Ecalibur w/ 12 x 15 SEF coil & - any clues?

[SandSweeper]

I have had an Excalibur 800 for about 4 yrs. I've never had any problems w/ the Excalibur, on Carolina beaches, its as steady as a rock. I mainly search the

areas from the high tide mark, dn to the trough. The biggest compaint is w/ the 8" coil, it like scrubbing a hall way w/ a toothbrush.

I have it hip mounted & w/ a straight shaft so, weight is not an issue. When everyone started talking about wiring the Excal's w/ the Sef coil - I'm there, I'm on

it, w/ both hands & 2 feet. I ordered the 12x15 sef BBS coil & a coiltek water proof connector (wiring it straight into the excal, after watching the video on youtube,

I decided not to chance it , plus if I didn't like it, I didn't have to break into the machine a 2nd time).

The 8" coil vs 12x15 SEF coil (for the Sovereign / Excalibur) - compare a dinner plate to a trash can lid - I couldn't wait !! I cut both coil wires, wired it temporarly

to check for function. I got good sounds on test targets, my threshold is functional, although it does not hold rock steady. I contribute the small fluxuation in the

threshold to back ground noises - alot of double 8' fluorescent lights, power strips, desk top computer in my work shop, etc. Coil as big as a sheet of plywood. HA

On the beach, the threshold is holding steady, solid hits on target, LOTS of bikins, life is GOOD. It's like going from a push mower to a 54" riding mower!!

WELL, approx. an hr later, it starts falsing like crazy. I adjust my sens, from hot to auto & back, everything - left / right - forward / back. Even w/ the treshold

lowered WAY dn - past where its normally silent - its still going bananas.

Time for a break, I go sit in the shade w/ a whiskey sour, lots of bikins - (Explorer SE back up) lifes still good. After a few drinks, I grab the Excal & go at it again

Its good as gold, I couldn't ask for better. About the time I figure the problem was cosmic radiation, solar flare, blip in the magnetic field, it happens again!!

For the rest of the weekend, the Excal sets quietly in the corner - FAR AWAY from my SE... Looking for any clue - Thanks Findmall.

 

[hershey1]

You could have a bad coil. I like the WOT myself it works very well. You might try putting that coil on top of a lamp shade to dry it out. If you have a leak shoe goo is a good temporary fix but epoxy is best. Good luck. Hope you get your machine straightened out.

 

[Critterhunter]

I'm guessing one of two things- Either you've got a random short in the wire connections you soldered (most likely I think), or you are picking up off and on intense EMI noise due to something nearby.

The third option like he said is that you could have moisture in the coil. The SEF coils come with the coil nut on the cable not even put on or at least very loose for shipping reasons I hear. Check and see if that nut is super loose. If it is, take it back off and let the thing dry out in the oven or something (at a VERY low temperture you watch closely, of course), or stick it in the hot sun. Once you're sure it's dry then hand tighten the nut, then slightly turn it just a tad more with a wrench. Not too much or you risk cracking the nut. Before I did that with all my coils (SEF or not), I put Shoe Goo on the threads as well as caked it onto the coil cable above the nut where the rubber sleeve will rest to insure further waterproofing.

Now, that said, even with the nut off I don't think water can enter the coil. Most coils are filled entirely with epoxy these days that excludes any water getting in anywhere even if there is a crack in the coil. Filling a coil with epoxy used to mean it was going to be heavy but these days they use what is called micro ballons which are tiny air bubble plastic things that they mix with the epoxy to really lighten it up.

Another potentional problem could be water and sand trapped under the coil cover. If you are using one, take it off and clean under it. I don't like coil covers, especially when water hunting, so I spray the bottom of my coils with 4 or 5 coats of spray on bed liner. Looks like a factory coil textured finish, too.

Oh, and I'd tap on the coil cable and connector where it screws into the detector to see if there is the common short that often happens right there.

 

[SandSweeper]

I used jewelers 3x glasses while soldering, plus I shrink wrapped each soldered point. Even so, it would have been a small job for Ken & barbie.

The soldering points are so small - 4mm x 2mm (length x width) ! I used a sealer on the cable where it enters the coil (under the threaded nut), also the waterproof

connector has the same threaded ends for cable on each side of the connector. I'm like you, I don't care for coil covers for the same reasons.

Whats so puzzling, is the time factor. I can hunt for about an hr before the threshold goes banana. If its a bad coil, its seem like the interference would start as soon

as I turned it on. The fact that the SEF coils are made on the other side of the moon, makes it tough for returns for testing. I noticed the post title does not include

the unstable threshold so, I'm going to repost it. Thanks for the help

 

[Critterhunter]

First, if you bought it from Kellyco they are in the US and thus it's rather easy to swap it for another coil in case you think it's bad. If you bought on Ebay or from over seas then yes it'll be a major pain to swap.

Second, your key point is that it works well for a while and then goes bonkers. That's the "A-ha!" moment for me. That pretty much rules out a short in the cable. Now I'm thinking you've got a coil with coil windings that are just near being out of balance with each other. The RX coil and the TX coil must be in pretty darn good perfect alignment to achieve stability. Let me go into more detail about that...

Years ago I found the QXT was the deepest machine *in my soil*, being a low frequency Whites (just under 7khz) that seemed to penetrate my soil better than any machine I ever used. I owned a few Explorers with did a bit better in depth, but they were far more tempermental in riding that "edge" in terms of sensitivity to achieve that little bit of extra depth.

Anyway, as I bounced back and fourth between QXTs (or QXT Pros, which were the same machine but with a tad more stability with about two clicks higher in sensitivity) and 3 Explorers, trying to find that happy balance between depth and stability *in my soil*, I came to a point where there were no other options to push depths deeper *in my soil* of the QXT or QXT Pro. So, I looked around for any coils that were bigger and thus larger than the 9.5" Whites stock coil...Which I *hear* is in reality not even a 9.5" coil because the coil windings are a good bit smaller than that. Bigger than an 8" Whites coil but not a true 9.5" in dimension.

Anyway, nobody made one. Whites I think made a 14" or 15" coil but I heard it was beyond the size (being a concentric) of showing deeper depth returns on coin/ring sized objects and was primarily meant as a cache or larger relic coil. Along came Jimmy Sierra, who made a coil named the Hot Shot that was a 12" concentric coil. Don't confuse this with the old Hot Head coils that Kellyco made, as those coils were most reported to be junk by most people. The only positive thing I heard about those was that on I think Garretts those larger coils did show depth improvements on coin/ring sized targets.

So, further anyway, I heard some good reviews of the Hot Shot 12" concentric, primarly on the 6000 models of Whites. As most of us know, the XLT, 6000, QXT, and I think a few other whites shared the same frequency and thus were coil compatible. So then I strapped a Hot Shot on my QXT in the hopes of gaining further depth.

The first time I used it, at a spot I knew deeper coins existed based on some prior Explorer experience at that site I had heard through the grapevine, I instantly dug two mercs within about the first 10 or 20 minutes in roughly the 8" range of depth. I was shocked and very excited. However, another 5 or so minutes into the hunt and things went bonkers with the machine. I tried turning it off and back on but no dice. I figured perhaps EMI was present now where it wasn't minutes ago, and so packed it into the car and drove to a more remote site.

Again, for about 10 minutes or so the machine was flawless. AHA! Must have been the EMI thing. But, another ten or so minutes into this new hunt and it was bonker city all over again like the machine was riding way too high of sensitivty.

This went on for several days, with the same first ten minutes or so being fine, but then the machine would go nuts, no matter if I pulled the battery and reset it, or if I dropped sensitivity way down.

So, I returned that coil and got another, but the same exact initial stability would happen with it going bonkers 10 to 20 minutes later. I finally gave up and returned the second coil with no clue as to what the problem was.

Years later, I gave more thought to it when I was researching building my own coils and then it HIT me like a ton of bricks..Those Hot Shot coils were white solid coils, and I had noticed that they were "mushy" if you squeezed them by finger. They had not filled those coils with epoxy to save weight, lacking the current technology were epoxy is filled with micro ballons to drop the weight of the coil. Lacking that weight saving technology of those days, they had not filled the coil with epoxy, and so the coil windings were only glued or epoxied in place without filling the entire coil. Here's the real "A-Ha!" moment...

Those coils were white, and good reason for that...I think it was an attempt to lesson the heat by heating up in the sun. As the coil warmed up the coil windings would migrate out of alignment, and thus the machine would become unstable. They weren't solid filled epoxy coils to lock the coil windings in place. That is CRITICAL in coil stability from my research of building my own coils! The reason why the machine would not work again even at power down/up at the same site, was because the coil was still hot. By the time I drove to another site with it in the car the coil would cool down and be in alignment again for another 10 or 20 minutes at the next site!

These days, that problem is not so much of a factor, as they can load the entire coil with epoxy and micro ballons to still not make it heavy, in particular solid coils instead of spider web designs, but just the same it's even done with "frame" style coils these days. So, what I'm saying to you, is that my best guess is that the windings of that coil are already in critical alignment variances, and although these SEF coils are filled with epoxy, when it warms up in the heat or sun it is already so far out of alignment that it doesn't take much movement from temperture change to push it over the edge.

 

[Critterhunter]

Incidently, I've noticed that some Whites V3 users are having trouble with the black SEF coils in terms of highest sensitivity/pre-amp settings. Along comes a *white* colored V-rated coil, which is meant for those machines and not needed (so they say) for the MXT/M6, which tend to be less "particular" about coil specifications. There are coils for the M6/MXT, that will work on the high end Whites, but not as good as a V-rated coil. Those high end Whites have very specific coil specifications from the way I hear it. So, why the need for a white SEF coil on them? I think it's due to the tight tolerances of what those machines above the M6/MXT expect, and making the coil white keeps it cooler and thus in the tighter specification tolerances of those machines *perhaps*.

Now, when it comes to concentric and DD coils, there is to an extent (from what I've read researching coil building) far less critical "mass" in terms of alignment of the DD coils compared to concentric ones. That's just one of the reasons why many say DD coils are more stabile, let alone the fact that DD coils ride on and see less ground "stew" than a concentric based on the field being generated. That's just one of the reasons why DD coils are prefered in rougher ground, let alone the fact that they also have a more uniform "depth" across the length of the signal than a similar sized concentric (in general), making it less of a need to overlap your sweeps as much. However, despite the less "touchy" nature of a DD in terms of coil windings alignment, never the less they still have somewhat tight tolerances, and so if they are already somewhat out of wack...Just heating up in the sun or warm tempertures could send the machine into a spiral of stability if they are that close to the edge.

So, long story longer, have you tried using that coil on a less hot day? In particular on a day where there is no sun, and that the coil hasn't been kept extra cool in an air conditioned car? If it's stable on a sunless/cool day then I'll put money on the coil windings being already near critical alighment, where a little bit of heat and/or sun is pushing it over the edge.

 

[SandSweeper]

I remember reading about the white vs black coil, & having to do w/ the heat.

I'm can't remeber if I was working both damp sand & water's edge while it was doing fine, or if it was just damp sand & going crazy. Hmmmmmmmm

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!ROAD TRIP !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I'll work the damp sand W/ freq trips into the water. I'll report on it after the weekend. Thanks

 

[Critterhunter]

Remember too that even in water if the water is warmer then your car ride then that might be enough to heat and expand things, causing the windings to warp enough for instability. I've never read any problems with the SEF coils in terms of stability. In fact, just the reverse...Everybody says they are more stable than stock coils, and not just on the Sovereign but also on the FBS machines. The Whites are a different matter. I've read of guys having problems with them in certain respects, and not just on the flagship models that want V-rated coils with tighter specs. So, I suspect you might have a bad coil where the windings are just enough almost out of alignment that slight temperture changes are pushing it over the edge. Another trick you might try is if it's a hot day (even with no sun) and it starts going bonkers, if you have a source of COLD water nearby such as a creek or something, stick it in the water for about 10 minutes and then pull it out and see if it is working fine again.

I may be wrong and you have something else odd going on, but a short wouldn't usually do that where it works good for a while and then always goes nuts. My money is on poor coil winding alignment.
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