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Old 25th January 2013, 05:38 PM   #171
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Quote:
Originally Posted by rikkitikkitavi View Post
I use triple insulated wire anyhow.
Care must be taken doing the insulation betweeen primary and secondary. Using the split bobbin lets you does not care about it so much.

Quote:
Originally Posted by rikkitikkitavi View Post
For a LLC operating around 100 kHz perhaps litz is a good idea considering the large circulating currents and losses.
At 100kHz the skin depth is 0,2mm, so the maximal reccomended wire width is 0,4mm. I use the strands of 0,25mm wire, which is a good choice up to 250kHz.

Quote:
Originally Posted by rikkitikkitavi View Post
Anyhow Lm cannot be calulated accurately unless quite large air gaps are involved sawmping.out differnces in u.
Lm can be calcualted accurately and the approximation i gave for the split bobbin is in +/-20% range

Here is the approximation again with the Al values
Lleakage=N_primary^2*Al_leak
And the Al_leak values are:
ETD29 54
ETD34 59
ETD39 64
ETD54 84
ETD59 120

My example data:
ETD29 split bobbin 23 turns primary: 30uH leakage (29uH from approx)
ETD39 split bobbin 15 turns primary: 15uH leakage (14uH from approx)

ETD39 with a special splitting: 1 part to primaray 2 part to secondary: 4uH (if i approximate te Al setting setting gap virtually as secondary winding width I get an 5uH)

As I remember Nigel used an ETD59 with 33 turns of primary. From my approximation this yields 131uH leakage inductance if he uses a split bobbin.

Nigel now has 120uH leakage. Nigel now you winded the transformer like a split bobbbin? (primary to one end and secondary to other end)
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Old 25th January 2013, 07:42 PM   #172
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Triple insulated wire is rated at about 9-15 kV breakdown voltage. You need not to worry about insulation tape etc, but must respect the creepage and clearance when the wires are leaving the bobin of course.
Triple Insulated Wire - TEX-FS : Insulated Winding Wires : Furukawa Electric

But this does not matter using a split bobin of course.

Perhaps the insulation thicknes helps increasing leakage inductance. I noticed that once, that was an ordinary wiring with secondary inbetween two split primaries.
No tape used. But it could also be sloppy winding tecnuiqe

Lm is no better than u(permability data) given by the manufacturer. Sometimes I have found that it is way off and is of course strongly dependant on clamping force etc. But of course the formulas are accurate.

Thanks for the data , I believe your aproximation holds a lot of value.
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Old 25th January 2013, 08:04 PM   #173
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[QUOTE=rikkitikkitavi;3342124]
Triple Insulated Wire - TEX-FS : Insulated Winding Wires : Furukawa Electric

What is the thermal rating? I cannot find it.

Quote:
Originally Posted by rikkitikkitavi View Post
But it could also be sloppy winding tecnuiqe
Its more likely.

But insolation is thick and this can be bad:
a 0,25mm conductor diameter wire has a 0,45mm diameter. Conductor area is 0,049mm2 but total area is 0,159mm2. Only 31% of the area is conductor.

This will make your windining window less utilizable. For example with a 0,25mm normal insulation wire, 3M insulation tapes, and a 1,5mm thick splitter I can manage to wind the window up to 50% with conductor!

With your wire the max is limieted to 31% (with 0,25mm conductor wire). Also there is some air between wire, you will need some insulator, so it will be about 20%.

This means that you will get much less out from the transformer (based on copper losses) with your triple insulated wire!

Your wire is good for low freq. An 1mm conudctor width wire has an 1,2mm total diamater, so for thick wires you can neglect the insulation. But for >100kHz you need stranded wire, so normal insulated wire is better.
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Old 25th January 2013, 08:11 PM   #174
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Class F = 155C
They have different classes.

Yes, the window is poorly used, for large transformers it is quite a waste. I have only done tiny ones (RM14, ETD29) where margin tape etc would have offset but anyhow I trust the wire, but not my taping skills as I can not Hipot the transformer.
Also using fairly low switchfrequency where skindepth is not a problem.

There is a 7strand wire with each strand as normal magnetic wire , and the compound triple insulated. But it is expensive I guess.

In the end it is a matter of design how much loss you can take.

I guess I have to reconsider if I try a resonant converter (now that Nigel has done all the hard work and your article is a very good starting point)
Interesting discussion, but I think we should leave Nigels thread alone for a while. Points are taken and will be absorbed in due time
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Old 25th January 2013, 08:29 PM   #175
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Quote:
Originally Posted by rikkitikkitavi View Post
Q: how do you design the transformer with the aim of a certain Lleak? .)
I wound on 33 turns primary and 2 lots of 9 turns secondaries.

I didn't have a split bobbin so just wound on the primary next to the secondary. Clearly I need to use tape to stop them touching on the final item.
Or try to find a split bobbin.
I got 700uH and 120uH which is spot on.

However I did have 1.5mH and 240uH to start with and so just gapped slightly one side of the core. This scaled the inductances down.
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Old 25th January 2013, 08:57 PM   #176
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Quote:
Originally Posted by nigelwright7557 View Post
I didn't have a split bobbin so just wound on the primary next to the secondary. Clearly I need to use tape to stop them touching on the final item.
Or try to find a split bobbin.
Search for an old telephone card, expired mobile upload card, or any other plastic card. Use a nail skissor to cut out something like this:
splitter.png

Then use epoxi glue, or other insulating glue to glue it on the middle of the bobbin. Now you got a split bobbin

(In Hungary I cannot by ready made split bobbin, so I make it myself)
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Old 25th January 2013, 09:04 PM   #177
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Quote:
Originally Posted by lorylaci View Post
Search for an old telephone card, expired mobile upload card, or any other plastic card. Use a nail skissor to cut out something like this:
)
I couldn't find a split bobbin in the UK so I will use a plastic card next time.

I did some more testing tonight and can get at least 7 amps out of the secondaries at +/- 45 volts.

The next step is to build one up completely tidier and safer and test that.
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Old 27th January 2013, 09:27 AM   #178
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Quote:
Originally Posted by nigelwright7557 View Post
I did some more testing tonight and can get at least 7 amps out of the secondaries at +/- 45 volts.
Great, Nigel!
How much heat was it generating then?
Be avare that iy you load the supply with more power you designed, it is possible that it will operate and ZCS mode. Of course it can be checked by scopeing the gate signal or the half bridge signal, as I said.

Quote:
Originally Posted by nigelwright7557 View Post
The next step is to build one up completely tidier and safer and test that.
If you want about 500W power, and ETD29 made of good materaial (EPCOS N97 or TDK PC47) can do the job of you design it good for >100kHz frequency.
From an ETD54 you can get out kWs if you are good.

But rist make it tidier and safer Safety should be considered over everything else. Use a splitter, and use proper insulation (like Kapton tape, or 3M 1350F or 3M 1350T tapes).
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Old 27th January 2013, 03:52 PM   #179
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Quote:
Originally Posted by lorylaci View Post
Great, Nigel!
How much heat was it generating then?
Be avare that iy you load the supply with more power you designed, it is possible that it will operate and ZCS mode. Of course it can be checked by scopeing the gate signal or the half bridge signal, as I said.

I didn't put heatsinks on the mosfets or output diodes so could only try it for a few moments.
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Old 28th January 2013, 09:44 PM   #180
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Hi Nigel,
to get a 2chamber bobbin I use a 'Kabelbinder' (cable tie?).
I'm just copying an chinese LLC converter, where they did it like that. Get a 4mm gap between pri and sec. Unfortunately the design uses a l6599, which is not esy to get for hobbyist (correct my spelling ;-) )
Greetings from Germany.
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