How to glue ferrite transformer cores? - Page 1
Forum section: electronics / repair

author: compet17
author_rank: Regular Contributor
timestamp: October 21, 2014, 01:34:08 pm
content: I have here a big SUN M4000 server with a defective 2100W power supply. This power supply failed in a rather unusual way.... the main transformer core did split in half!!It is a SMPS transformer with a ferrite EE-core. Normally the two "E" halfes are glued together to for a complete core. In this case the glue did not work and the E cores separated, making the P.S. fail.My question is what kind of glue can be used to repair this? I think of some silicone stuff because temperatures could be high inside that core. On the other way the air gap should be as small as possible, so I would need a low viscosity glue like super glue.Does someone know what glue is used in the industry to assemble ferrtite cores of high power transformers??Chris

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2014, 01:44:24 pm
content: Varnish. And there's supposed to be tape holding them together, besides... (Mylar or Kapton tapes are typical.)Epoxy or superglue is a good alternative, but beware (especially with superglue and other cyanoacrylates) they loosen at high temperatures, as varnish does too. If it's overheating, you have bigger problems than just the core falling out.Tim

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2014, 05:21:30 pm
content: Varnish, and a strong tape to hold the core together, or a set of clips or a pair of bolts and a strap.

author: Neilm
author_rank: Super Contributor
timestamp: October 21, 2014, 06:10:38 pm
content: You can not ensure that you will get everything back in there, so your air gap will increase. That could cause all sorts of problems. I would first ask what caused it to crack? Was it dropped?Personally, I would see it I could get the ferrite and just replace it.

author: compet17
author_rank: Regular Contributor
timestamp: October 22, 2014, 11:20:04 am
content: Replacing the ferrite does not solve the problem. Firstly, the ferrite halfes are not cracked, the just separated where they were glued together. Secondly, new ferrites have to be glued together too.I used some two-component araldite and made a large Ty-Rap around the cores to hold them together in case the glue softens.

author: mazurov
author_rank: Frequent Contributor
timestamp: October 22, 2014, 03:55:11 pm
content: Ordinary hardware store epoxy works well. Make sure you clamp the core well while gluing. If you have space consider using a spring clamp instead of glue to hold core halves together.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: October 25, 2014, 02:49:16 am
content: If you have a welder, you could just put a tack on each side and see if that's good enough.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 25, 2014, 03:12:48 am
content: Yeah, but make sure you preheat, use nickel rods, and peen the welds... even so, they'll probably still crackTim

author: tautech
author_rank: Super Contributor
timestamp: October 25, 2014, 07:19:10 am
content: Quote from: compet17 on October 22, 2014, 11:20:04 amThat should work perfectly.Often I will just use a cable tie(Ty-Rap) in prototypes in case I need to modify the transformer or even scrap it for something else.But your repair for a otherwise perfect transformer from a PSU that has no other issues and is of good design is the correct permanent fix IMO.

author: compet17
author_rank: Regular Contributor
timestamp: January 02, 2015, 11:59:24 am
content: Welding ferrite cores?? Are you joking?

author: SeanB
author_rank: Super Contributor
timestamp: January 02, 2015, 12:17:16 pm
content: Yes he is, but just using the epoxy resin and tie wrap works well. As to the original overheating it is possible that a failed fan ( or a failed speed control on variable speed fan) caused it to get hot enough from load to soften the original varnish. Check fan airflow as well, dust jungles will kill power supplies fast. I have opened some where you could not find the components under the dust fluff. There are websites which showcase this, but at the moment I cannot remember where, if you want the horror just google dirty computer images.

author: compet17
author_rank: Regular Contributor
timestamp: January 02, 2015, 12:37:24 pm
content: Update:The PSU runs perfectly with the epoxy/ty-rap repair solution.Did I write something about overheating? No problems with that! I think the ferrite core has separated because of a mechanical shock, maybe someone has dropped the PSU a bit too hard.I just was worried that the transormer core itself could get too hot and the epoxy could get soft. But with the ty-rap... no problem.

author: Richard Head
author_rank: Frequent Contributor
timestamp: January 02, 2015, 06:47:13 pm
content: I have manufactured literally thousands of switchmode power supplies with just polyester tape and no glue whatsoever. I have had returns from time to time, but not due to separated core halves. For higher temp applications I've used polyimide tape but it's probably not necessary.Also, the cores will tend to attract each other during operation. I think certain manufacturers use glue to avoid using the pricey metal clips (such as used on ETD cores and others).If the PSU uses current mode control then the power switches shouldn't fail as soon as the core halves separate as the pulse will be terminated as soon as the primary current exceeds the maximum allowable. Voltage mode converters will die immediately.

author: compet17
author_rank: Regular Contributor
timestamp: January 04, 2015, 01:58:08 pm
content: Obviously it did not die when the core seperated. Thanks for the info...."Separate the Warp Core from the ship!" "Aye Captain... core is separated"Sorry I couldn't resist