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Sorry, but a question about the ZVS.

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Platinum

Mon Jan 30 2012, 12:29AM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I recently fixed my ZVS, and I managed to blow a few MOSFET's, because I was using junk parts, but since my ZVS has been fixed, the wires go very hot and melt the insulation, why is this?

I have two IRFP250

1 18v zener, and one 7.5v zener.

Two random diodes. I think in4007?

and a homemade inductor.

Tank cap blew, so I have 700nf 1kv MMC.

Alex M

Mon Jan 30 2012, 12:33AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Change that 7.5v zener to something that is 12v-18v. 7.5v is not enough for a MOSFET to turn on fully and it will heat up.

Wires getting hot means they are too thin, use some domestic single core 2.5mm twin and earth wire.

m4ge123

Mon Jan 30 2012, 12:35AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

Which wires are getting hot?

Platinum

Mon Jan 30 2012, 12:42AM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Alex1M6 wrote ...

Change that 7.5v zener to something that is 12v-18v. 7.5v is not enough for a MOSFET to turn on fully and it will heat up.

Wires getting hot means they are too thin, use some domestic single core 2.5mm twin and earth wire.

I'm using normal insulated mains cable, I had to use a 7.5v zener as I went to Maplins and they didn't have any, so is there anything I can rip that uses a 12V zener?, I have a few old ATX PSU's and they only have in4148 75 zeners :(

The wires that are getting hot are just the ZVS output.

Also the MOSFET which uses a 7.5v zener does not get hot, just wires.

m4ge123

Mon Jan 30 2012, 01:57AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

The red wires need to be thicker than the magenta ones. Even with no load, there's a lot (Vin*2.22/sqrt(L/C)) of current going through the red ones. Those wires should be thicker. If it isn't already, your should solder your cap directly to your primary.

Platinum

Mon Jan 30 2012, 02:30AM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

But before I Used junk parts the circuit ran cool and wires didn't get hot even after 10mins of use, now I can't turn it on more than 30seconds without wires metling.

Alex M

Mon Jan 30 2012, 03:46AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Platinum wrote ...

But before I Used junk parts the circuit ran cool and wires didn't get hot even after 10mins of use, now I can't turn it on more than 30seconds without wires melting.

Well that might be the problem then, one or more of these junked parts are not suitable for this particular circuit. Either that or something is not connected together right.

Can you measure the current draw from your PSU? UK mains flex is rated for around 13 amps so they really should not be heating up that much.

m4ge123

Mon Jan 30 2012, 05:11AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

Did you change your primary or tank cap when you rebuilt your ZVS? That could change the current and/or frequency going through the tank circuit.

Platinum

Mon Jan 30 2012, 01:52PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Alex1M6 wrote ...

Platinum wrote ...

But before I Used junk parts the circuit ran cool and wires didn't get hot even after 10mins of use, now I can't turn it on more than 30seconds without wires melting.

My multimeter needs a new battery and I haven't got one, last time I measured it it was like 10-15a, I made it from a old CB radio PSU and had a circuit to limit the PSU at 14v 5a, now it's somewhere near 40v, I rectified it, and smoothed it, my bridge rectifier also gets hot due to power drawn. I stuck a nice heatsink on there.

I have about 700nf's of capacitance

I'm using IN4007 from my junk box, yet I have loads of nicer once. I also have 200v power diodes, they are in to-220

And I'm using a 7.5v zener and I think a 18v zener. maybe the difference of zener diodes is making my wires heat up?

Well I just got two brand new IN4007 off a circuit board (halogen transformer) they are IN4007, used as a bridge, and now the wires get slightly hot but, I can run it for extended periods of time. It only now gets hot (the wires) when I use an induction heater directly on the ZVS. It can make thick screwdrivers red hot. Also only the + of the ZVS gets hot. But all is well ^^

Forty

Mon Jan 30 2012, 03:55PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

You could use two 7.5v zener's in series for each gate. ~15v zener is probably better than mismatched 7.5v and 12v. check for any bad connections along the wires because a high resistance spot could heat up and then conduct the heat along the wire. I also wouldn't use it as an induction heater until you can get some more capacitance on it to drop the frequency.

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