Induction Balanced Coils, IB coils

[mschmahl]

After crashing one pic i get the TX board with coil working.
I have used the scope with 5V/Div and 20uS/Div. I didn´t connect ground, therefor the lines are not so clear.
I didn´t use a 0,1 Ohm resistor in series, because i don´t have one.

Here are some pictures:

messured on TX-End (after BU) without BU-Control connected


messured on TX-Start without BU-Control connected
It looks like the pictures from you tinkerer, but i have 5V/Div and not 200mV/Div. Is this OK?
Where you have connect ground from scope?


messured on TX-Start but with BU-Controll connected.

Greetings from Saxony

[mschmahl]

Today TX looks always similar to picture 3. No changing if BU-controll is connected or not.
One picture from RX, only connected scope on coilcable without RX-Board

[Tinkerer]

The BU control is only for fine adjustment.

Your balance of the coils is not good. Do not worry, it just needs adjustment.

Are your coils still on the nail board?
Remove the nails and tie the RX-BU at a few places. You will see some change in the wave form.
Then lift the RX-BU slightly on one side, while keeping the position centered.
If the voltage increases, this means that the BU is not enough.
If the voltage decreases, there is too much BU.

Why is it not correct?

The calculation does not take into account the difference in the inductance and surface area caused by thick or thin insulation of the wire. Also the mean diameter of the coils changes due to the insulation thickness and the tightness of the bundle tying.

You will notice that if you lift the RX-BU off the nails and then tie them tightly, they will not fit on the nails anymore.
These changes affect the balance. It is not a problem, it just needs to be adjusted.

There is one further mistake that often happens. The TX coil and BU coils need to be wound in opposite direction, or we could say, the current needs to run in opposite direction. If this is wrong, the Voltage on the RX will be very high. In this case just flip the RX-BU and you see how the voltage diminishes dramatically.

You don't have a 0.1 Ohm resistor. You can use 1 Ohm. You connect the scope ground on one side of the resistor and the probe on the other end. Careful, do not cause a short between the 2 ground clips of the scope. Disconnect the other probes from the scope when taking this measurement.

The purpose of looking at the coil current, is to see if the timing is perfect. Why would the timing not be perfect?
the TX coil and the Flyback capacitor form a resonant tank. Due to the tolerances of the capacitors (5%? 10%? 20%? and the inductance of the TX coil, the frequency will be different.
If it is off too much, we can adjust either the timing of the capacitance to make it perfect.

Tinkerer

[mschmahl]

Hello tinkerer,
i´m to stupid to balance the coil. Can you make for me a step by step instruction with information where i have to connect the scope (ground and probe) to make my pictures? they don´t look similar to your´s.

On the last pictures the BU+RX coil was flipover. My son must have touch it.

So i have made new one but now the RX-curves are not opposite. TX look´s wrong too.
The coil is placed on Plastic-boxes 1 m above the floor. The only metall in the near is the coilcable. It lays on the tx windingand hang down.

Should i rewind the coil and make a new one?

[mschmahl]

Or could it be the stw18nm80? On Pin 1 i see the TX-Pulse from the pic with 5V. On Pin2 this pulse is only 0,3V. And the stw don´t go hot although it going hot the first few times. Maybe i have destroyed it. But then i have to order a new one.

[Tinkerer]

Quick reply....

Post 34, the picture shows a problem with the TX.
The problem could be with the Mosfet drive or the Flyback capacitors.

The Mosfet should never get hot. If it gets hot, this indicates that there is a problem.

What is the working voltage of your Flyback capacitors? Are they OK?

A common mistake is to connect the TX - BU - BU control terminals the wrong way. The 47 Ohm resistor or the pot on the BU control will then burn out.

- check the pulse voltage on the Mosfet driver input.
- check the pulse voltage on the gate pin of the Mosfet.

Tinkerer

[mschmahl]

Thank´s tinkerer for your help.
Here are your questions with my answers:

What is the working voltage of your Flyback capacitors? Are they OK? They show 27,6 nF, they have 600V working voltage, these here http://www.digikey.de/product-detail...214-ND/1532434

A common mistake is to connect the TX - BU - BU control terminals the wrong way. The 47 Ohm resistor or the pot on the BU control will then burn out. These resistors are ok.

- check the pulse voltage on the Mosfet driver input.
Pin 2 of TC4452 is 4,09 V messured with multimeter, with scope 5V
- check the pulse voltage on the gate pin of the Mosfet.
This pin is 4,8 V, with scope 6V

[Tinkerer]

Thank´s tinkerer for your help.
Here are your questions with my answers:

What is the working voltage of your Flyback capacitors? Are they OK? They show 27,6 nF, they have 600V working voltage, these here http://www.digikey.de/product-detail...214-ND/1532434
This type of capacitors should be fine. I understand that the combined capacitance of the 2 capacitors in parallel is 27.6nF? This is just a little bit high, combined with your 419uH TX inductance plus any stray capacitance, it will make the Flyback pulse to be about 15us.
The Mosfet switches at 10 us, so this truncates the Flyback, causing the Mosfet to get hot.
If you reduce the parallel capacitance to less than 20nF it should be OK.
A different solution could be to change the Mosfet OFF time to 16us. However, this will reduce the signal response of small, short TC targets somewhat.
To see if the Mosfet is still OK, you could remove one of the Flyback capacitors. the Flyback will then be short enough. If it does not work, probably the Mosfet is bad.
A common mistake is to connect the TX - BU - BU control terminals the wrong way. The 47 Ohm resistor or the pot on the BU control will then burn out. These resistors are ok.

- check the pulse voltage on the Mosfet driver input.
Pin 2 of TC4452 is 4,09 V messured with multimeter, with scope 5V That seems to be OK.
- check the pulse voltage on the gate pin of the Mosfet.
This pin is 4,8 V, with scope 6V

Do not despair, very seldom things work on the first try. It is a good learning process.

Good luck

Tinkerer

[mschmahl]

There are allready 7,8 nF between +12V and Drain from Mosfet (i have soldered both Flyback-Cap´s out). With only 1 Cap the kurves look´s like before only with one spike more.
I don´t have an other STW. Can i use this http://www.sm0vpo.com/_pdf/FQ/FQP6N60C.pdf for test´s?

[mschmahl]

Some good new´s: the mosfet is OK. I have changed to the other(FQP6N60C) and the scope-picture was the same. I also have changed to an other tc4452 but the same scope-shoot.
I think i have connect the scope wrong. Where i must connect the probe and where the ground and how it must look like?
Is it possible to look on coilconnections without coil to see, if the TX-board is working right? How it must look like?
Sorry for my stupid questions.

[Tinkerer]

There are allready 7,8 nF between +12V and Drain from Mosfet (i have soldered both Flyback-Cap´s out). With only 1 Cap the kurves look´s like before only with one spike more.
I don´t have an other STW. Can i use this http://www.sm0vpo.com/_pdf/FQ/FQP6N60C.pdf for test´s?

It will be OK, a bit less current , a bit more power consumption, a bit warmer, but OK with heat sink.
The STW 18nm80 will consume about 50mV.
The FQ/FQP6N60C will use about 150mA, peak Flyback voltage will be about 400V.

The TC4452 would work better with 12V supply

[Tinkerer]

Some good new´s: the mosfet is OK. I have changed to the other(FQP6N60C) and the scope-picture was the same. I also have changed to an other tc4452 but the same scope-shoot.
I think i have connect the scope wrong. Where i must connect the probe and where the ground and how it must look like?
Is it possible to look on coilconnections without coil to see, if the TX-board is working right? How it must look like?
Sorry for my stupid questions.

For the TX, put the ground clip to the Battery ground. You should then see about 350 to 400V TX Flyback.

There must be no oscillations between the Flyback pulses.

Disconnect the TX coil completely. Reconnect only TX, no BU control.

Look at the scope, if not OK, invert the connection, still no BU control. If OK connect BU control.

[mschmahl]

Now my TX is working. I have testing the RX and after setting the BU-Controll i get a signal on one point for silver and no signal for iron. This is good. But my scope show´s other curves then your´s tinkerer. How can i balance the RX so that the curves go opposite each other, similar to your pic?
My scope is set at 0,5V/div and 2us.


Tinkerer´s picture

[mschmahl]

Today i had some time, so i rewound my RX-Coil. Both halves are now 73 uH together 306 uH.
My curves looks much better.

And i can detect coin´s in a good deep. Seen in the complete project.