Small low voltage transformers

What are your actual figures? What does the manufacturer's spec say about efficiency & regulation? If you got it off Stinky Pete, I'm not too surprised it's not behaving too well .

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Weeeeeeell, that's the prob, we have a regular supplier (in Malta)... I just asked for 0-115 0-115 primary 0-24 0-24 secondary 6VA _{no mention of regulation or efficiency baaad kitty.}
We use a similar 6va from him which is fine, so I didn't give it much thought.
It's the split primary which is possibly the prob, our other transformers are just 240v primary. It's all this Eurononsense bah humbug.

I had a sample which was ok, I asked him to take a volt of each secondary...then we got a batch of 100 which I suspect are the same as the original sample.
The load isn't well defined or consistent either as it may well drive various peristaltic pump configurations into a variety of back pressures.
It's ok...I'd just expect something a tad better, but I s'pose you get what you pay for. I'll bet BAE could get me a loverly transformer for a few hundred a throw
Del

Don't acherly see why the split primary should make much odds - is it one of those black magic things that only members of the Ancient Order of Winders know about?

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I just mean, 115+115=230, maybe running at 240 doesn't help.
Maybe I should have spec'd it 1-120 0-120 ?
I shall tweak it for the next batch (even if it screws up my pump delivery software fudges calculations)
Del

Wouldn't've thought the odd 4 - 5% would've made that much diff ?

Was it just me, or did CR4 die for about 25mins?

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I may be talking out of my nether regions, but I'm a tad confused by the way the stack of lams on transformers seem to be held together with a line of weld going across 'em. I thought this was a recipe for eddy currents, excess heat etc, but it seems to be the norm these days.
Any one care to enlighten me?
Del

I have a Power T with 2 wide strips of copper across the Lams for eddy currents.

In the past I've specified and designed my transformers for Marconi, where I worked.

The small cheap transformers save on laminations (quality as well as quantity) they will use a high current density in the windings etc... All to save money.

Trouble is they will run hot even with no load due to the losses.... In the 90's I had to design a transformer for a medical instrument, I told the winding company to F**k the cost, double the laminations c.s.a and to use a very low current density in the wires....

Boy!!! did I get a BIG transformer,,,, but I wasn't concerned about size (who is?) For that medical purpose it had to run cool and have a long life...

With no load the transformer was hardly warm, even at full load it was just warm...

So saving money causes lots of power wastage to heat up transformers....

Thanks... (GA...maybe we need a GQ category too?)
This tx is running at about 47 deg C it's been doing a bit of pumping as I'm running tests.
It's not a real prob, but it's smellier than my food bowl on a hot summer's day.
I'm pretty much stuck with the 100 batch I've got here, but I'll re-specify it for the next batch. I'll have some decent test data to go on by then.

I'd feel happier dealing with someone I could go and talk to in UK...although maybe a trip to Malta in December would be nice (as if...)
Del

(PS I don't get the c.s.a wassat mean eh? eh? eh?)

Yes, that's what I liked about working at Marconi's.... You could just walk to a different department and find a little old wrinkled gentleman in a corner who knew everything about transformers!!!!

There was always someone who knew someone to ask about any queries, I guess that's why I stayed there for so long, well, 8 years anyway....

John

Yes....and c.s.a?
I know it's tease Del week with my fluctuating GAs..198,199,200,198,199 _<sigh>
Del

Is it possible that you are linking the wrong 115 to 115 connections for 230 volts and they are "working against" each other? Maybe they connected one primary wrongly.

The same possibly goes for the secondaries if you pair them up together....

You need to apply a very low voltage AC across one of the secondary connections and look at the outputs of the primaries to see the phasing. I would use a dual beam scope with one channel on one output and the other on the other.

NOTE:-

Put both 'scope channels on ONE and the same output first just to make sure that everything is exactly equal and in phase......before comparing the other primary.....some scopes you can reverse a signal etc etc....and that would give the wrong indication.

The resulting waveforms must be exactly in phase with each other and exactly the same voltage.....if one is low or high.....another problem....

Is it possible that you ...
No
But thanks for the thought...
Del

You would have had a veryyyy warm transformer with 115 volt windings connected wrong way

I have run plenty of transformers with dual 115 prim on 240 without any problems, however did you compare the laminations csa with the other 6Va transformer which worked well?

If the transformer is designed for 60 Hz and connected to 50 Hz it will run much hotter.

Check with no load connected

schorschimi

Why would a manufacturer in Malta supply a customer in the UK with 60Hz trannies?

I've taken loads of measurements and decided I was..
a) being greeding, hoping to get the transformer to run two pumps.
b) Didn't spec it for the right output voltage, because I didn't have the necessary parts available to conduct the correct tests.

It turns out my 'normal' load is actually lower than I anticipated and the required output is a tad lower.

So my revised spec will be two 11v AC (into 150R each) normal load. Max load is into 75R each output. This represents one pump instead of two.
Interestingly, the existing transformer gets upto about 46 degrees C with no load at all... I shall ask that it remain below..err...I dunno...40? 35 ? any offers.
Ta for the input on this guys.
Del

46*C..!!!!!

The transformer laminations must be driving into saturation for that temperature.... The I^2 R losses must be phenominal....

Think of how much power is being used to generate that heat - all wasted!!!