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Old 25th August 2005, 09:33 PM   #31
Eva is offline Eva  Spain
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In most of these chinese PSUs the cores of are just glued with varnish and they will split quite easily if they are heated slowly, and then a small force is applied in hot during enough time (not enough to broke them!).

On the other hand, I've found very powerful adhesives in other PSUs whose cores I couldn't split.
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Old 25th August 2005, 10:05 PM   #32
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BTW
If you should ever find that your application is important enough that you want to spend money for a core, you can try these guys:


http://www.tscinternational.net/tscstoreetd.html

You can get an ETD49 for 76 cents, which is not bad. (you'll need two of those.

That's good for about 700W in full-bridge.

Adrian
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Old 26th August 2005, 07:07 AM   #33
mzzj is offline mzzj  Finland
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Quote:
Originally posted by funberry
BTW
If you should ever find that your application is important enough that you want to spend money for a core, you can try these guys:


http://www.tscinternational.net/tscstoreetd.html

You can get an ETD49 for 76 cents, which is not bad. (you'll need two of those.

That's good for about 700W in full-bridge.

Adrian
Dammit, cheapest so far what i have seen, but US only? Shipping to here would cost an fortune anyways.
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Old 26th August 2005, 07:13 AM   #34
mzzj is offline mzzj  Finland
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What comes to separating cores, I have used MEK(methyl-ethylene-ketone) and acetone mixed. Let it soak overnight or even several days. Some sorta paint stripper is probably even better, havent tried yet.
Edit: Name of most probably successive paint stripper just popped to my head, Nitromors
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Old 26th August 2005, 08:57 AM   #35
Loial is offline Loial  Sweden
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I've purchased my ferrite cores from
http://www.bejoken.se , a Malmö/sweden based company
Maybe shipping isn't that expensive to finland?
They charge SEK 11,54 ( approx. 1,30 euros? ) for ETD49 cores, not to expensive if you ask me... If you call/email them, perhaps you can pay them in advance, and have it sent to you by mail? I guess shipping would be 3-5 euros or something like that...

( hehe... they've got ETD59 siemens cores as well... i wonder what they are capable of... )
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Old 26th August 2005, 01:40 PM   #36
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(maybe we should start a new "Ferrite Core" thread)

Shipping to Finland might not be a fortune.

The US Post Office has a service called "Global Priority Mail - Flat-rate Envelope (Small)", which costs $5 to anywhere in Europe, and can weigh up to 4 pounds (1.8Kg).

The ETD49core weighs 45g (per half)
The ETD59 weighs 130g.

A few of these could fit nicely in a bubble-lined large envelope.

Maybe a group buy of ferrites for our EU friends?

Adrian
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Old 26th August 2005, 01:52 PM   #37
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IMHO, I still think if you're struggling with separating a core, you've got the wrong view on this.

To gain access to the center leg, and dissolve the glue there, you need to remove the bobbin, usually by destroying it.

I don't know about you, but to me, the bobbin is worth more than the extra comfort of re-winding the coil unhindered.

How much extra time does it cost to rewind with the core in-place?
And how much extra time, work, materials does it cost to dissolve the glue, and then measure/design/craft/improvise a new bobbin?

Good bobbins are valuable, they are not a trivial item, and if you want to buy one, they're often harder to find than the ferrite.

Adrian
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Old 26th August 2005, 02:42 PM   #38
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Quote:
I have used MEK(methyl-ethylene-ketone)
Methyl Ethyl Ketoene is a very good solvent. You have to work quickly with these things, and keep them very tightly capped, because they evaporate before your eyes.

Paint stripper is a mixture of solvents. I think they include one of each major type, an aromatic, a chlorinated, an ionic, an aliphatic, and maybe a branched chain or an alcohol. You really need a lot of trial-and-error, since some solvents are potentiated in a mixture, others do better alone by themselves.

Keep this stuff away from heat, and keep in mind that wifes have been known to divorce their husbands over keeping stuff like this in the house...
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Old 30th August 2005, 02:48 AM   #39
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Quote:
Originally posted by funberry
IMHO, I still think if you're struggling with separating a core, you've got the wrong view on this.

To gain access to the center leg, and dissolve the glue there, you need to remove the bobbin, usually by destroying it.

I don't know about you, but to me, the bobbin is worth more than the extra comfort of re-winding the coil unhindered.
Yeah I didnt even think of it like that... so many wasted cores. The picture is of one I cracked, width is 5.5cm, german brand.

Do you have a source for ETD49 bobbins? Or just an approximate cost?


I bought a couple cores and bobbins that are a bit smaller than the 49s off ebay, cost a lot more than 79 cents though

btw I also got some ferrite toroids, but I dont know if those are of any use at all? They would be much easier to wind, and could be stacked.
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Old 30th August 2005, 03:53 AM   #40
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btw I also got some ferrite toroids, but I dont know if those are of any use at all? They would be much easier to wind, and could be stacked.
Are you sure the toroids are ferrite? There are a lot of powdered iron toroids floating around, and it's not easy to tell them apart. If anyone out there knows how to use simple bench tests to differentiate between ferrite ans powdered Fe, please come forward and say.
You need to calculate the cross-sectional area of the toroid, make sure it's the same as that of the central post of the transformer you're replacing.

Quote:
Do you have a source for ETD49 bobbins? Or just an approximate cost?
Aaaaaaah.... the bobbins.... Now you understand why it's important to preserve them (with the core they're on). This is an even more elusive product than the ferrite. They seem to be about $3 when paying an "authorized disributor's" resale list price. You can't easily find a distibutor that has them, and is willing to sell just two or three.

The bobbin mfr. I know about is Miles-Platts, in England. There are others, but this one is most prolific around ETD cores.

You might work backwards, from Miles-Platts (email them) and find out all the distributors in your area.

Dexter Magnetics in Chicago, carries the Miles-Platts line. They may sell you a small quantity, if you say you're an engineer prototyping a new design.

If other members are interested, maybe we can buy in quantity and spread them around.

The truth of the matter is that ETD cores are one of the most expensive tranformer platforms in SMPS, because of the intricate design of both magnetics, and coil formers. Plain old square "E" cores may be easier to work with.

And then again, you can make that bobbin yourself. Cardboard won't do, because the cummulative force applied to each turn of wire causes deformation of the former. Eventually, even a small deformation of the cardboard bobbin is enough to make it not fit onto the core any more.

A plastic tube, with flanges of epoxy fiberglass PCB material, makes a strong bobbin. (make sure there is no copper on that PCB --shorted turn.

Adrian
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