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]

putted heatsink (35x35mm alluminium)... the problem it looks like the my power supply.....

no stripe on my lf357 ... thanks for the information I will take it with the strip

[waltr]

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

Step up would be some type of Switching regulator which may inject Noise into circuit. Also, a 12V Lead-acid (guessing this is what you are using) battery's Voltage can be 13.8 to 12.5V so close to desired regulator output of 12.0V. This can be tricky for switching regulators.
What is the Current Draw of the circuits powered from the 12V regulator? Multiple this current with the Voltage Drop. This is then the wasted power.
If wasted power is not too much for good battery life then maybe just a better heat sink on the 7812 will be fine. These 78xx regulator can work fine when pretty darn hot (hot enough to burn your finger).

The advantage of linear regulators is fairly low noise and good input ripple (noise) rejection.
Disadvantage is extra Voltage is dissipated as heat.

The older 78xx design has a fairly high drop out Voltage, typically 2V (this means input must be 2Volts or greater than output).
Newer designs have much lower drop out (LDO - Low Drop Out). Advantage is with a low Voltage input it runs cooler with the same current.

One way around the heat of a linear regulator and still have the noise rejection is to first run a switching regulator at an output voltage enough above the linear's input Voltage requirement (drop out V). Then the linear regulator drops the minimum Voltage and thus dissipates the minimum heat.

Power regulation with battery power devices can be tricky and involves trade-offs.

[useus]

so with 3x6v Lead-acid series batteries should be fine, right?

[qute1]

felezjoo volts

yes spot on but if you are worried there are variable voltage boards widely available on ebay etc which can be set to exactly 18v and upto 5 amps.

[gandolfi]

what do you think about 4x18650 ?
18v is hard to find on ali express 12v, 14.8 or 24v.

[qute1]

Personally i amusing 2 x 9v aa packs in series for circa 18volts and its been fine plus side is readily available good quality aa alkalines and the life is not bad at all 18650's tend to be a bit hit and miss quality wise and voltages can swing wildly unless well matched and charged seperately.

[useus]

9v aa packs?

[waltr]

I use 3 cell LiPo batteries for my PI detector. These are 12.4V full change to 11.1V discharged. I use these due to having a bunch of them from electric power model aircraft.
I also do not have a 12V regulator but do use a charge pump to produce inverted voltage then 78L05 & 79L05 100ma linear regulators.
The Coil is powered directly from the LiPo battery.

A switching Voltage converter if synchronized to the TX coil pulse (RX sampling) should not produce noise.

[basellafe]

12volt reglator is a rule for stablity u should get 9.5 v on ic 357 for best range

[useus]

my 7812 warmed up because the 18v 1a power supply that I used was delivering 24.6V LOL. Was fine that I did not burn anything. now I'm using two 9V batteries in series and everything seems to work properly.

[gandolfi]

Felezjoo need what amperage ? is it enough with 9V recahergeable 200 mAh ?

[qute1]

Felezjoo need 18v so use two 9v aa packs in series (or one 18v if you can get them from chinese) the small 9v square ones (2 in series) will work but only for a very short time (maybe 20minutes if good ones) but yes they do need at least aa for any run time really, a bank of 12 c cells is also an option or a step up regulator board capable of 18v at 2 amps or so.

[gandolfi]

what s happen if i use 4x18650 (14.8v) instead of 18v ? less depth ? less stability ?

[qute1]

the lights come on at 10v but there is no detection till 17.2 volts input or if there is its well iffy REALLY need 18v.