Question On Gold Racer Coil

[GB_Amateur]

5 hours ago, californiagold said:

My Gold racer coil had the overload with cover on, then not with it off, only a few times. Now it has never done it again. Had the same happen years ago with 2 gb pro coils. they stopped overloading with cover on after a few removals. I was leaning toward static buildup on plastic coil cover. Im not sure if that would make it overload. maybe Steve can elaborate some more on this very peculiar phenomenon.  Very twilight zone though. 

You may be onto something.  Magnetism and electricity are close allies (look up Maxwell's Equations on Wikipedia) and even a static field is going to cause problems with a dynamically sensitive device -- like a metal detector.  Modern coil housings have conductive inner coatings which have two purposes:  minimize static buildup and shield the coil from from electromagnetic interference (EMI).  If charge can build up between the outer surface of the coil housing and the inner surface of the protective cover one would expect problems.  (Would be nice if Carl M. or Dave J. could elaborate, but they're busy building a new First Texas megadetector.  )

[Guest]

Thank you all for these very informative replies on something I never heard of till now. As Fred says, it can shake a fella's confidence.

That static charge buildup sounds possible for sure. Repeated removal of the cover might dissipate such a charge. Given how sensitive this machine is, might not take much to make a difference.

Whatever the explanation, it seems others have had the identical experience with similar result. That is progress, thanks to you all.

[Guest]

Update, and hopefully the final chapter in this strange story.

Took the replacement coil to the very same beach this morning. No more phantom overloads, sensitivity could be run at max without overload, coil performs as it should. Different than the other coil in other ways, though the difference is hard to define. Sharper, more sensitive at same settings, subtle but enough to notice. Cannot think what the difference in the physical construction of the coil might be, but it clearly is a different animal.

This will be the default coil for this machine for now. For the hunting of micro jewelry in sites that can be very trashy at times, it just seems to perform better. Small targets come sharper, machine balances better, and until something better comes along this is it.

Because it is more sensitive to smaller metal than even the stock coil, the ground is noisier. Much noisier as the gain is increased, and exactly what should happen of course, but it can be a lot to listen to in the All Metal mode which I strongly prefer to the disc modes in spite of that. I had thought it would run quieter because there is less ground under the coil, but it does not. It is more sensitive to small so it sees more and is more noisy than stock. Sensitivity to my most desired target (gold stud earrings)  is lost quickly at gain settings low enough to quiet it down, so noisy is just part of the deal.

Ground coverage is slower of course too. Not just because the coil is physically smaller, but because there are more signals to evaluate with each swing. I have yet to find a way around this either, so for now that is part of the deal too. Whether that will mean more good targets recovered as compared to the stock coil is an open question that only time will answer.

Whether the small round coil might be a better choice is question that might have to be answered some day, for now I am going with this because I am just tired of spending money on gear this year.

Maybe you know all this, maybe not. Maybe it is right, maybe not. There is so little written about these coils for this machine, it could simply be assumed knowledge in your community or it could be that they get used so much less that there is just not much to be had in any case. For what it is worth, this is my experience.

Also for what it is worth, I am grateful for this place where these kinds of questions find answers. Thank you.

[johnedoe]

I hope what I have to share below wasn't mentioned in the above posts.... I went through them but may have missed it if it was there.... So here ya go and at the risk of being redundant I shall reiterate.

One thing I have found is if your going to use a coil cover..... thoroughly clean the coil and inside of the cover before attaching, then seal the edge seam where cover and coil intersect with a good silicone sealant. This prevents any moisture and fine soil/mineral material from getting in between the cover and the coil. 

You would be amazed at just how little material between the cover and coil it takes to cause some interesting fluctuations in readings and stability.

I learned this from experience.... machine was acting very strangely .... checked all my connections, batteries, etc. but it just would not hold a ground balance not to mention how it acted on a target.

The I remember reading about coil covers. So I pulled the cover off and there was just a tiny amount of dirt between the coil and cover.... Cleaned it out.... problem went away....... So when I got home, I cleaned everything up sealed the seam and haven't had a problem since.

 

 

[GB_Amateur]

6 minutes ago, johnedoe said:

One thing I have found is if your going to use a coil cover..... thoroughly clean the coil and inside of the cover before attaching, then seal the edge seam where cover and coil intersect with a good silicone sealant. This prevents any moisture and fine soil/mineral material from getting in between the cover and the coil.

 

There is another option which isn't quite as sound but also is easier to reverse:  tape.  I use Scotch Super 33 vinyl electrical tape (3/4 in width -- far the most common) which is widely available at hardware and big box lumberyards.  One key technique to remember when using vinyl tape:  don't stretch it!  If you do it will find a way to unstretch with time, often costing you your seal.  Even when done carefully the tape will eventually wear down, but I've got tens of hours on my Gold Bug Pro 5 inch round and it's still tight.

Silicone sealant is great and once you're sure you want to go that direction then I agree.  Its biggest problem is that sometimes it's too great, as in being difficult to remove.  You can usually break attached parts loose by cutting with a knife, but getting all the old silicone off is a real pain, as in nearly impossible with some surfaces without damaging them.  I once asked a GE chemical engineer (GE has a industrial brand called 'RTV' but also supplies the same stuff for home do-it-yourselfers which you also can get at hardware and lumberyards) how to remove RTV.  I was specifically looking for a solvent.  He said there was none known, but one solution that some have used is to soak in toluene or xylene, which causes it to expand and weaken.  I've tried that but you still have to scrape the surface in the end.  (You likely know those two compounds need to be handled carefully as they are carcinogens, although probably not so much so with only occasional use in well-ventilated areas.  Also a concern is whether they attack the plastic you're trying to clean....)

Another issue with silicone is that it doesn't adhere to all plastics.  In fact it's not great with some coil housings and covers.  (It seems to work well with some plastic compounds used for that purpose, but not all.)  So experiment if you can.  An even better sealant (IMO) for some coil housings and covers is Rust-oleum's LeakSeal (similar to "as seen on TV" Flex Seal but about half the cost!) because it has a petroleum base, unlike silicone which is, in my experience, either acetic acid or methanol based.  That helps by mildly attacking the plastic surface leading to a better seal.

Bottom line is that I agree with using sealants if you're making a permanent bond.  Otherwise don't trim your fingernails because you'll need them (plus time) to scrape off the cured sealant, preferably during some time-shared task such watching one of the many treasure shows on TV this fall and winter. 

[johnedoe]

Tape is fine as long as you have a solid coil and not one of the spyder type coils.

Here is another option for tape.... this stuff is incredible... Silicon Self Fusing Tape

Now regarding the removal of silicone sealant...... And many other cleaning jobs..... This stuff is also incredible. De-Solv-it Contractors solvent

i have used both and highly recommend them.

[Roughwater]

On 8/14/2016 at 0:56 PM, johnedoe said:

Here is another option for tape.... this stuff is incredible...

Sounds incredible too.  

I'll have to give it a try.