Sandbanks

[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.

[Andi68]

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

[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]

I think, 400/500 V Mosfets are enough

[Mr.Jaick]

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

[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

[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?

[Andi68]

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

[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.

[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

[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

[surfdetector]

Ok, Thank you.

[Andi68]

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

[bernte_one]

irf840 is ok you can use it

[surfdetector]

detector runs smooth with irf630
but i will try some updates like irf840, another damping resistor and maybe another gain factor
sometime the irf630 gets immediatly hot when i use other coils with higher resistance than 1R and more ?H

22AWG (0,6mm) copperwire 300?H is ok, but i think i will get trouble when building a 1m frame coil with 0,8 wire 8 turns + 2m of connection cable

maybe you have any suggestions

Did you try an IRF840?