looking to build a coil. anyone have a dead one you can part with

[fireguy]

I'm looking to build some homemade search coils. I'm looking for anyone that has a dead coil that I can use to reverse engineer. If I'm successful I will make you a coil. I would really like an ace 250 coil but will work on any machines coil.

 

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[christo000]

I don't have any dead ones but on ebay they have quite a few different styled empty ones available for you to make your own insides & specific coil wire for the machine ur using fairly cheap to

 

[airscapes]

I don't have any dead ones but on ebay they have quite a few different styled empty ones available for you to make your own insides & specific coil wire for the machine ur using fairly cheap to

Got a link or specific search string?

 

[christo000]

I'll pm it

 

[fireguy]

I'm also looking for dead coils so that I can double check the wiring and if there is any extra hardware not seen. Also I want to make sure I have the proper wire and wiring configuration. The end result I would like to be able to create custom sizes for people on here and myself.

 

[fireguy]

I don't have any dead ones but on ebay they have quite a few different styled empty ones available for you to make your own insides & specific coil wire for the machine ur using fairly cheap to

I need an example of a complete one to see if any what type of preamp there is in the coil. That's the main thing. I can wrap a coil with the turns and shape but the circuitry is what I need an example of

 

[christo000]

I'll check, some things & see what I can come up with for ya

 

[fireguy]

The biggest thing I need is the circuit board from inside the coil and the connector so I can configure the layout.

 

[christo000]

Nothing online I know in like manuals they kinda give you a layout of how stuffs placed inside,like in the,minelab e-book for the xterra's. Only thing I can think of on something like that would be keep an eye on ebay I have seen coils on there that say they don't work & for sure have seen machines on there from garrets to whites couple others that say buy as is worked then suddenly stopped working & there whole

 

[Alan Applegate]

Well.....

This statement gives me a bit of hesitation: I need an example of a complete one to see if any what type of preamp there is in the coil. That's the main thing. I can wrap a coil with the turns and shape but the circuitry is what I need an example of

There aren't any preamps per sé, but there are other electrical components. What they are depends on the brand and model. In any case, you best know a fair amount about resonant circuits among other things. If indeed you're trying to learn how metal detectors work, I suggest you start really simply, and design and build a BFO unit.

 

[fireguy]

I know how metal detector work and I have no desire to build a bfo. I have some knowledge of electrical components build I'm not looking to replicate the circuitry. I am looking to match the wire component and shape to fit a custom need while using the original circuitry. As I have stated before I am in a mechanical engineering program with some electrical engineering Courses under my belt. However one of my best friends is an electrical engineer and I will be double checking my work with him prior to testing. Not trying to be mean but I'm not going to open a good coil or buy a good coil to open up. So unless you have a bad coil that I can buy cheap save the life lessons for your kids.

 

[fireguy]

Sorry if I came off short. To many times people respond to threads without an answer to a question or just an opinion without any experience on the particular subject. Just looking for a cheap non working coil

 

[woof!]

I'm also looking for dead coils so that I can double check the wiring and if there is any extra hardware not seen. Also I want to make sure I have the proper wire and wiring configuration. The end result I would like to be able to create custom sizes for people on here and myself.

"would like to" are the operative words here. Heck, what could be easier than to build an induction balance searchcoil? Even Chinese counterfeiters get it right 1% of the time!

Sorry if I came off short. To many times people respond to threads without an answer to a question or just an opinion without any experience on the particular subject. Just looking for a cheap non working coil

Would you welcome an opinion with more than 30 years of metal detector industry experience as a lead design engineer? If so, I may be able to steer you in the right direction.

--Dave J.

[EDIT] Advice: begin with mastery of LCR circuits. That's just the transmitter coil, before you address the issue of induction balance. Until the searchcoil works, the preamp won't even matter.

I interview EE's as part of my job. Very few can describe what an LCR circuit does. It's shocking, this is the foundation of RF circuitry! Hell, 20% of 'em don't even know Ohm's Law, meaning that they can't explain what happens electrically when you screw in a light bulb. They're $50K deep in student loan debt and aren't qualified to do anything whatsoever in their chosen field even at minimum wage.

I do sincerely hope that at least you know Ohm's Law.

The hard part of IB searchcoils (once you know basic AC electricity) is induction balance. How precise does positioning have to be in order to maintain linear operation with a favorable S/N ratio, and how can that positioning be maintained over temperature and time and mechanical deformation forces applied to the searchcoil assembly? (This is all first year college physics.) Hint from the real world: what is a linear differential transformer and what are they used for in industry?

 

[roaddust66]

I see you are in Dayton Ohio. Dayton has an annual amateur radio gathering of about 30,000 ham operators each spring called The Dayton Hamvention out at Hare Arena. You are looking for an old guy who has been licensed 35 to 45 years and has built many many antennas. Also there are many books on building antennas. Alan Applegate gave you the two key words. " resonant circuits" . You absolutely have to know what this means before embarking on this. It is math. Plain and simple math. There is no voodoo to this. If you find a really smart ham radio operator and he can make something in a few hours. Also there is a device made by a company in Miss. called MFJ. It is called an antenna analyzer. With that analyzer you might be be building coils of all shapes and sizes very quickly. "Loop antenna" is what you need to research. Does this look familiar ? https://www.google.com/search?q=loo...bUsATPgoDYDA&ved=0CAoQ_AUoAg&biw=1152&bih=561

 

[fireguy]

Woof: yes I understand that and I have seen it first hand kids go to school pass classes but never learn the stuff. Get out of school and expect to get a big boy job without even trying. I took this on as a project to callenge myself. Especially while I have access to the engineering lab and things are still fresh in my mind. I don't claim that this will be easy but what I don't get is what is it hurting of these people. I'm buying the coil someone isn't using and if something goes wrong it's my machine breaking.

Road dust yep hamvention is big around here. Seems like we get people from all over the place. Thanks for the info and if you end up coming to that pm.


With all that being said. Still looking for a cheap coil. For new posters I gladly accept advise but leave the criticism.

 

[christo000]

Hey ya never know unless you give it a try, ideas are just ideas only you can make them a reality. Go for it

 

[woof!]

Sorry, Fireguy, I was overly sarcastic there.

If you just want to wind a coil for the heck of it, the only way you'll know if it works or not is to hook it up to the detector it was designed for. You can pick up a BH Junior brand new for typically about $60, that way you have both a detector and the searchcoil that goes with it. This model is particularly easy to wind searchcoils for because there is no tuning capacitor or other circuitry inside the searchcoil, and the transmitter and receiver windings are approximately the same inductance. The standard searchcoil is concentric but for experimental purposes you'll find a DD easier to get right.

People who are unfamiliar with metal detectors often get the idea that the "antenna" on a metal detector is pretty much like a ham radio antenna. It isn't. A better model is air core transformer in a condition of induction balance. And, nonmetallic electrostatic shielding is almost always necessary.

There's a technical forum where people from all over the world grapple with searchcoil issues, the name of the forum begins with a G. (Sorry, don't know if admins permit links to that particular noncommercial forum.)

Have fun!

--Dave J.

 

[Rob in KS]

I had an old Garrett that quit working. I tore the coil apart. It was welded together and took a while to tear apart. Multiple coils, short wires that acted like a coil, precise placement, things glued in place for no movement, buck, boost, phasing. It got complex in a hurry.

I ended up building a mono coil PI. That makes the coils WAY simpler. You can get a real education on coils over on Carl's forum.
The mods don't like us sending people to other forums. Fair enough. A little google should fix you up.

WOW EE's that don't even know Ohms law. It's been a while but isn't a linear differential transformer used for position sensing?

 

[roaddust66]

thanks for the enlightenment. I may get a wild hair someday myself and head for Ace Hardware , by some pvc , various gauge wire , purple foam and watch out !!! I have been to Ace before and the kids are rolling the wire out all the way to the front of the store. The kids say , watcha doin with all this wire. I say you wont believe if I tell. I'm going to talk to people all over the world. They grin and say sure you are. ( grin)

quote
People who are unfamiliar with metal detectors often get the idea that the "antenna" on a metal detector is pretty much like a ham radio antenna. It isn't. A better model is air core transformer in a condition of induction balance. And, nonmetallic electrostatic shielding is almost always necessary.

 

[Carl-NC]

Fireguy, I've never peeled on apart, but I'm guessing the ACE250 doesn't have any circuitry in the loop. Just 3 coils of wire. Sounds simple, eh?