More induction heating

[petespaco]

I suggest that you visit a website such as this one:
https://learnabout-electronics.org/PSU/psu12.php

Or:
https://www.physics.unlv.edu/~bill/PHYS483/power_supply_info.pdf
 or simply google:
"linear power supply design"   -since that appears to be what you want to use.

[Alberto]

I suggest that you visit a website such as this one:
https://learnabout-electronics.org/PSU/psu12.php

Or:
https://www.physics.unlv.edu/~bill/PHYS483/power_supply_info.pdf
 or simply google:
"linear power supply design"   -since that appears to be what you want to use.

Thank you!

EDIT: I have read the links. They explain very well how works the filter capacitors in a power supply. I have a idea about that. My problem is that I don´t know how much ripple is admisible to power the heater. I mean, of course the bigger the capacity the better but I don´t know how much it would be a acceptable value

[davekni]

I mean, of course the bigger the capacity the better but I don´t know how much it would be a acceptable value

For your induction heating application with separate gate supply, no filter capacitor is probably best choice.  Induction coil current will go up and down at 2x line frequency.  That is the way induction cook-tops work.  I had a 1kW ZVS oscillator that ran that way too, with rectified line voltage and no filter cap.

[Alberto]

I mean, of course the bigger the capacity the better but I don´t know how much it would be a acceptable value

For your induction heating application with separate gate supply, no filter capacitor is probably best choice.  Induction coil current will go up and down at 2x line frequency.  That is the way induction cook-tops work.  I had a 1kW ZVS oscillator that ran that way too, with rectified line voltage and no filter cap.

Thank you

Nice!! So I'll rewound the secondary of a MOT untill I get 35VDC after rectifying

[davekni]

Just thought of one caution if using no filter caps on rectified transformer output:  Switch power on secondary side of transformer, either before or after rectifier.  If the transformer primary is switched off, transformer inductance will create a voltage spike.  MOTs are particularly bad in that respect, running large magnetization current, so producing large spikes when primary is disconnected.
If primary will be switched off with secondary connected, either a TVS diode or filter caps are needed to absorb the transient energy.  (The FETs may be able to handle that transient energy themselves.  However, if they are already running hot due to high load, then they have less avalanche energy capability.)

[Alberto]

Just thought of one caution if using no filter caps on rectified transformer output:  Switch power on secondary side of transformer, either before or after rectifier.  If the transformer primary is switched off, transformer inductance will create a voltage spike.  MOTs are particularly bad in that respect, running large magnetization current, so producing large spikes when primary is disconnected.
If primary will be switched off with secondary connected, either a TVS diode or filter caps are needed to absorb the transient energy.  (The FETs may be able to handle that transient energy themselves.  However, if they are already running hot due to high load, then they have less avalanche energy capability.)

Thank you!

And another (probably) silly question. I said 15v to the gates because the guy in the video uses that, and you suggest using 60ohm resistors. But I have a lot 12V and 5v powers supply. Could I use one of these? In that case, wich resistor I should use?


And about the capacitors for the oscillator I have read that i should use WIMA MKP, but I have KEMET MKP X2 SH. Is there s problem with that?

And last, could anyone recommend me a book about learning basic electronics? I know ohm's law, the behavior of pasive components and that things.  But I'd like to learn more for example to stop asking these questions haha

[davekni]

And another (probably) silly question. I said 15v to the gates because the guy in the video uses that, and you suggest using 60ohm resistors. But I have a lot 12V and 5v powers supply. Could I use one of these? In that case, wich resistor I should use?

If you have three 5v supplies, wire them in series for 15V.  That presumes they are not grounded (have 2-prong plugs, not 3-prong).
12V might be OK, not less.  Trade-offs of lower (or higher) gate supply are a bit complex.  If 12V, reduce gate resistance as much as possible while remaining under 2W, so around 40 ohms.

And about the capacitors for the oscillator I have read that i should use WIMA MKP, but I have KEMET MKP X2 SH. Is there s problem with that?

WIMA vs KEMET doesn't matter.  Different MKP capacitors are designed for different purposes.  You need high AC current capability.  X2 caps aren't great in that respect (usually).  You could try them with good fan cooling.  If some overheat and fail, then buy replacements.  Look at RMS current rating in spec's.

And last, could anyone recommend me a book about learning basic electronics? I know ohm's law, the behavior of pasive components and that things.  But I'd like to learn more for example to stop asking these questions haha

I'm not much help here, having learned electronics many decades ago.  I do recommend trying things in analog simulation.  There are some fairly simple on-line simulators, and simulation programs free to download and use.  My favorite is LTSpice.  Probably not the easiest for novice learning, however.  There is good online forum help for LTSpice.  Whatever simulator you try, start very simple.  Verify Ohm's law with a voltage source and resistor, etc.

[Alberto]

And another (probably) silly question. I said 15v to the gates because the guy in the video uses that, and you suggest using 60ohm resistors. But I have a lot 12V and 5v powers supply. Could I use one of these? In that case, wich resistor I should use?

If you have three 5v supplies, wire them in series for 15V.  That presumes they are not grounded (have 2-prong plugs, not 3-prong).
12V might be OK, not less.  Trade-offs of lower (or higher) gate supply are a bit complex.  If 12V, reduce gate resistance as much as possible while remaining under 2W, so around 40 ohms.

And about the capacitors for the oscillator I have read that i should use WIMA MKP, but I have KEMET MKP X2 SH. Is there s problem with that?

WIMA vs KEMET doesn't matter.  Different MKP capacitors are designed for different purposes.  You need high AC current capability.  X2 caps aren't great in that respect (usually).  You could try them with good fan cooling.  If some overheat and fail, then buy replacements.  Look at RMS current rating in spec's.

And last, could anyone recommend me a book about learning basic electronics? I know ohm's law, the behavior of pasive components and that things.  But I'd like to learn more for example to stop asking these questions haha

I'm not much help here, having learned electronics many decades ago.  I do recommend trying things in analog simulation.  There are some fairly simple on-line simulators, and simulation programs free to download and use.  My favorite is LTSpice.  Probably not the easiest for novice learning, however.  There is good online forum help for LTSpice.  Whatever simulator you try, start very simple.  Verify Ohm's law with a voltage source and resistor, etc.

Thank you!!

Ok, since it will be difficult to me find a problem if it appears, I´ll stick with the exact components to get the best result. I don´t have 15V supply and you say 12V is not sure to be OK, but I have a lot 19V laptop power supply. Can I use it with a bigger resistor? wich resistance?

Thank you, I think I´ll get banned from this forum for making this questions

[klugesmith]

You can take 19 V laptop PS and reduce voltage to 15 V with a single-IC voltage regulator.  Should begin with an estimate of maximum current requirement.

[davekni]

Ok, since it will be difficult to me find a problem if it appears, I´ll stick with the exact components to get the best result. I don´t have 15V supply and you say 12V is not sure to be OK, but I have a lot 19V laptop power supply. Can I use it with a bigger resistor? wich resistance?

19V laptop supplies are convenient, and free when I collect them from recycling bins at work.  I use them for many projects.
Yes, I think 19V would be a fine choice for your ZVS gate supply.  100 ohm resistors will be just under 2W each.  One more detail:  At 19V and 100 ohms, power of 12V zener diodes in circuit will be about 0.42W.  Make sure zeners you use are rated for that with some margin, at least 0.5W rating.

Thank you, I think I´ll get banned from this forum for making this questions

Don't expect you will be banned, though you are correct that this forum is generally for users farther along in learning electronics.

I do hope someone else answers your previous request for beginner book recommendations.  Good luck with your project and with learning.

[petespaco]

Re: "book to learn electronics":
I too, learned electronics a long time ago, starting in about 1948.
If I were starting out today, I think I'd get one of those "learn electronics kits"

Here's one example:
https://www.sciplus.com/electronic-playground-48491-p?

[Alberto]

Thank to all of you!

I´ll use 3w 100ohm resistors to be safe (that is what I have) and the zener are 3w.

And this is why I´m making the triodes, for me that is the best way to learn.

[romy]

yes, learning electronics:

i made several attempts in my life. first was before internet. lacking a systematic education in the field i always got stuck pretty fast. last effort was one month ago, concentrating on power supplies and resonnant cirquits. i started with maxwells equations and prepared a list of symbols (two full pages). by the time i got acquainted with messrs. laplace, naba, poynting, shin et al, their complex conjugates and dyadic products i was done. now the little "j"-devil is haunting me at night.

zct, sct, zvt, ccm, llc, svt, zvs, svt, zcvt, lcc, zcs, elt, sp, dab, pol, pr, vfc, hhc, nr, vco:  abbreviations dont make it any easier.

there is a lot of material on youtube. today im trying to wrap my mind around this:

/>

[Alberto]

yes, learning electronics:

i made several attempts in my life. first was before internet. lacking a systematic education in the field i always got stuck pretty fast. last effort was one month ago, concentrating on power supplies and resonnant cirquits. i started with maxwells equations and prepared a list of symbols (two full pages). by the time i got acquainted with messrs. laplace, naba, poynting, shin et al, their complex conjugates and dyadic products i was done. now the little "j"-devil is haunting me at night.

zct, sct, zvt, ccm, llc, svt, zvs, svt, zcvt, lcc, zcs, elt, sp, dab, pol, pr, vfc, hhc, nr, vco:  abbreviations dont make it any easier.

there is a lot of material on youtube. today im trying to wrap my mind around this:

/>

In my case is because I like, like learning english, I´m doing to travel and learn this things better, so in that case is easier

[klugesmith]

Not much of a riddle in that video by Professor S B-Y.   
In that last picture, as current increased from unsaturated to saturated,
the incremental L value went down but the stored energy still went up.
We can't figure stored energy from (I^2 * L/2).   
We can get it by integrating the input power during the whole inductor-charging ramp: I * E dt.
With optional refinement of subtracting the power loss due to wire resistance: I^2 R dt.

Kind of like figuring the energy to charge a MOSFET gate, when charge is not proportional to voltage.

[romy]

its his method of teaching. see subsequent vid.

[romy]

I suggest that you visit a website such as this one:
https://learnabout-electronics.org/PSU/psu12.php

Or:
https://www.physics.unlv.edu/~bill/PHYS483/power_supply_info.pdf
 or simply google:
"linear power supply design"   -since that appears to be what you want to use.

Thank you!

EDIT: I have read the links. They explain very well how works the filter capacitors in a power supply. I have a idea about that. My problem is that I don´t know how much ripple is admisible to power the heater. I mean, of course the bigger the capacity the better but I don´t know how much it would be a acceptable value

i have been told 3% ripple by the seller on the 1800w heater.

[Alberto]

Thank you for your answer.

Ok, it´s done





The 2 "loop" wires are conecting all the capacitors in parallel

A and B are the wires coming from the drains and fast diodes. My concern is, Does it matter in what point of the capacitor bank I connect A and B?
C goes to the 2 chokes and the induction coil

Thank you

[klugesmith]

>>Does it matter in what point of the capacitor bank I connect A and B?

Your connection of work coil to capacitor bank at point C is not ideal.
The closest capacitor will get largest share of current, and the 20th capacitor will get smallest share of current.  It really matters, if you compare inductance and high-frequency resistance of the 20-capacitor bus wire pair to inductance of the work coil.
The connection of driver, at A and B, is much less important because the current is much smaller.

There's a good diagram of this issue in instructable by imsmooth.   Or just scroll down on this page:
http://inductionheatertutorial.com/inductionheater/induction3.html

Can you build the 20-capacitor bank cordwood style (look it up) with two sheets of copper clad perf board?

[davekni]

The connection of driver, at A and B, is much less important because the current is much smaller.

I agree that it is much less important.  However, I have experienced issues if wires to drains are too long.  Can end up oscillating at a much higher frequency than intended, one defined by drain capacitance and wire inductance.  Not likely an issue for you unless wires are longer than in the images shown.

Also agree that current between coil and capacitors needs to be better balanced.  Even just adding wires between the two banks at the coil end would help greatly.  Copper (heavy foil or sheet) for cap to coil connections is even better.