About amps transformer rewinding ?

[BGAmodz]

I have talked to a guy lately , he said that these transformers are not rewindable .

Can i manually rewind this transformer ?

**broken link removed**

 

[kubeek]

That is a high frequency transformer from a SMPS, and I doubt you will be able to separate the core and keep it intact. Nevertheless, why would you want to rewind it?

 

[BGAmodz]

Hi kubeek .

Its because i cant find a new one on sell locally .

 

[Nigel Goodwin]

As kubeek said, it looks pretty well glued together, unlikely you could split it without breaking it.

But assuming you can take it apart without breaking it, of course you can rewind it.

 

[BGAmodz]

It is well glued unfortunately , and i notice that unlike linear transformers , these use a special type of metal .

 

[Nigel Goodwin]

It is well glued unfortunately , and i notice that unlike linear transformers , these use a special type of metal .

It's not 'metal'

It's usually ferrite, a kind of metal 'dust' bonded together.

 

[BGAmodz]

I guess the ferrite pieces are glued with epoxy , can a heat gun help separate them easily ?

 

[tomizett]

I remember seeing someone posting about a technique to sepparate transformers with glued cores - I think it was on this forum somewhere, but can't think what the title might have been.
They'd posted pictures, and it involved a lightbulb, but personally I couldn't quite work out what they where doing...

On the other hand, I've re-wound transformers like that just by feeding the wires through the gap between the bobbin and the core. It's a tedeous job, but they usually don't have many turns.

If you're doing it for a personal hobby project, then I'd recomend giving that a go, but if it's a comercial repair then do ensure that you can do it safely before you go ahead.
The tape used to insulate the windings, I believe, is Mylar (correct me if I'm wrong). You'll almost definately need to replace this, and I've yet to find anywhere to get it here in the UK.

(asside: it's struck me that PTFE pipe tape would make a nice inter-winding insulator - any thoughts?)

I believe that some ferrites can have their magnetic properties perminantly changed by getting too hot. I doubt this applies to power transformer cores, but I'm sure someone else here will know better than I do.

Oh, and at the risk of stating the obvious, if it's a repair, then do make sure that it's actually the transformer that's failed (it's pretty unlikely) *before* you wreck it trying to re-wind it. Perhaps it has a thermal trip inside it (never seen one in a HF transformer, but there's always a first time).

 

[BGAmodz]

Hi tomi .

The thermal trip is good , and the unit containing it gives an over-current led signal , i have removed the thermal trip and started the unit briefly , and found that this transformer is getting so hot , also when i disconnect its primaries the led signal goes off .
I am thinking about getting a new one to avoid any further damage.

 

[dr pepper]

I have salvaged these and reused them.
If you heat the glued areas with a soldering iron and a hot air tip for a gas solder iron you can usually get the glue to soften nd release, sometimes the inner core is glued which makes things tricky.
If you break the core you can superglue it, it doesnt seem to change the properties much.
As mentioned if you heat the core too much and go past the curie point its properties will be ruined, but thats hard to do, the coil former would certainly melt first.
Keep the tape and reuse it, or salvage another trans.

 

[mbarazeen]

It can be rewound without any issue, even if you got the core broken it can be reused by avoiding airgap and get them taped together. One important thing to mind is about polarity of the windings. you should wind it exactly as it was in directions and terminate to right points.

 

[ronsimpson]

I have salvaged these and reused them.
If you heat the glued areas with a soldering iron and a hot air tip for a gas solder iron you can usually get the glue to soften nd release, sometimes the inner core is glued which makes things tricky.
If you break the core you can superglue it, it doesnt seem to change the properties much.
As mentioned if you heat the core too much and go past the curie point its properties will be ruined, but thats hard to do, the coil former would certainly melt first.
Keep the tape and reuse it, or salvage another trans.

You can also heat the transformer in a toaster oven. This way the heat is more even and controlled.

 

[tvtech]

Chopper transformers.....

If I had to write a book about the failures I have had with them in the last 25 Years or so....it would look like this:

Blank page. Book non existent. Seriously.

I have seen Choppers catch alight. I have seen them with pins that are burnt off due to continuous arcing. I have seen them go through hell...

Not the Choppers fault....dry joints and arcing on the PCB. That is why a Chopper normally fails. In my experience.

I thought I would just throw this out there.

Regards,
tvtech

 

[Nigel Goodwin]

I've replaced many chopper transformers over the years - but it is fairly rare, and it's only certain specific models where they do fail. It's VERY, VERY rare to get a 'one off' failure - if you come across a transformer failure in a particular unit, it's most likely you're going to get lot's of those units in with the same fault.

Faults I've seen include O/C windings, shorted turns, and even shorts from primary to secondary

From what I can remember we used to stock 3 or 4 different chopper transformers?, so that was the sort of number of common model failures we saw here in the UK.

 

[tvtech]

I've replaced many chopper transformers over the years - but it is fairly rare, and it's only certain specific models where they do fail. It's VERY, VERY rare to get a 'one off' failure - if you come across a transformer failure in a particular unit, it's most likely you're going to get lot's of those units in with the same fault.

Faults I've seen include O/C windings, shorted turns, and even shorts from primary to secondary

From what I can remember we used to stock 3 or 4 different chopper transformers?, so that was the sort of number of common model failures we saw here in the UK.

Thanks Nigel

When I go Technical and all, you are always there to guide me and talk. Pretty cool stuff that people can actually learn from
Like we spar and discuss and joke and correct each other. We know our stuff. That is why we respect each other (hopefully)

Pretty good. I think.

I need to spend more time on Technical stuff though. Time is the killer though.

All the best,
tvtech

 

[throbscottle]

WRT tape - I bought some yellow transformer tape off eBay a while ago. Cheap enough.

 

[BGAmodz]

In deed , i rarely find bad transformers on the units i repair be it on welders , PSUs, usually its either shorted power transistors , PWM ic or startup resistors .

 

[tvtech]

In deed , i rarely find bad transformers on the units i repair be it on welders , PSUs, usually its either shorted power transistors , PWM ic or startup resistors .

Good call BGAmodz

Rep for you. Cause I can and you learned something.

Regards,
tvtech

 

[BGAmodz]

Good call BGAmodz

Rep for you. Cause I can and you learned something.

Regards,
tvtech

Lol i still have a CRT scope to deal with , am just too lazy to get into it , those are friggin hard to even disassemble .

 

[dr pepper]

Observe corect winding polarity?, surely there is no way of knowing on a salvaged trans which end of the winding is which + or -.