Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"

[klugesmith]

Just an estimate though based on other youtube videos the larger MOTs usaully get about 1V per turn.  Thanks for correcting - I need some more of that.  Still struggling with how best to wire 4 same size larger MOTs to get somewhere close to 3KW @ approximately 50 volts on a 220V outlet.

Hope we are not cluttering Pete's thread with this discussion.

Obviously, no combination of series or parallel connections can magically increase the useful power per transformer core.   For max power per core, each primary needs to get the voltage it was designed for, and to run more than 15 minutes you need forced-air cooling.  (or oil immersion and active liquid cooling)

I agree that 1V RMS per turn needs a pretty big MOT (large core area passing through the coils).  You need even more core area if you are in 50-Hz land, or if you want to avoid the near-saturated operating point that's acceptable in fan-cooled MOT's but not in ordinary power transformers. https://www.electrical4u.com/core-of-transformer-and-design-of-transformer-core/

If you want to combine the power of four identical MOT's, and they have 220 V primary windings, the primaries all go in parallel on your 220V power source.  If the MOT's have 120 V primaries, two primaries in series can go on 220V power, but if it's split phase 240 as in North America, I'd recommend connecting both to the neutral wire at mid voltage - what is gained by letting the load circuit determine the voltage division?

For your 50V output goal, it seems like connecting four 12.5 V secondaries in series is best.  Then the current is automatically the same in all transformers.   Fewer turns to wind on each core.   You can easily operate at 3/4 or 1/2 or 1/4 voltage by switching out some of the transformers, and the switching can be done on primary side if "unused" primaries are short-circuited by the switch.

For efficiency it's important to use as much copper as you can fit. Divide core window area by number of turns & choose your wire accordingly.  If it were my project, I would try stranded copper building wire.  If the insulation occupies too much area, combine uninsulated stranded wire into a bundle of the right size and add a thin insulating sleeve (heat shrink or nylon braid?) over that. The resulting bundle can assume non-round cross section for better packing into the window.  Or do a multifilar winding with smaller wire, but the parallel secondary windings on same core need to be very closely matched.

[hightemp1]

Hope we are not cluttering Pete's thread with this discussion.

I hope so too, am so slow - so sorry to waste everyone's time.  Will try to be as breif as I can.  Your specific example is good for uneducated like me.  For us in the states with 120V MOTs, could you please be even more specific on how to wire the 4 primaries? I understand and think all your other ideas are spot on - thank you!

If I understand, each primary leg of 220V line gets 120V, and with 2 MOTs in series on each leg, from our previous example, output/leg would be 25V@ 80amps, assuming 1kw/mot?? If so, then 4 series connected secondaries would get 50V @ 80A.

[petespaco]

and the switching can be done on primary side if "unused" primaries are short-circuited by the switch.

?

[klugesmith]

No time to draw schematic.  The model I had in mind is four MOT's, with 12.5 volt 60 amp secondary windings permanently connected in series.    Primary windings independently switched to mains voltage. 
To operate at 3/4 of nominal secondary voltage, we can turn off one transformer, using a 2-way switch so its primary is shorted when not connected to power source.  Otherwise that transformer would greatly impede the output current, while developing 3x nominal voltage across its primary.

It would be conceptually simpler, maybe practically simpler, if the switching is done in secondary circuit with sufficiently big switches.  And what I talked about would not work if two 120-V primaries are connected in series across 220 volt power -- then you can not short one primary, it would put whole 220 V across the other primary.

[hightemp1]

If the MOT's have 120 V primaries, two primaries in series can go on 220V power, but if it's split phase 240 as in North America, I'd recommend connecting both to the neutral wire at mid voltage - what is gained by letting the load circuit determine the voltage division?

 Thank you klugesmith - so each 120V leg of a 220V AC line would have 2 mots in series? How then would each of those 120V pairs be tied together?
Regardless of MOTs rating(120V or 220V), would output be the same - 50V@ 60A?

[hightemp1]

Odd that the only actual 4-array MOT low-voltage applications I could find were done with 220V mots.  Anyhow, I think I can get 27 winds of 8 gauge (four 12 gauge in parallel) through each mot.  So now have a question on the secondary wiring as well.  If I get 48 volts on each series wound primary leg can I wire the secondary in parallel to get more amps?  Anyone care to tackle any or all my many questions?

[petespaco]

So now have a question on the secondary wiring as well.  If I get 48 volts on each primary leg can I wire the secondary in parallel to get more amps?

   I don't understand this question.   Are you suggesting to apply only 48 VAC to the primaries?

[hightemp1]

I was thinking that primaries could be in some kind of series/parallel combination to maintain 120V to each mot and full power to all of them?

[hightemp1]

I was thinking that primaries could be in some kind of series/parallel combination to maintain 120V to each mot and full power to all of them?

Apparently not.    How about linking two seperate 220V lines together somehow? 

If no way, then this makes 120V mots much less useful than 220v mots since hooking maximun of 2 Mots to 220V seams to be the maximum?


If so then, how about using 4 mots on 120V mains in some sort o series/parallel combo with a dedictated 30 amp circuit?

[klugesmith]

Pictures might help here.

There is no power to be gained from putting less than nominal voltage on any MOT primary.  Half voltage on primary would not allow double current in primary, because of primary wire gauge and resistance.
There's no power to be gained from putting more than nominal voltage on any MOT primary, because core saturation will get you.

If you have 120V MOT's, the primary options appear to be

* 120V 30A circuit, all primaries in parallel.

* 2 MOT's in parallel on one 120V circuit, and 2 MOT's in parallel on a different 120V circuit.

* 240V center-tapped circuit, with 2 MOT's on each side (all four primaries having one end connected to neutral).

* 240V circuit without center tap (uncommon in North America): MOT's are in pairs with primaries in series.  For any pair with primaries in series, the secondary windings must be matched, and secondaries permanently connected in series or in parallel. That makes the 240V divide evenly between the two primaries.  You could wire small 120V indicator lamps across each primary, to show that the voltage is split properly.

* You might get satisfaction with three MOT's, primaries in series on 240V circuit for 80 volts each.  Then you are far below saturation, and could enjoy much less no-load current and core loss.  Limitation could be copper loss, at (say) 15 amps primary current for about 3600 watts total power.  The three secondaries need to be matched, and wired in series or parallel.

[hightemp1]

* 240V center-tapped circuit, with 2 MOT's on each side (all four primaries having one end connected to neutral).

Pictures are what my thick skull needs and I finally found one but can not post due to copy-rights.  Maybe why using 120v mots with 220v is so uncommon is because the MOTs voltages need to be almost perfectly matched, not to mention this complex series/parallel array.  Unfortunately, my 220V does not have a neutral, just two hots and a ground, I think.(my 220v outlet does have a common neutral/ground wire.  So I will try to explain -- all four mots are connected in parallel, two on each hot leg with a series connection across the hot lines.  So I think voltages & amps would be approx. 50V & 60A on primary side?

If ok, now wondering how to wire the secondary to keep same VA power thinking is just tying all beginning primaries together and all ending primaries together?

UPDATE: My outlet is older style with a common neutral.

UPDATE: Here is a great example of the design I was looking for:

/>  & here is a schematic of an 8 mot welder:

[petespaco]

hightemp1, what country do you live in?

In countries that have 220 volt service to the home with NO NEUTRAL, just a protective ground, Microwave Ovens for home use will have transformers with 220 primaries.
I don't  think I have ever seen  a 220 volt Microwave Oven in the USA.  At least not for home use.
So---- if you are finding references to 220 volt MOT primaries, you must be seeing videos or webpages produced in Europe, etc..
   I don't know what the "standard" household outlet uses for breaker rating, but, if it's high enough, you can just keep paralleling 220 volt transformers across the line.  Or, if you can, you could wire in extra circuits until you get to the overall wattage that you need.
However, since you have talked a lot about 120 volt MOT's, that leaves ME confused, since you say; "Unfortunately, my 220V does not have a neutral, just two hots and a ground, I think. "  It's the "I think" that worries me.
You might be better off simply "biting the bullet" and locating a commercially available power supply.
Heck, maybe it would be easier (and safer) to round up 5 good sized 12 volt car batteries and put them is series to get 65 to 60 volts.
You know, if you do go the MOT way, you still have to rectify the output and do something to smooth it so the induction heater isn't calling for current close to a zero crossover.
  Some of the folks on this forum would certainly be up to that challenge, but it's not as easy as it sounds.

[hightemp1]

Here in the good old USA.
Yea, almost every MOT array of more than two on the internet is with foreign 220V rated MOTs.  Seams to be more complex and dangerous using 120v mots on 220V.
I think, just an expression - I know for a fact my 220V outlet has no neutral :-)  WRONG
Commercial PS is definately the way to go.  This is just something I always wanted to do, and do not recommend even attempting unless you are an engineer, or have lots of time and mots on hand and can have it verified by electrical engineers.
5 good batteries would be hard to find or terribly expensive, but always a reliable alternative.
Rectification is not just simple bridge rectifier properly rated with smoothing cap?
Also, using Dan's welding design with variable SCR power control, gives more options with power input/output. Adding more MOTs is doable too.
Did Dan Hartman's 120V MOT primary array on 220V schematic on page 51 make sense to you.....?

[petespaco]

I know for a fact my 220V outlet has no neutral :-)

Then there is something wrong with your wiring. OR-----
The receptacle you are looking at is wired according to an old or outdated standard.
If you check the voltage between either hot leg and "ground", I think you WILL see about 120 volts.

If you plan to proceed with this experiment, I strongly suggest that you somehow start with a properly wired outlet.
  I have to admit that, back in 1985, I wired a single purpose circuit where the motor required only 220, in the way you mentioned.
But when I rewired it recently, knowing that I'd need both 220 and 120. I ran  a new, separate neutral so the green wire is simply the protective ground.

[hightemp1]

Found this quote from internut so must be true.
“ 220 does NOT need a neutral. Some newer appliances require it for parts of the system that run on 110 volts. Almost all installations more than a few years old do not have a neutral
Please read next two posts for the real deal...

I HAVE NO ELECTRICAL BACKGROUND SO PLEASE IGNORE WHATEVER I MAY BE THINKING !!!

[petespaco]

“ 220 does NOT need a neutral. Some newer appliances require it for parts of the system that run on 110 volts. Almost all installations more than a few years old do not have a neutral

Sorry, but this is misleading and, in some places, downright wrong .

The following only relates to the USA----
Yes, an appliance that doesn't use any 120 technically does not need a neutral.
The "some newer appliances--- " sentence IS wrong.
Should read " ANY "220" appliance that uses 120 volts requires a neutral."  (220 volt Clothes dryers have been using 120 volts to run the timer and motor for decades.
Regarding the " Almost all installations----" sentence:
How can he even say that?  It simply assumes that 220 appliances NEVER use 120.
Check the NEC code book and any state and local code books  if you don't trust me.
There IS a bit of ambiguity on this subject, but in general, it's only certain existing installations where the neutral is not required.

Note: my comments are simply made in the spirit of keeping readers safe and alive.  I don't want to get into a "pi----ing" contest.
This will be my last post on this 220 wiring topic.

[klugesmith]

This is in support of Petes' statement.  In old 220V outlets with 3 contacts, in NEMA land, the 3rd one is "neutral", not "ground".   Unlike green wire ground, it's intended to conduct current during normal operation.   ( In a recent twist, light switch circuits in new construction must have neutral as well as ground at the switch.  Smart switches used to be allowed to use green wire to return the half mA of control current. In even older buildings, only hot and switched-hot wires run to the switch box.)

In my house from 1950's, electric clothes dryer has a 3-prong plug that fits a matching receptacle.  NEMA 10-30, long deprecated but still perfectly legal.

The center pin is connected to white wire from the panel. It's the Neutral, technically the Grounded Conductor.   Referred to as Center Tap in my previous post here.   Used for 120V timer/controller, and also serves to ground the dryer's metal frame and skin for safety.  There is no separate pin for green wire, technically Equipment Grounding Conductor.

I could easily and legally install a receptacle for 4-prong plug, NEMA 14-30.   Equipment grounding connection would be made through the steel conduit in which the other wires run.  I measured its resistance back to panel, and it's substantially lower than that of the white wire.

For 240V hobby experiments, I made a 4-wire 10-AWG extension cord.  The plug end has 3-prong dryer plug + green wire pigtail with a ring lug, attached to a stud on grounded box and secured with a wingnut. 

By the way, in case this gives anyone ideas, the "grounded" and "grounding" resistances were measured from the far end of extension cord kluge.  With a low voltage transformer I sent 20 amps through white and green wires, round trip to grounded bus bar at the panel.  The far-end junction voltage was monitored through one of the hot wires, while the circuit was switched off.

Not really the right thread for this, but the work was part of an exercise to get 277 volt power at home.  Voltage out of the wall was typically about 251 V, easily stepped up beyond 277 with a dual variac.  In experiments with a 315 VA control transformer configured to Boost that, I got 321 V with 8.75 A one day (2800 W).  Load being three 120V lamps in series: two 1000's and a 1500.

[hightemp1]

My sincere apologies to you Pete, and entire forum. Thank you for emphasizing safety first.  Thanks to this thread, I believe I now have the knowledge to proceed very cautiously building a 3kw MOT power supply. Any further questions would be in another thread or forum.  As always, thank you Pete, klugesmith and company for sharing your professional knowledge. Lots of great advice, excepting mine, gleaned from the masters.

PS -- I was of course dead wrong.  My 220v outlet is an old style Nema 10-50 having a neutral that also served as ground, assuming it was properly installed 60 years ago by whoever built the house.

[rikkitikkitavi]

I say only 400V 3N~ @50Hz
 
I did actually used two phase + neutral with  2 identical 10A variacs to create a 0-400V variable AC source for testing a equipment ( an electrical heater at 4kW) . But gettin your head around 3phases takes some time.

Back on track :

I was thinking about the induction heater , is there a good way to asess the heat loss in the resonant caps ? Or is it just to bop until they pop?
I have a couple of handfulls of Wima FKP, and datasheets have diagrams with maximum voltage applied for difference capacitances and frequency.
My experience is that these datasheets are very conservative.

That should be translatable to rms current based on capacitive impendance at specific frequency? (Urms /Xc = Irms)

And then parallell enough for a good total capacitance and sufficient current handling?  Provided a proper layout with good current sharing of course.

Or am I missing something here?

[rikkitikkitavi]

I reply myself.

Had a look at the datasheet and it has been updated this february and now not only diagrams of maximum voltage applied vs frequency but also diagram of maximum current vs frequency is listed, for different voltage ratings and capacitances .

The constraining factor for the given data is  hot spot temperature rise internally of the capacitor <15 degrees (Centigrade/Kelvin).
typically a 0,47 uF FKP1 cap can take about 8amps of current maximum under this condition, but it variates a bit with the voltage rating.
Higher voltage rating means larger size in general due to thicker dielectric and therefore higher current rating.

Fex for a 68nF cap:
630VDC   = 2,5 A (27,5mm pin spacing)
1000VDC = 3A (37,5 mm pin spacing)
2000VDC = 6A (37,5 mm pin spacing)


The reason for my interest is that the caps represent a much higher cost than the transistors. A 0,1uF 630VDC FKP1 cap costs as much as a transistor, but I also realise that there are many more ways for the transistors to perish (ie release of magic smoke) due to erraneous behaviour of a self-oscillating induction heater.

Hot spot temperature rise is proportional to power loss so by keeping surface temperaure down , fex with forced convective cooling it is possible to really push the caps to the limit, aswell as the semiconductor switches.

The copper tubing is less prone to temperature degradation but resistive heating will lead to higher resistance and more loss, and eventually power limiting, depending a bit on the actual design. Contacting the tubing is probably the limit here. Or what is the general opinion?