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  #26  
Old 06-21-2009, 10:22 AM
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Originally Posted by J_Player View Post
Sure .. that is done all the time. The older TIG welders used a transformer that converted 220VAC to about 40VAC. The current from the secondary was sent through a saturable core reactor. This is kind of like an adjustable choke. By passing DC through the control coil, you can saturate the core, so it will not allow more current to pass from the main AC coil that passes the 40V welding power. The welder power control adjusts the saturable core reactor control coil to set the maximum current that can pass at the welding tip on the TIG welder.

More modern TIG welders use very large thyristors to control the current. Instead of weighing 800 Lbs, they can be carried by hand, and are the size of maybe two large PC boxes. In either the old version or newer TIG welders, there are many air cooled cables that carry the current to the tip. These air cooled TIG welders are usually up to about 175 amps. They have a 40 % duty cycle or less before the cables get too hot. Most serious TIG welders have water cooling. The #8 cable is inside a hose that has a continuous flow of water through it to carry away heat from the conductor. This water is usually recirculated in a 10 gallon tank, or can be discharged to a drain.

But here is an idea for getting your 500 amp pulse to the search coil.
This method will only work for a PI detector that is towed with a vehicle that contains the power and circuitry on the vehicle:

There are high power thyristors and SCRs used in large power controllers. Some can carry over 200 A at 220VAC. Start by mounting a large electric generator on the back of your 4-wheel drive truck. Then put the power circuitry alongside the generator. We will use a 220 VAC mains from the generator and rectify it to 220VDC, then send it to a huge capacitor bank. The capacitors must be very large. The kind used for Tesla coils, lasers, etc. So the capacitors have a large capacity, and a large supply to feed them.

Next, connect your SCR or thyristor circuitry to create the pulses from the 220 v charged capacitors. These pulses will be sent to a transformer with a secondary of 12 v. Now since we are sending DC to the transformer, we do not expect an output except from the leading and trailing edge of the pulse. So, the idea is to keep the pulse short... in the range of the time needed for the secondary to finish producing a full voltage spike, then terminate the pulse, andd watch the returned eddy currents from treasure after. The coil can be a 5mm solid copper wire passed through a 6mm teflon tube. I think a 30cm dia coil with about 4-5 turns could beworkable for air cooling. (this will be a small treasure finding machine... The 3 meter dia coil is for true LRL usage).

Now let's see... at 220V and 200 A passing from the capacitor to the 12 v transformer primary, we have up to 44KW of power moving in the coil for a very short time. But more important, the current can be up to 3666 amps, depending on the resistance of the coil and any resistor added. But regardless of how much added current, I bet you see some real deep treasures.

Best wishes,
J_P
Hi,
yes indeed... I think people never made such kind of MDs cause of power problems and weight issues... that requires a vehicle and cannot be good for handheld or any other man-carried thing.

The fact we haven't already such kind of stuff around is also related to magnetometers that are widely used in THing for decades now... but limited to the ferrous stuff locating.

But many THunters need iron and iron-alloys detection more than other stuff... like happens in ship-wreck search... where mandatory setup is in most of the cases having both a side scan sonar and a very sensitive and fast magnetometer... then , when wreck is located, they use rov or at small depth people go with waterproof MDs etc ... or simply cut the wreck and recover the valuable things on the expedition ship.... like happened about a gold bars payload inside a wreck some years ago.

But... what about big natural gold nuggets ? Or large treasures mostly made of noble metals (gold/silver etc not iron) ?

I think older methods have no usefulness with big, deep e.g. gold stuff...
cause magnetometer will no see that stuff... and conventional MDs have too limited range for some places.

I remember that I read many times of gold nuggets found in Australia at considerable depth... several at meters underground during excavation for roads/tunnels and similar stuff: no MD of what we know can detect such stuff in meters of Australian hi-mineralized soil.

Same apply to some middle-east and central-asian treasure locations.... rooms at 10meters and more depth!

Same for some US nuggets, very rare and very BIG... but covered by meters or tens meters of sand!

So... the idea, though not exactly an MD for everyone... or everyday search have good applications in the right place I think.

The capacitor bank idea is employed in some older german designs... and that's a good idea indeed cause in such hi power delivery at coil it's easy charge a capacitor bank to mantain energy levels between pulses... more easy than , instead, try to make a bank of mosfets to share the current and so the heat generated...

maybe someone will made one of these monsters in the next future... who knows!

Kind regards,
Max
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  #27  
Old 06-21-2009, 01:17 PM
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Quote:
Originally Posted by Max View Post
Hi,
yes indeed... I think people never made such kind of MDs cause of power problems and weight issues... that requires a vehicle and cannot be good for handheld or any other man-carried thing.

The fact we haven't already such kind of stuff around is also related to magnetometers that are widely used in THing for decades now... but limited to the ferrous stuff locating.

But many THunters need iron and iron-alloys detection more than other stuff... like happens in ship-wreck search... where mandatory setup is in most of the cases having both a side scan sonar and a very sensitive and fast magnetometer... then , when wreck is located, they use rov or at small depth people go with waterproof MDs etc ... or simply cut the wreck and recover the valuable things on the expedition ship.... like happened about a gold bars payload inside a wreck some years ago.

But... what about big natural gold nuggets ? Or large treasures mostly made of noble metals (gold/silver etc not iron) ?

I think older methods have no usefulness with big, deep e.g. gold stuff...
cause magnetometer will no see that stuff... and conventional MDs have too limited range for some places.

I remember that I read many times of gold nuggets found in Australia at considerable depth... several at meters underground during excavation for roads/tunnels and similar stuff: no MD of what we know can detect such stuff in meters of Australian hi-mineralized soil.

Same apply to some middle-east and central-asian treasure locations.... rooms at 10meters and more depth!

Same for some US nuggets, very rare and very BIG... but covered by meters or tens meters of sand!

So... the idea, though not exactly an MD for everyone... or everyday search have good applications in the right place I think.

The capacitor bank idea is employed in some older german designs... and that's a good idea indeed cause in such hi power delivery at coil it's easy charge a capacitor bank to mantain energy levels between pulses... more easy than , instead, try to make a bank of mosfets to share the current and so the heat generated...

maybe someone will made one of these monsters in the next future... who knows!

Kind regards,
Max
Hi,

very high current in the coil also means extreme high Flyback voltage. Insulation problems become dominant.

Max, I have a question: You have mentioned in the past that fired clay shards are a problem when detecting with a PI. The ferrous content in fired clay indeed responds to the strong PI pulse.
I have been working on a discriminating PI design for some time now. There are still some problems with certain FE targets that give about the same resistive response as reactive response and are therefore not well discriminated. But, MOST of the FE response is eliminated. The sensitivity to all FE is minimal, (see http://www.geotech1.com/forums/showthread.php?t=15441) the sensitivity to non magnetic metals is greatly enhanced.

Would such a PI detector, that has a good depth penetration be useful in the areas that you mentioned?

All the best

Tinkerer
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  #28  
Old 06-21-2009, 05:05 PM
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Hi,

very high current in the coil also means extreme high Flyback voltage. Insulation problems become dominant.

Max, I have a question: You have mentioned in the past that fired clay shards are a problem when detecting with a PI. The ferrous content in fired clay indeed responds to the strong PI pulse.
I have been working on a discriminating PI design for some time now. There are still some problems with certain FE targets that give about the same resistive response as reactive response and are therefore not well discriminated. But, MOST of the FE response is eliminated. The sensitivity to all FE is minimal, (see http://www.geotech1.com/forums/showthread.php?t=15441) the sensitivity to non magnetic metals is greatly enhanced.

Would such a PI detector, that has a good depth penetration be useful in the areas that you mentioned?

All the best

Tinkerer

Hi,
indeed was real pain... more the power ...more the troubles...

the concept I already know before making e.g. GSIV clone... but when tested that on such sites it become really apparent the device couldn't be productively employed in such scenario , if not in the depth variation... with a big coil suspended far from soil.

I discussed with Alexis the problem and realized that , indeed, the real possible use was just that, depth version, coil far from soil.

If your new PI is capable of discriminating fired clay, pottery and other ceramics ...well it's worth for sure in such kind places.

That's cause using VLFs some deep targets are undetected at their depth and use of conventional, old PIs is simply impossible with small coils near soil (like for coinshooting and other small stuff search).

I hope you'll go ahead with that project... will be very nice hear of complete immunity to ceramics and pottery with hi-iron-oxides content.

Kind regards,
Max
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  #29  
Old 06-21-2009, 10:00 PM
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Quote:
Originally Posted by Max View Post
Hi,
indeed was real pain... more the power ...more the troubles...

the concept I already know before making e.g. GSIV clone... but when tested that on such sites it become really apparent the device couldn't be productively employed in such scenario , if not in the depth variation... with a big coil suspended far from soil.

I discussed with Alexis the problem and realized that , indeed, the real possible use was just that, depth version, coil far from soil.

If your new PI is capable of discriminating fired clay, pottery and other ceramics ...well it's worth for sure in such kind places.

That's cause using VLFs some deep targets are undetected at their depth and use of conventional, old PIs is simply impossible with small coils near soil (like for coinshooting and other small stuff search).

I hope you'll go ahead with that project... will be very nice hear of complete immunity to ceramics and pottery with hi-iron-oxides content.

Kind regards,
Max
Thanks for the feedback. The TINKERERS project is moving ahead slowly but surely. We hope to have a simplified version, V1 out soon so that others can test the idea of a PI with FE discrimination.
Any help is welcome.

Tinkerer
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