Effect of Frequency on Heater

sunilwani; the heater will not know the difference, how ever if you have a blower it may run faster at 60 HZ perry

P = U*I, so frequency is not involved in electrical power. The water will heat up just as fast (or slow) at 60 Hz as at 50 Hz.

Yes , there will no be any Effect of frequency( 50 or 60 HZ) on Heater wattage but what will effect on Heating Element as it is designed for 50 HZ & using on 60 HZ frequency

Very little, as others have correctly indicated, unless it has significant self-inductance in which case the current drawn will be lower than at 50Hz.

Since heater is a pure resistive load any change of frequency will not have any affect on its wattage rating. Even if you supply 220 V DC it would be same .

220VDC will glow hotter than 220VAC

I have done this test with a light globe, and found they don't last as long..

Also a incandescent globe will blow at about 310VDC, with a audible POP

That should not be true as the AC voltage given is a nominal voltage (it is varying both above an below this value if checked on a scope!!) that is equivalent to a DC voltage with regard to the amount of "work" that it can do.....first year electrical theory....

In this case, my memory tells me that "work" is equivalent to heating effect......

So I would assume that your 220VDC and your 220VAC were actually not as exactly the same as they could/should have been or your meter was way off between AC & DC and had never been correctly set up....

Ergo, your statement is fundamentally wrong.

I beg to differ. If you connect AC heater to a DC supply the resister coil will burn out. Remember there is something called inductance.

When working on AC heat load consist of Resistor load+ Inductance Load whereas in DC only Resistor load will apply. To explain it further....

If you take a coil the overall resistance is SQRt ( SQR(Res)+ SQR(Inductance)). In AC overall resistance is applied whereas in DC only Resistance is applied. Hence DC supply though at same voltage will have a higher current. Since heat is SQR(I)* Resistance the heat generated in DC will be very high compared to AC.

This is my understanding in Basic electric Engg. Mind you I am a Mechanical Engineer and so I may be wrong!!

I would appreciate if someone can explain the effect of frequency difference between 50Hz and 60Hz on the inductance load.

Yes sir you are wrong as the questioner mentioned heater element only. Pure resistive load will not have any effect of frquency.It will not burnt out with Dc power.

Very well sir.....

The inquiry talked of a heater of 230 V 4 KW , 50 HZ and not of a pure resistive load of 4KW

May be due to my ignorance I thought all heater elements consist of both Resistive and Inductive loads.

At least heater (hot plate) coils they sell used to have such loads. In my country normal voltage is 230V 50Hz but remote tea estates used to have 230V DC generators. Even an ordinary tea estate labourer knew they cannot use a 230V AC heater with DC and that it will burn out.

Anyway thank you for enlightening us all engineering folks about pure resistive load heaters!

Have a good day!

Sorry one part of my reply has been omitted which would give a wrong meaning

I also wanted to say 230V AC and 230V DC are not same.

If you look at the sinusoidal curve V changes from o to 230V. So one should get the RMS value of AC voltage.

Inductance was just a factor but may be only minor.

Please correct me once again if I am wrong.

Hi Sisira,

Just a minor correction, 230 VAC, the sinusoid actually varies from 0 to 325V. The 230VAC rating is typically accepted to mean the RMS voltage of the wave form not the peak.

Best regards,

Shawn

Thanks Shawn33 for correcting me.

I learnt a lot from this forum...I don't know how I lived without it in those days.

Theoretically if the resistive element is a coil (and only then!), you are right, but the differences should make little or no "real world" difference!!!

If the resistive element is not a coil, then what you say is simply not true.

You have to be slightly careful with your comment as quite often the resistive heating element can be a wire (or wires) that have been coiled.....the inductive effects are small, but still easily measurable.......

If in a steel case, the inductive effects can be such that if the case earth gets dislodged or broken, you can get a shock off the steel case even though the insulation check says that it is greater than 1 megohm.....been there, done that and got the shock!!!

There will be no real change in BTU output. If it has a fan with an AC motor it will run faster due to the frequency increase fron 50 to 60HZ.

Hi Sulniwani

Just cut off the connection and wire it up to the new 60Hz.

But since you didn't know the answer and had to ask,

just maybe you should have an electrician do it for you.

Just to be safe.

Take care

Jens

Hi, If it is a ordinary resistance heater, change of frequency will not at all effect on the performance of heater or power drawn. But if the heater is connected with a blower, then blower speed will increase by 20% and the motor will draw higher current than it's rated capacity which is harmful to the motor in a long run.

Power (Watt) = Voltage(V) x Current(I) and Voltage = I x Resistance(R).

Therefore W = I^2 x R , which you will notice is free from Frequency.

Frequency plays important role where inductive loads are involved.

Hope you are clear with the above explaination.

Regards.

I believe I am correct in saying that although a 50Hz induction motor (motor type was not indicated!!!!) will tend to slightly speed up when connected to 60Hz, (load IS a factor) its actually running current will be slightly less...due to the higher frequency....

But a 60Hz motor will run slower and hotter on a 50Hz supply of the same voltage for exactly the same reasons!!!

If the motor was of a "Universal" type, no significant changes in speed will be noted, but a slightly lower current will flow......again load IS a factor.

Fans are not usually of the Universal type......except in DC only situations of course!!!

Ther will be no change of heating effect with either power supply.

the engineering genesis of that lies in the fact that nominally the voltage stated is the Root mean square ( RMS) value of the power frequency sine wave .

RMS is based on the heating effect of the ac supply.

May I add a little to your correct comment to make it slightly more correct:-

RMS is based on the heating effect of the ac supply in comparison with a DC voltage producing the same amount of heat.

I trust that our readers will understand the addition slightly better.....

Keep in mind that most heater elements are coiled so there is some inductance, so there will be an AC impedance which is frequency dependent. I have seen a heater blow out because someone used DC on an element designed for AC. There might be enough effect to matter about a shift of 10HZ - I am not sure, but if I remember correctly, raising the frequency should raise impedance, so apparant current should drop.

X l = 2pi*FL

Where

X l = Inductive reactance (the overall resistance in an inductive device)

F= frequency in hertz

L= Inductance in henrys

Inductive reactance (resistance) will increase as a function of frequency. The result will be a coresponding decrease in current flow. The henrys found in a heating coil are very low and will probably not even be measurable. If it were a transformer, then frequency would be much more important, i.e. more coils of wire and closer together.

Good Answer.

The actual inductance of a resistive heating element is extremely low. So low infact, that you would be hard pressed to even measure the difference with a change of only 10 hertz. As long as there are no transformers or induction motors (Blower) in the unit, the frequency change should make no difference.

BTW I am an EE

Let say 230VAC 50Hz i.e there's 50cycles (+230V in 25cycles and -230V in 25cycles) of 230V AC sine wave in one second. An equipment designed at 50Hz, can nominally transform electrical energy to others. When source is 230VAC 60Hz, thus 60cycles in one cycles.

I think your heater's elements will get hotter faster than 50Hz.

By supplying 220VDC, of course, it will be hotter because in DC system there're no minus voltage as in sine wive.

cheers

Very imaginative answer, but totally and completely wrong.

If you had taken First year electrical theory, (and fully understood it!), you would not have posted such an incorrect answer!!

Let me say once and for all the following:-

230volt AC 50 Hertz supply makes a resistive heater of say 100 Ohms resistance exactly as hot as a 230volt AC 60 Hertz in the same amount of time as does a 230volt DC 50 Supply. The heating effects will all be identical.....no more, no less......

There will be NO difference between the amount of heat generated between ANY of the above supplies......for a purely resistive heater.

AC supplies are given a voltage number (the RMS value) which is exactly equivalent in heating effect to a DC supply of the same voltage!!!! This has been stated several times in this Blog by several people, you do not seem to want to understand it for some reason?????

Surely it is really quite simple?

If you need to see the mathematics, I can recommend the following web site:-

Root mean square

there you will find there the following paragraph also, please note the underlined sentence below!! Its extremely important if you really wish to correctly understand and just not show your ignorance on this matter !!! (For constant signal in this case, they mean DC!!!)

Average electrical power

Engineers often need to know the power, P, dissipated by an electrical conductor of resistance, R. It is easy to do the calculation when a constant current, I flows through the conductor. It is simply:

However, if the current is a time-varying function, I(t), the calculation is more complicated. Instead, the average power is used. That is,

	(where denotes the mean of a function)
( R is constant, and so it can be brought outside the average)
(by definition of RMS)

So, the RMS value, I_RMS, of the function I(t) is the constant signal that yields the same average power dissipation.

Thanks Andy Germany for correct & fiiting reply to No.28

Thank you kind Sir!!

+ve or -ve voltage across a resistive load will not make any differance, as resistive elements are non-polarised...

Well, not exactly true, .... when I was doing 1st year electronics, one of the brighter of the students asked which end of a resistor is positive and which is negative, so he knew which direction to insert it in the circuit.

I said that the gold tolerance band goes to the -ve of his circuit.

Then was promptly asked what happens if I needed to use it a AC circuit, I said he'd need to use the resistors with the Brown band, and make sure the 1st cycle went positive, or he'd have a problem.

I wonder if he is still following your advice today?

I hope so, its the only way to learn....

post a wrong answer, and then you either get flamed, or you get at least 1 answer that will enlighten you how it should have been answered.... its easier than saying "I don't really know, but I'll give it a go anywayz"

Dear Mr.Sunilwani,

Since you have mentioned HEATER - which is a Resistive Load, the frequency has NO IMPACT. If by chance some Inductance or Capacitance is found, then The Frequency variation will have an impact on the working.

DHAYANANDHAN.S