I received a used toroidal transformer but it was faulty.
It isn't a very expensive one. A dual 9V secondary from Farnells.
It is pre 1995 judging by the phone number on the sticker.
I have removed the tape and discovered a broken winding.
when I test for continuity, I get continuity from one end of the broken wire to blue and the other end to brown. (brown and blue being 240V primary)
I have continuity between both of the secondary wires and no shorts from one secondary to another.
(sorry that I am probably using the wrong words)
Nor any continuity between either primary cable and any of the secondaries.
I am aware that there might be other issues, but that bodes well right?
It wasn't packed all that well unfortunately.
But it seems like I have just the one breakage on the winding.
Is it safe/sensible/effective to effect a repair?
Or is this a supply of enamelled wire?
Thank you.
If you re connect the broken tail and insulate your soldered join then wrap the coil with tape, I see no reason to not use it again.
Without a Megger, it is difficult to test the insulation accurately.
Without a Megger, it is difficult to test the insulation accurately.
Thanks. That is what I thought, but often I think that and discover that it is much more complicated 🙂 .
Does it matter what I use to join the two ends? They don't quite reach.
Also, is a bit of electrical tape sufficient? Under and over.
Or do I need to think different?
Does it matter what I use to join the two ends? They don't quite reach.
Also, is a bit of electrical tape sufficient? Under and over.
Or do I need to think different?
Since the mechanically damaged wind is an outside wind, maybe you can unwind 1 turn (which won´t affect transformer at all) and now you have enough extra wire to burn and scrape enamelled wire ends, twist, solder and insulate them.
Then plug transformer primary into a series lamp bulb limiter with a smallish bulb, say 25W, and check it does not glow bright, but dull red at most.
You need a filament bulb, not a modern LED/CFL/etc.
Then plug transformer primary into a series lamp bulb limiter with a smallish bulb, say 25W, and check it does not glow bright, but dull red at most.
You need a filament bulb, not a modern LED/CFL/etc.
If you are going to ”remove one turn” and it’s a bifilar secondary - the usual for these toroids - do the same to both. If you ever run with the secondaries paralleled they need the same number of turns. A mismatch in the number of turns between two parallel windings will result in increased idling current draw.
I would personally unwrap both to where the break is, then repair. Heat-shrink wrap the joint. Then rewind the turns and re-tape. If it’s one turn short so be it. Dim-bulb test it, of course. Then make sure you use a proper primary fuse on whatever you power with this - in case there is more damage you can’t detect yet. Broken wires happen for two reasons - overload or mishandling. If it has been dropped or something, you may have a short waiting to happen. May fail in a month, maybe never. I’d want a fuse if it does.
I would personally unwrap both to where the break is, then repair. Heat-shrink wrap the joint. Then rewind the turns and re-tape. If it’s one turn short so be it. Dim-bulb test it, of course. Then make sure you use a proper primary fuse on whatever you power with this - in case there is more damage you can’t detect yet. Broken wires happen for two reasons - overload or mishandling. If it has been dropped or something, you may have a short waiting to happen. May fail in a month, maybe never. I’d want a fuse if it does.
Thanks for the information and advice.
But the break is in the primary isn't it?
I have continuity from the break to the brown and blue.
So the above is not relevant, correct?
Obviously the bulb test is still relevant, as is the fuse.
It is a good point about it being damaged.
It was posted to me. It wasn't particularly well packed.
It looks like there was a bit of a ding in the damaged area.
It is a good point about it being damaged.
It was posted to me. It wasn't particularly well packed.
It looks like there was a bit of a ding in the damaged area.
My advice...
I wouldn't use it in anything that was going to be put into routine use, it's not really reliable. On the other hand it could be used for a piece of test gear or something, like a simple bench supply maybe.
Mike
I wouldn't use it in anything that was going to be put into routine use, it's not really reliable. On the other hand it could be used for a piece of test gear or something, like a simple bench supply maybe.
Mike
Yes.
Clearly there was an impact against some hard sharp object.
One wire broke, those behind it must have certainly bent or even dinged ... just didn´t actually break buy may be compromised.
As suggested, I would not "send it away" to an uncontrolled place (customer´s home) but keep it near, "just in case".
Clearly there was an impact against some hard sharp object.
One wire broke, those behind it must have certainly bent or even dinged ... just didn´t actually break buy may be compromised.
As suggested, I would not "send it away" to an uncontrolled place (customer´s home) but keep it near, "just in case".
Thanks Mike,
I think I shall heed your advice.
I hadn't thought about it having other currently undetectable damage.