Probe for Garrett Sea Hunter

[rgecy]

I wanted to know if anyone had any ideas on making a waterproof probe for the Garrett Sea Hunter Mk II?

Robert in SC

[Carl-NC]

The probe itself shouldn't be too difficult... just wind up a mono coil with about the right inductance and good settling characteristics. Just be careful in adding a switch box for it, keep things shielded and parasitics low.

- Carl

[rgecy]

Carl, this is where I get lost. What is the right inductance and how will I determine it. Settling characteristics?????

What I was going to do is buy an additional 8" mono coil and cut the coil off. This will give me the right connector and length of wire.

How should I wind the coil for the probe? What should I use to wind it around? What size wire? How many turns?

Does anyone have any schematics to guide me?

Thanks in advance,

Robert in SC

[bbsailor]

How to make a PI probe

Rgecy

Go to the following web site and order either 3 or 7 of the following.
ICH-ROD7.5/50. http://www.surplussales.com/FerRods/FerRods.html Three to make a three rod triangular core or 7 to make a larger core with a center rod with 6 rods placed around the center rod.

The size you choose depends on what diameter probe pipe you can find.
I'll assume you want to use common 3/4" ID plastic pipe.

Any ferrite rod you choose to use should be soft ferrite. The test is to ensure that the ferrite rod is not detected at the lowest delay setting.

Making a DIY PI probe.

1. Wrap three 7.5mm diameter ferrite rods together with tape
2. Run a 6" length of desoldering braid in the center of the three ferrite rods to ground them.
3. Bend a short length of braid over the end of one ferite rod and wrap with a .25" wide piece of electrical tape (Cut .75" wide tape into three .25" wide lengths of 6" long.)
4. Place a 6" length of tape on each end of the ferrite rod bundle to hold the wire.
5. Obtain AWG30 magnet wire from Radio Shack and wind 98 turns of wire around the three rods. This will make a coil with the same resistance as your coil. (I checked this.) Where the wires and ground exit the coil will be the coil back end.
6. Once 98 turns are wound, tape over the top to hold the windings secure.
7. Go to www.hayselectronics.com and order a coil strain relief (letter E). This is the type that is supplied with each coil housing but can be purchases separately.
8. Cut your .75" ID plastic pipe a convenient length.
9. Obtain two .75" ID pipe nipples to cover the pipe ends. Drill a hole in one to fit the cable strain relief.
10. Mount the straign relief on nipple end.
11. Obtain 4 to 6 ft of RG8X marine coax from a marine supply store. This coax has a stranded center conductor. Cut this length to suite your needs.
12. Place the coil wire leads through a short piece of plastic tubing that will fit into the plastic pipe. This will ensure that the rod coil wire leads stay elongated and don't move once pushed inside the pipe.
13. Solder the inner coil lead to the center coax wire.
14 Solder the outer coil lead to the coax ground along with the wire braid. This braid connetion will ensure that the rods are also grounded to minimize noise.
15. Test on you PI machine. You should obtain about 4" to 5" on a coin, maybe a little more.
16. Slide the 3-rod-core coil into the pipe with the plastic tube around the coil leads.
17. Pack some stryofoam pieces into the pipe backend to keep the coax wire from moving.
18. Secure the coax on the strain relief.
19. Use pipe dope to cement the two nipples on the probe pipe.
20. Enjoy your new probe.

I hope this helps.

[Carl-NC]

Thanks for the detailed reply BB...

Robert, I think the connector Garrett uses is available, but I don't know where to get it. You could call and ask them. In general, yes, you want to achieve the "right" settling characteristics, which means trial-and-error. Or follow BB's instructions.

- Carl

[Buzz(ID)]

Ferrite Rod 3C80

Ferrite rods used in probes are they made of 50% iron and 50% carbon composite material? I see the 3C80 material is no longer in use?

Buzz

[bbsailor]

Buzz (ID)

The most appropriate ferrire rods for PI probes are made from soft ferrite or the power type of core material typically used for switching power transformers made from Mn-Zn.

The 3C80 core is a high permeability ferrite core for use in pulsing transformer and broad band transformers.

Other cores in the 300 series are: 3C80, 3C81, 3C85, 3C90 etc.

Go to the link below to see a ferrite cross reference chart.
http://www.tscinternational.com/ferritepartcross.html

The true test for using a ferrite that is appropriate for a PI probe rod is to ensure that it is not detected at the lowest possible delay. The 3C80 rods that I recommended are not detected at a minimum delay of 7.5 uS with my 11" mono coil. They make a reasonible probe, are cheap and can be purchases in small quanties.

Other larger ferrite rods .5" X 8" cost as much as $35.00.

Iron is not appropriate for use in a PI probe.

bbsailor

[Buzz(ID)]

Good Info

Many thanks BB very good info!


Buzz

[rgecy]

BB,

Thanks for the detailed reply. That should be fairly straight forward. I will certainly let you know how it turns out.

Thanks guys for all the replys and info.

Robert in SC

[rgecy]

Can you guys recommend an epoxy for sealing the connector to the housing. Since this is supposed to be waterproof, Garrett recommended a "High Impact Polyurethane Adhesive" called "Ura-Bond 24N". Heres the website. The thing is, you have to buy a special applicator and mixer which cost $90.

http://www.ellsworth.com/display/pro...1&Tab=Products

Any suggestions?

Robert in SC

[rgecy]

Thanks guys for the replys. I ordered enough to build 3 probes since there was a minimum order on the ferrite probes. I finished my winding my probe last night and hope to have it working tomorrow. I hope it performs as well as you guys say it will. I have used the Fisher Pulse 8 probe and got very little distance on coins; maybe 2" at best. With that, two buddies of mine decided they would also like to have a probe for their unit if it performs as stated.

Carl, I think you know Darren in NC. He has a Tessoro Sand Shark.

Brad is over in Wilmington and he has a Garrett Infinium LS.

So what I need to know is what the induction of the coil would be for these units.

Also does anyone have any suggestions on building a waterproof switchbox?

Thanks in advance,

Robert in SC

[bbsailor]

Coil Probe

Rgecy

Go to the link below and click on "coil parameters". Make your coil the same inductance which is usually more coil windings but less resistance than an air core coil . Then, add a resistor in series with the coil so the total probe resistance is about equal to the air core coil resistance. In most cases a 10 ohm 1 watt metal film resistor from Radio Shack will work fine. You can try it without the series resistor or a lower value, but monitor the heat on the coil driver MOSFET. If it is too hot to keep your finger on, you need to add or increase the series resistance.

http://geotech.thunting.com/cgi-bin/...&file=info.dat

Let us know if this helps. You should get a minimum of about 5" on the probe I described.

bbsailor

[Carl-NC]

Robert,

My Infinium has the DD coil; it measures 310uH and 520uH. I suspect the 310uH is the TX coil and also should be the mono coil inductance. The SS is 360uH.

For a switchbox, I would go with one of those really small Radio Shack black plastic project boxes. Seal the lid with RTV before screwing it down. Maybe even fill it with RTV to weight it down, then it won't matter if the lid leaks.

- Carl

[Buzz(ID)]

Probe

Hi BB
I rewired my probe for my GQ, I was only getting 3 inches before and now I get 5 inches. I used 22 AWG w/ insulation stranded wire 68 turns on 12.3 mm ferite rod 2 1/2 long .4 ohms and .7 ohms with the cord on it. Works a lot better, thanks BB for getting me started The probe was not made by Eric, it was some other brand I did mod on.

Buzz

[rgecy]

BB,

Now you threw me another curve, whats a coil driver MOSFET and where do I get one?

You didn't mention this in your first post.

Robert in SC