Multi Voltage primary step down transformer

[Gito]

Hi Pat

It's not an 1000 watt transformer ,its small transformers ,maybe 50 t0 100 watt,the looses is not in the cable,but most in the iron  with 8000 gaus ,1kg iron has a lost of 2.4 watt,and with 12000 gaus it has a lost 3.5 watt per Kg

So an 150 watt transformer ,used 4 kg Iron /core  has a lost of 14 watt.if + the lost in the email cable ( primary R is 10 Ohm) and the current flowing in the primary is 150 : 220 =  0.75 . than the lost in the primary winding is .75 X 10 = 7.5 watt . and the secondary is 30 v  and  say the secondary has also 150 watt rating (no looses), than the current is 150 : 30 = 5A  ,since the cable  resistance is 1 Ohm , the lost is 5 watt

So the total lost is 14 + 7,5 + 5 = 26 watt,  not including other looses .


Gito

here's a picture taken from ARRL handbook

[N4LTA]

All of the radio world is on fire with all these transformer losses?

Gito


I spent many months -  many years ago testing transformers in the Daniel basement lab at North Carolina State University. I did not enjoy it, but I learned quite a lot about AC transformers. 


AC Power transformer are among the most efficient energy transfer machines that are know to man - That is the opening sentence in my Electromagnetic Machinery textbook.

You keep on telling people how you thing they work and I will just be quiet and go away.

BTW  - Resistive power is I x I x R   - Not I x R

[KD6VXI]

Here's a decent website, complete with graphics for those text challenged

http://ecmweb.com/news/electric_overcoming_transformer_losses/

Interestingly, it shows that transformer efficiency goes UP as the load does as well.

SO, lightly loading my 75 KVA xformers will cause them to loaf, BUT at the same time, work MORE inefficiently?  Uggh.....  My only other xformer is a 12A vault xformer.  It would be even WORSE!

Good thing I live in California where electricity is cheap and plentiful


--Shane

[N4LTA]

Shane - That makes sense.

There are two types of losses in a transformer - magnetic and eddy current losses which are constant with load and IR losses which are resistance losses in the windings. If you plug in a transformer and have no load connected to it - the amount of energy that is consumed is very close to exactly the magnetic losses. If you connect a 1 ma load  - the efficiency would be horrible

 - as the transformer is loaded - more power is transferred and the efficiency rises even though the IR losses rise.

A well designed copper winding transformer should have low IR losses.

A Google on the net states that poorly made Chinese made wallwarts have an efficiency of about 85% due to the poor IR and poor quality windings.

[Gito]

Hi

I begin to understand the difference thinking  between us.
As we know there are looses in the Iron/core of the transformer that stays the same even loaded fully call it A
and there 's looses in the enamel cable /Cu cable.

As I wrote before my 150 watt transformer ,the looses of it ,is 26 watt.( core looses + Cu looses.The Efficient is low around 80%

So I'm talking about small transformers.
Pat is talking about big transformers.

After thinking and reading I found that the bigger the Transformer ,the bigger the Efficiency is ..

For instance ,fortunately I have a 1000 Watt transformer in my house,it weight around 14 kg ,and with  1 ohm  in the primary winding.resistance

so the looses is 14 X 3.6 = 50.4 watt and looses in the primary winding is   1 X 4.5 X.4.5= 20.25 watt.
for the easy calculation  ,we make the secondary looses the same 20.5 watt.

So the looses in this transformer  is 50.4 + 20.5 +20.5 = around 90 watt.
As we see the efficiency off this around 91%,
Since it a 14 kg iron  transformer I think it can get very hot for 90 watt disipation

So Pat is not wrong because the bigger the transformer,the looses in the email cable became smaller ,because using bigger diameter cable.( R is small)
Pat is writing  about transformer more then 10 kw maybe 1000 kw (looking at the total looses is 13.4 kw and the efficiency is 98.64%)

So for big transformers the looses is only in the Iron/core.

So I believed big transformer can get 98% efficiency.

But I'm writing about small transformers, the smaller the trans former ,the smaller the Efficiency is,because the resistance in the email wire got bigger.

Sorry for my English,I lived in Indonesia ,my native language is Indonesia.
So maybe there are some mistakes to express my thinking in English.

Gito

 
I think using the cable size is dependable from the core size and how many Watt it needs,and also he room in the core to wind this cable.
So of course if we can we used the biggest cable to wind this transformer to make the cable resistance smaller. But since the room is limited ,we used smaller cable to wind this transformer with a compromise value,so we cannot at will using this email cable size.
that's why the resistance of the email cable is quite high for small transformer and make a big role to the Efficiency of the Transformer.

[N4LTA]

Gito,

You are correct in that many small transformers have low efficiency -. BUT it does not have to be the case.

A small transformer from a quality manufacturer with low resistance copper windings can be very efficient.

An ideal way to find out is to measure the DC resistance on the windings and using the full load current to calculate the losses using P=I x I x R  - I squared R

I have just wound a toroid transformer for 10 amps at 88 volts on the secondary. I used parallel #12 wire for the winding which makes a very efficient 880 VA transformer for a class E transmitter modulator.

[capt.m]

hi to all,,

As an example I have in hand now a 1000VA 90Vac-0-90Vac, 0-240Vac transformer 60hz and uses EI lamination core and with the Bmax of 1.2kg, and it uses #16 awg copper wire in the primary and #14awg copper wire secondary. and it is use for a 750watt rms 8ohm amplifier. BUT I do not know what is the effeciency of this transformer.

[Opcom]

What do you use that big amplifier for? Nice one..

[Gito]

hi. Capt.m.

As the "books" wrote there are loses in transformer,which are iron/core loses ,and also cu (cable) loses,and actually there are other loses.
To determined the Iron/core loses,we must know the weight of it.
If we have 2kg Iron that has 3.6 watt loses (per 1kg at 12000 Gaus) than we have a 7.2 watt loses.
The loses here depend the quality/grade of the transformer.( depending the grade ,the loses of iron is)


To determined the loses in the cable ,we must know the resistance in the wire, we can simply used an Ohm meter to find it.

Your transformer has a 1000 Va rating ,that means at full load the current in the Primary winding  which has 240 VAC input is  1000 : 240 = around 4.2 A.
so the loses in the primary winding is 4.2 X4.2 X Primary resistance = ......watt call it P1

Secondary winding  has 180 VAC output ,we assumed that it has 1000 VA rating so the current  flowing in the Secondary winding is 1000 : 180 = around 5.5 A
so the loses in the secondary winding is 5.5 X 5.5 X secondary resistance = ....watt
call it P2.

So the Efficiency of your transformer is around (1000 / 1000 + P1 + P2 + Core loses) X 100%. =  ...% transformer efficiency


Rereading the  sample of "big transformer" by Pat about the efficiency 98.64% Transformer using aluminum cable,It must be a very big transformer because it also stated that the total LOSES is 9.6 kw= 9600 watt ?

That means, is this loses  transformed as HEAT?


Gito

[capt.m]

well done Gito and to all the members who shared their knowledge...

I really like this forum, it is educational... I earn some additional ideas about transformers.


thanks