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Registered Member #11363
Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19
Hi all ppl. Im new here, more than 2 years that i read the forum, but only now i want to show some of my circuits ps: im from Brazil, my english is poor.... i will try to do my best :D here a video of my first zvs: Its uploaded on 4shared, because youtube are blocked here at my work ^^ My ZVS are made with 2 fet IRF3205 (55v / 110A 8.0mOhm) , have 5+5 turns of a 0,8mm cooper and the supply is a transformer from a nobreak and gives 22V at 15A +/- , have 21.500uf for filter. A traditional flyback from a crt monitor. The indutor i got from a atx psu. diodes zenners are 12v 0,5W and the diodes are UF4007. My only problem, is the fets burning with +/- 5 minutes of working... Next weekend, i want to try to do a tesla :D .
Registered Member #11363
Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19
Of course, sorry for my mistake, its because ZVS Schematic are easy to find on google^^ I use this schematic: this is with P80NFS fets IRF3205 my Power Suply ^^ and my first experiment for a tesla: 84 turns 0,84mm wire on 60mm diameter. FETS: IRF3205 / P80nFS are good too. CAP: 220nF MKP Zenners: 12v 1W Resistors 470ohms 7W Resistors 10k 1/4w Diodes: Uf4007. i will edit the first post, and put a picture of the board :) *idk how to put miniatures =/
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Hi Whiplash,
Re. the fets burning up within 5 or so minutes of operating in ZVS, I think this is quite normal. Fets can heat up quite quickly in a ZVS especially if running it pretty hard. I would make sure you've got a sufficiently big heatsink and some thermal grease to increase the thermal conductivity between the back of the fets and the heatsink.
Also do be aware that the maximum rating of fets will decrease as their temperature increases. For IR3205 fets, the current capability decreases to 80 amps @ 100 deg Celcius though I don't think this is a problem. It's more likely a voltage spike that killed the fets becauses they're only rated for 55v. For more reliability I would get fets rated into the 100s of volts.
Try improving this if you can as I'm sure it will help and let us know if you have any problems.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Also, would it be possible to take some current nd voltage measurements of the ZVS circuit running? The values you've said for the transformer power supply are probably the no load voltage and maximum current rating, if not correct me but I'm just assuming.
You will probably find that the voltage will drop due to the internal resistance of the windings in the transformer (depending on how well it's made) and the current will peak quite high when you are arcing.
Registered Member #11363
Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19
Jozef C. I will try to buy better fets today. About my power supply, its 22V and more than 20A now (better bridge for 50A). I use an "shower resistance" to test him up, and give me this values, have a ammeter analogic and goest to 22A with that resistance.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Ok - just clarifying, would you be able to measure the current drawn when you are drawing/stretching the arcs out? Because from there I could calculate the power your IRF3205s would be dissipating and this would be helpful just to get an idea of how we should be wary of heating.
Don't worry about buying new fets soon - there's no rush. Some fets are very expensive so don't spend all your $$$ on high power ones. I think the IRFP250 (200 volts 33 amps) or the IRFP260 (200v 46 amps)would be suitable for yours (it's the generic mosfet used in the ZVS circuit).
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