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Re: [Amps] E-core transformer

Subject: Re: [Amps] E-core transformer
From: Manfred Mornhinweg <>
Date: Fri, 06 Dec 2013 17:52:53 +0000
List-post: <">>

unable to follow Peter's suggestion, due to a pronounced and pretty long
standing lack of virgins available for sacrifice to the gods of recycled
electromagnetics, I still resort to plain old heat to get them apart.

I've tried heating with a heat gun, but the ferrite falls apart
before the varnish gets soft. Any suggestions?

Sure. Don't use a heat gun! It heats far too fast and unevenly. Ferrite is brittle, and will crack from differential thermal expansion.

And boiling water only sometimes does the trick. Most of the time, it's not hot enough to weaken the glue.

Instead use an oven. I use a simple, small electric kitchen oven. The same I use to make my cakes. I place the transformer inside (that's inside the oven, not inside a cake), roughly in the middle, then switch the oven on, with the thermostat set to 140 degrees Celsius. I let the transformer heat up slowly to that temperature - at least 15 minutes. Most bobbins and insulating material survive that temperature. I then use thermally insulating gloves (the ones your wife uses to grab hot cooking utensils) and try to lovingly but decidedly wrestle apart the two core halves. If they still cling together like two good friends, I punish them by putting them back in the oven and increasing the temperature some more. Eventually they all raise the white flag, but if the glue is too heat resistant, the bobbin might melt during the escalation of the procedure, so that you can recover just the core and not the bobbin.

One can make new bobbins from cardboard and carpenter's glue, or from more fancy materials like fiberglass sheets.


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