felezjoo PI(the best pulse induction metal detector that I made until now)

[dbanner]

Put a heatsink on the regulator.
Does your LF357 have a stripe on it? It does, then it is for sure the original national semiconductors part lf357n

[useus]

no i keep 1M

- Is it best change ? Resistor of 100ohm by 280ohm or 1M by 220k ?
- can we change 7812 by a better regulator ?
- how we can verify true or false LF357 ?
- is there difference in performance between 14.8v (4x18650) and 18V (5x18650) ?

thanks

-I'll try 280ohm (if I find it or I can do it) and I'll do the comparison
-7812 alternative i don't kown... lm338?
- apparently it is not possible

[gandolfi]

did you even change 1mohm resistance with a 470k resistor?

no i keep 1M

- Is it best change ? Resistor of 100ohm by 280ohm or 1M by 220k ?
- can we change 7812 by a better regulator ?
- how we can verify true or false LF357 ?
- is there difference in performance between 14.8v (4x18650) and 18V (5x18650) ?

thanks

[useus]

Yes. The Heat (Watts) of linear regulators = Voltage Drop times current. Higher Voltage input really drops the efficiency due to excess Voltage producing Heat.
Also, these older 78xx regulators are rated for 1Amp only if the Heat size size is infinite.

thanks do you recommend 3x 6v in serie batteries (4,5ah) or single 12v (7ah) battery with step-up converter?

[waltr]

one last help, 7812 is really hot, can it be due to the fact that I'm feeding the metal detector with an 18v 1A power supply?

Yes. The Heat (Watts) of linear regulators = Voltage Drop times current. Higher Voltage input really drops the efficiency due to excess Voltage producing Heat.
Also, these older 78xx regulators are rated for 1Amp only if the Heat size size is infinite.

[useus]

I put resistance 220k, now the values are quite good! anyway I'll be looking for an lf357h to make a comparison

A294 B727 C816

one last help, 7812 is really hot, can it be due to the fact that I'm feeding the metal detector with an 18v 1A power supply?

[useus]

It's hard to know if it's original I bought 20 pieces from Serbia all were defective I bought from Bulgaria and everything was right ..

you're telling me that I have to spend 100 € to find one right... LOL

[Orbit]

do you think this is original?
https://www.ebay.it/itm/Lot-x2-ci-LF...UAAOSwy0JaHR06

It's hard to know if it's original I bought 20 pieces from Serbia all were defective I bought from Bulgaria and everything was right ..

[useus]

do you think this is original?

https://www.ebay.it/itm/Lot-x2-ci-LF-357-N-LF357N-wide-bandwith-JFET-Input-Op-Amp-Motorola-PLA039/192042545227?hash=item2cb6a0b04b:g:ExUAAOSwy0JaHR06

[useus]

The whole problem is of 357 ... Find the correct 357 or 356 !or 1m with 470k or 330k....

A262 B658 C775

delay 22


thanks!

now I try 300k and the values should become almost perfect

[Orbit]

The whole problem is of 357 ... Find the correct 357 or 356 !or 1m with 470k or 330k....

[useus]

I have changed the 100 ohm resistor by 280 ohm.

some person change the IRF840 by IRF740

did you even change 1mohm resistance with a 470k resistor?

[gandolfi]

i replace the 1m resistor with 470k, values are A241 B578 C713, autodelay 26 (with 1m are 24)

I think I still improve the values by finding the right value of the resistance

if I go down under 470k resistor risk of burning something?

I have changed the 100 ohm resistor by 280 ohm.

some person change the IRF840 by IRF740

[useus]

i replace the 1m resistor with 470k, values are A241 B578 C713, autodelay 26 (with 1m are 24)

I think I still improve the values by finding the right value of the resistance

if I go down under 470k resistor risk of burning something?

[samii]

Hello

try lf357j or metalic lf357h from Motorola to get near 300 700 800 A B C and replacement with 470-570k for 1M near 357