Author Topic: Mazilli ZVS Driver Modification Problems  (Read 1358 times)

Offline Andrew321

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Re: Mazilli ZVS Driver Modification Problems
« Reply #20 on: January 31, 2020, 10:22:46 PM »
Sorry, my mistake. I am using the 1200v IGBT's, part number IHW40N120R5XKSA1 and your right about the UF4007's. In both broken circuits I have at least 1 broken UF4007 and I think both zeners are dead (realized I was testing them wrong after the fact so I'll double check those zeners today).

The gate supply I used is just an old transformer connected to mains. I use a full bridge rectifier and a smoothing cap on the secondary and while drawing 100mA through the 220ohm resistor it reads 25VDC at the cap. With no load its a bit more voltage at the cap, but I cant recall how much. So I would still need a Zener diode unless I want to take some coils off the secondary, which I might. My other option is that I have a laptop charger from my old broken down computer. It puts out 16.5V and 3.65A Could this work with the appropriate resistor?

Good news on the P-fet front though! I did manage to get them to work. I had to keep the voltage at 18VDC to make sure I didn't damage the IGBT gates, but it worked. I'm going to order some 17V 5W zener diodes soon, but if they give me trouble I'm opting for the laptop charger or altered transformer. Good to have those options in place.

About the TVS diodes. They're cheap enough so I'm going to get some, but looking at the ratings has me all turned around again. Let me see if I understand this correctly. Normal operating voltage that the IGBT sees is pi x 170 = 534VDC. However from the power feed inductor to the source is half this value, putting it at 267VDC. That would mean I want a TVS diode with a working voltage as close to or slightly over 267VDC but a clamping voltage low enough to protect the UF4007, so 400 preferred to 500V max? Also, does it matter if they are uni or bi directional?

That's interesting about the low power oscillation. I think I' going to poke around at that a bit and will most likely include it as a start up switch in the final version.





« Last Edit: January 31, 2020, 10:31:08 PM by Andrew321 »

Offline davekni

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Re: Mazilli ZVS Driver Modification Problems
« Reply #21 on: February 01, 2020, 04:51:52 AM »
16.5V for gate drive can work.  There is some advantage to a higher voltage and zener clamping, however.  For a given current, the resistance is higher, so closer to a constant-current source.  That way the current doesn't drop as much at the IGBT's Vge plateau voltage, about 9V for your part at 40A.  Your 25V transformer solution could be fine, but 0.1A limits gate-drive current options.  Small 24DC supplies are somewhat common too - laptop style or even wall-warts.

Concerning TVS diodes, yes I think you understand.  The 1.5KE300 family should work well for the transformer center-tap, or two in series for the IGBTs collector-to-emitter.  Since they're fairly cheap, multiple sets in parallel is a good idea, to make sure the total energy stored in the power-feed inductor can be dissipated.  For this use, uni or bi directional are both fine.  Use whatever is cheaper.  (Uni-directional, of course, need to be wired the correct way around.  Bi-directional devices are just two uni-directional ones in series back-to-back in one package.  The extra forward-biased device slows down the speed a bit for very-fast voltage spikes.  ZVS circuits don't generate such fast voltage rise-times.)

Keep having fun!  And, good luck with your final voltage-multiplier use.
David Knierim

Offline Andrew321

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Re: Mazilli ZVS Driver Modification Problems
« Reply #22 on: February 07, 2020, 05:45:01 PM »
Good news! It worked! I was about to give up and settle for less input voltage  when I decided to test something. If you remember I built my two E  sections of the transformer out of two UU sections glued together to form the E (4 U sections in total). On the central limb of the E I had the primary and on the outer limbs two secondaries in series. My gut told me there was something there so I separated the secondaries to test each one. I don’t know why, but one coil produced more power than the other. I just tested my drawing an arc at 60VDC input and one was hot and fiery while the other more blue and wispy. Testing the resistance of each coil showed they were about the same (16.6 vs 17.1 ohms) So my guess was that cheap amazon cores are to blame. I swap the coils around and sure enough its one limb gives more power than the other (forgive my lose use of the word “power”).

I decided to pull the whole thing apart and used just 2 U sections. I rewound a new primary and secondary for each limb and used acrylic to introduce a core gap of 2mm. From what I understand, core gap is one way to introduce leakage inductance and reduce coupling factor. No idea what mine is at, but it seems to work! Only problem I’m having is that at max input voltage the alligator jumpers and wires get so hot the plastic casing on them starts to melt! Easy fix though: more litz wire in the permanent set up.
 I no longer hear the oscillation and I can push it all the way to 170VDC input. For the gate drive I use 220 ohm resistors and found a different transformer that, after being rectified and filtered, put out 40VDC. I will continue to test and will be posting the complete constructing with pictures, parts, and links to videos once its done. I just need to look up how to build a soft starter because I’m worried If I were to just plug this thing into the wall it would just explode. It draws 14.5amps while pulling an arc at 120VAC input so it will trip the breaker if I used it for too long.

Thanks again for all your guys help.

Offline davekni

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Re: Mazilli ZVS Driver Modification Problems
« Reply #23 on: February 08, 2020, 05:13:57 AM »
Great to hear of your success!

My soft-start is just an incandescent light bulb across the switch.  That gets oscillation started at low power as soon as line-voltage is applied.  A power resistor would work as well.  Another option that I might try next time is a diode from the gate-drive supply.  If your 40V transformer has enough current capability, you could do that, starting your ZVS oscillator at 40V before switching in 170V.

A single secondary winding is good too.  The two separate ones are less efficient even if working properly - more wire for a given voltage.  I'd guess that the issue was a defect in one of the windings - perhaps a shorted turn, rather than an issue with the cores.
David Knierim

Offline Andrew321

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Re: Mazilli ZVS Driver Modification Problems
« Reply #24 on: February 08, 2020, 04:42:46 PM »
I forgot about that! Here I am thinking about getting relays and mosfets and all sorts of stuff to build this soft starter, but really all I need is a high wattage load to start up (like the light bulb) and then a switch to bypass it once its started up.

Your idea about the gate drive transformer for start up is interesting, but I'm not sure my transformer can supply enough current. Something I'll have to check out. If I did choose this route I would leave the negative wire connected to the emitter and then a diode from the positive to the "line side" of the power feed inductor (not sure what to call the side of the power feed inductor that attaches directly to the capacitor). Once started up I should just be able to turn on main power. Would the start up transformer be constantly supplying current long side main power? Should I toss in a start up switch to disengage the start up transformer once full voltage is running?

Offline davekni

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Re: Mazilli ZVS Driver Modification Problems
« Reply #25 on: February 08, 2020, 06:29:10 PM »
Yes, that's the correct connections for the gate-drive soft-start diode.  There's no need to switch it off.  That's what the diode is for.  Once line power is switched on, the ZVS input inductor is at 170V.  The diode blocks that 170V from feeding back to the 40V gate-drive supply.  (Without a diode, the gate-drive would fry at 170V.)

If your power is rectified line voltage without filter capacitors, then it will drop below 40V momentarily at each line voltage zero-crossing.  The gate-drive supply will feed a little bit of current at those zero-crossings (120 times per second).  Shouldn't be an issue for this case either.

If you go with gate-drive, I'd love to hear how it works.  I haven't tried that option yet - didn't think of it quite in time for my last ZVS project.  Expect it will work, and avoid a high-power resistor.
David Knierim

Offline Andrew321

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Re: Mazilli ZVS Driver Modification Problems
« Reply #26 on: February 10, 2020, 12:09:08 AM »
More good news Dave! The low voltage gave drive soft start works! I had to make a few changes, probably will make more later, but as is:

The gate drive is rectified and smoothed with a capacitor. When just the gate drive transformer is pugged in 20VDC is seen at the capacitor, when drawing an arc it drops to about 18.5VDC. The soft start current idles at about 0.2A and tops out at around 1A while pulling an arc. When main power is applied, soft start current drops to 0A (as expected) and the gate drive voltage rises to 21.1VDC and only drops to 20VDC when drawing an arc.

Offline davekni

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Re: Mazilli ZVS Driver Modification Problems
« Reply #27 on: February 10, 2020, 05:29:33 AM »
Andrew,

Wonderful!  I'm thrilled for you, and for the confirmation of what I plan to try next time I make a ZVS circuit.
David Knierim

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Re: Mazilli ZVS Driver Modification Problems
« Reply #27 on: February 10, 2020, 05:29:33 AM »

 


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