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# How does a transformer work?

Mon 23 Jul, 2012 09:17 am
How does a transformer work? What does a transformer do? Why are they used? And any other information you may have on transformers please, lol.
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aspvenom

1
Mon 23 Jul, 2012 10:03 am
@SuzaneK,
Simply coils, and when electrical current passes through the primary coil, it creates a magnetic flux that induces a voltage in the secondary coil. If primary has more coils than secondary it's a step down transformer, and if secondary has more coils than primary it's a step up transformer. Power is the same in both coils.
Pin=Pout
P=I*V
So what that tells you is that amperage and voltage are inversely proportional to each other in the two coils.

That's what I know from the top of my head, you can do further reading in a Physics textbook, or google it.
raprap

1
Mon 23 Jul, 2012 10:29 am
@aspvenom,
They only work when the current is changing--that's why transformers don't work with direct current.
aspvenom

1
Mon 23 Jul, 2012 12:23 pm
@raprap,
Yes, the flow of electric charge has to be non-direct, or alternating (AC).
dalehileman

0
Mon 23 Jul, 2012 12:57 pm
@SuzaneK,
Suz, Asp and Rap have described it pretty well but I for one as an electronics person and erstwhile inventor am curious as to your curiosity
0 Replies

roger

1
Mon 23 Jul, 2012 01:09 pm
@raprap,
Sure. You can also interrupt a direct current to get the same effect. I used to have a Model T ignition with a simple buzzer mounted to the box. Crude, but fun to play with.
Chumly

1
Wed 24 Dec, 2014 09:38 am
@raprap,
raprap wrote:
...that's why transformers don't work with direct current.
Not so, both half-wave and full-wave (unfiltered) DC will allow a transformer to function. In fact steady state DC will allow a transformer to function but then only upon connection and/or disconnection and then only for a given number time constants.
0 Replies

Chumly

1
Wed 24 Dec, 2014 09:43 am
@aspvenom,
aspvenom wrote:

Simply coils, and when electrical current passes through the primary coil, it creates a magnetic flux that induces a voltage in the secondary coil. If primary has more coils than secondary it's a step down transformer, and if secondary has more coils than primary it's a step up transformer. Power is the same in both coils.
Pin=Pout
P=I*V
So what that tells you is that amperage and voltage are inversely proportional to each other in the two coils.

That's what I know from the top of my head, you can do further reading in a Physics textbook, or google it.
Wrong, the formula in question is VAin = VAout + losses. In fact, transformers do not use power at all (notwithstanding losses).

Also, there are transformer that do not use so-called "Simply coils" in that they have only one coil (from an electrical continuity perspective). They are called auto-transformers.
0 Replies

Chumly

1
Wed 24 Dec, 2014 09:45 am
@aspvenom,
aspvenom wrote:
Yes, the flow of electric charge has to be non-direct, or alternating (AC).
Wrong, it only need vary in magnitude not direction.
Chumly

1
Wed 24 Dec, 2014 09:49 am
@roger,
roger wrote:
Sure. You can also interrupt a direct current to get the same effect. I used to have a Model T ignition with a simple buzzer mounted to the box. Crude, but fun to play with.
The effect of mutual induction under the conditions you ascribe will be only for a given number time constants.
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Chumly

1
Wed 24 Dec, 2014 09:54 am
oscar83 wrote:
There re different type of transformers. for instance distribution transformers are used to distribute electricity and instrument transformers are used for measuring. for more info http://www.esitas.com.tr/en/urunler.aspx
Irrelative of a transformer's application or configuration, they all work on the same principle of mutual induction, unless referring to auto-transformers which (arguably) use the principle of self-induction given there is only one coil (from an electrical continuity perspective).
0 Replies

dalehileman

1
Wed 24 Dec, 2014 12:42 pm
@aspvenom,
And Asp we might add, the application of DC to the primary will cause a single pulse out of the secondary
Chumly

1
Wed 24 Dec, 2014 01:00 pm
@dalehileman,
dalehileman wrote:
And Asp we might add, the application of DC to the primary will cause a single pulse out of the secondary
Wrong, there is DC half-wave and DC full-wave which would allow ongoing mutual induction, in fact as long as the DC is changing in magnitude, there would be continuous mutual induction and thus a continuous induced voltage in the secondary. Also your claim of a " single pulse out of the secondary" even under steady state DC is incomplete as there would be an equal induced voltage upon de-energization, and not only that, but due to Lenz's Law there would be a counter-EMF induced in the primary which will oppose the source voltage.
dalehileman

1
Wed 24 Dec, 2014 01:34 pm
@Chumly,
dalehileman wrote:
And Asp we might add, the application of DC to the primary will cause a single pulse out of the secondary

Quote:
Wrong, there is DC half-wave and DC full-wave which would allow ongoing mutual induction,
Thank you Chum but I'm not sure what you mean by "DC half-wave and DC full-wave"

Quote:
in fact as long as the DC is changing in magnitude, there would be continuous mutual induction and thus a continuous induced voltage in the secondary.
That's true, and I apologize if I was misunderstood. Of course if, eg, the source DC V were to increase in amplitude then yes one single continuous sec DC V would result but eventually wouldn't the increasing pri I burn it out

Quote:
Also your claim of a " single pulse out of the secondary" even under steady state DC is incomplete as there would be an equal induced voltage upon de-energization,
Yes of course. Simply didn't think it important to the discussion

Quote:
...and not only that, but due to Lenz's Law there would be a counter-EMF induced in the primary which will oppose the source voltage
Yes Chum, again, of course there would, but still I don't see how this fact negates my assertion, eg, the immediate effect in practical case of connecting a battery across the primary

Forgive if I wasn't clear. I'm continually amazed by what the contributor considers a simple, obvious statement of fact gets misinterpreted

All bets would be off Chum but it might be interesting to speculate upon the results if the batt internal R and the xfmr sec pri were both to be of zero R
0 Replies

Chumly

1
Wed 24 Dec, 2014 02:29 pm
dalehileman wrote:
Thank you Chum but I'm not sure what you mean by "DC half-wave and DC full-wave"
Quote:
By definition DC need only NOT periodically change polarity, as such the unfiltered output of a rectifier is DC, and if we are talking about an AC sinusoidal single-phase input to a rectifier, then you can either have half-wave DC or full-wave DC as the output.
dalehileman wrote:
That's true, and I apologize if I was misunderstood. Of course if, eg, the source DC V were to increase in amplitude then yes one single continuous sec DC V would result but eventually wouldn't the increasing pri I burn it out
Quote:
Nope, it would not necessarily have to cause an over-current condition, see my examples above as to half-wave DC or full-wave DC or consider a DC sinusoidal input.
dalehileman wrote:
Yes Chum, again, of course there would, but still I don't see how this fact negates my assertion, eg, the immediate effect in practical case of connecting a battery across the primary
Quote:
Because it is not a so-called "immediate effect" due to exactly what I referring to i.e. the time constants and Lenz's Law.
dalehileman wrote:
All bets would be off Chum but it might be interesting to speculate upon the results if the batt internal R and the xfmr sec pri were both to be of zero R
There are super-conductor inductors with massive circulating currents and intense magnetic fields however VAin = VAout + losses would still would hold true, bearing in mind that the losses here would approach if not equal zero. I'm not a physicist, so my knowledge is limited when talking about devices with no resistance, but I can tell you that Ohm's law would mathematically allow infinite current with zero resistance (as long as the voltage was greater than zero), however the limitations of the VA of the supply would prohibit infinite current, even if the entire system had zero resistance, as that would contradict the conservation of energy i.e. "no free lunch".
dalehileman

1
Wed 24 Dec, 2014 03:18 pm
@Chumly,
Quote:
you can either have half-wave DC or full-wave DC as the output
Chum, I hear ya. Of course as a former electronics tech it's increasingly clear that I was using the abbr "DC" in its usual sense and except for my laziness if I had reread your posting your meaning would have come across more clearly. When you suggested a DC power supply my old mind assumed the usual filter caps and inductor to smooth it out . Of course a pulsating DC will cause an AC output from the xformer

Quote:
..or consider a DC sinusoidal input
That'n had me goin' too Chum. My guess, it'd cause a sinusoidal sec, of course swinging both wayas

Quote:
I'm not a physicist, so my knowledge is limited when talking about devices with no resistance,
Mine too I have to admit, eg:

Quote:
but I can tell you that Ohm's law would mathematically allow infinite current with zero resistance
Yes a source providing a steadily increasing DC voltage to its xfrmr primary would cause--for a while anyhow--increasing primary current so steady DC secondary voltage

...I guess

But something I've always wondered about: if the xfrmr pri also were of zero resistance (don't quote me now) acting simply an inductor but the source pure DC, wouldn't its forever expanding field hold down current to a very small value

Not zero current I'd suppose 'cause you'd have no field at all. So I readily accede to much ignorance under these impossible conditions

So I'd imagine a very weak field expanding into the void forever
Chumly

1
Tue 30 Dec, 2014 05:21 am
@dalehileman,
Hi dalehileman,
If you could continuously raise the voltage then you would continuously have a counter EMF (limiting current) but this would be a function of the coil's inductance, and the speed of the voltage rise, even under zero resistance conditions, but...

given that T= L/R and XL = 2pifL, then T is proportional to L and XL is proportional to f, assuming all else stays constant. However you cannot have an infinitely increasing magnetic field due to saturation, so although again I am not a physicist it would seem there would be a limit to the CEMF and that's a function of inductance which is a function of the flux density (Tesla).
dalehileman

1
Tue 30 Dec, 2014 12:56 pm
@Chumly,
Quote:
However you cannot have an infinitely increasing magnetic field due to saturation
That's of course if the inductor has a core

I'm still curious about the effect of an increasing voltage if its resistance is zero, a conflict of sorts, because how would one get a counter emf if the current were zero

But Chum, it would, wouldn't it

Quote:
given that T= L/R and XL = 2pifL, then T is proportional to L and XL is proportional to f
Sorry Chum you've got me here, not quite sure what t is, and I'm absolutely in the dark except where you refer to f and I had assumed we were talking about dc

You're conversing with a math blockhead who sees everything he can in intuitive terms
Chumly

1
Wed 31 Dec, 2014 02:04 pm
@dalehileman,
Current lags voltage in an inductor
dalehileman

1
Wed 31 Dec, 2014 02:52 pm
@Chumly,
Quote:
Current lags voltage in an inductor Smile
Yea Chum and I do realize that, thanks, I am smiling, but how does it relate to my puzzlement
0 Replies

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