Sandbanks

[surfdetector]

Ok, Thank you.

[bernte_one]

An IRF740 also works very well.
If the transistor is replaced by a mosfet,
the voltage divider must be adapted to the required gate voltage of the mosfet

which parts did you change?

i inserted irf740 direct with no changes and it runs

[bernte_one]

I tried to drag a jpeg image unto editor, without success.
Marty, everything looks good. I changed 3 resistors from RM5 to RM7,5
I exported the JPEG image but forgot to save the updated Sprint file....
It is better all resistors footprints are kept to fit 1/4W so as to avoid mounting verticle. The damping resistor footprint should also be changed for possible 1W resistor.

Marty, all looks good. Very well done.

820k under lf357 changed to 1M

[Mr.Jaick]

Hello forum
I just wanted to share this little experiment that i had last night with my Pi Polones(it's funny)
I made a 50cm round coil:
1mm stranded wire
19 turns 0,6 ohms DC resistance
yeah you guessed it, toasty as hell




imagine IRFZ46 (high current VMOS) with a big heat sink was cooking like a piece of steak in a pan
rewind it and test it at 15 turns with 0,4 ohms resistance
same result
it didn't detect any thing, with damping resistor range of 180 ohms to 1.2k i don't know if it was the coil or the circuit ?!

now i've rewind all of that to go with something more reasonable
my available options for copper wire are:
0,5 mm enameled
0,75 mm enameled
1 mm enameled

1mm is not gonna work i've already tested the stranded one.
I've done the 0,5mm before for a 60cm loop 14 turns but not any satisfying result
now i'm thinking of 0,75mm maybe 15 turns
my target is slow, big, and Deep

Any suggestions on that will appreciated.

[Andi68]

I took R6 / 27 ohms, R7 is the same.
At the gate I now have about 10V voltage.

[Qiaozhi]

19 turns of 1mm wire on a 250mm radius coil should result in an inductance of 565uH.
If your mosfet is getting very hot then the problem is something else. I assume you know that the IRFZ46 only has a breakdown voltage of 55V?

[Mr.Jaick]

19 turns of 1mm wire on a 250mm radius coil should result in an inductance of 565uH.
If your mosfet is getting very hot then the problem is something else. I assume you know that the IRFZ46 only has a breakdown voltage of 55V?

damn it, i knew that very well but i thought the emf made up on drain is gonna get limited due to the back to back diodes in the pre_amp input
and i saw the back emf is cutting off around 55v....ahhh
silly me i rewind it all the way back
do you think it would work ?
i have IRF740 , IRF840
i can make it again no problem if it helps the depth

[Mr.Jaick]

is 400v(IRF740) or 500v(IRF840) breakdown voltage enough for such a coil?
Or may I go with 1000v(11nk100z)?

[Andi68]

I think, 400/500 V Mosfets are enough

[Mr.Jaick]

I think, 400/500 V Mosfets are enough

thank you very much guys, all of you
now the question is does it worth it to make that coil(described above) for higher depth?
Or I can make another one with enameled 0.75mm to perform just as good ?

the strengths of that coil that i made last night are:
higher magnetic field(strong TX) --> due to it's lower resistance and more current flow
high inductance(better RX) --> as master said 19 turns makes about 550uH due to coil calculator
lower Capacitance(faster swipe) --> because of that PVC insulator

(It sounds like a commercial, doesn't it?)

downsides:
it's freaking HEAVY.

correct me please if i'm wrong.

[Andi68]

So I have the impression, PiPolones, Sandbanks
prefer low inductances, 200-250?H
Wire length approx. 12.5 m

[surfdetector]

which parts did you change?

i inserted irf740 direct with no changes and it runs

I am happy to hear that. I did not want to have to buy more parts.

[kt315]

basket coil https://www.geotech1.com/forums/show...l-for-baracuda

[Mr.Jaick]

So I have the impression, PiPolones, Sandbanks
prefer low inductances, 200-250?H
Wire length approx. 12.5 m

thank you Andi
now my plan is to use 0.75mm and start winding up to 11 turns which will give me around 210uH for a 50cm loop
and from there start testing the performance without cutting the wire, just make the contact and go up to 15 turns
hopefully I'll find the right number of turns for my application.

by the way i find a good looking speaker wire to use as box to coil connector
here is a pic if you can see it's flexible and feels fancy:



should i use it or keep the faith in RG58 like cables?

[Andi68]

https://www.youtube.com/watch?v=eZQyVUTcpM4