CapacitorsCapacitors101101

The Facts about Capacitors and The Facts about Capacitors and Capacitive Electrical Capacitive Electrical

Filters...Filters...

BASIC QUESTIONS:BASIC QUESTIONS:What are CAPACITORS?What are CAPACITORS?

What are their MEASURES?What are their MEASURES?

How are they BUILT?How are they BUILT?

What do they DO?What do they DO?

How are they used in FILTERSHow are they used in FILTERS??

#1) What is a capacitor?#1) What is a capacitor?A circuit A circuit device that device that conducts AC conducts AC current and current and doesn’t doesn’t conduct DC conduct DC current.current.

Physical examples of commercial capacitors

You can buy them in all sizes and values.

#2) What are a capacitor’s measures?#2) What are a capacitor’s measures?Basic unit of capacitance: Farads (F).Basic unit of capacitance: Farads (F).

Just like Volts of a battery or Ohms of a resistor.Just like Volts of a battery or Ohms of a resistor.Very large unit Very large unit –– usually we use milliusually we use milli--Farads Farads (mF=0.001 F), micro(mF=0.001 F), micro--Farads (Farads (µµF=10F=10--66 F), nanoF), nano--Farads (nF=10Farads (nF=10--99 F) or picoF) or pico--Farads (pF=10Farads (pF=10--1212 F).F).They are rarely equal to the value marked. Most are They are rarely equal to the value marked. Most are W W 20% tolerance.20% tolerance.

They have a maximum working voltage They have a maximum working voltage specification.specification.

Exceeding that specification may damage the device.Exceeding that specification may damage the device.

They must be specifically designed and They must be specifically designed and marked for DC use or for AC use:marked for DC use or for AC use:

For DC use, the polarity should be marked.For DC use, the polarity should be marked.–– Reversing the polarity may damage the device.Reversing the polarity may damage the device.

Using a DC rated capacitor for large voltage AC use Using a DC rated capacitor for large voltage AC use may damage the device.may damage the device.

#3) How is it constructed?#3) How is it constructed?

Dielectric region

The dielectric may be one of the following:

Air Certain plastics:Paper & mineral oil PolyamideMica PolycarbonateGlass PolyethyleneCeramic PolypropyleneTantalum oxide PolystyreneAluminum oxide Polyester

PVCMylar

Metal plate

Metal plate

The simplest capacitor is a parallel plate type as

shown here. Two conductive plates that do

not touch are separated by a dielectric space region.

Parallel plate test capacitorParallel plate test capacitor

Insertable Plexiglas dielectric

Two Aluminum plates separated by a small air

gap. One wire to each plate

What difference does the dielectric material make?What difference does the dielectric material make?

INPUT WAVE 4 V. pk-pk, 10 kHz

TEST SET UP

C

I

If more AC current flows through the circuit, a greater voltage will be measured across Zin.

Plastic dielectric increases the capacitance over an air dielectPlastic dielectric increases the capacitance over an air dielectric.ric.

VOLTAGE ACROSS Zin

AIR DIELECTRIC

PLEXIGLAS DIELECTRIC

1.7 V. pk-pk

2.3 V. pk-pk

An increased capacitance allows more current to

flow at a given frequency.

C=12 pf

C=22 pf

Constructing a practical capacitor.Constructing a practical capacitor.

Aluminum foil

(2 sheets)

Waxed paper

(2 sheets)A

B

Just roll the two plates

together with dielectric

material as a separating medium.

Overall plastic

covering

HandHand--building a prototype capacitorbuilding a prototype capacitorTwo aluminum strips and two wax paper strips ready to align and roll. (Three feet long, 4.5 inches wide.)

1 2

3 4

Rolled up and taped.

Resistance check: open

line (OL)

Capacitance value =

0.067 µF.

3

#4) How is a capacitor used?#4) How is a capacitor used?As a temporary store of DC electric As a temporary store of DC electric charge charge –– almost like a battery.almost like a battery.As a timing element in DC circuits.As a timing element in DC circuits.As a phase shifting element in AC As a phase shifting element in AC circuits.circuits.As an RMS voltage support element As an RMS voltage support element in AC power circuits.in AC power circuits.As a block of DC signals and a As a block of DC signals and a passageway for AC signals.passageway for AC signals.As a AC circuit filter element.As a AC circuit filter element.

How does a capacitor How does a capacitor react to DC current and react to DC current and

voltage?voltage?The reaction is temporary.The reaction is temporary.No steady state (longNo steady state (long--term) DC term) DC current flows through the current flows through the capacitor.capacitor.See the charge/discharge See the charge/discharge schematic and waveform in the schematic and waveform in the next two slides.next two slides.

Charging/discharging with DCCharging/discharging with DCCapacitor discharged Capacitor charging, temporary current flow

Capacitor charged, but discharging by leakage Capacitor discharging, temporary current flow

Charging/discharging with DCCharging/discharging with DC

2

1

3

4Discharged

Charging through R1

Naturally discharging slowly through its own internal leakage resistance

Quickly discharging through R2

1Discharged

C

#5) What is an electrical filter?#5) What is an electrical filter?A filter selectively passes or does not pass a A filter selectively passes or does not pass a portion of the total range of AC frequencies portion of the total range of AC frequencies

applied to its input (pass means unattenuated).applied to its input (pass means unattenuated).

Practical filters begin their filtering at a Practical filters begin their filtering at a frequency of 1/10frequency of 1/10thth the “knee” frequency or the “knee” frequency or

end their filtering action at 10 times the “knee” end their filtering action at 10 times the “knee” frequency depending on the filter type.frequency depending on the filter type.

Four types of filtering action:Four types of filtering action:Low passLow passHigh passHigh passBand passBand pass

Band rejectBand reject

Low Pass FilterLow Pass Filter

No attenuation of the input frequency until a certain frequency point, then as the frequency through the filter increases, the input is attenuated more and more.

“Knee” frequency

High Pass FilterHigh Pass Filter

As the frequency through the filter increases, the input is attenuated less and less until a certain frequency point, then there is no attenuation of the input.

“Knee” frequency

Band Pass FilterBand Pass Filter

Within a certain range of frequencies, there is no attenuation of the input, below a certain frequency point and above a second frequency point, the input is attenuated.

“Knee” frequency 2

“Knee” frequency 1

Band Reject FilterBand Reject Filter

The input is attenuated within a certain frequency range, below a certain frequency point and above a second frequency point, the input is not attenuated.

“Knee” frequency 2“Knee”

frequency 1

Low Pass Filter ActionLow Pass Filter Action

Low frequency

High frequency

Unattenuated

Attenuated

High Pass Filter ActionHigh Pass Filter Action

Low frequency

High frequency

Unattenuated

Attenuated

A real filterA real filter

INPUT WAVEFORM

4 V. pk-pk.Higher

frequencies that pass through are more attenuated.

“Knee” frequency = 1 kHz

A real low pass filterA real low pass filterOUTPUT WAVEFORMS

10 Hz

100 Hz

1,000 Hz

10,000 Hz

Input Frequency

Unattenuated

Filtering action beginning

“Knee” frequency, filtering very evident

Very attenuated

Size does matter!Size does matter!

Continuous Input Sinewave (fixed frequency)

Low Pass Filters

Oscilloscope

““Knee” frequencies for test fixture:Knee” frequencies for test fixture:

1 kiloHz1 kiloHz

10 kiloHz10 kiloHz

100 kiloHz100 kiloHz

1 MegaHz1 MegaHz

10 MegaHz10 MegaHz

Knee freq.Knee freq.

Very attenuatedVery attenuated

Filter action very evidentFilter action very evident

Filter action just beginningFilter action just beginning

UnattenuatedUnattenuated

UnattenuatedUnattenuated

Results for LP filterResults for LP filter

10.0 10.0 µµFF

1.0 1.0 µµFF

0.1 0.1 µµFF

0.01 0.01 µµFF

0.001 0.001 µµFF

CapacitorCapacitor

Remember: Input frequency = 10 kiloHz

RReessuullttss

Switch position

1

2

3

5

4

0.001 mfd

0.01 mfd

0.1 mfd

1.0 mfd

10.0 mfd

Results of capacitor sizeResults of capacitor sizeAs the microFarad As the microFarad size increases, the size increases, the 10 kHz input 10 kHz input frequency current is frequency current is more easily shunted more easily shunted to ground.to ground.This increased This increased current flow current flow through the through the capacitor (lower capacitor (lower and lower and lower impedance) results impedance) results in less and less in less and less voltage drop across voltage drop across the capacitor.the capacitor.

0.061.5910.0 mfd

0.5515.91.0 mfd

2.51590.1 mfd

3.815900.01 mfd

3.98159000.001 mfd

Vc pk-pkin OhmsCapacitor

CalculatedImpedance

Hertz10,000Frequency =

Vin = 4 v. pk-pk R1 = 100 Ohms

Capacitor filter Capacitor filter conclusionsconclusions

The higher the AC frequency of a The higher the AC frequency of a current through a capacitor, the less current through a capacitor, the less attenuation occurs. The lower the AC attenuation occurs. The lower the AC frequency of a current through a frequency of a current through a capacitor, the more attenuation occurs.capacitor, the more attenuation occurs.The larger a capacitor (in microFarads), The larger a capacitor (in microFarads), the less attenuation for high frequency the less attenuation for high frequency AC currents through it. The smaller a AC currents through it. The smaller a capacitor (in microFarads), the more capacitor (in microFarads), the more attenuation for high frequency AC attenuation for high frequency AC currents through it.currents through it.

A Capacitor Across Home Power Lines (Phase to Neutral) A Capacitor Across Home Power Lines (Phase to Neutral) Acts like a Low Pass FilterActs like a Low Pass Filter

For a low frequency (60 Hz) circuit that has For a low frequency (60 Hz) circuit that has some additional high frequency (noise) content, some additional high frequency (noise) content, the filter will pass the low frequency and not the the filter will pass the low frequency and not the high ones.high ones.

60 Hz with high

frequencies60 Hz

In saying that, however, we In saying that, however, we must realize... ... ...must realize... ... ...

TThe high frequency he high frequency electrical energy does not electrical energy does not simply “disappear”.simply “disappear”.It flows through the It flows through the capacitor from the phase capacitor from the phase conductor to the neutral conductor to the neutral conductor.conductor.

Home wiring without capacitorHome wiring without capacitor

Home with CapacitorHome with Capacitor

Grounded

Before After

Experimental test set upExperimental test set up

phase

neutral

RESULTSRESULTS–– Lamp on Lamp on

dimly dimly

No 20 mfd installed

Test Condition

20 mfd installed

V

I

V

I

The low pass filter action of the capacitor allows more current flow through the neutral.

Same voltage wave

Does NeutralDoes Neutral--toto--Earth voltage change?Earth voltage change?

0.2 v pk-pk

0.8 v pk-pk

0.9 v pk-pk

1.2 v pk-pk

What would it look like if I used a 10kHz high pass What would it look like if I used a 10kHz high pass filter to view the voltage and current waveforms filter to view the voltage and current waveforms

before and after the capacitor is installed?before and after the capacitor is installed?

The oscilloscope will not show the 60-Hz 120 Volt wave

The 10 kHz high pass filter reveals a lot about what The 10 kHz high pass filter reveals a lot about what this capacitor filter does.this capacitor filter does.

No 20 mfd capacitor With 20 mfd capacitor

V

I

Large voltage spike

Small voltage spike

Small current spike

Large current spike

What if I just used a Fluke 77 DMM?What if I just used a Fluke 77 DMM?

This DMM has a moderately low frequency response, so you cannot discern much other than an increased

current with the capacitor installed.

0IYESON0 IYESON

0.82 A.INOON0.46 A.INOON

14 mV.VYESON13 mV.VYESON

120.5 V.VNOON

120.4 V.VNOON

0IYESOFF0IYESOFF

1 A.INOOFF0INOOFF

8 mV.VYESOFF9 mV.VYESOFF

122.6 V.VNOOFF

120.8 V.VNOOFF

valueV or I10 kHz filter

LAMPvalueV or I

10 kHz filterLAMP

20 mfd filter installedno 20 mfd filter

Use a Fluke 87 III DMM....Use a Fluke 87 III DMM....

25 mA.IYESON18 mA.IYESON

.87 A.INOON.64 A.INOON

48 mV.VYESON105

mV.VYESON

120.4 V.VNOON

120.3 V.VNOON

0IYESOFF0IYESOFF

1 A.INOOFF0INOOFF

14 mV.VYESOFF14 mV.VYESOFF

122.5 V.VNOOFF

120.7 V.VNOOFF

valueV or I

10 kHz HP

filterLAMPvalueV or I

10 kHz HP

filterLAMP

20 mfd filter installedno 20 mfd filter

The increased noise current with the capacitor installed has most of its frequency content below 10 kHz.

This DMM has a much higher frequency response.

NEV changesNEV changes

Volts0.250.23InOnVolts0.190.13OutOnVolts0.280.29InOffVolts0.0070.02OutOffUnitsFluke 87Fluke 77CapacitorLAMP

Fluke DMM NEV measurement

Where is the neutral connected?Where is the neutral connected?

Code: Neutral and grounding conductors are bonded at the service entrance panel.

Current source point

Without capacitors, noise voltage is only on the

phase wire that you do not touch.

With capacitors installed, noise voltage is on the neutral/ground system which you do touch.

Some claims Some claims from a from a

commercial commercial vendorvendor

The monitor has a high-pass filter that only measures noise voltage from the phase to neutral above 10 kHz. This voltagevoltage will be reduce by the capacitors. The monitor measures neither NEV nor current on the neutral.

What happens to the level of What happens to the level of EMF near the capacitor?EMF near the capacitor?

1.9 mG without capacitor plugged in.

3.9 mG with capacitor plugged in.

So what EMF is reduced?

What about the proof that is offered?What about the proof that is offered?Oscilloscope pictures of PhaseOscilloscope pictures of Phase--toto--Neutral voltage.Neutral voltage.––Before capacitor is installed.Before capacitor is installed.––After capacitor is installed.After capacitor is installed.

Picture of phasePicture of phase--toto--neutral noise neutral noise voltage using a 10 kHz high pass voltage using a 10 kHz high pass filter on the oscilloscope input.filter on the oscilloscope input.––Before capacitor is installed.Before capacitor is installed.––After capacitor is installed.After capacitor is installed.

No NEV picture.No NEV picture.No picture of current on Neutral.No picture of current on Neutral.

10kHz hi-pass

Waveforms offered as “Proof” of capacitor action. “Before” picture.

20 mfd

Noise voltage can be seen on phase conductor

Nominal amount of expected noise voltage, common to all electrical systems. Approx. 40 mV pk-pk with occasional spikes.

Note the scale

This is the wave they claim they see:This is the wave they claim they see:

Time scale expanded by factor of 10 to see sinewave shape.

Same vertical scale

Same vertical and time scale.

10kHz hi-pass

Waveforms offered as “Proof” of capacitor action. “After” picture.

20 mfd

The 60-Hz wave is still noisy after the 20 mfd. filters

are installed!!

The spikes are filtered, but the average noise voltage is not reduced. It is still approx. 40 mV pk-pk.

Note the scale

This is the wave they claim they see:This is the wave they claim they see:

Same vertical and time scale

AnalysisAnalysis1)1) The noise spikes appear to be random and The noise spikes appear to be random and

are not a continuous waveform.are not a continuous waveform.2)2) Being random, they will have different Being random, they will have different

durations of existence and various durations of existence and various amplitudes whenever they occur.amplitudes whenever they occur.

3)3) There is no way to determine a “frequency” There is no way to determine a “frequency” because there is no continuous waveform, because there is no continuous waveform, other than the 60other than the 60--Hz wave the noise is riding Hz wave the noise is riding on.on.

4)4) ‘RF Energy’ is a term that only applies to ‘RF Energy’ is a term that only applies to frequencies above 10 kHz and more usually frequencies above 10 kHz and more usually above 100 kHz. ‘RF’ means ‘radio frequency’ above 100 kHz. ‘RF’ means ‘radio frequency’ which are the frequencies receivable by a which are the frequencies receivable by a radio.radio.

96 mV difference

10kHz hi-pass

?1/0.06ms = 16.6 kHz in this one area only

Note that the voltage analysis below does not always jibe with the instrument data

?

10kHz hi-pass

1/1.28 ms = 781 Hz at this point only

Max. amplitude = 80 mV pk-pk, Avg. = 40 mV pk-pk.

ditto

?

20 mfd

????

The best you can say is there

occurred 3 noise spikes of about 100, 500

and 750 millivolts of

about 60 microseconds duration that appear to be

non-synchronous

with the power wave. Source

is unknown but most likely

from a near-by equipment

switching event (on or off).

1

32

These three spikes appear on this waveform too, but are too small to see in comparison with the 340 V. pk-pk. of

the 60-Hz wave. If you don’t touch the 340 V. pk-pk wave, you will not contact the 750 mV, etc. spikes.

The filter obviously shunted some the spikes, if they recurred, to the neutral/ground circuit, leaving a continuous background noise level of about ±40 millivolts peak (=28 mV rms). This level is imperceptible to humans as universal common electrical noise. No discernable frequency exists. The conclusion that spikes were solely from the utility is unsupported. There is no RF energy involved since there is no steady-state frequency above 10 kHz.

Select any two other adjacent wave peaks and the calculated “frequency” will be different. It is random, not fixed. On this horizontal scale, 10 kHz would occupy 1/20th division. 100 kHz would occupy 1/200th division. This is not ‘RF’ voltage.

CONCLUSIONSCONCLUSIONSTo say that the installed capacitors To say that the installed capacitors reduce noise voltage on the phase reduce noise voltage on the phase conductor is generally true, but....conductor is generally true, but....It only reduced the spikes, if they It only reduced the spikes, if they recurred, not the commonly found recurred, not the commonly found background noise voltage.background noise voltage.What is also true, but unstated, is What is also true, but unstated, is that there is an increase in neutral that there is an increase in neutral conductor noise current and an conductor noise current and an increase in neutral conductor 60increase in neutral conductor 60--Hz Hz current as well as an increase in current as well as an increase in NeutralNeutral--toto--Earth voltage (NEV) due Earth voltage (NEV) due to those currents.to those currents.

CONCLUSIONSCONCLUSIONSAnyone can touch this NEV, but Anyone can touch this NEV, but they do not usually touch the 120they do not usually touch the 120--Volt rms phase voltage.Volt rms phase voltage.Therefore, the conclusion that Therefore, the conclusion that adding these capacitors will reduce adding these capacitors will reduce a person’s exposure to high a person’s exposure to high frequency electricity is wrong. frequency electricity is wrong. Capacitors enable a person to be Capacitors enable a person to be exposed to more high frequency exposed to more high frequency (and 60(and 60--Hz) electricity in the form Hz) electricity in the form of elevated touch potentials on all of elevated touch potentials on all grounded objects.grounded objects.

CONCLUSIONSCONCLUSIONSConclusion about “RF” energy Conclusion about “RF” energy being involved is wrong being involved is wrong –– there is there is no RF energy involved in these no RF energy involved in these graphs.graphs.There is only a normal amount of There is only a normal amount of environmentally common noise environmentally common noise that can be found at any and every that can be found at any and every similar measurement point at any similar measurement point at any time using this inappropriate time using this inappropriate measurement protocol.measurement protocol.