Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 11921 times)

Offline Bert911

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Hello everyone,

I got around to test the new arrived heating unit. It came with a different coil (4 instead of 6 windings).  I have to correct my thought about the current limiting potentiometer. It's a bit strange, you can limit the current and you can trim the shunt resistor.Therefore, a real current meter is a have to. Maybe it's some sort of current limiting in the first 50% and shunt tuning with max current at the last 50% or something.

Here are the results from some testing:
Coil with 6 windings, 50 mm high, 45mm inner diameter
with no workpiece:
In 24,4V 45W; Out 74V peak on the caps
In 38V 90W; Out 112V peak on the caps
In 50V 185W; Out 152V peak on the caps
In 60V 250W; Out 188V peak on the caps
The voltage over the caps are pretty much spot on the PI times input voltage. Due to the higher oscillating current, the power loss increases also.

Heating up a workpiece:
Steel bolt 22mm diameter and 60 mm high
In 52V, used power 1600W at beginning, 2100W peak and 700W at around 900°C.

I maybe solder a copper pipe direct at the capacitor connection to cool them with the water too. A cooled heat sink for the mosfets would be great to, since the get a little bit warm at high currents.

The used resistor is a 5.1 Ohm, so I updated the schematics, the simulation is much more stable now.

Offline hightemp1

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Picked up one of these crucibles. Price is not too bad. Not 100% graphite, but has some silicon carbide in it along with some clay, maybe.  Hoping it is more durable but kinda doubt it, though it is thicker than the graphite ones -almost 11mm.   Chipping may mean it has less bonding strength and is more prone to breakage.  Hoping it heats as well, seems to have a lot of graphite (feels slippery like ones we are using).  Holds a little over 1 pound of copper.  OD is 3" wide by 3" long so with insulation the coil would have to be wider, about 3.75" and about 6 turns.  ID is 2.2" but narrows to 1.5". 

https://www.ebay.com/itm/Silicon-Carbide-Graphite-Crucible-Tool-Metal-Melting-Casting-Cup-Shape-Furnace/254233218790?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Description says: "Surface can be treated with antioxidant."  Sound like Chinenglish, not sure what it means.  Maybe this silicon/graphite type will accept some type of wash that could increase longevity?

Having some power supply issues so it maybe sometime before I actually melt anything, if ever.  :(
« Last Edit: June 23, 2019, 08:45:57 PM by hightemp1 »

Offline T3sl4co1l

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If that's the traditional combination of materials, it probably won't be very conductive, and the coating is a flux/slag material that tends to bead up on the surface and drip off (presumably can be refreshed with the right goop).

SiC is a modest conductor when heated, making microwave heating possible, and maybe induction still (but maybe with higher voltages/frequencies than are available here).

SiC-graphite crucibles can practically be quenched in water; they're very tough, as ceramics go. :)

Tim

Offline hightemp1

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If that's the traditional combination of materials, it probably won't be very conductive, and the coating is a flux/slag material that tends to bead up on the surface and drip off (presumably can be refreshed with the right goop).

SiC is a modest conductor when heated, making microwave heating possible, and maybe induction still (but maybe with higher voltages/frequencies than are available here).

SiC-graphite crucibles can practically be quenched in water; they're very tough, as ceramics go. :)

Tim

Maybe it will do induction with insulation?  If not, then this crucible may be relegated to melting lower temp metals and/or internal non-ferrous heat treating..

Microwave melting sounds interesting - wonder how long to super heat a pound of bronze in modified microwave with a typical 1200 watt microwave. 
« Last Edit: June 22, 2019, 06:27:25 PM by hightemp1 »

Offline flyrod

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I finished the circuit for the unit.

Thank you for posting that!  I think that explains the 6 small transistors I was seeing in the ebay pictures.  I tried to ask about it in this thread:

https://highvoltageforum.net/index.php?topic=167.0

So the 12v for the gate drive comes from a separate DC-DC board?

Also, what is the big capacitor that is not part of the tank?  Is this C8 in your diagram?

Finally, are there no bypass capacitors on the supply to Q3 and Q4?  If not, I would be curious to see what this point looks like on a scope.


Offline Bert911

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I finished the circuit for the unit.

Thank you for posting that!  I think that explains the 6 small transistors I was seeing in the ebay pictures.  I tried to ask about it in this thread:

https://highvoltageforum.net/index.php?topic=167.0

So the 12v for the gate drive comes from a separate DC-DC board?

Also, what is the big capacitor that is not part of the tank?  Is this C8 in your diagram?

Finally, are there no bypass capacitors on the supply to Q3 and Q4?  If not, I would be curious to see what this point looks like on a scope.


Hi there,

The first transistor switches the supply voltage for the gate drivers on/off, the second one switches the relay and the other 4 are the gate drivers.

There's an additional 12V power supply for the microcontroller, fan, pump and the gate circuit.

The capacitor C8 reduces the current/voltage spikes during the mosfet switching, reduces the impact of wiring inductances from the power supply and smooths the measured voltage for the microcontroller.

The transistors have no additional parts, there is no gate resistor, unfortunately.

I tested my new arrived "IXFX100N65X2-ND" mosfets and they didn't really work. During the ordering I didn't notice the slower body diode.
The heater didn't turn on at voltages over 40V or with a load and stalled at 20A current using. So I hooked up my Tektronix 2225 with my "very fine" 100:1 Chinese probes and measured the gate signal with the analogue differential add function. With no loads it was a near perfect square wave, not like the simulated one, but with increasing current the ringing was really visible.
Like 20V peak-peak at 20A. Could be a bad measurement setup, the Chinese probes or most probably the slow diodes.

Similar to this, just worse:
https://highvoltageforum.net/index.php?topic=648.msg4550;topicseen#new

As supposed here, it gets worse with the rising current.
https://www.mikrocontroller.net/topic/207864#2057621

Also the Voltage in the oscillator tank dropped at 20A to 60% from the unloaded one.

So I'm waiting for the real 260n mosfets, measure them with the scope and maybe buy some other mosfets with higher voltage ratings.
Something like these:
https://www.digikey.de/product-detail/de/rohm-semiconductor/SCT3030ALGC11/SCT3030ALGC11-ND/6204894

But I want to check the circuit with the original mosfets first, maybe they are also ringing, but with them it doesn't matter as much.

Greetings

Offline hightemp1

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« Last Edit: June 29, 2019, 08:28:19 PM by hightemp1 »

Offline hightemp1

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0. Use a thick, fairly conductive crucible (e.g., steel) to shield the melt from magnetic field.  (Marginal for aluminum, and not practical for cuprous alloys.)  Note that graphite has to be quite thick to provide much shielding.


Tim

Too thick is bad as well.  This quy could not melt anything with a 20mm thick custom made crucible.  More power required to heat larger crucible so can't get to superheat pouring temps.

https://highvoltageforum.net/index.php?action=post;quote=4362;topic=530.120

UPDATE:  Correct link should have been:
/>At the end of video he realizes that 20 mm is too much of a load.


« Last Edit: July 10, 2019, 06:53:36 PM by hightemp1 »

Offline Mads Barnkob

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Maybe we should split the topic, so that this stays for electronic discussion of the heater and the heating of metals, but the melting, casting and crucible discussion has its own thread?
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline petespaco

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Pushing the limits with a small work coil for annealing brass cartridges.  For this video, I make and use the smallest diameter work coil yet for the 1000 watt ZVS induction heater.   Although I focus on annealing a brass cartridge casing very quickly, this video is really a next step in my ongoing series about work coil design and  work coil frequency limits for reliable circuit operation.
It is here:
/>
(I stopped just BEFORE melting anything)

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

Offline hightemp1

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Finally got my ZVS unit.  While hooking things up, I realized that my planned auto fuel pump is not designed for pumping water and would ruin the pump in short order.  Wondering what would make a good pump?  I scavenged a small radiator and a huge server fan that will be used for water cooling. Possible pumps I have thought of:  submerged aquarium pump, auto windshield pump - any other ideas, and I assume flow rates of above mentioned pumps would be sufficient?

Online johnf

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garden supply store for fountain pump or similar

Offline petespaco

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While the garden pump mentioned by johnf might work okay, I suggest this one (or one like it):
https://www.amazon.com/Yosoo-Circulation-Brushless-Selling-Quality/dp/B00PXXJEHE/ref=asc_df_B00PXXJEHE/?tag=hyprod-20&linkCode=df0&hvadid=198097979185&hvpos=1o5&hvnetw=g&hvrand=17395343945830728741&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019020&hvtargid=pla-348418857326&psc=1
  It's about USD $20.00, but is rated for hot water, which certainly will be an issue.
As I mentioned in my most recent video, I was pleasantly surprised at how much flow I got from it even when using the 1/8 inch OD copper tubing for the coil.  I also suggest that you try to minimize the "head" that the pump has to work through.  In other words, don't put the radiator  all the way down on the floor making the pump have to work real hard.  As the "head" gets higher, the pumping rate and pressure goes down.

Pete Stanaitis
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Offline petespaco

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Subtopic:  Adding a (Cheap?) frequency meter (counter) to my induction heaters-

I just uploaded this page:
https://spaco.org/Blacksmithing/ZVSInductionHeater/MakingAFrequencyCounterForNoisyAndSineWaveInputs.htm

It's actually a story about what NOT to do, but it turns out okay.


OT for hightemp1:  That water pump that I recommended----  I would not consider it to be submersible.

Pete Stanaitis
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Offline Mads Barnkob

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Pushing the limits with a small work coil for annealing brass cartridges.  For this video, I make and use the smallest diameter work coil yet for the 1000 watt ZVS induction heater.   Although I focus on annealing a brass cartridge casing very quickly, this video is really a next step in my ongoing series about work coil design and  work coil frequency limits for reliable circuit operation.

Pete, I love your videos, you really get deep into the topics, do a lot of experiments and share your results. Kudos to you Sir.

You video editing was also really good in this video, keep up the good work, it had a nice flow and I enjoyed it from start to end!
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline petespaco

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Thank you for your kind words, Mads.

Now I want to talk about a "Cheap" Frequency counter for the ZVS Induction heaters:

I am certain that most people who get into this  "World of  Electrical Oscillations" do have frequency measuring equipment.

I have an old Tektronix 422 Oscilloscope that I use to roughly measure frequency by counting  the number of cycles I see on the screen at a certain sweep rate.  I also have an inexpensive tiny battery powered DSO-112 touch screen  oscilloscope that has the ability to give me a digital readout of the incoming frequency (if I push the right spot on the screen at the right time and have my magnifiers on).

  That's not much in the way of frequency measuring equipment, but it's enough for my BENCH needs at present.

  However, my projects are often scattered about my shop and I can't always get my bench scopes to the unit under test.  And, the touch screen of the little scope isn't all that handy for big fingers when I am in a hurry.
  I currently have two different ZVS induction heater systems.  My testing has made me realize that it is important, for several reasons, to know the tank frequency at any given time, so I decided to dedicate a frequency counter to each machine so I'd instantly and always know the tank frequency.
  To that end, I went through an all-too-lengthy process to choose/build/connect "cheap" frequency counters to my heaters.  (I even built two extra sets while I was at it).
  Here is a webpage that I just put up which takes you through the whole process:
https://spaco.org/Blacksmithing/ZVSInductionHeater/MakingAFrequencyCounterForNoisyAndSineWaveInputs.htm

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

Offline Bert911

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Good thing that my multimeter can handle these frequencies, after making a new coil it's always interesting how the inductance is.

As I said earlier I had some ringing Problem with the IXTH62N65, because of there really slow body diode (typ. at 25°C 445ns).
As a comparison, the IRFP260N (typ. at 25°C 268ns) there's also some ringing but it's not consistent and gets better with heavy load.
I also tested some FGH80N60 (typ. at 25°C 61ns).

The FGH80N60 worked just fine but they got really hot.
So I ordered some IKW50N65 (typ. at 25°C 52ns) which should be fast and cool enough. I'm not sure how the relative slow turn off delay time will matter, but I'll see.

The next step for 200V input voltage would be some good capacitors, but there are the next problems.
With these high frequencies and "high" voltages of the standard 2000W heater model, the capacitors are already at there current rating with only 50V input.
So that's not a long term solution. Other similar capacitor like the used MKPH-R or Dawncap aren't that suitable. If the overall capacitance is too low the frequency rises, which is a bad thing for the slower IGBT. If the capacitance per capacitor is too high, the currents are way above the ratings.
So more small capacitors would be the way to go, but these won't fit more than four on the original board.
I could make a new board/circuit, but the start/stop routine works really good and I want to keep it (no need for turning off the big PSU...).

With 4 capacitors which cost 15 to 25 € I can also go with some seriously big stuff like this:
http://www.eectech.store/cs-30122-solid-state-high-frequency-film-capacitor-12uf-500vac-p0319.html
Which can handle the voltage, current and frequency. It's even smaller than 4 big film caps. With some cutting at the PCB it will fit nicely.

However, my previously statement with the 6mm copper pipe isn't true in that case and a10mm pipe is probably more suitable.
Since I have two units, I put 4 originals caps on the IRFP260N unit with 6mm; 1/4" connectors and the second one with the new cap, IKW50N65 and 10mm; 3/8" connectors.

That should power things up. The oscillating current should increase with the higher capacitance which lead to a smaller working coil, which should be better for screws and non crucible stuff, which I use it for.

There's also a mains powered updated version of this circuit:
http://www.joretronik.de/Oszillatoren/Oszillatoren.html
This can't hang up at start up and can't fail like the royer.
Since my PSU is limited somewhere to 4kw-6kw I don't see a need to go higher up in voltages/complexity right now.
I'm not that firm with high energy stuff at that high frequency. For a proper circuit you would need a start/stop routine, over current protection, a relay and so on.
I try to get this thing working, build a housing and that's it, since i have seen many "super big" induction heater projects which never finished...
« Last Edit: July 09, 2019, 09:24:53 AM by Bert911 »

Offline hightemp1

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'Morning all & Happy Saturday!  Newbie here. :)

Today I'm working on a PS for my recently purchased 1800W unit.  After seeing Mads videos, I obtained some HP DPS-750RB PS's and am performing the isolation mods as I type this.  I understand everything except for what to do with the ground pigtail that was captured under the of longer of the board mount screws.  Should it be clipped off & discarded or reinstalled under the nylon insulator?

I noticed on another forum that it's recommended to leave one of the series connected PS's un-modded (not isolated) but Mads modifies all 3 in his video.  It looks like either way will work but is one preferred over the other?

DICKYBIRD, how are these in-series server power supplies working out for you?  Supposedly, there are two 750 watt versions and one of them can not be DC isolated.  Which version are you using?

MADS, I just noticed from a prior post (page 2 or 3 of this thread) - that you may be assembling some of the units together for resale, and that you are waiting for fiberglass braiding to complete them.  Have you received the braiding and please update us on your progress?

I am also attempting to run four of these together but am confused on DC isolation and possibly burning them up if they are not DC isolated.
« Last Edit: July 18, 2019, 06:05:00 AM by hightemp1 »

Offline hightemp1

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I'd personally ground (by not modifying) the supply in the middle of the chain - that way each end is only half the voltage with respect to earth. This would not work if you had to put a non-differential scope probe on the IH though.

Hydron, where would you put the DC grounded power supply if you had four units in series (ie 2nd or 3rd position?).  My tests show that 3 of my 4 power supplies have the dc ground isolated from their individual cases.  When I put them in series with the grounded one in position 1 as MADs advises, then I get 50 volts when measuring all four DC rails to cases.  Don't know if this is best position or, frankly, if present configuration has the DC "floating". :-\    Any and all advice greatly appreciated.
« Last Edit: July 18, 2019, 07:04:06 PM by hightemp1 »

Offline DICKEYBIRD

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Hiya hightemp.  I did the isolation mod on all 3 of my PS's and got over 36v.  I tried leaving 1 of them un-modded as suggested elsewhere but it wouldn't work.

As far as how well they work under load for long periods, I can't say yet as my IH project had to be put on hold due to some paying machining work.  I did run a 36VDC motor with it for an hour or so & it worked fine.

I hope to finish up the project soon.  I can't wait to see it work! :)
Milton from Tennessee ya'll

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