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Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Here's a setup to power flybacks using a ZVS driver without winding the symmetrical primary. It uses an intermediate core 5+5T primary 12T secondary:
A flyback connected:
It runs good, but under certain conditions (like heavy load on the secondary) both the inductor in the ZVS setup and the 5+5 primary are getting hot. I will replace the inductor since I need one with ticker wire, but the 5+5 primary already uses 1.5mm copper wire. The capacitor and mosfets remain cool. Usually this setup receives 12V from a supply that can give 20A max. The gates are connected to the supply via a L7812, but I didn't make much use of that since I use low voltages.
What I would like to understand is what's the reason for the 5+5 primary to get that hot? Also, what is core saturation and how does it apply to this case?
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Electricity isn't the only thing that copper conducts. Do you think that the heat created by the inductor could be simply traveling to the primary? Replace the inductor to find out...
Core saturation means you are trying to magnetize your transformer beyond its physical limit, so instead of producing a stronger magnetic field, it produces heat. This would also cause your primary to heat by contact.
If you raise the power and notice that output stops increasing at a certain point, that's an indicator of saturation.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
You misunderstood the first part: I didn't say the inductor heats the primary, I said both the inductor and the primary are getting hot.
Thanks for clarifying the saturation part. Do you perhaps know why the primary is getting that hot, when using a heavy load (close to short circuit) on the secondary?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It's getting hot because there's lots of current flowing in it. Because the ZVS is a resonant circuit, lots of current flows in the primary irrespective of the load on the secondary.
If the core were near saturation, it would get very hot too.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Let's follow the second assumption. Other Royer oscillators I've put together have a cooler primary, and most of them use the same tick, PVC insulate 1.5mm cooper wires. However this is a smaller core, as compared to the previous ones.
Are there any changes on the secondary side, that could make the core saturate?
Does the "saturation level" change going from open circuit to short circuit?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Did your other Royer oscillators use the same size of tank capacitor? The larger the capacitor, the higher the Q (more resonant current in primary) and the lower the frequency (greater risk of saturation)
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Thanks for your reply.
The one in the pictures bellow was using 3x2.2uF 630 Volts caps and didn't notice the primary getting hot (when used with a ferrite core): 2xIRFP460, 2x270 Ohm5W on gates, 2x15V Zenner
The new one that heats the primary on load is using: 2xIRF540, 2x460 Ohm on gates (with L7812), 2x10V Zenner . Another difference is the smaller Ferrite core, as can be seen in the pictures. The primary has 5+5 Turns and the secondary 12T (not a Flyback secondary, another difference). On load I also noticed an increase in the power consumption from my supply (more current).
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Hot Primary - what's causing it?
