Why is this Toroid BUZZing and getting hot?

I've got a toroidal transformer wired up. I checked everything over carefully, and I can't figure out why it's buzzing and getting hot. I thought it might somehow be a shorted turn, so I even took the mounting screw out and just have it on the table, but it's still buzzing and getting hot (I unplug it immediately). It's one of them "mini" amveco's TE62022 (Datasheet here)
I have the primaries wired in parallel, and the secondaries in series with the center tap grounded.

Any ideas?

do you have more than one, and if so, do they both act the same way?

I've only gotten torroid buzz like that when I've had something hooked up wrong.

ju

What's the load on the transformer? Looks like that little guy can only handle 200 mA!

E.

No, I only have one. :sad:
I've checked over and over to make sure the Pri is in parallel, and the Sec in Series.

The Yellow and Red are going to one AC lug, the Black and Violet to the other AC. On the secondary side, the Red and Brown are connected together and grounded, and the output from the Blue and Green...although the blue is connected to a switch that has it disconnected from the circuit. So it's not connected to a load.

No fuse?

A quarter amp fuse would tell you if there's a short in the transformer.

What if you disconnect the center tap? Still buzz??

You might conceivably have the primaries wired in counter-parallel... double check the wire color sequence perhaps? -As a test with no significant load on the secondary, disconnect one of the primaries and see if things improve.

Keith

I disconnected the center tap to ground, and there's no buzz when it's floating. Why is that? I've been trying to experiment with different kinds of voltage multipliers and this particular one won't work without the CT referenced to ground.

But why would grounding it make it buzz?

It's not necessarily the grounding of the CT that is causing the buzz. The top winding (Green/Red) is still seeing a load, even when the bottom winding (Brown/Blue) is open circuit due to the switch, since the CT (Red/Brown) is grounded. There is still potential between Green & Red, and somehow the load that is connected (rectifier?) is drawing enough current during the positive peaks of the AC waveform that it's overloading the transformer. (??)

That's my shot-in-the-dark guess anyway.

Can you post a schematic?

As an experiment, I would say forget your multiplier circuit for a moment, and make a simple rectifier/filter/dummy-load that will draw near the rating of the transformer (200 mA) and see if the problem persists. That way, you can tell if there is an internal problem within the transformer.

Cheers,

E.

Thanks Electro...
Well here's a general schematic:



Just to summarize...
The transformer buzzes and gets hot with the center tap grounded and one side (the blue) of the secondary disconnected. Funny thing though, with the blue-secondary connected the buzzing dissappears but the transformer still rapidly gets hot. Floating the center tap, all problems go away, but then the doubler doesn't work. This is all without an actual load.

Any more idearrrrs?
Thanks a lot!

Are you using enormous capacitors? And there's really no load connected? My next guess would have been that the conduction angle was so small that the ripple current was huge, causing the transformer to freak out.

Maybe I don't know what the hell I'm talking about.

I just wondered why you are using the Caps in series with the transformer. What are you trying to achieve with this topology? Normally I'd just put the transformer wires straight to the bridge rectifier, or am I missing something?

martin

[quote author="martingriffith"]am I missing something?[/quote]

You are. The circuit is a voltage multiplier.

Peace,
Al.

I thought maybe it could be that the initial current surge was high enough to put strain on the transformer, but then shouldn't the heat go down after the caps are charged? That still wouldn't quite explain why the buzz when one side of the secondary is disconnected and the center tap grounded...

No One else has experienced this?

An initial current surge can make fuses blow, but it won't heat up anything. I haven't built a bridge doubler, but here's a set of schemo's for half, full, and bridge doublers.

http://cdharris.members.beeb.net/Voltage Doublers.pdf

One immediate difference I see is another pair of diodes. Where did you get the basic circuit?

-Jon

Ethan did you try Keith's suggestion yet?

Ethan's wiring matches the diagram on the datasheet, so unless the transformer was wired wrong from the manufacturer, the polarity should be correct.

Hey Ethan, did you try just a simple rectifier and 200 mA load to see if the transformer can indeed produce the rated voltage at the rated load without getting hot or buzzing?

-E.

That was what I was thinking---maybe the transformer color code is wrong. But then that wouldn't make sense with some of the other behavior.

That voltage multiplier example set is interesting. The so-called full wave bridge doubler with the two extra diodes is something I'd never seen before. In that respect Ethan's is the standard circuit, essentially two half wave doublers, one from each side of the center tap with the outputs tied together. It's been used widely and successfully.

It's always bothered me that the initial transient has a 50-50 chance of reverse-biasing one of the electrolytics. But that event is over in a hurry.

Hey Ethan, did you try just a simple rectifier and 200 mA load to see if the transformer can indeed produce the rated voltage at the rated load without getting hot or buzzing?

Click to expand...

Yes, but it still gets hot (when the center tap is grounded). I can't leave it on for more than about 4 seconds before the heat starts to worry me.

Do you think I would sound like too much of an idiot if I explained the problem to the applications engineer at amveco?

What happens if you remove the two diodes on the right hand side of your schematic. Does it still heat?

[quote author="Ethan"]Do you think I would sound like too much of an idiot if I explained the problem to the applications engineer at amveco?[/quote]

Bah... Who cares? They don't know you!

The datasheet boasts "low temperature rise" -- I say call the dude.

The sheet says it should change by 29°C, which is 84°F, which is 155° operating temperature when added to room temperature. You got a thermometer?