Hands off! ..or is it just different in the US

[pacificblue]

Coming from here. SoIL4x4 uses an Antek AN-3222. Here is what the webshop tells about it.



And this is from the datasheet.



I uploaded both today.

What am I refering to? The webshop offers a 300 VA transformer with
2x22 V, 2x6,8 A secondaries for 2x115 V primary voltage.

If I bought a transformer with those specs in Germany, that would mean when I connect 115 V to both primaries, and load the transformer with 6,8 A on the secondaries, I can expect 22 V there leading to 300 VA output.

120 V on the primaries should lead to 23 V at 6,8 A and to 24,5-25 V at open circuit. The load test shows 21,1 V at 6,55 A (276 VA) and 22,3 V at open circuit.

Are transformer specs OR correlated in the US?
If you want nominal voltage, you can't have any current?
If you want nominal current, you can't have nominal voltage?
Nominal power is what goes in and not what comes out?

Or is Antek cheating with its webshop specs and the customer should read the datasheet instead?

Why is the load test not done at nominal secondary current?
Why is it done at higher than nominal primary voltage?

[KatieandDad]

22 x 6.8 x 2 = 300VA with my calculator.

This is its nominal output.

At full load you have 276W as quoted in the datasheet, this is down to copper and iron losses in the transformer. The remainder will be heating it up.

It would be foolhardy to operate the transformer continually at its maximum rated output, if you need 22V at 6.8A - CONTINUOUSLY - then I would opt for a 500VA transformer.

[pacificblue]

Originally Posted by KatieandDad

22 x 6.8 x 2 = 300VA with my calculator.

According to mine too.

Originally Posted by KatieandDad

This is its nominal output.

It obviously isn't for the Antek. The voltage drops to 21,1 V before even reaching the nominal 6,8 A and that is with higher primary voltage than specified.

Originally Posted by KatieandDad

At full load you have 276W as quoted in the datasheet, this is down to copper and iron losses in the transformer. The remainder will be heating it up.

And that's the question. Here in Germany, and as far as I know all over Europe, the nominal power is the available output power. Is it different in the US? Or is it just different for Antek?

Originally Posted by KatieandDad

It would be foolhardy to operate the transformer continually at its maximum rated output, if you need 22V at 6.8A - CONTINUOUSLY - then I would opt for a 500VA transformer.

And if I would not operate it continuously at rated output, but would still need the rated current at rated voltage every now and then? Could I buy such a transformer in the US - if it was not from Antek - the same way as here in Europe, by simply relying on the nominal specs? Or would I have to read the datasheet, derive the voltage drop from there, adjust the values to the nominal input voltage and leaf through the entire catalogue until I find the right transformer for me?
It seems that if I want 22 V at any current other than 0 A from Antek, I would have to buy at least a nominal 24 V transformer.

[KatieandDad]

The first comparable UK 300VA transformer that I have looked at has load regulation of 8%, this would equate to the loss that you are looking at at FULL power.

http://uk.rs-online.com/web/p/toroid...rmers/2575203/

If you read the spec closely, it does say that you could - although not recommended - pull 20% more load than the transformer is rated for.

The core is thus conservatively rated at 300VA and the specs just show the effects of regulation at full load.

So at 21V you could pull 300/21 = 14.28A or 7A per secondary. (However the voltage will drop a little due to the extra load)

[AndrewT]

Antek specify how they measure their transformers.

There is no deception.

But Antek's method is unlike any other manufacturer/retailer I have read.

As far as I can determine the rated (output) VA is determined from the rated output voltage while delivering the rated output current/s when fed with the rated input voltage.
Antek does not use this method.

[KatieandDad]

NO transformer is going to give you a regulated supply.

ALL will droop as their load current increases.

All you can do is massively overspecify the transformer so that the 8% load regulation occurs well outside where you are intending to operate the transformer.

400% is a regular over estimation for Class A operation. ie If you need 300VA then use a 1200VA transformer.

In practice though this is usually unneccessary. 500VA should be fine.

In Class A/B or above (Classes B, D, T and all the fancy digital variants) just be careful that the low load current doesn't cause the voltage to increase above the maximum voltage of the circuit.

[pacificblue]

Originally Posted by KatieandDad

NO transformer is going to give you a regulated supply.

ALL will droop as their load current increases.

No need to repeat the obvious and yell at me. The question is whether the way Antek specifies their transformers is typical for all US transformer manufacturers or not?

When I buy a transformer from a European source the nominal voltage is the voltage at nominal current. The no-load voltage is higher than the nominal voltage. The nominal rated power is nominal voltage multiplied by nominal current. Nominal rated power and actual rated power are identical.

When I buy an Antek transformer even the no-load voltage is lower than the nominal voltage, because it is given at higher than nominal input voltage. The relationship between nominal rated power and actual rated power is not obvious at first glance. It takes reading the datasheet and calculating to determine the actual rated power.

If the Antek was rated according to European standards it would be a 2x20 V 272 VA transformer instead of 2x22 V 300 VA.

Do other US manufacturers spec their transformers like Antek or like Europeans?

Originally Posted by AndrewT

Antek specify how they measure their transformers.

There is no deception.

It may not be deception from a legal point of view, because they link to the datasheet where they put things into context. But it is at least creating a wrong impression, and I bet many customers buy that thing relying on the webshop specs and thinking they made a bargain.

[SoNic_real_one]

Originally Posted by pacificblue

When I buy a transformer from a European source the nominal voltage is the voltage at nominal current. The no-load voltage is higher than the nominal voltage.

So you prefer to fry your capacitors because you didn't know how high the no-load voltage is? You don't pay the transformer per voltage, so there is no "deception" or "bargain" here.
You pay by the power (higher is more expensive) and short-circuit impedance (lower is more expensive), so it would be a deception if they say is capable of 100W and in reality is capable only of 50W or if the impedance on label was 5% and measured is 10%.
I doubt that European manufacturers give the "nominal load" voltage on label - when I was working there, the label voltage was the same no-load voltage.

PS: In the professional world of power distribution you have as specs the no-load voltge and short-circuit percentage (that is the internal impedance).
With both of those you can derive the output voltage at any load (voltage regulation). That percentage alone will tell how stable will be the voltage (lower is better).
In the first post example, the short-circuit impedance is 6.2V/115V=5.4% That is very good, usually for that kind of transformers you have 10 or even 20%...

[6L6]

Originally Posted by pacificblue

Or is Antek cheating with its webshop specs and the customer should read the datasheet instead?

There's the answer. You should always read the datasheet.

I guess it really comes down to exactly what your needs are, and that there are probably no established testing criteria for transformers in the US. The good thing is that Antek does give you the criteria that they use, as well as some data-points. Other manufacturers give a vague 'load regulation' expressed in percentage of loss. What that loss is, (current or voltage) isn't said.

As someone said, all transformers will sag the voltage under load, so how stiff you need the transformer to be will determine how oversized you should buy. Also, (as previously mentioned) do consider your no-load voltages.

Nelson Pass uses Antek transformers in the FirstWatt stuff now, and plenty of people have used them with great success in DIY projects. I personally have used 4 and have 2 more on order.

They are a good product, and they give enough information on the website so that the consumer can make a good and proper choice.

[pacificblue]

Originally Posted by SoNic_real_one

You don't pay the transformer per voltage, so there is no "deception" or "bargain" here.

No, but I decide for a voltage and expect to get what I order. A transformer that doesn't even reach the nominal voltage at open circuit is a deception.

Originally Posted by SoNic_real_one

You pay by the power (higher is more expensive) and short-circuit impedance (lower is more expensive), so it would be a deception if they say is capable of 100W and in reality is capable only of 50W or if the impedance on label was 5% and measured is 10%.

So selling a 272 VA transformer as 300 VA is...?

Originally Posted by SoNic_real_one

I doubt that European manufacturers give the "nominal load" voltage on label - when I was working there, the label voltage was the same no-load voltage.

I don't know when and where you worked here, but I can assure you that the nominal voltage is the voltage at nominal current. The reason is quite simple. Imagine you have to feed a group of electrical valves that need 24 VAC. Depending on how many of those valves are switched on the voltage sags. If all valves are on, the voltage must still be 24 VAC or higher, because if it is not, the valves may not reach their desired state properly and only be partly open when they should be fully open or be partly closed when they should be fully closed. Having to calculate the voltage sag first, then having to subtract it from the no-load voltage, which again must first be derived from a primary test voltage that is not identical to the nominal voltage is not an acceptable way of working.

Originally Posted by SoNic_real_one

PS: In the professional world of power distribution you have as specs the no-load voltge and short-circuit percentage (that is the internal impedance).

You cannot imagine how much I wish all manufacturers shared your opinion.

Originally Posted by 6L6

there are probably no established testing criteria for transformers in the US.

Are there or aren't there?

Originally Posted by 6L6

Nelson Pass uses Antek transformers in the FirstWatt stuff now, and plenty of people have used them with great success in DIY projects. I personally have used 4 and have 2 more on order.

I don't doubt that they serve their purpose. All I want to know is whether their way of specifying the technical data of transformers is normal in the US.