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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi guys,
In the video I'm actually using two UPS transformers wired in reverse, in series - rectified and filtered with a bunch of caps. I have a MOT too but I don't want to hammer out it's secondary and I'm actually building a transformer now from some huge cores I had around from old dead OBIT's.
I suggested a MOT as an easy solution for a power supply for soemone who has acces to lots of MOT's.
Gabriel: I don't know what type your caps are so I can't tell whether they'll be good or not, but also their capacitance seems a bit too high individually, unless they can handle 20-30amps per cap I wouldn't use them. If they are polyester, which they most likely are, the circuit might not work at all or they may just burn out.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Beautiful construction, all your compact projects are great!
May I ask what the overall voltage and RMS current rating is of the MMC bank you are running? It must be rather high by the amount of power you are putting into it!
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
oh whoops. i thought by "I don't have a proper power source though, I feel sorry killing my only MOT to rewind it." you meant that you already had killed your mot and currently feel bad. sorry for responding incorrectly on your behalf.
i wonder too about using a bank of mismatched capacitors (i've got lots of salvaged mkp x2 box caps.) I suppose it would be fun to try it out and possibly explode a few. anyone ever used an ac oil filled cap (like a MOC) in a high current tank circuit? i've got 3 10.5uf 520vac oil filled caps from a large ballast and no idea what to do with them.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Forty wrote ...
oh whoops. i thought by "I don't have a proper power source though, I feel sorry killing my only MOT to rewind it." you meant that you already had killed your mot and currently feel bad. sorry for responding incorrectly on your behalf.
i wonder too about using a bank of mismatched capacitors (i've got lots of salvaged mkp x2 box caps.) I suppose it would be fun to try it out and possibly explode a few. anyone ever used an ac oil filled cap (like a MOC) in a high current tank circuit? i've got 3 10.5uf 520vac oil filled caps from a large ballast and no idea what to do with them.
Different-valued caps will share current unequally, leading to possible failure of some of the capacitors. Don't use oil/paper/mylar caps in a tank circuit. You'll be real sad when it fails and spits boiling oil at you.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
hi guys,
If you have the caps from same manufacturer, of same technology and voltage rating but different capacitance I think they should do reasonably well when paralleled. Caps will form a current divider and all of them will share portions of current proportional to their capacitance.
The downside is that not all of the caps may be able to take the same power dissipation punishment due to surface area of their package. Due to square/cube law a lot of small, low-value caps are of benefit here,
So if you have caps that are like 0.27uF and 0.15uF mixing them should work fine, but you wouldn't be able to run 0.15's to their maximum without cooking the other ones. So I say mix them and have fun - just watch them not to overheat. The general rule for polypropylene caps seems to be, if they're too hot to touch, they're too hot, as I found out the hard way.
Goodchild:
I'm not sure what exactly is the current rating of the caps, but dividing the tank voltage with it's characteristic impedance yielded a current value of as much as 150A - and without water cooling the coil gets sizzling hot in seconds. I'm very surprised how well are the caps holding without blowing up so far.
They are 160V DC caps and I'm running them up to 70V AC,which seems to be about the limit considering they get quite hot.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Can you post a video of your oscillator melting a screw? Or Something like that Marko? It's so nice to see things melting and burning with it, and quite impressive too.
Hey guys! I'm back, and got my new IRFP's260N and everything is working nicely, but now i have one problem... Like Marko said, when the workpiece is introduced on the work coil, the voltage drops a lot, in my case, I got a transformer very simmilar to the one that appears on Marko's video. It's rated 24V AC, Rectified it becomes 36vDC, when i turn the circuit on, it drops to 31, and with work, it drops to 24vDC... I've made some calculations here, I got 11.8A as maximum current draw, and when the workpiece meets curie point it starts droping and keeps at 9A, so, my power source drops down to 24vDC, it gives me a real power of ~276W and aproximately 230W when curie point is reached... With only 276W i alredy got the screw to become RedHot and I'm pretty excited to get more power with it, I think something around 1200W
As for the supplys, whats the advantage on using a separate 12v supply for the mosfets gates and a higher voltage for the power stage?
Someone knows a way to avoid that and make the thing work at full power?
As Marko noted, I can go up to 60v, because I'm using IRFP260N as switches.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Gabriel35 wrote ...
Hey guys! I'm back, and got my new IRFP's260N and everything is working nicely, but now i have one problem... Like Marko said, when the workpiece is introduced on the work coil, the voltage drops a lot, in my case, I got a transformer very simmilar to the one that appears on Marko's video. It's rated 24V AC, Rectified it becomes 36vDC, when i turn the circuit on, it drops to 31, and with work, it drops to 24vDC... I've made some calculations here, I got 11.8A as maximum current draw, and when the workpiece meets curie point it starts droping and keeps at 9A, so, my power source drops down to 24vDC, it gives me a real power of ~276W and aproximately 230W when curie point is reached... With only 276W i alredy got the screw to become RedHot and I'm pretty excited to get more power with it, I think something around 1200W
As for the supplys, whats the advantage on using a separate 12v supply for the mosfets gates and a higher voltage for the power stage?
Someone knows a way to avoid that and make the thing work at full power?
As Marko noted, I can go up to 60v, because I'm using IRFP260N as switches.
Thank you!
To get more overall wattage, you can lower the inductance/resistance of the work coil for lower impedance which raises the current, or use more voltage which would also raise the current.
The 12v supply for the mosfet gates is a good idea. I doubt i will be making any more ZVSs without that kind of drive. With a 12v supply, the gate resistors have to drop less voltage, and thusly heat less. This means more efficiency and smaller resistors, i used a single 1/4 watt resistor for each gate and they remained well within their resistance tolerance range. However, i would probably use less than 500 ohms, because as the voltage drops, so does the speed the gates charge.
A big transformer is needed for the wattage you want, and even a MOT wound with too thin wire could be 50v output with no load and drop to 25v with 10 amp load. You can use ohm's law to calculate the amount of voltage that will be dropped across the resistance of the secondary, if you know the resistance of the secondary.
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Royer induction heater
