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Thread: large coil PI detectors

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  1. #16
    si
    Nov 2017
    Countryside
    DBP2010, eeTH
    21
    22 times
    All Types Of Treasure Hunting
    I am using coil made from thicker wire flat computer cable suspended on plastic frame made from 4 cm diameter plastic sewer water pipes. The frame is held approx. 0.5m abowe the ground, suspended on 4 ropes attached on a pipe i am holding across my sholders. The coil is on my right side, manvrable by the help of my knee and the detector in bag om my left. All plastic pipes are assembeled on a spot from 1m and 0.5m long pices. Walking inside the coil with the detector over the neck does not work for me, due to metal parts (batteries) moving and swinging in the coil's field setting off the machine.
    MDCLXVI likes this.

  2. #17
    us
    ARRG

    Feb 2005
    Sarasota, FL
    Whites Surfmaster PI Pro and Whites Surfmaster PI, Minelab Excal NY blue sword. 2 White's Dual field pi, Garrett sea hunter pi II (but don't use it for obvious reasons) 5' x 3 1/2' coil underwater Pi
    2,106
    237 times
    Shipwrecks
    I have a PI coil that is 48” x 48”. It will go very deep on big metal objects. Through the air 35’ on a car. 25’ on a metal garbage can. Air on a beer can 8’. In saltwater about 12’. When I use it in the water I tow it about 12’ plus off the bottom, just to not get beer cans. It will not find tiny coins and pull tabs. If I take the coil and fold it over to be a half sized coil about 36” x 36” it still will go very deep and still will not find tiny things. If I fold it again to a 24” x 25” it will find tiny things, maybe not a gold alloy ring because it is not hot on that, too slow of a pulse. But it will go pretty deep on a big object. Just a 10” Pulse coil will go 5’- 6’ on a big iron object like a 24” iron anchor. I have dug that, and find gold alloy rings. I would assume a 10’ x 10’ coil would still pick up beer cans at any depth. Maybe if you can slow the pulse rate it will eliminate small stuff. I will try that and get back to you. It will still pick up beer cans (my detector) on as slow a pulse as I can go. Maybe not as deep? I will try that out. My big PI has automatic SAT self adjusting threshold, which helps when going over different types of soil, it does not have to be ground balanced. That will also allow you to have metal inside the coils detection range and it will quit sounding off, but it will be slightly less sensitive. It is like ground balancing with a target under the coil. So if you had a PI that has auto SAT, you could have a couple beer cans near the coil making it less sensitive. It would eliminate some tiny trash. Possibly could have enough cans in the zone to eliminate beer cans. I never tried that though as I would be counter productive, but could eliminate beer cans would help you. I will try that. And let you know.
    Last edited by stevemc; Mar 15, 2019 at 07:54 AM.
    TheGreenBoy and MDCLXVI like this.

  3. #18
    us
    ARRG

    Feb 2005
    Sarasota, FL
    Whites Surfmaster PI Pro and Whites Surfmaster PI, Minelab Excal NY blue sword. 2 White's Dual field pi, Garrett sea hunter pi II (but don't use it for obvious reasons) 5' x 3 1/2' coil underwater Pi
    2,106
    237 times
    Shipwrecks
    I really important thing about a real big PI coil is, that to test it out you need to be far away from any big power lines. The big coil is like a big antenna dish. Can pick up pulses from a long way away. Will make a lot of quaking noises. And lower your detection ranges. Regular house is not bad but any power line is bad, the bigger, the worse it is. A big open beach should be good. Underwater it goes way down too.
    MDCLXVI likes this.

  4. #19
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    I want to thank Greenboy and stevemc for there input ....Greenboy do u remember when u made the coil was the resistance and inductance the same as the stock coil ? if i remember right plus or minus 10% is ok ...i think my unit is 2 ohms 400 uh 15t.... minelab has a calculator for coils ...u also gave me a idea of sliding stand for my 20x20 like a table on a snow board ...ill experiment first maybe i don't need a new coil

  5. #20
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    stevemc i want to thank u for the in the saltwater info and the timing info it will help on the wet part of the beach i search and it gave me ideas if i search from a boat over the water ...your info is making me think that the 20x20 is big enough with a stand

  6. #21
    si
    Nov 2017
    Countryside
    DBP2010, eeTH
    21
    22 times
    All Types Of Treasure Hunting
    Large coil has 3 ohm of ohmic resistance and 600 uH of inductivity, smaller one is 2.5 ohm and 620 uH. The circuit is tunned with large coil.
    Well, a fair PI is still quite expencive in my naighborhood, so mine is home made along with the coils, so they are both original as fare as it goes - i guess.
    MDCLXVI likes this.

  7. #22
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    as what i seen different companies all used different specs ...minelab i think was 300 uh chinese clone 400 uh your are 600uh +- 10% ....as what i seen with a few different models they all give different depth readings on the same size object i have to do more research to better understand y ..stevemc i think uses garrett which seems to go deeper then the ones ive seen but florida sand not like iron sand so theres so many factors involved...AARC was florida sand also ...thanks greenboy for your help

  8. #23
    si
    Nov 2017
    Countryside
    DBP2010, eeTH
    21
    22 times
    All Types Of Treasure Hunting
    There is no direct coleration between inductivity of the coil and performance of detector. The coil must match the machine consisting the tunned part of the circuit. Coils with lower inductivity are deemed to be faster and produce weeker magnetic field at the same current. However, the magnetic density (strenght) depends on energy the coil is powered with, the discharging speed depends on dumping shant resistor as well. The speed of field forming is directly colerated with coil inductivity, but this is usually not critical if the pulse rate frequency is keept low enought. The two other values, ohmic resistance and capacitance are both parasitic and should be keept as low as possible.

  9. #24
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    what u said is what i also heard the other factor i notice minelab coils are smaller for there models and might be faster for there intent large nugget targets ,,,my machine probably designed around the 20 inch size ..and yours is probably designed for 40 or bigger very large target i could be wrong about this if i remember right most coin machines are 300 ....since u know 100x more then i do how much does the type of sand play in depth because everything i read dosn't match what the florida boys say where am at its iron sand and hot rocks ...or maybe its designed for smaller targets then there models

  10. #25
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    I figured i start with a 36" stand on a plastic sled made out of 4' drain pipe i try this on the beach wet and dry sand with my soda can (under 2"of sand ) and my 20 kilo nickel bronze target ( under 2 feet of sand ) remember am only interested in the top 2 feet on the wet beach

  11. #26
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    The funny thing after going over what ive tested and found in the past i might need a smaller coil 16x16 for the wet beach ,,,,im guessing upland 40 dry beach 20 wet beach 16 in the sea 12 ...i have to give this some more thought

  12. #27
    si
    Nov 2017
    Countryside
    DBP2010, eeTH
    21
    22 times
    All Types Of Treasure Hunting
    Well designed PI shoulden't have much problems with salti and mineralized soils and should give you more depth one is willing to dig. Any soil always takes some depth away, the only exception i have seen are PIs with exstreme energy pulses, powering those is another story, though. But if you use anythig usual, such as XR71, DBP2010, Pulse star, or similar detector, you shulden't have much problems.

  13. #28
    us
    point man

    Jul 2016
    sing sing N.Y
    403
    173 times
    Thanks again Greenboy ...am flag stupid where do u search old ww2 sites in euro ...where am its illegal to look upland without a permit ....tourist are beach only here ...i guess no uxb on the beach here thats the reason i heard ... good luck with your hunts

  14. #29
    si
    Nov 2017
    Countryside
    DBP2010, eeTH
    21
    22 times
    All Types Of Treasure Hunting
    Thanks MDCLXVI. The legal aspect is quite complex in my country. Simplified, one can search anywhere where is not forbiden (there is a map resembling the Swiss chesse) as long as he or she doesn't find anything.....
    MDCLXVI likes this.

 

 
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