CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@raghunathreddy36 • 27 Jan, 2010
The dc supply is given to transformers are may get dameged, what is region?
@Saandeep Sreerambatla • 27 Jan, 2010 I dont think it will get damaged.

But according to the principle the alternating voltage in primary will generate a magnetic field which induces voltage in the secondary and thus the secondary voltage is generated.

But if you give a DC supply , the DC voltage doesnt change , it just generates magnetic field in the core which will generate a pulse at the secondary.
but the secondary voltage will be zero after the pulse may be because of the static secondary magnetic field.

Transformers will work on DC a bit ineffectively , we can make them work giving DC series of pulses.

This is my understanding , if you have any questions post them.
@vibhor_one • 27 Jan, 2010 I agree with him completely
@tashirosgt • 28 Jan, 2010 if the DC current is switched from "Off" to "On' on the input coil of the transformer, there will be a change in the magnetic field of one coil, which should induce a current in the output. I wonder if this presents any practical problems in the transformers used by power companies. Do they require some protection against such "transient" currents?
@Saandeep Sreerambatla • 28 Jan, 2010 I think companies use AC as a input and they convert again to DC after transforming the voltage!'

If DC is given sometimes a high magnetic field will be created in the primary which burns out the primary windings of the transformer.

Moreover , the pulse voltage which is induced at the secondary may burn out the secondary winding but it depends on the voltage !!
@piyushh • 28 Jan, 2010 sorry for interrupting..but i guess..it wll get damaged..if we'll give dc supply, because the main power content will be dessipated in the form of heat.. the heat generated will further melt the insulation between the wires in coil..finally full coil which was been wounded as coil or turns will act as the single conductor
@Saandeep Sreerambatla • 28 Jan, 2010 Hey Piyush its not interrupting , its discussing and we encourage this 😀

Yes the transformer gets damaged , but every coil can withstand upto certain voltage this if we give 12 V DC for suppose not a continuous one but as a series of pulses , the output will be transformed to series of pulses.
But the efficiency and longevity of the transformer reduces and there is a risk of burning too!

Ps. Please don't use SMS text!! sry == Sorry 😀 and the long dots (....) too!
@piyushh • 28 Jan, 2010 but , i guess if we apply dc pulses of some time duration..how come it will produce emf at secondary. i hav read that for induced emf at secondary the very first condition is that we must have instantaneous value voltage(i.e changing) i.e change in flux..,,so does the equation gives the differentiation
...so for the time duration of a dc pulse their is no change ..n finally no emf..?
@devildev44410 • 30 Jan, 2010 Hi, i am Dev. 4th year E.E branch
If d.c. supply is given to transformer then after a time duration the transformer will be fully damaged because of the constant property of d.c and the d.c pulses also.
@imnitsy • 30 Jan, 2010
piyushh
but , i guess if we apply dc pulses of some time duration..how come it will produce emf at secondary. i hav read that for induced emf at secondary the very first condition is that we must have instantaneous value voltage(i.e changing) i.e change in flux..,,so does the equation gives the differentiation
...so for the time duration of a dc pulse their is no change ..n finally no emf..?
well, when we give DC supply in form of DC pulse at primary,
the induction will occur during the interval between the two pulses!!!
thus the secondary will have emf during this time interval,
and more pricisely a series of pulses comes from the secondary winding of the transformer!!!😁
@manoranjan • 30 Jan, 2010 if we will give dc supply to a transformer it will not be damaged upto a certain range of the voltage of the dc pulse.but if more voltage we will give then there is a chance of getting damged of transformer cores.now when the dc pulses turns from zero to maximum value at that instant there will be a change in the magnetic field which will lead to a disconinious value of the voltage induced.and is not quite efficient for practical use
@sanks85 • 30 Jan, 2010 i dont think dc can be applied in the form of pulses and i think that the generation of eddy current in secondary coil due to flow of dc in primary winding will cause to burn the secondary winding... but morover it depends on the voltage applied....😉
@piyushh • 30 Jan, 2010
imnitsy
well, when we give DC supply in form of DC pulse at primary,
the induction will occur during the interval between the two pulses!!!
thus the secondary will have emf during this time interval,
and more pricisely a series of pulses comes from the secondary winding of the transformer!!!😁
i guess imnitsy..there will be no emf induced during the interval between the two pulses..because the fundamental says there should be "change" in FLUX for transformation action right?and flux changes when field changes and finally field changes when the voltage applied at pimary "changes" ..right??

as your supply is contant during an interval..finally no emf.😀.rather it will damage the core of transformer
@imnitsy • 30 Jan, 2010
piyushh
i guess imnitsy..there will be no emf induced during the interval between the two pulses..because the fundamental says there should be "change" in FLUX for transformation action right?and flux changes when field changes and finally field changes when the voltage applied at pimary "changes" ..right??

as your supply is contant during an interval..finally no emf.😀.rather it will damage the core of transformer
i mean that when we supply DC pulse the dc voltage keep on changing from maximum to zero volts!!

when such change occur there will be emf induced in the core and thus there must be a pulsated output.

but if we do not apply the DC supply in form of Dc pulses, then there will not be any change in input voltage and thus there will not be any emf induced!!

your suggestion is absolutely rite but for the later case.😒

may be i am wrong but we are considering pulses, and a pulse always drops from its maximum value to minimum and vice versa!!

and as this change is occuring at the input so the induction will be there!!!
@piyushh • 30 Jan, 2010 for transformation action u need to have flux changing "WITH RESPECT TO TIME" /i.e instantaneous ..iin theory we say dc pulse require no time for transition..but practically it does take..so some emf will be indused.. it will get damaged in few cycles only due to constant pulse for a time interval
@imnitsy • 30 Jan, 2010 very true!!😁
@Mohit parnami • 04 Feb, 2010 hey ur previous disscussions were a gr8 help for me but i 've a doubt i want to know in detail about what do u exactly mean by dc pulses or dc series pulses
@sanks85 • 04 Feb, 2010 this DC pulse maily reffers to the ripple in the DC uotput... when we obsrve the dc output without using any filter circuit rippled DC output can beobserved but when we use filter circuit the striaght line is observed showing pure DC output...
@Rifaa • 04 Feb, 2010 Guys!!!
Bear in mind that transformer are not to be used in steady current.
If the PSU you are using have high current capability then the any transformer with a low DC winding resistance will burn instantly if the PSU does not have short circuit protection.
Do not try this.
Or may be u can, if you like burning things up. but do it at your demise.
TX can only be used if the current through it varies or pulses, a current which should not have steady rate that can allow the winding to heat up.

Now please try not to debate this or prove me wrong cause you can't. Do a google search and u can learn a lot.
Only ask if you are in doubt and we will explain.

Rifaa
@erpiyush • 05 Feb, 2010 hey friends for the first time i am using this site.but seeing ur discussions i feel inclined to use this daily
@manoj_2all • 30 Mar, 2010 Re: wat is the different b/w wi-fi and wi-max

Transformer must not be connected to a DC Source because if the primary winding is connected to DC Supply mains, the flux produced will not vary but remain constant in magnitude and therefore no EMF will be induced in secondary winding except at the moment of switching ON. Also there will be NO Back EMF induced in the primary winding. Therefore a heavy current will be drawn from the supply which may result in the burning of the winding.
@sasuke • 06 Apr, 2010 I think u can search for SMPS technology (Switching mode power supply). This technology use switching DC in primary side. Interesting.
@saurabh2486 • 08 Apr, 2010 o agree with english as DC is constant
@saabhinav • 25 Apr, 2010 transformer works only for ac because link can be associated for alternating emf.If dc is applied then no alternating flux would be generatd in secondary winding of transf,but such continuous power of dc will burn the transformer.
@saabhinav • 25 Apr, 2010 I think transformer will get damaged.

The basic reason is that when dc no changing flux would be linked with the primary coil and hence a/t Lenz law no back emf will be linked with primary.
This will result in high amount of dc in primary and as a result of resistive heating of coil wires it will burn.
@Chaitali Sumita • 27 Apr, 2010 hii..
actually a transformer cannot work on dc supply ..we know that seondary voltage is induced from the primary..if we supply dc voltage then there will be no flux linkage ,as a result of which dc power is not transmitted between the coils of the transformer...this leads to excessive heating,thus burning of the windings...

yes,a transformer may work if we provide pulsating dc.....
@jensiline • 04 May, 2010 When dc voltage is applied to a transformer winding as that circuit is closed & based on the impedance present in that winding current starts flowing but the nature of this current is also dc. This d.c current produces a magnetic flux which is of d.c in nature i.e constant magnitude (because flux mmf/reluctance current x no.of turns/reluctance if current is dc flux will also be dc ) flux is constant i.e

d(flux) =0
dt


so emf produced will be 0 & the total current flowing through that winding will be


applied voltage-0
impedance


So if the magnitude of dc is higher enough then in that case the current
flowing through the winding may exceed the current carrying capacity of that
winding thus the winding will be damaged
@eldritchmyer • 10 May, 2010 thi is true if you working with dc only, however if you look at a dc series of pulses, then you can break it up into a fourier series, which will then be a number of AC sine waves. The transformer will be optimised for a certain frequency (ie, if it is a mains transformer then 50/60Hz), so provided the fundamental wave is of the same frequency then you should be able to get a fair signal out of the secondary. If you drop the frequency below this however, then yes, you will have dc effects, but provided you are sending dc signals at 50Hz, I think you should be fine. The higher order harmonics will be filtered as with any inductor (and therefor will be a loss into the core), so you should probably derate quite a bit (Ie, on a 1 VA transformer, if you are feeding it will dc pulses, don't try todo much more than about 0.5VA).
@aj_onduty • 26 Aug, 2010
English-Scared
I dont think it will get damaged.

But according to the principle the alternating voltage in primary will generate a magnetic field which induces voltage in the secondary and thus the secondary voltage is generated.

But if you give a DC supply , the DC voltage doesnt change , it just generates magnetic field in the core which will generate a pulse at the secondary.
but the secondary voltage will be zero after the pulse may be because of the static secondary magnetic field.

Transformers will work on DC a bit ineffectively , we can make them work giving DC series of pulses.

This is my understanding , if you have any questions post them.
Dear friend, DC voltage doesn't have inductance, so it will not support mutual inductance, the phenomenon on which the transformer works. But DC voltage will have to face the resistance of the coil. The resistance dissipates enough heat to melt the coil and damage it.
@Saandeep Sreerambatla • 29 Apr, 2011
aj_onduty
Dear friend, DC voltage doesn't have inductance, so it will not support mutual inductance, the phenomenon on which the transformer works. But DC voltage will have to face the resistance of the coil. The resistance dissipates enough heat to melt the coil and damage it.
I am sorry I didnt understand, what is meant by "DC voltage doesn't have inductance"?

Does AC have inductance?

Moreover, my answer was not always correct but it depends upon the rating of both transformer and the voltage we give.
@Mr.Don • 29 Apr, 2011 The transformer will simply wont work if DC is given because DC does not produce any flux as it has to be generation for the transformer.

Remember transformer works on the principle of mutual induction. It says it all. When AC is given there will + and - charges and have the inductance.

For DC there will no variation and hence it does not produce any flux hence there will be no mutual induction and hence the voltage cannot be passed to the secondary.

Otherwise the supply will go pass to any closed path.

and remember about closed paths.

if there is no closed path or there's no load connected then there is a possibility to produce reverse currents or even for the equipment to get damaged.

Here because when DC is applied to the transformer and because of the generated input power is not consumed to load through secondary there is a possibility for the transformer windings to burn because of reverse currents/voltages.
@PraveenKumar Purushothaman • 29 Apr, 2011
English-Scared
I am sorry I didnt understand, what is meant by "DC voltage doesn't have inductance"?

Does AC have inductance?

Moreover, my answer was not always correct but it depends upon the rating of both transformer and the voltage we give.
Electromagnets work in the principle of Induction. When a coil containing flow of electrons is present, a magnetic field is generated as in:

[​IMG]

In order to generate this magnetic field, the current should be an Alternating Current and not Direct Current. The principle of transformers work this way.

[​IMG]

The flux which is generated at the primary end will make the whole core magnetised and using the flux at the other end, electricity is again generated by reverse faraday's law (faraday or the other one?)...

So, its just a transition like: AC - ElectroMagnet - AC... 😀
@Mr.Don • 29 Apr, 2011 @Praveen Great Work
@PraveenKumar Purushothaman • 29 Apr, 2011
dileep k
@Praveen Great Work
Thanks, just thought it would be nice to explain with illustrations... 😀
@aj_onduty • 29 Apr, 2011 Let me rewind some things which I learned a bit back.
When you apply a DC voltage across a coil, the current starts increasing. Initially it is zero volts, then it starts increasing til it reaches a particular value, and then stops. This change in the value of current doesn't take much time, most probably, a fraction of a second or something of that magnitude. Now, I think we all know that to induce a current in a coil(Coil A), that is by mutual inductance, we need another coil(coil B), which has the value of the current flowing through it changing, inconsistent. If we use DC for this purpose, we can induce current in coil A only for a fraction of a second. Well, that is really too small for practical use.
If we observe AC, the current value never remains the same for a particular point in time. That means, the current keeps on changing. This type of a current is the ideal one for inducing current in coil A, by passing it through coil B.
Now, In a transformer, we find coil B at the primary, and coil A in the secondary.
@shubhankar • 30 Apr, 2011 inductance is a phenomenon. not a quantity that can be attributed. inductance is basically the rate of change of flux with respect to current..the effect produced by varying the current on flux is called as Inductance.
@PraveenKumar Purushothaman • 30 Apr, 2011
shubhankar
inductance is a phenomenon. not a quantity that can be attributed. inductance is basically the rate of change of flux with respect to current..the effect produced by varying the current on flux is called as Inductance.
This rate of change of flux can be generated only by an AC and not a DC!!! 😀
@d_vipul • 01 May, 2011 @All :CEAN:.

Transformer will transform some of the voltage which is due to noise present in the DC and transients..........

It will not be damaged unless and until it exceeds its ratings..............

I have tested this.........

I used a 230/ 110 V transformer.......in which I gave 110 V DC to its primary and I found 7-12 volts at its output.........
I carried out this test 2 times........first time I found that Transformer gets heated after 2 Hrs......When I found it unbearable I stopped the test.........

Second time, after 2 days, I carried out this test at 50 V for which the output was 2-6 V.......and the transformer start heating after 3.15 mins...........

Hope this helps you,..............

Regards,
VIPUL
@Harish Sarma • 02 May, 2011 sir,
As I've learnt transformer works on the principle of mutual induction i.e when theres a change in the current in primary coil the flux linked with secondary coil changes and this change occurs only incase of an alternating current......
@Ramani Aswath • 02 May, 2011 Generally the transformer primary has a low Ohmic resistance though a high impedance. If a steady DC is apllied a large current flows and there will be no output at the secondary except at the instant of switching on and switching off.
However, there are pulse transformers made which will accept a pulsed DC at the primary and produce a corresponding pulse (more or less distorted) at the secondary, the voltage being decided by the turns ratio.
This gives some info:
https://www.rhombus-ind.com/app-note/circuit.pdf

Bioramani
@Harish Sarma • 02 May, 2011 yes u r right sir but the discussion is about purely dc supply and not about pulsed dc
@Ramani Aswath • 02 May, 2011
harishksharma
yes u r right sir but the discussion is about purely dc supply and not about pulsed dc
If so, then it is a pure Ohmic circuit and Ohm's law should apply. Depending on the coil resistance and the voltage applied one can have a fire hazard.
Bioramani
@shubhankar • 03 May, 2011 with dc supply there would be no alternating flux and hence no change in flux and hence the faraday's law of electromagnetic induction does not hold good. hence no secondary emf is generated. more over i think the core will saturate early as compared to when ac is passed and cause overheating and damage the Xmer.
@ashokjain • 15 Oct, 2012
eldritchmyer
thi is true if you working with dc only, however if you look at a dc series of pulses, then you can break it up into a fourier series, which will then be a number of AC sine waves. The transformer will be optimised for a certain frequency (ie, if it is a mains transformer then 50/60Hz), so provided the fundamental wave is of the same frequency then you should be able to get a fair signal out of the secondary. If you drop the frequency below this however, then yes, you will have dc effects, but provided you are sending dc signals at 50Hz, I think you should be fine. The higher order harmonics will be filtered as with any inductor (and therefor will be a loss into the core), so you should probably derate quite a bit (Ie, on a 1 VA transformer, if you are feeding it will dc pulses, don't try todo much more than about 0.5VA).
Transformer works with AC and not DC that is quite abvious , question is if Dc pulses are given to primary of transformer with secondary shorted there will transformation to secondary .How the pulse will appear when current waveform seen at primary terminal .
Initially due to sudden change in voltage( 0v to peak voltage) there will be changing flux and hence secondary voltage then for certain time voltage will remain only in primary and again when the pulse comes from peak to 0V there will be again voltge in secondary until it becomes zero . Is this OK ???
@Jeffrey Arulraj • 15 Oct, 2012 Yeah true to the best of knowledge a pulsating signal is similar to AC signal as it has a frequency

If a voltage pulse has frequency then it can be used to drive a Transformer
@Naman Agarwal • 16 Mar, 2013 Actually when dc is applied across the primary, a pulse will be there at the secondary for very short peroid but then the secondary voltage will drop to zero and there wil be no mmf induced in the secondary. Basically we need difference of mmf b/w primary & secondary to be zero. But here it wont be zero because primary has mmf but secondary has no mmf. So Difference of mmf 's will be equal to the mmf of primary and it is high. So due to this, windings of secondary may be burned out. So no transformer action takes place.
@ashokjain • 16 Mar, 2013 DC Pulses will do transformation and there will be Emf induced in secondary . Only issue will be of Demagnetisation of core , which can also be controlled if pulse width is maintained properly .Only thing is how the current waveform will look like.
@Ramani Aswath • 16 Mar, 2013 https://www.butlerwinding.com/store.asp?pid=28355
@piyushh • 16 Mar, 2013 Please be advised; not to post links/references directly, rather it'd be better if you explain us what you have understood from the content with reference to thread

This would be helpful to keep this place informative in itself

Thanks
@n.rajeev sharma • 27 Mar, 2013 it will get burned due to short circuit
@Anand Tamariya • 27 Mar, 2013
d_vipul
@All :CEAN:.

Transformer will transform some of the voltage which is due to noise present in the DC and transients..........

It will not be damaged unless and until it exceeds its ratings..............

I have tested this.........

I used a 230/ 110 V transformer.......in which I gave 110 V DC to its primary and I found 7-12 volts at its output.........
I carried out this test 2 times........first time I found that Transformer gets heated after 2 Hrs......When I found it unbearable I stopped the test.........

Second time, after 2 days, I carried out this test at 50 V for which the output was 2-6 V.......and the transformer start heating after 3.15 mins...........
Hope this helps you,..............

Regards,
VIPUL
What was the source of 110V DC that you used?
@aakash.kaasina • 28 Mar, 2013
piyushh
sorry for interrupting..but i guess..it wll get damaged..if we'll give dc supply, because the main power content will be dessipated in the form of heat.. the heat generated will further melt the insulation between the wires in coil..finally full coil which was been wounded as coil or turns will act as the single conductor
yeah..the heating effect is because of the DC component present
@aakash.kaasina • 28 Mar, 2013 Also i think there will be no current in the Transformer Secondary.Because of DC input...the Flux will remain unchanged and hence no current is Induced in the Secondary Winding 👍
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