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Dr. Dark Current

Thu Dec 04 2008, 04:23PM

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

I heard it is not advisable to integrate the (leakage) inductance into the transformer.

Can anyone explain why is this?

Steve Ward

Sat Dec 06 2008, 04:30AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

From what i could tell, it was because "integrating" leakage inductance, typically meant small air-gap, or something, which lowered the magnetizing inductance. For good stability with open load, you want Lmag >> Lleak so that you are far from resonance when Lmag comes into play with an unloaded secondary circuit.

Dr. Dark Current

Sat Dec 06 2008, 08:04AM

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

Steve Ward wrote ...

From what i could tell, it was because "integrating" leakage inductance, typically meant small air-gap, or something, which lowered the magnetizing inductance. For good stability with open load, you want Lmag >> Lleak so that you are far from resonance when Lmag comes into play with an unloaded secondary circuit.

Hmm, you can increase leakage by putting the primary away from the secondary, this has also the advantage of better cooling. You don't need to introduce any gap at all into the core.

Edit: I am gonna try it anyway. I got two big cores for free and two minibrick FETs for free too

That should make a multi-kVA inverter, for almost no cost

baleworker

Sun Dec 07 2008, 06:15AM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

What is an open circuit resonance on SLR topology? I thought since it already operates on its resonance frequency by design?

I had a few HV rectifiers fried on my SLR inverter and all with open circuit. I still dont know the exact reason. Its either one of the diodes broke down due to overvoltage, or potting epoxy didnt adhere well enough to them (since I havnt cleaned soldering flux residue) and it simply arced thru.

I wish I could dissolve epoxy with soemthing and do a betetr failure analisys.

Steve Ward

Mon Dec 08 2008, 03:40AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Hmm, you can increase leakage by putting the primary away from the secondary, this has also the advantage of better cooling. You don't need to introduce any gap at all into the core.

Sure, but in my case i found the leakage L was too small for the operating frequency i wanted.

Conundrum

Mon Dec 08 2008, 06:54PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

apparently boiling solvents (possibly something fairly nasty like ac*t*ne or m*th*l e*h*l k*tone) might shift it. However this is a very bad idea. A slightly more human-friendly approach might be boiling water, this is often used to decapsulate varnish-potted coils.

-A

Dr. Dark Current

Mon Dec 08 2008, 07:16PM

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

Steve Ward wrote ...

Sure, but in my case i found the leakage L was too small for the operating frequency i wanted.

All right then. I will put as much of the L as possible into the transformer and see if its enough. Why complicate the design if you can keep it simple.

LutzH

Mon Dec 08 2008, 07:17PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

How to Disolve Epoxy:

First Remember MC will disolve almost any polymer except fluoro ones, and it is somewhat toxic, do outdoors!!!

Methylene Chloride (MC) is the key, if you cannot find it in pure form, look at the ingredients of your locally available paint strippers, the more MC in the brand the better. Jewelers use it to remove epoxy set stones etc.

I have used this chemical to correct epoxy "oopses" but keep in mind it will eventualy attack even the epoxy based body of silicon rectifiers, and the enamel coatings of magnet wire (Polyimide is the most resistant) For a forensic analysis it may do the trick. Just bury it in the MC, or MC based jell and wait for the epoxy to turn to jelly.

Take Care.....Lutz :)

Firefox

Mon Dec 08 2008, 09:51PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Dr. Kilovolt, from reading a few articles on the subject (I am faaarr from an expert), it seemed that builders liked to keep the leakage inductance small and use an external inductor because it allowed the builder a wider choice in drive frequencies.

Dr. Dark Current

Mon Dec 08 2008, 09:57PM

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

Firefox wrote ...

Dr. Kilovolt, from reading a few articles on the subject (I am faaarr from an expert), it seemed that builders liked to keep the leakage inductance small and use an external inductor because it allowed the builder a wider choice in drive frequencies.

Yeah but this way I can use small or none external inductor. The frequency is (in my case, experimentally) determined for optimal operation and does not need to change during normal use of the inverter. So it makes more sense to achieve the same result with less components (if possible).

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