Efficient method for converting 230V AC (Germany) to 30V AC with only 5-10mA needed?

[tomizett]

If transformer A has more load it will try to pull more load from the power line causing it to have less voltage across its primary.
Two unequal loads in series (across a voltage source) will not divide equally. You likely will have too much voltage on one 15V output and not enough across the other.

Hi Ron - I see what you mean, but my thinking was that, with both secondaries in series, the currents would be equal and the load would split equally. In any event, if the secondary voltages added to 240V, the seondaries should add to 30V.

Maybe I would have been better expressing it as "running a 480V transformer at 240V".

I get the impression (I've no data to pove it) that these small transformers used in plug-in power supples, battery chargers, etc, have quite high losses even at low load. The one in my little battery charger get raging hot just charging a couple of AAs. My train of thought was that they may be run rather closer to saturation than we might like for optimum efficiency, in order to keep the size down.

However, as anyone who has read many of my posts will know, I'm no expert on magnetics...

<EDIT>
I see the cause of the confusion; I made a mistake in my original post. I meant to say two 240V to 30V transformers in series. Otherwise it makes no sense!

 

[ronsimpson]

I see what you mean, but my thinking was that, with both secondaries in series, the currents would be equal and the load would split equally. In any event, if the secondary voltages added to 240V, the seondaries should add to 30V.

I agree with the idea that (110 Primary-110 Primary in series and 15 Secondary - 15 Secondary in series) The 240 will make 30V. If the load do not equal then the center point will not be at the center.

Parallel primaries and series secondaries will work just fine.

have quite high losses even at low load.

The primary has a inductance. (even with the secondary removed) When attached there is some current that flows in the primary even with no load. This is some times called the magnetizing current. Remember this: Xl=2 * pi * L * F You can find the current by knowing the inductance and frequency and voltage.

Low cost transformers put less turns than normal and the inductance is too low, current is too high. But they saved two copper coins.
More wire will make this (unloaded current less).

If you found a transformer that runs cool with no load them use it.
I have big boxes of "wall worts" like phone charges. (made with switching power supplies) Two 15V supplies can be combined to make +/- 15V.

 

[raxon]

That looks like a capacitor power supply. I happen to need AC, however.
The image 2733 shows a capacitor labeled with 2.2µF and 275VAC. It looks like this is the one being attached to your 220VAC. This seems tight to me. Here in Europe (230-240V), you'd need one with 600VAC or more, unless you cut off/limit it otherwise. ;-)

 

[kubeek]

That looks like a capacitor power supply. I happen to need AC, however.
The image 2733 shows a capacitor labeled with 2.2µF and 275VAC. It looks like this is the one being attached to your 220VAC. This seems tight to me. Here in Europe (230-240V), you'd need one with 600VAC or more, unless you cut off/limit it otherwise. ;-)

Why? 240V is less than 275V, so I don´t see any reason to use higher rating than that.

 

[Nigel Goodwin]

Why? 240V is less than 275V, so I don´t see any reason to use higher rating than that.

I suspect he was quoting a DC figure, not an AC one - but the entire thread is a mystery, and we've no idea what he's trying to do and if he's doing it in the best way. I'm incredibly horrified at the idea of using a potential divider across the mains as a power supply

 

[raxon]

Why? 240V is less than 275V, so I don´t see any reason to use higher rating than that.

About the same question answered briefly: link => Voltage rating for capacitor in capacitive power supply
My bad. Your capacitor seems to be rated X2 and therefore should withstand 1500V impulses = you should be safe.

 

[tvtech]

Yip

About the same question answered briefly: link => Voltage rating for capacitor in capacitive power supply
My bad. Your capacitor seems to be rated X2 and therefore should withstand 1500V impulses = you should be safe.

Yip )

In tens of thousands of CRT repairs....maybe 4 failures from an X2.
And its not even part of the problem.

They tough and can handle everything you throw at them.

They always amazed me as an old tv tech

Sets come in...........TV totally knackered
Like a huge mains surge.

X2 is happy.
Rest of set blown up.

Love ya

 

[Nigel Goodwin]

Yip



Yip )

In tens of thousands of CRT repairs....maybe 4 failures from an X2.
And its not even part of the problem.

They tough and can handle everything you throw at them.

They always amazed me as an old tv tech

Sets come in...........TV totally knackered
Like a huge mains surge.

That's because you have crappy mains!

Same in Spain actually, we used to get quite a few Sky boxes sent back from Spain blown up by excessive mains voltage.

 

[tvtech]

Memorable morning with my friend when I tested Light Buddy....

We've 3 phase here.
So anyway.....

He knows im up to stuff. He says "leave it alone" . Im OK.
So he goes. I open the Spot Welder. Find a phase...

Get 380V.........turn on
Fluke watching
Temperature probe hugging the regulator.
Im waiting for BANG.

Nothing.

Im ......yeah ))))

So...did I did another run at 380V that evening for 5 mins.
Ive never like smiled a bigger grin before. I was )))))))))

................

Next morning im cocksure lol
He comes to work.
Im.....check this out

So its all set up.
3 runs at 380VAC for 5 Mins
2 minute wait between runs.

Its been 5 years now. Little Duris E3 are happy still. Been through 2 PP3 batteries though.

We tested the casing.......by chucking it and bouncing in on concrete here.
Played football with it. No breakages.

So, all i'm saying is X2 caps and proper design can yield amazing results.
5 years of 24/24 testing don't lie.

 

[gary350]

Variable transformer called, variac.

https://www.ebay.com/itm/Variac-Tra...128833&hash=item283f8d2c42:g:KQAAAOSw9N5bFpDO

 

[raxon]

I can see at least one safety issue with the capacitor power supply in the image 2733. The electrolytic capacitor above the main's capacitor can spill its (conductive) spunk on the platter, which then gets you in trouble. Those capacitors sometimes do nasty things like that.
Tom's Hardware has a series where they take apart cheap USB-chargers from China and such. Many are far worse than that. Those articles are funny, though in a morbid way.

 

[tvtech]

Cap is Rubycon YXF series quality. No problems so far.

BTW, this has always been a long term project. No corners cut.

If Osram or any other manufacturer bring out something better than the Duris E3.....the head can be changed to suit their product. The footprint per LED probably might change a bit. My boardhouse has the files and etc........

Simple to do without messing with the rest of the unit

3 of these babies have now being lighting where everything else fails in real life stuff.

Anyway, I wont bore you guys.

Love ya

 

[Diver300]

Variable transformer called, variac.

https://www.ebay.com/itm/Variac-Tra...128833&hash=item283f8d2c42:g:KQAAAOSw9N5bFpDO

Variacs aren't isolated, so there's not much point for the OP

 

[JonSea]

Since the OP hasn't answered any questions about his application, there's not much point in this entire thread.

 

[Nigel Goodwin]

Since the OP hasn't answered any questions about his application, there's not much point in this entire thread.

I fully agree, but the variac suggestion was particularly weird?

 

[raxon]

I've seen a variac in action once (studio equipment). They can best be described with these words: Vintage, incredibly expensive and huge.
However, I love the concept. It is simple and somewhat beautiful as that. Still, you will most likely find them in a museum.

 

[Nigel Goodwin]

I've seen a variac in action once (studio equipment). They can best be described with these words: Vintage, incredibly expensive and huge.
However, I love the concept. It is simple and somewhat beautiful as that. Still, you will most likely find them in a museum.

Standard item of equipment, in fact I used one today.

 

[Diver300]

Standard item of equipment, in fact I used one today.

Variacs are expensive, heavy and quite large, but not much heavier or larger than an isolation transformer of the same rating. Raxon may have seen a large one being used.

I agree with Nigel that they are a standard bit of equipment. Modern electronics may have reduced the number of applications where variacs are the best choice, but there are still plenty of places where they are an excellent solution. Variacs are still being made and Farnell and RS each sell over 50 different types.

 

[raxon]

Indeed. The one I saw ages ago had the size of two shoeboxes and went for the prize of half a car. I haven't seen one since, but I don't doubt there is a niche for them somewhere.

 

[Pommie]

Indeed. The one I saw ages ago had the size of two shoeboxes and went for the prize of half a car. I haven't seen one since, but I don't doubt there is a niche for them somewhere.

Not too expensive. Certainly not comparable to the price of a car. https://www.ebay.com.au/itm/Auto-Va...402378?hash=item41eab1e94a:g:wdwAAOSw0F9be9E-

Mike.