# Frequency Question -- 24 VAC, 60 Hz versus 24 VAC, 20 Hz

• nicy12
In summary, the conversation discusses the use of two different sources (1. 24 VAC, 60 Hz and 2. 24 VAC, 20 Hz) to power a load and the potential effects on the load and current flowing. It is determined that for a purely resistive load, the frequency does not significantly affect the power delivered. However, if the load includes other elements such as a transformer or parasitic elements, the frequency may have a greater impact. The conversation also mentions the importance of considering parasitic elements and their effects on frequency.
nicy12
Suppose that I have two sources: 1. 24 VAC, 60 Hz and 2. 24 VAC, 20 Hz
Then I will use it to power into certain load (maybe we can assume a purely resistive load to simplify the question). What would be the effect of those sources to the load? How about the current flowing? I think (1) and (2) would produce same magnitude but does its frequency follows the the frequency of inputs? or it will differ?

The power dissipated in the resistor is I*I*R. Where I is the RMS (root mean square) of the sinusoidal current.

The RMS of a sinusoid is 0.707 of the peak value and independent of frequency.

nicy12 said:
Suppose that I have two sources: 1. 24 VAC, 60 Hz and 2. 24 VAC, 20 Hz
Then I will use it to power into certain load (maybe we can assume a purely resistive load to simplify the question). What would be the effect of those sources to the load? How about the current flowing? I think (1) and (2) would produce same magnitude but does its frequency follows the the frequency of inputs? or it will differ?
Series connection of such voltage sources and the load (in the most simple case) gives voltage drop waveform like this one
If the load is resistor current is of the same shape i(t)=v(t)/R

Its hard to understand exactly what you are asking. You want to connect one supply or the other to the load? Or, you are connecting them in series to the load? And I have no idea what you mean by "the effect of those sources to the load"

But the current at any time is the result of the instantaneous voltage across the load.

The power dissipation due to the sum of 2 AC waveforms depends on the correlation between the waveforms. If they are phase coherent (exact frequency multiples) the end result is different than if they are not exact frequency multiples. (read about summing RMS voltages)

nicy12 said:
Then I will use it to power into certain load (maybe we can assume a purely resistive load to simplify the question).
I understand you to be using one source at a time. As others have explained, for a resistive load the frequency does not alter the power delivered. The waveform still spends half of its time positive, and the other half negative, regardless of frequency of that sinewave. So with equal amplitudes of sinewave, the power will be the same for either source.

nicy12 said:
Suppose that I have two sources: 1. 24 VAC, 60 Hz and 2. 24 VAC, 20 Hz
Then I will use it to power into certain load (maybe we can assume a purely resistive load to simplify the question). What would be the effect of those sources to the load? How about the current flowing? I think (1) and (2) would produce same magnitude but does its frequency follows the the frequency of inputs? or it will differ?

If your load is not purely resistive (like if it includes a transformer), then the frequency makes a *big* difference.

davenn
berkeman said:
If your load is not purely resistive (like if it includes a transformer), then the frequency makes a *big* difference.

yes indeed, and people that bring back to their own country devices with electric motors in them, they get a transformer to convert the AC voltage 110-220V or 220 - 110 VAC for example that then wonder why their unit plays music at the wrong speed and other problems the 50 / 60 Hz makes quite a difference

Dave

nicy12 said:
Suppose that I have two sources: 1. 24 VAC, 60 Hz and 2. 24 VAC, 20 Hz
Then I will use it to power into certain load (maybe we can assume a purely resistive load to simplify the question). What would be the effect of those sources to the load? How about the current flowing? I think (1) and (2) would produce same magnitude but does its frequency follows the the frequency of inputs? or it will differ?

To Clarify My Question, I made an image to show it:

What will be the effect of each sources to the 10K resistor? is there any siginificant difference when the frequency was change?

Assuming 24VAC RMS sinewave. Also, assuming no parasitic capacitance or inductance (which is impossible in the real world)
In both cases the circuit will conduct 2.4ma AC and the resistors will dissipate 57.6mW.
You could theoretically have a resistive element with a fast enough thermal time constant that could be detected by a temperature sensor of some sort. Other than that, there is no difference.

You could draw in parasitic elements such as capacitance and inductance, radiation resistance, etc. Those elements would be affected by frequency.

meBigGuy said:
Assuming 24VAC RMS sinewave. Also, assuming no parasitic capacitance or inductance (which is impossible in the real world)
In both cases the circuit will conduct 2.4ma AC and the resistors will dissipate 57.6mW.
You could theoretically have a resistive element with a fast enough thermal time constant that could be detected by a temperature sensor of some sort. Other than that, there is no difference.

You could draw in parasitic elements such as capacitance and inductance, radiation resistance, etc. Those elements would be affected by frequency.

So in this example, you are favoring for source with 60 Hz rather than the source with 20 Hz?

I have no idea what you mean. I'm not "favoring for" anything. In what way do you conclude I am "favoring". I don't think I said or implied anything judgmental about either source. I'm not even sure what your overall point is in this thread. Am I missing something?

The only real difference I see is that the 60Hz circuit is on the left.

When I said "In both cases the circuit will conduct 2.4ma AC and the resistors will dissipate 57.6mW." I probably should have added that the 60Hz source produces 60 Hz current and vice versa, but I thought that was too obvious to have to even mention.

What are you getting at?

I am afraid that I misunderstood your comment. But regardless of that, I think this quote answered the difference of the above circuits (which have different frequencies) :
meBigGuy said:
You could draw in parasitic elements such as capacitance and inductance, radiation resistance, etc. Those elements would be affected by frequency.

I'm glad that quote works for you, because I also felt it pretty much summed up the differences. Glad to help

## What does 24 VAC, 60 Hz versus 24 VAC, 20 Hz mean?

24 VAC refers to the voltage of the alternating current (AC) power supply, while 60 Hz and 20 Hz refer to the frequency of the AC power. This means that the power supply is capable of providing 24 volts of electricity at either a frequency of 60 cycles per second or 20 cycles per second.

## What is the difference between 60 Hz and 20 Hz frequency?

The main difference between 60 Hz and 20 Hz frequency is the number of cycles per second at which the AC power is delivered. 60 Hz is the standard frequency used in most residential and commercial power supplies, while 20 Hz is a lower frequency that is less commonly used and may have different applications in certain industries.

## Which frequency is better for electrical systems?

This depends on the specific requirements of the electrical system. In general, 60 Hz frequency is more widely used and is considered to be more efficient for most electrical systems. However, some specialized systems may require a lower frequency such as 20 Hz for optimal performance.

## What impact does frequency have on electrical systems?

The frequency of an AC power supply can affect various aspects of electrical systems, such as the speed of motors and the efficiency of transformers. It can also impact the stability and reliability of electronic devices, as some may be designed to operate at specific frequencies.

## How is frequency controlled in AC power supplies?

The frequency of an AC power supply is typically controlled by the power grid and can vary slightly depending on the demand for electricity. In some cases, frequency converters or inverters may be used to convert power from one frequency to another for specific applications.

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