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separating smps transformer cores

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Avalanche

Fri Aug 18 2006, 01:48PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Hi,

I've broken about 3 cores now, and I have one left here

I have a few smps transformers, and I have salvaged the former from one (by breaking the ferrite), but now I need the two ferrite halves to make a complete transformer again. I have managed to cut the former and wire off some others, leaving just the two halves of the core stuck together with some kind of white resin. The problem is, the resin is pretty strong. I have tried boiling one for about 20 minutes, but still the ferrite breaks when I try to separate the two halves... Any ideas? Is it even possible to get this glue to soften, maybe soaking it in petrol or something?

I have a good supply of these transformers, so I can experiment. If all else fails, I'll have to just wind my transformer on one of the salvaged cores, leaving the former out... that would be a shame though.

Wilson

Fri Aug 18 2006, 02:01PM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

Perhaps acetone?

btw, you can glue the broken ferrite back together with CA glue, and it works as new :P

Marko

Fri Aug 18 2006, 02:07PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

ATX transformers are dipped in epoxy and getting them apart is usually very frustrating and messy job.

I got one core out only once by heating the transformer with 500ÂºC hot air fan, I made terrible mess, stunk out whole room and mutilated the former.

Temperature required for epoxy to melt is simply way higher than ferrite is 'rated' for.

Core formed microfractures, and when I took the core later it just fell in two pieces.
I fixed it with superglue but I'm not happy at all with it.

Most cores and formers I tried to pull apart that way were trashed in beggining.

Cooking in water usually helps only with very small transformers, temperature isn't too high and core usually survives if you are careful.

Perhaps acetone?

No way..

Avalanche

Fri Aug 18 2006, 02:59PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Thanks for the replies

I've changed my mind about these transformers now, they are so difficult to separate I might as well just use them as they are. By modifying the way the windings come out, I should be able to use them as a GDT for a halfbridge.

Something I did want to do though was make a mains inverter, I managed to separate a larger monitor transformer by boiling it. Just for the record, it appears that the brown glue (whatever it is) melts a lot easier than the white epoxy.

Marko

Fri Aug 18 2006, 03:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

If you re-use an ATX transformer you can make yourself a nice halfbridge SMPS.

You can use small drive transformer from ATX supply as GDT if main transistors were mosfet's.
You can use another small transformer for a mini flyback SMPS (I failed to get results from that, witohut regulation voltage spikes are real pain).

TV and monitor transformers tend to use flyback topology due to their low power, but I think you could run them with a fullbridge for some really fierce output.

Hazmatt_(The Underdog)

Fri Aug 18 2006, 06:20PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

didn't someone sometime mention microwaving the transformers to separate the cores?

Marko

Fri Aug 18 2006, 06:28PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I doubt ferrite would get to several hundred deg to actually melt the epoxy, since it's a high frequency electromagnetic core afterall.

It would get heated from the former and windings, but I believe think it would be much better than hot air or water (??)

Somebody tried it..?

ragnar

Fri Aug 18 2006, 08:51PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

With the white epoxy, you generally need to butcher it with a screwdriver to 'crack' off all the blobs of glue around the join, then sand until the only glue left is actually between the ferrite halves. If you then boil the transformer for a bit, and use gloves (stinking hot) you should be able to lever the top out, but I've found it _essential_ that any forces are applied on the round centre axis, otherwise you of course snap the ferrite wings off.

If there are largeish (0.3mm+) spacers in there, you can also rest the ferrite such that everything but the spacer is supported, and then with a knife etc 'crack' it out sideways, but it's difficult to get enough force.

If you've done it enough, it becomes a science and whenever you see some good ferrite, you'll know what to do with it. =P

Marko

Fri Aug 18 2006, 09:19PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Epoxy ''around edges'' isn't the problem. Problem is that space betweent he core and former is completely fiilled with epoxy. It is impossible to soften that amount of epoxy by boiling, or physically remove it somehow.

Some transformers are much easier to get apart, smaller ones are cooked easily but ATX are really vain.

Self Defenestrate

Sat Aug 19 2006, 12:19AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I've had some luck with those ultra thin diamond dremel cut off disks, if you hold the core in something soft to ease the vibrations. Once the outside is done, I can usually boil and twist the cores apart. The inner rod part of the core is sanded a bit to flush everything up, and there you have it.

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