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rp181

Thu Aug 07 2008, 11:01PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

Today i pulled out a flyback core from a modern T.V. (came out easy out of hot water). When the tranformer was assembled, the 2 halves were seperated by a segment of magnet wire, do i need to keep the 2 air gaps or can i just have the 2 halves touching? About how much power do you think the core can handle? I want a output of 800v, for charging capacitors.
heres a pic:

core is 2 5/8in long and 1 3/8in wide.

teslacoolguy

Fri Aug 08 2008, 12:47AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
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Posts: 792

You are going to need some kind of spacing between the 2 halves (i use 2 layers of electrical tape) or the core is going to saturate quickly, get hot and rob you of power. Yes that core should be sutable for makeing a 800v supply for capacitor charger just dont go trying to push 2kw into it

Dr. SSTC

Fri Aug 08 2008, 04:37AM

Registered Member #1407 Joined: Fri Mar 21 2008, 07:09AM
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Posts: 222

i think you would be able to push 500-700watts trough it

as for the air gap i think if your running it with a single switch or ZVS you need the air gap

how ever if you are using a half bridge or Full-bridge they need to be touching

Myke

Fri Aug 08 2008, 05:22AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

I would think that you would want to put it under oil if you are going to run it at around 500W because oil conducts heat way better than air does.

Dr. Dark Current

Fri Aug 08 2008, 06:58AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Guys, this core will run just fine at 1500W, assuming it's for a voltage supply.
If it's for a current supply (drawing arcs, charging capacitors), it'll be fine with 400-500W.

cbfull

Fri Aug 08 2008, 01:15PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

I can't debate other's experiences with flybacks and airgaps, but I think there is a lot of misinformation about the necessity of the gaps. One of the benefits of it is to raise the resonant frequency, but at a loss of effeciency due to stray inductance. A transformer is a magnetic loop much like a circuit, and the air gap is like adding a resistor to that loop. It keeps power levels down and thus the core is less prone to heat build up.

For making high voltage arcs, it is up to you whether or not to have air gaps. Your circuit will be able to deliver more power to the secondary and your transistors should stay cooler, but that is my experience from using bridge design as well as push-pull.

You will likely find that without the gaps, the frequency may drop to audible range, and your core will sqeal loudly. There are two ways I know of to eliminate this. One way is to of course put the air gaps back. The second way requires some small mods to the circuit, such as adding a small ferrite transformer at each transistor base. This esentially raises the resonant frequency by making the circuit "think" the flyback is saturating much sooner. This is acutally a design that was taken from a motorola application note. The nice thing about this method is, no excessive stray inductance and you also still get max power throughput.

Dr. Dark Current

Fri Aug 08 2008, 01:41PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Gaps must be used in: Flyback inverter (to store energy) , "mazilli" ZVS inverter (to keep high Q of the circuit) and everywhere else where you need to store magnetic energy in the core.

Gaps should not be used in: Half/full bridge inverters, push-pull inverters and any other drive methods with symmetric drive waveform not requiring any "Q" in the circuit.

rp181

Fri Aug 08 2008, 01:53PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

thats good, my PVC secondary former will work with cores touching, and with a gap. So far my secondary consists of 1 layer magnet wire (i dont know AWG, i got it from the primary side of a low current transformer, out put was 300ma from 120v). I dont think i will try multilayer.

rp181

Sat Aug 09 2008, 07:24PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

i wound a new secondary with 2 layers, sepearated by teflon tape and paper ( i was going to put in oil, didnt though) with a laptop psu shorted through the primary, i get a tiny spark, and i can feel the output. I am looking for a new secondary former, with 1/2in pvc, the windings are too far from the core.

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