Bad transformers

Looks like both transformers are saturating, with current limited by a lot of copper resistance.

These may be designed to be (class II?) impedance-limited transformers, capable of surviving a shorted load forever. Or maybe they are just total crap.

John

It is specified for a 70C ambient. With a 75C rise measured on the outside that means 145C. The insulation is specified up to 130C. The winding must have a higher temperature than I am measuring on the case.

So basic math says it's crap.

I wouldn't want to seem to be putting words in your mouth, but these transformers could be total crap.

What's the primary DCR? Does that correspond to the flat-top current you're seeing?

John

Original link updated

Looks well saturated but I'm not sure what manufacturers normally try and get way with.

On a sunny day (Fri, 23 Oct 2009 16:48:48 +0100) it happened Raveninghorde wrote in :

It is a bad transformer, probably bad iron, or damaged iron (shorted sections), send it back... No energy star, or a falling energy star :-)

You don't include a pic of the transformer, but assume that it's one of those potted flat pack pcb mount types with half the primary and half the secondary on each leg of a rectangular core ?. Most likely internal shorted turns or not enough primary turns. Magging current is far too high, as is the temperature. Might help to check the magging current on each primary half in turn with 115v...

Otherwise, bad transformer or batch...

Regards,

Chris

That's the type.

I thought about the problem driving home. Clairtronic transformers were failure prone and made in Malta. This type is also clearly crap.

My guess is that it is the harmonization of mains supply across Europe. I'm sure you know but for the benfit of our colonial cousins I'll explain. Europe aka foreigners over the channel were on 220V supply. Good old blighty was on 240V supply. This has been harmonised to 230V across the EU. As far as I am aware no one has actually changed their voltage. I certainly measure around 240V out of the wall.

My guess is these nominal 230V transformers which should cope with the variations across the EU are still actually 220V and can't cope with real electricity.

I will specify UK manufactured, not UK supplied, transformers in future. A secondary voltage that turns out too low is better than a primary that burns out.

On a sunny day (Fri, 23 Oct 2009 19:49:53 +0100) it happened Raveninghorde wrote in :

Bull, Netherlands, I measure 230 exactly. But UK alway was weird, no hope for them. And that was many many years ago (220-240 issue).

Does UK manufacture stuff like this any more? Most of the magnetics we buy, even the USA-designed custom stuff, is made in China or India. Some of the really big iron is still made in USA.

John

used to be 220V +10%/-10%, then it was changed to

-Lasse

Fire your buyer.

Cheers! Rich

Can't afford the divorce :)

That's the theory. I don't see a change to 230V nominal here.

Here it is ... *BAM* ... zero volts. Whoops, was on amps.

Yeah, I thought I heard something from the east, just after the lights blinked.

John

After looking at your cac-ku-lations

Seeing that you state your PRI to be 400 Ohms DC R, something tells me you may have the PRI wired incorrectly? Assuming that these xformers may have a dual PRI, so that one could config for 120/240..

Just something smells fishy..

WAS, now infinite..

"Raveninghorde"

With primary R = 400 ohms and I mag = 57mA, the off load copper loss = 1.3 watts.

This is a *normal* value for such a transformer rated at 10VA.

There will be some iron loss as well, but less than 1 watt with a tranny that weighs only 295 gms.

Your claimed 96C surface temp figure seems too high for the numbers YOU quote.

The thing to measure is the rise in primary R after a hour or so - from this you can easily compute the actual primary temp.

.... Phil