Induction Balanced Coils, IB coils

[Pete the Builder]

Hi Tinkerer,

you're intending to drive the TX coil with high current obviously (due to thick coil wire bundle).
I might have an interesting new TX for you. It supports boost-mode.

It will be published as soon as I have more time.

Cheers,
Aziz

G'day Aziz!

I'm looking forward with much anticipation to the publishment of your new "Aziz' Amazing Amperage" high-current boost mode TX driver!

I am planning a very high-current search head for my eventual design too. (I like high currents... in my gauss rifle designs, I maxed out #4 connecting cable between the cap bank and the coil. I measured approx. 1270A for 1.11 mS, before my 'hockey puck' SCR smoked it's last cigarette. ...But I achieved a muzzle velocity of nearly 1,100 m/S, which was very exciting (and noisy)... I don't think this will work well for a metal detector, but imagine the depth of the pulse we might obtain!)

I am learning so much from you. Thanks for all your explanations and images. It all helps so much (like Tinkerer's photos and explanations!)

Cheers,
Pete

[Tinkerer]

Hi Tinkerer,

you're intending to drive the TX coil with high current obviously (due to thick coil wire bundle).
I might have an interesting new TX for you. It supports boost-mode.

It will be published as soon as I have more time.

Cheers,
Aziz

I am looking forward to your new TX. The way I see it, a stronger TX gives a better S/N.

The coil above should handle up to around 3A average coil current. This amounts to about 170mA battery consumption at 12V. at 5000 pulses per second.

[Aziz]

I am looking forward to your new TX. The way I see it, a stronger TX gives a better S/N.

The coil above should handle up to around 3A average coil current. This amounts to about 170mA battery consumption at 12V. at 5000 pulses per second.

Hi Tinkerer,

I know you like the TEM TX very much. I'm sure you will love the new TX as well.
But the preparation takes a lot of work and time and time is, what I've not much at the moment.

Cheers,
Aziz

PS: Pete, no worries!

[Tinkerer]

A new, experimental coil design. The first "Power ON". What does it look like?

Below is the picture of the coil current, measured across a 0.1 Ohm resistor in series with the coil. The scale is 200mV/div.
We see a long ramp, about 100us and then a sharp drop of about 500mV. This amounts to about 5A current during about 5us or 1A/us di/dt.

There is a little delay at the end of the drop, before the switch On. This mismatch in timing can be fixed by increasing the Flyback absorbing capacitor or by changing the timing. As it is, it will work.

Next, let's look at the signal coming from the RX coil. The setting is 500mV/div. We got a fairly large air signal, but there is no Flyback of several hundred volts.
There are also some HF oscillations. This is due the fact that the damping resistor is still missing.
The coil balance is not very good either. We will need to fix that.

Of course, I could show you the coil with everything perfect, but when you try to build your first coil and switch it on, you will see something that is not perfect, like the above.

Enjoy your coil building.

[Aziz]

I am looking forward to your new TX. The way I see it, a stronger TX gives a better S/N.

The coil above should handle up to around 3A average coil current. This amounts to about 170mA battery consumption at 12V. at 5000 pulses per second.

Tinkerer,

start your circuit simulator and try the new TEMV2.0 and the CLASS-E-TEM.
You will like it.
See my laptop project thread.
Aziz

[Jose]

Tinkerer, I not see the RX coil data, but doing calculation with MiSCeL, should walk in 25 to 26 laps, with double wire for a 150 +150 uH inductance.
I guess the diameter of the wire should be about 0.4 mm in diameter.
regards

[Tinkerer]

Tinkerer, I not see the RX coil data, but doing calculation with MiSCeL, should walk in 25 to 26 laps, with double wire for a 150 +150 uH inductance.
I guess the diameter of the wire should be about 0.4 mm in diameter.
regards

Jose,

that should be OK. When you use MiscEL, you start with the inner diameter, however, afterwards you must use the medium diameter for the calculations. Often, when you wind the coil on the nail board, once the bundle is bound, the inner diameter is less than the nail board diameter you used.

All the best

[Tinkerer]

Balancing the coil

When we took the first look we took at the coil balance, we saw that the balance was not very good. The coils in the pictures are wound with stiff magnet wire. This makes it difficult to make a nice tight bundle.
Massaging the bundles, the balance got better. Pushing one of the coils a few mm off center and the balance improved to about +/-250mV. Not very good but usable.

Now we want to see right away if we get a target response. We place a silver dollar at the center of the coil and see that the signal trace changed.

Remember, this is the signal on the cable coming from the RX coil, before the input filter.

First picture:signal with no target
Second picture: signal with silver coin at center of coil

Tinkerer

[mschmahl]

Now i´m starting to wind a coil for the tinkerers_SB. This is my "coilwireringtable".

The coil-spect´s are from post 247 from here http://www.geotech1.com/forums/showt...project/page10
It is a 50 cm coil.

[Tinkerer]

Now i´m starting to wind a coil for the tinkerers_SB. This is my "coilwireringtable".[ATTACH]23718[/ATTACH]

The coil-spect´s are from post 247 from here http://www.geotech1.com/forums/showt...project/page10
It is a 50 cm coil.

Excellent,

remember, as this is your first coil, there are many variables. The calculations are right, but the execution can induce many variables, like insulation thickness, tightness of bundle, final average diameter, actual type of wire etc.
Therefore do not glue the coil before testing.

The first test will show how good the balance is. Then correct the balance and only when the coil is perfectly balanced, solidify with glue.

Good luck
Tinkerer

[mschmahl]

The coil is assembled.
These pictures are made with irfanview, thanks tinkerer for the link.




Some questions i have:

My RX-coil is with 295 uH and 1,4 Ohm total(Start to End). Messured from center tap to start is 81uH and 0,8 Ohm and from center tap to end is 70uH and 0,8 Ohm. It should be 150 uH every side, or not?
TX is 398 uH and 0,5 Ohm total(with BU) and only TX (to BU-Controll) 419 uH and 0,4 Ohm. BU (to BU-Controll) is 39uH and 0,2 Ohm.
So i´m out of spect´s and have to wind a new one? Or can we use this?

[Davor]

Messured from center tap to start is 81uH and 0,8 Ohm and from center tap to end is 70uH and 0,8 Ohm. It should be 150 uH every side, or not?

No. You forgot mutual inductance. With different orientations it will either increase or decrease total inductance of the coils. In case orientation is the same it will be L1 + L2 + 2M
In case it is in opposite, it will decrease, L1 + L2 - 2M

So in case you have two coils of the same inductance, and their coupling is 1, the total inductance will be either twice their sum, or zero.

Your bigger problem is that your Rx coils are not equal. Most probably you did not wind them bifilarly. The best practice is to weave two wires together, wind them (together), and connect the ends to form a centre tap. That way you'll have perfectly coupled coil with perfect ratio viz. the centre tap.

In your case:
L1=70uH
L2=81uH
k=0.9562 (I got it by calculation and it is very good)
____________________________________________

M= k * sqrt(L1*L2) = 72uH

L = L1 + L2 +2M = 295uH

L1 and L2 should be equal! Do them in bifilar fashion.

[Tinkerer]

Nice coils! Neat winding.

If you did not make a mistake in the amount of turns, the difference in inductance is because the average diameter of one half of RX coil is different that the other half.

Bi-filar winding, like Davor says, helps avoiding this problem.

Before you rewind the RX coil, connect and observe the balance, as is. It will give you an indication as to any changes needed.

When you test, move the loose wires and observe the changes in the balance that this causes.

Tinkerer

[mschmahl]

Thank´s for the tip´s and explanations tinkerer and davor. I have about 0,5-1m cable on each side left, to correct some fault´s or use it as coil connection cable. If i wind an extra turn for the weaker RX-side then it could fit. Perhaps I have miscounted the windings.

[mschmahl]

I have add one winding on the weaker RX-side. Now i have 81uH from rx-start to center tap and 84uH from center tap to rx-end. RX-total is 322uH now.