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Audio Description – Course 2, Lenz’s Law and the Counter Electromotive Force

– Clip 1 Introduction – Clip 2 Course Description – Clip 3 Test Parameters – Clip 4 Test Equipment – Clip 5 Lenz’s Law – Clip 6 Coil in Circuit – Clip 7 Switch Closed – Clip 8 Switch open, Back EMF – Clip 9 With Transistor and Diode – Clip 10 Overview – Clip 11 Light Bulb as load – Clip 12 Sine Wave at 5 Volt – Clip 13 Shunted to ground – Clip 14 Calculation 1 – Clip 15 First Summary – Clip 16 Light Bulb connected – Clip 17 Load and coil connected – Clip 18 Calculations 2 – Clip 19 Second Summary – Clip 20 Change from Sine wave to Square wave – Clip 21 Analyse Square wave to load – Clip 22 Calculations 3 – Clip 23 Third summary – Clip 24 Measure floating ground Back EMF – Clip 25 Replace power supply with Battery – Clip 26 Analyse charging behavior – Clip 27 Calculations 4 – Clip 28 Conclusion – Clip 29 End of Course 2

Clip 1

Clip 1

In this course I will highlight the condition under which a Back EMF occur. I will demonstrate that the load connected to the back EMF source via the Diode is in fact getting all the power from the battery. We will then analyse options to harness the Back EMF without power penalty.

Clip 2

Clip 2

Lenz’s Law and the Back EMF

– State the function of the counter electromotive force on a coil
– Analyze the Bedini circuit as example for harnessing Back EMF
– Prove false assumption of back EMF charging and harnessing
– Show options to efficiently utilize this excess energy

Clip 3

Clip 3

Test Parameters

1. Voltage source is a Bench Top Power Supply
2. One Amplifier Module with 2N3055 Transistor
3. Isolation transformer with one coil in use
4. Bedini circuit and the freewheel diode
5. A 5 Watt 12 Volt light bulb
6. 8AH, 12 Volt Sealed lead acid battery

Clip 4

Clip 4

Test Equipment

Tools

– EA, PS 2000 B, 84 V 5 A, Power supply
– Agilent/Keysight InfiniVision 3000 Series oscilloscope DSO3014A
– Agilent/Keysight U1232B, U1242B DMM
– Agilent/Keysight U1453A Series Insulation resistance tester
– Agilent/Keysight 34450A Bench Top DMM 5.5 digits
– Agilent/Keysight U1115A Remote logging display
– Agilent/Keysight U1117A Class 1 Bluethooth to IR adapter
– Agilent/Keysight U1177A Bluetooth to IR adapter

Clip 5

Clip 5

Lenz’s Law

is a common way of understanding how electromagnetic circuits obey Newton’s third law
and the conservation of energy.
An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes
the original change in magnetic flux.

Lenz’s law is shown with the negative sign in Faraday’s law of induction:

Which indicates that the induced emf (ℰ) and the change in magnetic flux (∂ΦB) have opposite signs.
As such it is a qualitative law that refers to the direction of induced current and its magnetic field without
quantitatively defining their magnitudes.

Clip 6

Clip 6

 

Clip 6

A coil in a circuit operated by a switch. the switch represents any semiconductor or physical switch

Clip 7

Clip 7

When the switch is closed the current moves from the negative
pole of the battery to the positive.

 

Clip 8

Clip 8

When the switch is opened the stored energy in the material of the core of the
coil is reversing polarity and is rushing back to the positive polarity of the battery.
In this scenario it does not happen because the circuit does not offer any path
back to the power source and causes damage through surges on the switch or in the windings,Clip 9

 

Clip 9

The switch is now the transistor and the back EMF is given the path via the diode to either a load like a lamp or to a battery to charge. We will now investigate what that means in terms of power draw from the source power.
This subject was briefly discussed by using the freewheel diode to remove the Back EMF voltage spikes in a motor.

Clip 10

Clip 10

We will go now through the individual values from the diagrams in experimental test. I have applied a sine wave with 500 Hz and set the voltage to 5 Volt. We have as components the Isolation transformer with one coil used. The 2N3055 power transistor. I will present in the future the Oscilloscope display here on an external monitor for easier viewing. I measure with the new Agilent 34450A DMM. We will use a load later on. A 5 12 Volt, 5 Watt light bulb. The monitor shows the green graph for current and the yellow graph for voltage.

Clip 11

Clip 11

The DMM is currently connected to the load and is showing the cold resistance of 2.795 Ohm. The red wire on the transistor is marked for the output of the Back EMF. As seen in the diagram. If this wire is not connected to a load. You risk to destroy the transistor or the winding’s of the coil.

Clip 12

Clip 12

Our first test to connect the Back EMF wire to ground and measure the impact. We are connected with a sine wave signal. The transistor is energized with a 500 Hz signal and we measure 61mA at 5 Volt. current draw. Here the Back EMF is not shunted to ground. On the monitor you see the stretched sine wave. This is caused by the soft iron core and the type of winding configuration.

Clip 13

Clip 13

We connect the Back EMF wire now to ground and measure the restricted current of 1.35 A. I used current restriction and the voltage did float back to 3.5 Volt. What happened. We just connected the power supply poles through the coil and short circuit it. We do now the same test with the light bulb.

Clip 14

Clip 14

We integrate our measurements into the formula

Sine wave 500 Hz, 5 Volt, 0,062A = 0.31Watt
PK-PK Volt = 8.9 Volt, I = 0.047A and 0.164 W

Back EMF now shunt to ground
Volt limited to 3.9 Volt for I = 1.347 A and 6 .735 Watt

Clip 15

Clip 15

First Summary

Sine waves do not inherit voltage spikes in form of back EMF. Therefore
all values on the scope are very low and the trace curve symbolizes
a reduced sine wave.
This characteristic is based on the parameters of the Isolation transformer

Shunting now the back EMF to ground does show that we short circuit.
The current is in the example restricted to 1.35 A which does result in the
reduction of voltage to 3.5 Volt.
The transformer has only little resistance to play a crucial role in
reducing the current draw.
We move on to test it with the light bulb

 

Clip 16

Clip 16

I will now connect the light bulb. I have conducted the same test in Ohm’s law. You might be familiar with the outcome when you have seen this video. The light bulb on its own is drawing 0.38019 A for 12 Volt. We conduct the same test as before but will run it via the coil.

Clip 17

Clip 17

We have now the light bulb integrated into the circuit via the Back EMF wire and measure the result. We measure at 11.9 Volt 0.412 A. this value is the sum of the coil plus the load. We take now off the signal to the transistor and see the load continues to run with its own current requirement. We measure 0.350 A. That is a bit lower but we have to consider the resistance of the coil on top. A load under this circuit configuration does not require any signal via the transistor to run. If we reflect on what we just learned you will figure out that a battery instead of the load will be charged by the source battery. In Bedini’s configuration he uses two batteries in series. This has even a larger impact as more current is drawn from the source battery, because the potential is higher. The Back EMF is not charging anything at all. The power would be far too low to have any impact on the battery.

Clip 18

Clip 18

We integrate our measurements into the formula

Load is now a light bulb with 12 Volt and 5 Watt
First, connected to the power source direct.
V = 12 Volt, I = 0.379 A = 4.548 Watt
For cold resistance of 2.748 Ohm

Connected now via the Back EMF and the coil
V= 12 Volt, I = 0.412 A = 4.944 Watt

No signal to coil
V = 12 Volt, I = 0.350 A = 4.2 Watt
This value is inclusive the resistance of the coil

Clip 19

Clip 19

Second Summary

It is the same scenario as it was with the shunted Back EMF to ground
The light bulb draws its current to the level it is allowed by the
resistance of the coil. When the signal is connected the coil used the
additional 60 mA missing from the no signal measurement to the bulb.

Now, where is the magic?

Well, not here. The Bedini circuit uses the arrangement of the batteries
to charge each other. The Back EMF is restricting the current flow
to the batteries and therefore pulsed DC. More details at the end.Clip 20

 

Clip 20

We restart the original configuration with a sine wave. At the monitor you will see the little impact it has when compared to spikes we like to see. If we change that now to a square wave we see a different picture. We see a slightly higher current requirement. We also notice the voltage spikes we like to see. We have 165 Volt spikes. On the cursors I can measure the individual source. Here is the current shown. I switch that to voltage.

clip 21

Clip 21

On the voltage cursor I see a -16 Volt which is the original propagation trough the coil and the bounce back voltage of 165 Volt. The power we see is much higher. However it is not used at all. We use 1.2-1.3 Watt but see a higher value on the scope. Harnessing the Back EMF has the same impact by drawing the current from the power source. By connecting the load we shunt to ground and pull back the Back EMF so that more current can flow trough the load. The voltage drop does indicate 24 Volt as left over voltage from the Back EMF. Also the current is distorted and the overall power we did measure before is almost gone. Not gain here. That is how the battery sees the current.

Clp 22

Clip 22

We integrate our measurements into the formula

We change the signal to a square wave and measure the following
V= 12 Volt, I = 0.7121A = 1.452 Watt

Back EMF values
PK-PK V= 165 Volt, I = 0.130 A, and 6.84 Watt

Connected to the Load of the light bulb
V = 12 Volt, I = 0.466 A = 5.592 Watt

Voltage drop of the Back EMF
PK-PK V = 24 Volt, I = 0.132 A, and 1.38 Watt

Clip 23

Clip 23

Third Summary

The change to the square wave does provide the Back EMF spikes.
Current draw is slightly increased. When we connect the load we see the
same picture as before. Now the voltage drop is kicking in but the current
is not used from the Back EMF, resulting in an decreased power output.
All power is drawn from the battery and is added on top of the coil power
requirement. This is a waste effort of circuit topology. There is no Back EMF
harnessing.
We will look now what can be done to change that.

Clip 24

Clip 24

One option to look at is to harness the Back EMF in a different fashion. Goal here is not to use the power from the source but only use peaks to store it in capacitors. I use couple of new instrumentation to demonstrate that. Still have be aware that the Back EMF as such is not access energy from the coil. This energy was provided by the power source and is released in a very short time. You should replace your mains depending power source with a battery. Both the initiator circuit and the storing circuit need to have a floating ground. If ground is direct connected we draw again power from the source. I have two ground systems or Three to be precise. The house ground to mains. A copper rod array and a zinc plate ground, 3 feet deep in the ground. I use this for the capacitor bank as ground. there is a potential between house ground and my zinc ground of 1.5 Volt. At 11 volt it draws 107 mA and does not change much over the charging cycle. current goes slowly up. You notice on the monitor that the Back EMF will increased based on the charging level. We see a different picture from a power requirement. When I shunt the capacitor to ground we draw more current. this is indicating that we still have a link to the power source. We replace the power source now with a battery.

Clip 25

Clip 25

I wan to make sure now not to use a common ground. I replaced the bench power supply and the bench DMM with handheld versions. With OLED display is the 1453A a resistance meter with DMM capabilities. I use the remote logging device the U1115A and have connected the other two DMM’s because the display is switching off after 5 seconds.

Clip 26

Clip 26

I connect now and have 112mA current draw. the battery is at 12.69 volt. WE see almost no change in current draw during the charging period but it goes slightly up over time. The current variation is between 2-3mA. If I keep the push button pressed I shunt the current to ground and draw more current from the power source. I indicates 135mA. That can be related to the circuit not 100% common ground floating. The Oscilloscope and signal is connected still to ground. They have to be independent.

Clip 27

Clip 27

We integrate our measurements into the formula

We harness the Back EMF into a capacitor back via a bridge rectifier.

Bench Power voltage is 11 Volt, I = 0.110 A = 1.21 Watt

Battery voltage is 12.6 Volt, I = 0.113 A = 1.424 Watt

The current of the back EMF does not change and is steady at 132 mA
The Back EMF is during the charging time reduced and increases with
charging level of the capacitor bank.
The battery current various between charge about 2-3 mA
The test was not entierly without gound connection. The Oscilloscope
used ground. To be accurate I would recommend to do the test independend
from ground. This should not show any penalty anymore for current draw from
the back EMF when short circuit as load.

Clip 28

Clip 28

Conclusion

The back EMF is the result of the counter motive force and exist only when sharp
pulses and low frequency is available. They are only exposed when the core
material is storing energy and suddently released. This is only possible with
square or pulse waves as in turning on a switch.
To harness the Back EMF the system has to have a floating ground. No current
will be drawn under that condition from the power source. The power available
is the power to drive the coil. When the coil is not in use as transformer most of
the energy is wasted and not utilized. The overall power efficiency is far below
100%. Correct utilization and avoiding the back EMF is more beneficial. To mark
this circuit as a Back EMF charging circuit is not true. It is pulsed DC from the
power source and controlled by the Back EMF. Current is restricted by using
a resistor on the power source. This is proven, as tested not able to fully
charge a battery.

Clip 29

Clip 29

 

Clip 29

The End Course 2

Lenz’s law
Counter Electromotive Force

Go to top

Clip 30