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Transformer's primary winding power consumption

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RETFIE

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Hello, can somebody give me advice how to calculate the power consumption of the transformer's primary choke, when no load is applied to secondary winding please?

My transformer parameters are:

primary winding voltage rate = 230V
primary choke impedance = 2000 Ohms

I just know only abut this formula P = V * I * cos(phi) but this is probably unusable for me.

Many thanks.
 
The current taken by the primary is entirely dependent on the saturation of the core.
The DC resistance of a 500VA transformer is about 50 ohms and yet the transformer consumes only about 5 watts when no load is applied to the secondary.
However if and air gap is introduced to the magnetic circuit, by placing a few sheets of paper between the ends of the E's where they touch the I's, the quiescent current will increase considerably.
There is absolutely no way of working out the "no load current." You have to build a transformer and measure it.
 
A quick and dirty way is to plug it in, unloaded, and leave it for 24Hrs. Come back and put your hand on it. If it is very hot, then it is wasting ~20W. If it is just warm to the touch, then it is wasting only ~2W. If you can barely detect any warmth, then it has a very small excitation current.
 
Hello there,


Actually, the way this is estimated in practice is the Watts Per Pound vs Excitation curve is examined for the level of B used for the transformer. That curve gives the wattage for every pound of core material used in the design and for that particular level of B. Obviously you have to have the curve for your particular type of core material or can find it online to do it this way. You then calculate B for the design and then read off the curve the watts and multiply that by the weight in pounds and that gives you the estimated no load power consumption.
 
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Power = V squared/R = (230x230)/2000 = 3.45W
That give 3.45 volt-amps, not the power since the choke impedance is reactive, not resistive.
 
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Thanks to everybody for each respond.

I see that the best way for me will be to buy transformer which I need for first, and than measure it.

Best regards.
 
True. I once worked in a place that wound transformers and just out of curiosity, I measured "idle current" with no load. I think the measurement was about 50 milliamps. Then I added 20 turns to the primary and the idle current went down to 10 or 15 milliamps. The moral of the story is: You can't calculate the idle current. You have to pick a transformer and measure it.
 
Hello again,


Actually, there are curves for that too. "Exciting Volt Amperes per pound vs flux density" would be the curve to look for. Obviously you have to have the data on the core material for this too.
 
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This I gotta see.

The laminations are grain oriented silicon steel from 1976.
The core is called EI 138
The stack height is 1.109 inches (including enamel coating)
The length along the leg side is 2.85 inches
The width across the 3 legs is 3.375"
The primary winding is 212 turns of #20 single enameled magnet wire.

What is the RMS idle current at 123.0 VAC RMS applied input?
 
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This I gotta see.

The laminations are grain oriented silicon steel from 1976.
The core is called EI 138
The stack height is 1.109 inches (including enamel coating)
The length along the leg side is 2.85 inches
The width across the 3 legs is 1.375"
The primary winding is 212 turns of #20 single enameled magnet wire.

What is the RMS idle current at 123.0 VAC RMS applied input?

Hi there,


We also need to know what kind of material it is and what thickness the laminations are
and what the frequency of operation is. I'll assume 1x1 interleaving just to keep it simple.
Also, the stack height is about 1.1 inches but just to make sure is the center width about 1.375 inches across or something else? That's the width of the center portion of the core only.

We know the primary turns, that's good, and we know the operating voltage, that's good too.
Now we need to specify the center width and type of material and frequency.

I could not find any data on line for a core EI138 of any type of material (didnt look real hard yet though) but i do have data for a core EI1 1/2 (that's EI one and a half) which may be close to the size you are talking about. I have data from about the same period for core types M19 26 gauge, M6 Orthosil 29 gauge, and Orthosil 0.006 inch. I also have 10KGauss data for a few other cores on hand, but anything else would have to be obtained from the manufacturer.

Basically the procedure would go something like this...
1. Using the dimensional data, calculate the weight
2. Using the voltage and frequency, calculate the flux density
3. Find the right curve for the right material at the right frequency with the same interleaving
4. Look up the exciting volt amperes per pound
5. Multiply the pounds times the value found in step 4 above


If we dont know and can not get the right material data, we can estimate but from the data i have i can already see that with different materials we can see a difference of 2 to 1 in the exciting volt amperes, so it would be best to know the material type too.

If we can not get the right material data i can give an example of a core using some known type of material (with published data) if that would help.
 
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Thank you, MrAl

I think you have sufficiently shown that calculating the current through the primary of a no load transformer is completely beyond the abilities of most people.

Obviously, I have the transformer that I described, and it isn't labeled with exactly which material it is made with. Neither are the transformers we find in stores. Even if we, the users of transformers, could go around breaking a lamination out of the enamel and measureing its thickness, that still wouldn't be enough information. Thus I say, to the vast majority of people, You'll just have to buy one and measure the current.
 
If the reactance is known and the DC resistance is known how would you calculate the real power that's lost in the coil vs the apparent power? There should be some way to do this no?
 
You cannot work out the quiescent current as you don't know the actual air gap that is present in the final design. The air gap is microscopic if the surfaces are lapped but come into the calculation if a gap is intentionally included. The gap is to prevent the core saturating when a DC voltage is present such as when the transformer is used as a battery charger or when the "transformer" is used as a choke. (A single winding "transformer" is called an inductor or choke).
The mathematics for all these things is devised afterwards - to fit the conditions. The only way to determine any characteristic is to build a model and test it.
 
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I found this article which seems pretty informative, apparently the air gap preventing saturation isn't exactly the whole story.
**broken link removed**

I pretty much avoid this stuff like the plague it's more black magic to me than electronics initially was when I knew nothing. The math on that page is beyond my understanding that's for sure because I've never had the want to design anything that depends on the saturation characteristics of ferrite materials.
 
Like MrAl suggested, it's not all that "black magic" when you have all the specs for every part and you're trying to build one. Trying to guess how it acts without the exact core material, lamination thickness, number of turns, and the air gap is when it gets magical.

When Harry Potter World opens in Orlando next week, we'll all be able to buy a magic wand and end this foolishness.
 
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Hello again,


[see attached data for magnetic laminations]

bychon:
Well, it's simple algebra, and after all the question was how to calculate the power and such so i presented a method for doing it. If you dont want to do it that way that's fine. Of course we need the data, and we need to know the material as i had said before. This information is always available at the time of design. Certainly if you cant get the data or the material type then you're stuck with measurements, and measurements are always a good idea anyway of course.

Sceadwian:
Yes there is a way to estimate it, and that's what i'll show more explicitly now.

colin55:
We assume here he is working with line frequencies, and sine waves. A butt stack is handled via an appoximated stacking factor, as are different interleaves such as 1x1 or 3x3.


Whomever:
For the people more interested in this, take a look at the attachment.


Also, air gaps are especially helpful when used with cores that have to carry DC current to prevent easy core saturation.
 

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It's not that I don't want to do it, it's that the EXACT number of which grain oriented silicon steel was used in a particular transformer is not available to me, and neither is it available to the vast majority of people who use transformers. The number of turns on the primary is not available to the vast majority of users. The thickness of the laminations is not available to the vast majority of people.

However, we all await the example of how these calculations can be done with what we have to work with. Go ahead, please.
 
It's not that I don't want to do it, it's that the EXACT number of which grain oriented silicon steel was used in a particular transformer is not available to me, and neither is it available to the vast majority of people who use transformers. The number of turns on the primary is not available to the vast majority of users. The thickness of the laminations is not available to the vast majority of people.

However, we all await the example of how these calculations can be done with what we have to work with. Go ahead, please.


Hello again,


Ok sure, but when you see how easy this is you'll wonder why you were a little negative about doing it this way :) I'll be back here in a little while with an example.
 
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