dave
Junior Member
Posts: 56
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Post by dave on Nov 17, 2016 13:53:58 GMT -8
Hi everyone , I couldn't find a relevant thread so Ive started this one . My question is probably for the more knowledgeable of you who understand theory well . Having built a couple of DD coils to a specific design I have noticed an anomaly . Originally the coil halves are wound with a straight back side ( just like the letter D ) . No matter what I tried the coils were EXTREMELY difficult to set up and gave inconsistent performance , as in very poor range and no detection of gold ( 1 gram 21 ct ear ring ). So becoming frustrated , I bent the backs of the coils in a curve ( as many DD coils are ) . Presto .... really good detection on small gold ( TGSL build ) , coins etc. Discrimination is very good on iron and aluminium . The machine is much easier to adjust and is more stable also. Now for the question .... could anyone provide an explanation of what is taking place ( even a theory will help ) as I have had to do this with both coils . The straight back design will not work for me . These coils are constructed well and shielded , but would not work without the curve in the back of the D. Looking forward to any answers to this question , cheers , Dave .
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Post by radioman on Nov 17, 2016 14:31:22 GMT -8
Hi Dave, While I have absolutely no experience with DD coils used with metal detectors, your question is an interesting one to me from the perspective of changes in inductance in coils in general. Question to clarify: So when you bent the back of the coils in a curve, the coils' shape then resembled a circle, more or less, rather than in a "D" shape? Thanks! R-M
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Post by Gary Lecomte on Nov 17, 2016 14:42:13 GMT -8
How about a Picture of your before and after.
"I bent the backs of the coils in a curve ( as many DD coils are )"
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dave
Junior Member
Posts: 56
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Post by dave on Nov 17, 2016 21:42:23 GMT -8
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Post by Gary Lecomte on Nov 17, 2016 22:12:06 GMT -8
INTERESTING:
In the Past, I have made Numerous DD Coils, but never tried changing the Angles like that. Maybe I'll try it on my home made Bandido detector.
My personal opinion is Resistance does Not matter. Just the inductance and the Associated Capacitors to get correct frequencies, relative to the Detector. 0.5mm wire is a 24 AWG. That is Fairly Large for this type of coil. A 0.2mm (32 AWG) might be better. And Litz Wire will probably also help for these higher frequencies.
Now I mostly just like PI Detectors. And don't worry about discrimination. Just because something isn't Gold, Doesn't mean it is Not Valuable.
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dave
Junior Member
Posts: 56
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Post by dave on Nov 19, 2016 1:29:20 GMT -8
Thanks Gary , I will try .2mm wire. Any advice on the type of litz wire I should use as there are many types and gauges . Also, could you tell me what TPMS22 wire is as I cant find any references to it other than a mention on a video of minelab's use of it pre-dating the use of litz wire in their coils . Cheers , Dave .
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Post by Gary Lecomte on Nov 19, 2016 7:23:16 GMT -8
Pi Detectors require a Larger wire because they put out Higher current to the coil.
Basically all the other types of detectors only need a Small gauge. Any Gauge between 30 to 40 is OK, But working with 36 to 40 is getting pretty small and easy to break. The Greater to number of Strands in the Litz Wire, Allows for the Highest Frequency. But your detector is not really high in frequency, so almost any litz wire would be OK.
Sorry, I have never heard of that TMPS22. But do a Google Search for "TPMS22 Wire". INCLUDE the Quotation Marks as Shown here and you will find some info on it.
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