And isolation from line is needed for safety.)

Using two additional low-threshold-voltage FETs for gate drive (instead of pull-up resistors and diodes) can dramatically reduce gate drive power while simultaneously speeding up gate drive:
https://highvoltageforum.net/index.php?topic=1439.msg11002#msg11002
I've made several ZVS oscillators with variations of the above circuit.  So far none at 5kW, as I don't have any use for such, nor a sufficiently-large DC supply.

davekni, thanks so much for your hands-on reply.  Would really appreciate your suggestions for my turbo add-on board idea for these 2.5kw ZVS induction heaters(basically somehow increasing power to the stock 2.5kW circuit board from China so output is closer to the power supply's 3kW capability).  Increasing power by 20% puts 10 more amps or 500 extra watts into work load.  Not a huge deal of course, but for my application it would be really sweet.

What's your opinion of the 3kW induction furnace in the video from schematic above?
« Last Edit: March 02, 2021, 12:16:23 PM by hightemp1 »

Offline davekni

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To clarify, voltage and current increase together for a given coil, given frequency, and given impedance of object being heated.

If I understand correctly, you have two goals:
1) lower frequency
2) increase current at a fixed supply voltage

Lowering frequency for a given coil is done by adding capacitors.  The resonant current (current oscillating between capacitors and coil) will increase.  Power supply current (input power at fixed voltage) might go up or down depending on impedance of the object being heated.  I don't know enough about what objects are being heated and how they respond to frequency.

More turns within the work coil will also lower frequency, and lower resonant current.  It will likely lower power at fixed voltage, as volts/turn is lower.

Adding capacitors will certainly help with lowering frequency, and might increase power draw.  If power draw doesn't increase, then add yet more capacitors and reduce work coil inductance (fewer turns).  That will increase power draw.

Now the critical piece - how to keep the board from overheating and failing at 3kW:
First, you will likely need larger inductors.  Lower frequencies require larger inductances.  Higher power (at fixed voltage) requires higher inductor current capability.  Both cause inductor physical size to grow.  I don't know specifications for what is there already, so don't know what margin may exist.  (BTW, total size can be a bit smaller with a single inductor feeding the center-tap of a ferrite transformer, transformer ends to the FET drains.  Simpler to stay with two inductors and increase size.)

I also don't know specifications for the FETs being used.  A significant portion of power dissipation may be switching loss with the simple pull-up resistor gate drive.  If so, reducing frequency may be sufficient to get 20% more current from the existing FETs.  Switching losses can be reduced with stiffer (lower value) gate pull-up resistors.  To avoid absurd power in the pull-up resistors, a pair of PFETs can be added in series to switch them on only when needed:


The above uses only one pair of power FETs.  However, it should work with many in parallel.  A single pair of PFETs should be able to switch out all of the pull-up resistors, allowing much lower pull-up resistance.

BTW, if you use a separate 12V supply for node "V12" instead of a pull-up resistor to the main supply, turning on that 12V gate supply first before the main 3kW supply solves the start-up issues that these circuits sometimes have.
« Last Edit: March 02, 2021, 10:30:06 PM by davekni »
David Knierim

Offline petespaco

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I couldn't find specs for: I320N20.
What is it?
What is its RDS on?

Pete Stanaitis
---------------

Offline davekni

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The full part number is IPP320N20N3 G, 0.032ohms 200V TO220.  I'm not recommending this specific part, although it does switch quite fast with very low miller charge.  Instead I was showing the circuit topology.  If I understand correctly, your goal is to modify an existing 2.5kW ZVS induction heater to 3kW.  My thought is to add two PFETs and lower-ohm gate resistors and a 12V supply to your exiting board.  For that you will need somewhat larger PFETs than I used, as my circuit had only a single pair of IPP320N20N3 G parts as the power devices.  That specific circuit is used as a 200W driver using a 19V laptop supply with only a bit of copper foil for heatsinking and no fan.  You will need PFETs that can conduct for short periods the current of all gate resistors in parallel for one side.  If you use 10-ohm gate resistors pulling up to 12V, that will be roughly 1A per resistor (after counting for diode and NFET voltage drops).  If there are say 6 FETs per side, then the PFETs need to handle short times (~1us) of 6A, say STP10P6F6 or FQP7P06 or IRF9Z24.

In other words, I'm suggesting a circuit topology, not those specific parts and values.
David Knierim

Offline hightemp1

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The full part number is IPP320N20N3 G, 0.032ohms 200V TO220.  I'm not recommending this specific part, although it does switch quite fast with very low miller charge.  Instead I was showing the circuit topology.  If I understand correctly, your goal is to modify an existing 2.5kW ZVS induction heater to 3kW.  My thought is to add two PFETs and lower-ohm gate resistors and a 12V supply to your exiting board.  For that you will need somewhat larger PFETs than I used, as my circuit had only a single pair of IPP320N20N3 G parts as the power devices.  That specific circuit is used as a 200W driver using a 19V laptop supply with only a bit of copper foil for heatsinking and no fan.  You will need PFETs that can conduct for short periods the current of all gate resistors in parallel for one side.  If you use 10-ohm gate resistors pulling up to 12V, that will be roughly 1A per resistor (after counting for diode and NFET voltage drops).  If there are say 6 FETs per side, then the PFETs need to handle short times (~1us) of 6A, say STP10P6F6 or FQP7P06 or IRF9Z24.

In other words, I'm suggesting a circuit topology, not those specific parts and values.

Top notch advice -thx so much.   I am least qualified in this forum to suggest mods to my proposed add-on Turbo Board, hither known as TB.  To clarify application, basically trying melt more bronze in a taller 1.5kg graphite crucible for larger size castings (2lb range). And, also wish to add aluminum melting capability with taller/wider based 150ml. crucible.  Looking for frequencies in the 10-20kHz range -present china config with 1kg graphite crucible is 40 kHz. Here are ideas for TB, good or bad as they may be: 

1.Board currently has 12 caps.  Would a good start be adding 10 same spec'd caps in parallel directly attached to current ones on the underside of board? At the same time widening traces of all the caps, both inductors, and one trace to each mosfet?
2.Both inductors measured about 37uH in circuit.  Go bigger OK, maybe start by doubling them to, say 75uH?
3.Present circuit board has (6) IRPF260N mosfets (pic added).  Maybe start by adding two of the same spec'd mosfets - thinking no room on circuit board for them? (see pictures of circuit board in post #323 further up this page-17).  If no room, then both new mosfets would go on the proposed TB, along with matching diodes (there are no diode markings on china board -can someone please suggest a part number?), and matching resistors (1 power resistor (see pic-5W 470ohm) and 1 regular resistor(would this be the resistor you suggest decreasing. If so, I assume replacing them all and what resistance might be best?).
4.Incorporating a 300W 12 volt DC adapter into TB.  Didn't have time to figure that one out. but would appreciate advice on attaching/wiring it in TB.
5.20% more amps is goal, but bigger coils unfortunately give less power to load.  To keep from increasing inductance on a new taller coil design for bronze, use same amount of material in the coil but widen spacing between coils.  For Al the newly designed copper coil's inductance will have to increase to accomadate both wider and longer coil.  Lower Al melting temps should hopefully allow for this. Both new coils could be packed with high temp castable ceramic insulation, and swapped out with flared brass hardware.

As you know by now my electonics knowledge is sparce.  Above ideas are both specific in places and vague in others but at least is a start to TB.  Don't trash em too badly.  If you would please assist by filling in gaps, offering superior plans, both general and specific to proposed TB for Chinese 2.5kW ZVS induction heater.  Finally, since my schematic reading abilities suck, simple wiring explanations of components to TB would be sweet.  Thanks kindly in advance.  :)

PS if your niech is blacksmithing, I think same MODS specific to circuit boards would apply.  Basically we are just trying to juice an extra 10 amps or 500W out out this stock chinese 2500W zvs induction heater, and at the same time take full advantage of the commonly used 3000W server power supplies.


Disclaimer: I am an electronics knob.  Do not follow what I do.

« Last Edit: March 05, 2021, 02:03:18 AM by hightemp1 »

Offline davekni

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There are many better MOSFET options compared to IRFP260.  That part must be cheaply available in China (or some Chinese knock-off version).  3kW looks possible from 6 of these parts IF they are kept cold.  That appears to be the strategy of the claimed-3kW versions on EBay.

If you can change MOSFETs, a quick Digikey search shows FDA70N20 as a good option - higher gate threshold voltage, lower resistance, about 1/3rd of the gate charge.  No need to increase gate-drive power with better FETs.  These list as $3.17 in singles or 10 for $26.63 on Digikey.  May be cheaper other places.  Or, for a bit more money, IXTQ76N25T is a 250V option for a bit more voltage margin.  There are many others that are better than IRFP260.  The IPP320N20N3 part I used is also better, but in the wrong package for a retrofit here.  There are likely many IGBTs that would also work here too, but there also might be unpleasant surprises with such a more substantial change.  (Gate zener diodes would need to increase to 15V for IGBTs too.)

In short, if you are willing to change FET parts, there is no need for additional parts.

Fans blowing down on the board would be great - both to keep FETs cool but also to keep caps and ECB traces cool.

Additional caps on the back is fine.  With fans blowing on the board, adding trace thickness may not be necessary.  If back-side caps get too warm, blow air at the board from both sides.  By fans blowing on the board, I mean something like the 3kW EBay models show, but duplicated for the back-side caps.

That leaves the only hard problem: inductors.  Power inductor design is somewhat complex.  Current rating is even more important than inductance.  For these powdered iron cores, saturation current isn't a hard value, but rather a continuing drop of inductance as current increases.  You need higher current for increased power and higher inductance for lower frequency operation.  Think of something big, like this 3" core on EBay:
https://www.ebay.com/itm/Large-Toroid-Core-3-Inch-Diameter/202733471216?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D63b757a18a3244079717fbb1554b26b4%26pid%3D101195%26rk%3D2%26rkt%3D12%26mehot%3Dpf%26sd%3D274175297983%26itm%3D202733471216%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseUnbiasedWeb&_trksid=p2047675.c101195.m1851
Wind with perhaps 2 strands of 14AWG wire.
« Last Edit: March 15, 2021, 08:44:25 PM by davekni »
David Knierim

Offline hightemp1

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In short, if you are willing to change FET parts, there is no need for additional parts.


Please forgive my ignorant questions -now it's clear to all why I flunked physics.  Replacing just the six current FETs with the more efficient FDA70N20 FETs will increase power to work piece in current ZVS stock configuration by roughly how many watts?

Example: Currently when Peter places his #1 crucible in his matching coil it draws about 40 amps @ 50 volts.  Just by upgrading to superior FDA70N20s FETs, the same coil/crucible will now draw more amps, say 48 amps @ ZVS's fixed 50 voltage?
« Last Edit: March 05, 2021, 05:00:28 AM by hightemp1 »

Offline davekni

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Sorry, I wasn't clear.  Changing FETs avoids the need for additional FETs (and associated diodes and resistors).  Changing FETs will not by itself change power significantly.  (Perhaps 2% increase due to lower voltage drop and faster switching.)  Changing FETs will keep the circuit from burning up when caps and/or work coil are changed to increase power to 3kW.

So you still need to add caps to reduce frequency, which may increase power.  If not enough increase, then add yet more caps and decrease work coil inductance.  (Or, change to 250V FETs and increase input voltage from 50V to 60V.)
David Knierim

Offline hightemp1

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Just call me a knob -thanks for not laughing out loud.:-[  Assuming work coil inductance stays about the same, can you ball park about how many more capacitors would be needed for a 10% boast?  Currently, I think there are six .33uf in parallel or 12 total caps.

Many of these 3kW server PSs do have hidden POTs for cracking up voltage.  So that may be the quickest way.  48v to 53 would be a nice 10% boast. 

Just noticed that my ZVS board model has an isolated fan line not tied into circuitry.  Some have so fan speed automatically varies accordingly to load -easiest way to MOD for auto fan speed? If too complicated, a boast converter could crank amps on fan to maybe 15 volts?

I don't have any coil that size in my parts bin but have some smaller ones.  In the video above by Schematix, he gangs two smaller inductors together to effectively get same larger inductance.  I don't have a scope to test circuit, but do have an inductance meter to measure - you said maybe 3 turns.  Current inductance on each existing Inductor is 37uH, roughly about what uHenry should I be shooting for on each pair of two smaller ganged inductors?   

Indeed, I am a little slow.  Thanks so much for your patience and time, and for sharing your knowledge.  :)



« Last Edit: March 05, 2021, 06:46:59 AM by hightemp1 »

Offline petespaco

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You don't need to do anything with the two inductors that are connected between the power supply and the tank circuit.  Their purpose is to minimize coupling back to the power supply.  They don't contribute to the tank's operation in any meaningful way as far as I can tell.

Offline davekni

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A 10% voltage boost should give a 21% power boost.  Voltage is 1.1x.  Current will follow, so be 1.1x.  1.1 * 1.1 = 1.21x (power is current * voltage).

If you stay at 40kHz the existing inductors might suffice.  They appear to work for the 3kW units sold on EBay, which look like this 2.5kW unit with large fans added.  If you add caps to reduce frequency, you will almost certainly need larger inductors.

A bit of explanation on the inductors - please ignore if it doesn't make sense:  When current increases, iron-core inductors saturate, so inductance drops.  At high current, inductance can drop to a tiny fraction of what you measure with a meter.  The low inductance causes high current ripple.  High ripple current can cause two problems.  First, it may cause your DC supply to shut down due to over-current spikes.  Even if the supply doesn't shut down, high ripple current is heating the supply's output capacitors, which may lead to eventual failure of the supply.  (The supply's intended server use doesn't draw significant ripple current from the supply.)  The other issue which may show up first is added FET current.  The high ripple current comes from the supply and is conducted through the FETs.  Even with the better FETs I suggested, if ripple current gets high enough, the FETs forward voltage drop will be too high to keep the opposite FETs off.  The result will be fried FETs.

Unfortunately, there is no simple way to design inductors.  Measuring with your meter gives inductance at low (almost zero) current.  Saturation can make the inductance drop by an order of magnitude or more at high current.  High-current inductors are usually custom-made for specific applications.  I don't know of any good source for pre-made 50A inductors.
David Knierim

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