Voltage on my coil is 40V, not 350V

[dotniet]

Hi guys.

I have problems with my Minipulse Plus rev D.


Step 4
The voltage on coil is about 40V. The coil is 52 turns, 23 cm diameter. If I am not wrong this should be 400uH.
I have a weak high pitch sound in phones when I put them 15-20 cm to coil.

Oscilloscope image:



Step 5
The voltage here is not DC, as shown by my oscilloscope.
HOWEVER, when I measure the voltage with a multimeter on TP3 (with the other multimeter wire connected to TP10), I have 3.6V, dropping to 3.1V when I put a pot top (thin stainless steel - 15cm diameter) near it.
(Sorry, I don't drink cola so I don't have a cola can - but I will buy one - I haven't done it in years).

Oscilloscope image:



Step 6
No matter how much I turn R6 (100K trimmer) I cannot change the sample delay. The main sample starts always immediately after the TX pulse. Adjusting R6 only makes the main sample wider.


Yes, the pin 2 was shortcut to pin 3 on PL3.
I switched the two IC between them, the the problem remains.
I double and triple checked the board for accidental shortcuts and the parts for correct placement. Everything seems fine.

[Qiaozhi]

Hi guys.

I have problems with my Minipulse Plus rev D.


Step 4
The voltage on coil is about 40V. The coil is 52 turns, 23 cm diameter. If I am not wrong this should be 400uH.
I have a weak high pitch sound in phones when I put them 15-20 cm to coil.

52 turns is far too many for a 23cm diameter coil. This will give an inductance value of around 1.69mH.
Please use the Coil Calculator here -> Coil Calculator

For 400uH, you will need 24 turns.

[dotniet]

Thanks Qiaozhi for such a quick answer!

I used exactly that calculator.

Index.html doesn't work (the calculator doesn't load properly) so I used coilcalc.html
I have no clue about the thickness of the wire I use so I put 0.05mm. It seems a decent value. I will measure it as soon as I will get a micrometer.
I took the wire from the a coil located on the cathodic tube of a monitor. You know... those 2 red deflection coils with strange shape and big ferrite core that make together a cylinder.

Now I re-downloaded the program you linked too and this is what I see for the number of turns (24) you gave me:

So, for the same input numbers it gives me a different result.

(Please see the inline image and ignore the attached image which is wrong).

[WM6]

Are you trying to build Minipulse pinpointer?

Or you have problem with metric values?
Namely you calculate almost micro-coil.

There are set millimeters (mm) in calculator form.

Probably should be centimeters (cm).
Par example 23cm = 230mm (not 23mm).

[dotniet]

WM6 sorry for uploading the wrong image. I updated the correct image.


For:
Wire diameter: 0.45mm (is this thick enough?)
Coil diameter: 230mm
Turns: 16

I get inductance of: 0.42mH.



__________


Update:

Now I know the diameter of my wire. About 0.45mm
I am going to test the new coil.

[Qiaozhi]

Index.html doesn't work (the calculator doesn't load properly) so I used coilcalc.html

You are supposed to launch the calculator using coilcalc.htm
It does actually state that in the Coil Calculator thread

I have no clue about the thickness of the wire I use so I put 0.05mm. It seems a decent value. I will measure it as soon as I will get a micrometer.

0.05mm is only 50um thickness, so I doubt that is correct.
It's more likely to be something like 0.56mm.

Now I re-downloaded the program you linked too and this is what I see for the number of turns (24) you gave me:
[ATTACH]32802[/ATTACH]
So, for the same input numbers it gives me a different result.

You've made two mistakes here. As WM6 pointed out, the first field is in millimetres, not centimetres.
And ... this is the value of the radius of the coil, not the diameter.
The value you should enter is 115mm.

[Qiaozhi]

WM6 sorry for uploading the wrong image. I updated the correct image.
[ATTACH]32803[/ATTACH]

For:
Wire diameter: 0.45mm (is this thick enough?)
Coil diameter: 230mm
Turns: 16

I get inductance of: 0.42mH.



__________


Update:

Now I know the diameter of my wire. About 0.45mm
I am going to test the new coil.

Try entering the correct values:
Inner Radius = 115mm
Wire Thickness = 0.45mm
Number of Turns = 24

The answer should be: Inductance = 0.407mH (i.e. L = 407uH)

[dotniet]

You are right. It is radius not diameter. Thanks A LOT!
Probably I should work during daytime at my detector, not in the middle of the night...

I left a connection right in the middle of the coil. I will try to connect use that (for testing). I hope the unused half of the coil will not have a big impact on measurements. Tomorrow I will build a proper coil.

[Qiaozhi]

You are right. It is radius not diameter. Thanks A LOT!
Probably I should work during daytime at my detector, not in the middle of the night...

I left a connection right in the middle of the coil. I will try to connect use that (for testing). I hope the unused half of the coil will not have a big impact on measurements. Tomorrow I will build a proper coil.

OK - good luck!

[dotniet]

still not working

I built the proper coil (I really screw up the calculation of the first one).
The parameters have improved now but still not OK.

For example:


TP1:
Frequency: 93ms (instead of 100mS)
Pulse width: 48uS (instead of 58uS)



TP3:
1.5v drops below 1v for a 15cm steel pot top


Voltage on coil is now 150V. Much better but still not 350V.



And most importantly I still cannot change the sample delay in step 6:




Please I still need help.

[Qiaozhi]

First things first ... what is your battery voltage?

[dotniet]

Sorry. I wanted to mention that in the previous post but I forgot.
Is 12.1V. But it is not battery. It is a transformer (from a network switch, I think). Does it has to be battery? I have enough 1.2V rechargeable batteries to build a 12V block if necessary.

[Qiaozhi]

It depends on whether the power supply is able to provide enough amperage. It might be worth re-testing with a battery pack.

[dotniet]

The transformer can give 12V/1A.
It should be enough. I think.

[CAS]

I wouldnt have thought that would be enough. Even though MPP doesnt draw a lot of current overall, on each TX turn on there will be a large spike in current. I tested my MPP with a dc supply but used a 5A power supply. You may find the voltage drop in the power pack you are using is causing issues. I would try it with either a larger supply or a battery pack.