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

[petespaco]

I wouldn't be in favor of ever putting a 30 amp breaker on a 120 volt line  except in the unlikely event that the circuit had 10 gauge or heavier wire.
How about putting the primaries of two MOT's in series across 220 volts? 
Maybe this goes without saying, but please keep "one hand in your pocket" as they say,  when working with mains voltages.  Plenty of opportunities to get dead.

Pete Stanaitis
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[davekni]

You can use the primaries in series for 240V or 220V.  Best when the two series transformers are identical (same initial model number and exact same output turn count).  If you aren't sure of the turn counts being identical, then use series primaries only with parallel secondaries.  Turns ratio still needs to be close.

[rikkitikkitavi]

I am not sure about US MOTs with 120V primary, but our here in EU are very cheaply wound and therefore they are well into saturation with a magnetising current in the amps range causing high idle losses. Judging from size I would say they are rated at about 3-400W at 100% duty.

My advice would be to use atleast three in series for 220V supply.

Also measure the primary resistance. Calculate the actual primary current that would lead to 5% losses (0,05*U primary *I primary = I primary^2 *Rprimary) and then you get a ball park figure about the actual 100% duty rating.

Also, as they are designed for high leakage with a magnetic shunt they have a lot of voltage drop when loaded. This helps stabilise output voltage though when you add enough capacitance as the leakage inducatnce and rectifiying caps form a LC filter. But the voltage will be load dependant.

MOTs are fairly easy to rewind though due to a large winding window, and with the windings separated not concentric but side by side in a split bobin. I have never successfully opened an EI transformer core to rewind it and successfully reassembled it with the same efficiency ( idle current, low noise etc) but maybe it is a matter of just getting enough experience.

[hightemp1]

I am not sure about US MOTs with 120V primary, but our here in EU are very cheaply wound and therefore they are well into saturation with a magnetising current in the amps range causing high idle losses. Judging from size I would say they are rated at about 3-400W at 100% duty.

My advice would be to use atleast three in series for 220V supply.

Also measure the primary resistance. Calculate the actual primary current that would lead to 5% losses (0,05*U primary *I primary = I primary^2 *Rprimary) and then you get a ball park figure about the actual 100% duty rating.

Also, as they are designed for high leakage with a magnetic shunt they have a lot of voltage drop when loaded. This helps stabilise output voltage though when you add enough capacitance as the leakage inducatnce and rectifiying caps form a LC filter. But the voltage will be load dependant.

MOTs are fairly easy to rewind though due to a large winding window, and with the windings separated not concentric but side by side in a split bobin. I have never successfully opened an EI transformer core to rewind it and successfully reassembled it with the same efficiency ( idle current, low noise etc) but maybe it is a matter of just getting enough experience.

You guys know your stuff.  I could not find a single video of two or more 120v MOTs being used in series on 220V here in US, let alone three or more.   So I think knowing that 120v mots can be used with 220 is great (CORRECTION--matching 120v MOTs  to 120v wiring is necessary else 120v MOT's insulation may fry with 220v - two 120v MOTs can be used with 220v if their  primaries are wired in series so each MOT gets 120V). 
And, 30 amp 120v circuits are very rare in the states. Only use I could find, is people who plug their travel trailers up to their homes since many motor homes require 120v @ 30a.  So if one has to make another circuit it would seem logical to use the more common, more useful 220v circuit. 

Shocking that EU mots are rated at less than 500 watts.  The larger ones here in the states claim 1200+ watts, but an electrician who worked on microwaves once told me that most all these larger MOTs are all basically the same and only rated at 1kw.  He did not say what duty cycle that is - for me, I have never ran a micowave for more than 30 minutes. Come to think of it, my 1200W rated unit does possibly cycle power on and off -that sucks.   For 3kw or larger PS, I agree that three or more in series would be required.  Assuming 1kw per MOT is correct, then with losses from rewinding, it may take 4 to get  ++3kw, at an unknown duty cycle?  For melting larger quanties of metal in bigger crucibles a 50% or better duty cycle would be best (does 50/50 mean on half an hour then off half an hour)?
 
Again assuming that most of these larger MOTSs are all pretty much the same, then maybe overloading one will not be a huge deal.  I found one person who has re-wound several MOTs for welders (two Mots in series on 120V)- he says that they all eventually fail due to one MOT taking too much of the load.  He just accepts having to do another every few years.  When they do blow, does it take all of them or just one, and maybe some type of simple overload circuit; or, even simpler for me, a fuse(s) could be added in the circuit somehow to prevent blow ups?

Update: Randomly checked five mots in mothballs.  Only 2 were identical & looked medium sized.  3 larger ones varied in weight, windings metals & primary ohm readings.  So findling matching larger sized MOTs may be more difficult so getting very close voltage matches with matching iron cores seems to be challenging.

[rikkitikkitavi]

Well, I have a 1000W EI transformer core (actually it is an old autotransformer 220/127V from the time we had 127V in Sweden) and it is substantially larger than any MOT I have seen on video, US /EU/JP/UK/wherever

I would say twice the size. All MO are made in China. All MOTs are made in China. I really doubt they would spend a single won extra on copper or magnetic steel than necessary, considering you blast your MOT at full power not more than a few minutes and the heat loss is absorbed by the thermal capacity.
When you operate your oven at longer periods it is with reduced power, it is run with low frequencye PWM (like 1 sec on/ 1 sec off)

At my office we have a couple of MO in the pentry, and during lunch hour they blast away constantly as each individual trying to heat the lunch box and soon the smell of food is mixed with that good ol´overheated Xformer core insulation smell. They are frequently replaced due to breakdowns  but finally the house maintainence crew have found some good brand tht last longer than usual. And now in Corona times everyone is working from home so...

My point is that an EU transformer ACTUAL rating is close to 500W, but not officially so. There is no rating on these. The nameplate says something like the magnetrone power output and perhaps something about minimum current drawn from wall socket.

You have to investigate this by perhaps doing the primary resistance evaluation. I would expect an US MOT to have some margin due to the less demanding requirments of lower primary voltage and higher frequnecy or, if the manufacturer have reaaaally done it dirt cheap it has the same flux density as an EU MOT. And hence they capaity is larger.
 
A power supply for an induction heater needs to be able to deliver full power for atleast an hour.
A home made welding xformer have a very low duty, unless you are an experienced welder who can just lay down fillet after fillet successfully
But eventually you stick one pin to much or something like that and wham the magic smoke is gone and you test your circuit breakers...

[hightemp1]

Well, I have a 1000W EI transformer core (actually it is an old autotransformer 220/127V from the time we had 127V in Sweden) and it is substantially larger than any MOT I have seen on video, US /EU/JP/UK/wherever

I would say twice the size. All MO are made in China. All MOTs are made in China. I really doubt they would spend a single won extra on copper or magnetic steel than necessary, considering you blast your MOT at full power not more than a few minutes and the heat loss is absorbed by the thermal capacity.
When you operate your oven at longer periods it is with reduced power, it is run with low frequencye PWM (like 1 sec on/ 1 sec off)

At my office we have a couple of MO in the pentry, and during lunch hour they blast away constantly as each individual trying to heat the lunch box and soon the smell of food is mixed with that good ol´overheated Xformer core insulation smell. They are frequently replaced due to breakdowns  but finally the house maintainence crew have found some good brand tht last longer than usual. And now in Corona times everyone is working from home so...

My point is that an EU transformer ACTUAL rating is close to 500W, but not officially so. There is no rating on these. The nameplate says something like the magnetrone power output and perhaps something about minimum current drawn from wall socket.

You have to investigate this by perhaps doing the primary resistance evaluation. I would expect an US MOT to have some margin due to the less demanding requirments of lower primary voltage and higher frequnecy or, if the manufacturer have reaaaally done it dirt cheap it has the same flux density as an EU MOT. And hence they capaity is larger.
 
A power supply for an induction heater needs to be able to deliver full power for atleast an hour.
A home made welding xformer have a very low duty, unless you are an experienced welder who can just lay down fillet after fillet successfully
But eventually you stick one pin to much or something like that and wham the magic smoke is gone and you test your circuit breakers...

Ok, so you are saying that even though the MO may be pulling over 1kw intermitantly, the duty cycle for an induction furnace should be 100%, so one would need six or more MOTs in series for correct duty cycle?  Not sure I would need 100% duty cycle though?  Due to cost of graphite, I would not want a melt to last longer than 1/2 an hour. so maybe I can get by with only a 55% duty cycle or 4 MOTs in series?  Just call me slowhand.  Aggressive air cooling would help.  Though another potential problem is cost - pulling 60 amps requires maybe 6 guage wire and wiring 4 MOTs with that would not be cheap?  Suddenly, the cheap MOT idea may not be so cheap anymore - help??

Other minor tweeks I've read are:
1.leave the shunts in or out - see it done both ways, or even using wood shunts - which is best?
https://theeducationalblog.quora.com/Repurposing-rewinding-a-microwave-oven-transformer
2.lengthen the primary wire for increased stability - trade-off power reduced?
3 a. magnetic wire for more power -though more prone to damage while wiring
3 b. thicker insulated welding type wire for less power but easier to work with.
4. E type MOTs can be cut open for easier bobbin installs, otherwise rewind old fashion way

[Mads Barnkob]

I built a handheld 150 Watt induction heater, but it failed and caught on fire!

I thought I would be able to get "some" run-time on 6x 18650 batteries, but apparently not

[hightemp1]

Great idea.  V.2.0 could make a fortune. 
See through acrylic is always facinatiing.
Maybe a trigger hold/release button.
Some flashy LEDs and/or Laser Rays
Ray Gun sound effects, and/or
Nuclear Reactor Core sound effects.
"The Heater" or the "Mini Nut Buster"
Ok, I quit. 

[petespaco]

I am a bit concerned about all this talk about "3 or 4 MOT's in series across 220 volts" or whatever.
Are we all on the same page here?

When I suggested that a person could put two 120 volt MOT's in series, I meant that you would put the PRIMARIES in series.  This supplies 120 volts to each transformer, so each transformer can still deliver full power, whatever you guys think that is.
  If you saw the spreadsheet in my video:
 

/> you saw that the "regulation" wasn't all that bad, at least in my opinion.  By the way, that was the SMALLEST of 3 sizes of MOT's that I have in my shop.

But, if you are considering 3 or 4  120 volt MOT PRIMARIES in series with the 220 volt line, you are simply reducing each individual MOT's input voltage well below 120 volts and thereby reducing the available output power.  But, even worse, with a lower-than-designed input voltage, you would need even more secondary turns to get the voltage up to where you need it.
    I guess I'd spend more time scrounging up a couple of big fans than I would spend worrying about over heating some MOT's that you get for free.
At that price, you could even have two banks of MOT's and allow them to cool alternately if you really NEED heat for longer periods of time.

Pete Stanaitis
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[hightemp1]

Yes, sorry everyone, all this rewiring is really Greek to me so basically ignore anything that I blurt out - please forgive my ignorance.  

To me it is just not clear how to best re-wire same rated MOTs to get a +3kw PS with, say a 60 volt 60 amp rating, and a duty cycle allowing 1/2 hour runs for melting metal. 

My pea brain assimulates comments and thinks  3 or 4 Mots with series primaries & cooled, might work but really no clue.

Update: another suggestion - runing two as Pete recommends and having a third wired so it can be added in series, when Power falls at melting temps; or just runing 6 in a some even more confusing 3x3 parallel/series combo?

[davekni]

I would say twice the size. All MO are made in China. All MOTs are made in China. I really doubt they would spend a single won extra on copper or magnetic steel than necessary, considering you blast your MOT at full power not more than a few minutes and the heat loss is absorbed by the thermal capacity.

They spend extremely little on copper.  All the MOTs that I have are wound with aluminum wire.

[hightemp1]

I would say twice the size. All MO are made in China. All MOTs are made in China. I really doubt they would spend a single won extra on copper or magnetic steel than necessary, considering you blast your MOT at full power not more than a few minutes and the heat loss is absorbed by the thermal capacity.

They spend extremely little on copper.  All the MOTs that I have are wound with aluminum wire.

I have unwound two mot transformers - both had aluminum secondaries and copper primaries.  The MOs that I find have had:  burnt out magnetrons, burnt out switches, burnt stirrer motors, or are were just tossed because inside paint pealed or MO was just too greasy.   Do not believe I have ever found one with burnt transformer windings.

UPDATE: Just checked 5 of my MOTS & two have copper primaries and four have aluminum primaries.  Depending on size copper MOTS weigh 1-2lbs. more and have smaller gauge wire 15-16 vs 12-14 for alum.  Did not check secondary metal.

[petespaco]

They spend extremely little on copper.  All the MOTs that I have are wound with aluminum wire

The older MOT's seem to have copper primaries. 

[davekni]

The older MOT's seem to have copper primaries.

Interesting.  The only reason for split material that comes to mind is that they hadn't yet figured out how to make reliable connections to aluminum.  The secondary has enough voltage to break through any thin oxide layer that forms withing the crimp connection, while the primary may not.

[hightemp1]

Taking a break from the MOT 3.5KW(60v/60a) power supply design.  Everyone seems to have different ideas, and a best design is a just a clusterfuch to me. 

On ZVS design, found this good simple intro video for nobs like myself.

/>
PS. Pete, his video uploads your modified schematic from your website of the 1kw ZVS heater - immitation is most sincere form of flattery.

[hightemp1]

Dan Hartman used an array of 8 large MOTs connected to a 240V 50amp circuit; and, illustrates his recommended way of hooking up anywhere from 2 to 12 transformers for welder use. He advises against rewiring with magnetic wire for higher amp welders due to diffculty of wiring 6-10 guage, also said sourcing 6-8g was difficult or impossible. (regular wire is fine for high amp/short burst stuff like spot welders but not high duty cycle apps cause you basically lose half your Watts -best to use magnetic wire so you get full power out of MOT).  As Pete has pointed out, Power Supplies for ZVS have different requirements than welders.  Higher voltages are better for ZVS and huge amperages used by welders not so important.  My unique application here requires a PS cable of 60V @ 60A with a continuous run time of 30 minute.  I know this DIY stuff can just be seat of the pants guess work but I am still questioning  - What would your MOT array look like to meet above requirments??

I know some of you have opined on this already so if you prefer ignore.  I just have a mental block on figuring out the best wiring configuration for a more robust 60v@60a Mot PS. Maybe, assuming 20 turns of 8 gauge regular stranded building insulated wire on each MOT, then would 4 MOTs in some kind of series/parallel combo possibly work?  Also just noticed that for welders Dan connects the primaries in parallel and the secondaries in series.  That seems to be just the opposite what we are advocating here for a Mot ZVS power supply?

UPDATE: In video link above the guy has a whole video series on rewinding MOTS.  For Continuous Use he recommends like Pete to not use thick insulated wire but magnetic wire for getting higher duty cycle.  Good tip, again like Pete said, is to wrap two or more lesser gauge wire in parallel.  Problem with ordinary household wire is over 50% of its area is damn insulation.

/>

[MRMILSTAR]

For 120 volt input, I've often wondered about the possibility of wiring the primaries in series and the secondaries in series for two 120 volt MOTs. The result would be essentially like a NST with a center-tapped secondary. The input voltage and output voltage of the combined MOTs would be the same as a single MOT. Each MOT would have 60 volts on the primary. The possible advantage would be that the cores would not be in saturation and they would act more closely like a proper transformer.

[hightemp1]

For 120 volt input, I've often wondered about the possibility of wiring the primaries in series and the secondaries in series for two 120 volt MOTs. The result would be essentially like a NST with a center-tapped secondary. The input voltage and output voltage of the combined MOTs would be the same as a single MOT. Each MOT would have 60 volts on the primary. The possible advantage would be that the cores would not be in saturation and they would act more closely like a proper transformer.

Sounds great!   If I understand correctly series wiring of MOTs with 120 volts seams to remove some of the innate MOT inefficiences due to MOT design (less copper/alum. in primary windings).

Assumption:  {I have 4 same size MOTs rated @ 1KW and can get 25 turns of 8 gauge wire on each MOT & get 1 Watt Volt per Turn}

If I wire each pair in series, then wire the series pair in parallel would I then get 50V output using 220V mains outlet.
And if I use the same wiring on the output, ignoring inefficiencies for the moment, what would be the AMPERAGE output?
Or alternatively, if the output is all wired in series, what would be the amperage output?
And, of course, is it practical to wire in above configurations?  If not, what would be the best way to wire 4 MOTs to get approx. a 3KW (55v@55amps) power supply?
 

[petespaco]

Assumption:  {I have 4 same size MOTs rated @ 1KW and can get 25 turns of 8 gauge wire on each MOT & get 1 Watt per Turn}

I suspect you mean one VOLT per turn, not one watt.
Do you KNOW this or are you estimating?     In my own tests, I have been getting about 0.7 volts per turn.

[hightemp1]

Assumption:  {I have 4 same size MOTs rated @ 1KW and can get 25 turns of 8 gauge wire on each MOT & get 1 Watt per Turn}

I suspect you mean one VOLT per turn, not one watt.
Do you KNOW this or are you estimating?     In my own tests, I have been getting about 0.7 volts per turn.

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?