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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I don't think any ripple would represent a problem as long as the voltage never drops into danger zone of <10 volts. I only used like a few thousand uF as well for filtering.
Also very hard to tell why is your circuit blowing up.
Have you tried scoping it? If there is excessive ringing present adding some ferrite beads in series with mosfet source could help.
I find it bizzare your bridge receifier is blowing up. I suspect it a chinese fake. Direct mains short is probably among the worst overloads a bridge rectifier like that can see and I've never killed one before blowing a fuse. So installing a breaker or a fuse on the transformer secondary side might be a good idea too!
I used a 25 amp bridge rectifier and didn't even use a heatsink.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Oh! Interesting to know that, I think that this bridge is fake so...
But... a more logical thinking makes me think that for some reason is the royer that is ceasing to oscilate (i don't know why) and shorting the bridge... What do you think?
Whe the circuit shorts it takes with it one mosfet or two?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
But... a more logical thinking makes me think that for some reason is the royer that is ceasing to oscilate (i don't know why) and shorting the bridge... What do you think?
Yes, that's what happens. Some people have blamed parasitic oscillations which get bigger and bigger with increase in supply voltage. If you can scope and confirm them it'd be interesting to see if they can be stopped with some ferrite beads.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve Conner wrote ...
That's right, but the root cause of the parasitics is the FET that is supposed to be off not turning off fully.
I've seen 6 amp bridge rectifiers sold as 60 amp on EBay.
Well, not sure about that anymore; it might be just a part of a problem. I've successfully implented capacitive and inductive feedback without diodes which should allow for better turn off (and even driving the gates below zero!) but the drain waveforms still looked like mad mess at 1Mhz. Putting ferrite beads on mosfet sources apparently reduced their high frequency gain and helped huge time. The beads got quite hot though.
Gabriel, I'd suggest you start using an oscilloscope on your circuit to see what's going on. As far as I remember, Roger in Ohio also had his mosfets blowing upafter a certain voltage, but he seemed to have fixed it by placing some steel nuts around some of his wiring.
By the way, I've just realized that the parasitic oscillations are actually common mode between the mosfet drains, with the parallel LC tank cap representing a low impedance path. If that's true, then a common mode choke between the output and the tank might turn out a much better solution than ferrite beads.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Nice to know that. Ill try scoping the circuit to see whats realy happening. Thank you so much for your help since now friends! Thats the only reason that I can imagine that is causing the problems...
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Hey guys! I got some videos...
The description of the videos says everything as well as their titles:
The first one shows it melting an steel washer. There are videos of aluminum melting and cooper heating too. Proud to present my first water cooler tank! Works pretty nice, I made a radiator for it using two XEON pure cooper dssipators and some cooper coil turns soldered to it, works like a charm.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi gabriel
What was the problem then with your setup before when you complained it doesn't give enough pwoer? You just added more caps? :P
I hoped you would post some scope waveforms, preferably of higher voltage runs where you said your ih tended to blow up. Then try adding some ferrite beads to see if they get better.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Hi Marko! Yes, I really need to get some scope tracings as soon as possible to investigate that misterious failures... But I don't have a Scope at home, I need to take the whole circuit to the place where I study, they have lots of Digital 100Mhz scopes, So, I'm just waiting to have some free time to do this.
I think about measuring the DC input voltage, to see if ripple is present and if it's significant. The gate waveforms, the output of the mosfets and the tank waveform.
About Ferrite beads, that's a great idea, I plan to use it as soon as possible since it can only bring good characteristics to the circuit, and nothing that could bring the things worse.
Should I use them just on the gates?
About the power, I got some days ago, a big 15V tansformer from a 700VA UPS... So, I wired it with the previous 24v big transformer that I had... Now the voltage sags on a very good level!
Registered Member #5737
Joined: Sat Jul 14 2012, 01:57PM
Location:
Posts: 1
What happened to Marko's Induction Noobheater circuit? He had the best design for connecting all the capacitors. Can anyone come up with a great design for connecting all the caps in parallel without soldering them?
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Royer induction heater
