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Registered Member #16903
Joined: Thu May 09 2013, 08:00PM
Location: Sumter, SC
Posts: 23
Hello I'm trying to build a zvs driver for a flyback/induction coil. so i've finished it today but every time i plug it into a 18v de-walt nicad battery from what im seeing is nothing but one of the outer wires to the 5+5 turn starts to smoke like its shorted but its not. i'm using a stw78n65m5 mosfet and stth6004w ultra fast diodes. also i have some STW88N65M5 mosfets lying around that i could use also if that could help. i might just redo the whole driver since its kinda sloppy
Registered Member #16018
Joined: Fri May 03 2013, 07:19PM
Location:
Posts: 53
it might be that your wire on the primary is too small and the flyback is dead. the polarity could also be wrong. are the 2 coild in the conter tap wound the same direction? i would try using the IRFP 250
Registered Member #16903
Joined: Thu May 09 2013, 08:00PM
Location: Sumter, SC
Posts: 23
I've checked the polarity twice and still nothing to be sure It's the one wire that comes from a ultra fast diode into a .47uf cap (if that's not enough capacitance I can put another in parallel) then off that same side in to the coil. also the only other mosfets I have STW88n65m5. I can get a hold of some STMicroelectronics brand mosfets but you would need to tell me which one.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
teslarevolution wrote ...
I've checked the polarity twice and still nothing to be sure It's the one wire that comes from a ultra fast diode into a .47uf cap (if that's not enough capacitance I can put another in parallel) then off that same side in to the coil. also the only other mosfets I have STW88n65m5. I can get a hold of some STMicroelectronics brand mosfets but you would need to tell me which one.
--thanks
Both mosfets you've listed seem ok. They have a high voltage rating, plenty of current capacity and a low on-state resistance, they should be fine for a decently powerful ZVS.
I don't think we can provide satisfactory answers without much more info. Things like: pictures of the ZVS and all connections, as well as a schematic with all your part values and power supply included.
You mention using this for powering an induction coil as well as flybacks. What sort do you mean, something similar to an old car ignition coil?
Registered Member #16903
Joined: Thu May 09 2013, 08:00PM
Location: Sumter, SC
Posts: 23
Ok i've rebuilt it and now it's getting the same problem but now one of the mosfets which are heatsinked gets really hot but the other one does even get warm and im positive that i have it wired correctly im going to get pictures soon
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Can we please see some pictures of your circuit? A common mistake is to connect the ultrafast diodes from the gate to the drain of the same MOSFET, rather than to the other fet. This results in large amounts of heating and can lead to failure. If your primary is smoking, that has to be a short circuit because smoking wires generally means
As long as the MOSFET has a fast enough switching time (which the STW78N65M5 does, in the order of nanoseconds and not to mention 650v 69amps is plenty) the circuit should be fine. The simplest mistakes are often the most overlooked and this can easily happen when you're excited about getting it working.
Building the circuit neatly is also very helpful, as it allows you to see everything and where each component goes. Double and triple check to the schematic once the circuit is finished.
But for now, a couple of different pictures would do justice. Happy to help
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ZVS trouble
