No secrets ML DD 11inch

[Alexismex]

Hello forum friends, here is a radiograph of the Minelab 11inch -DD for the GP 3000, Very nice adjust, see the long nail (mesure 9,5 inch) in the center and another strange things!!!!
THis coil work extraordinary well in heavy mineraled ground,it is my own personal experience, I found a 12mm old THINNNN coin in 16 inch (yes sixteen) of very very mineralised soil ,full of hot rocks , can discrimine very well with a perfect audible sound signature ......BRAVO Minelab.........

[Ferric Toes]

I suspect the long wire with a bend, is the drain wire for the shielding. The shadowy feature in the bottom left, inside the receive coil would be the few turns needed for the balance winding.


Ferric Toes

[Sean Goddard]

Sorry, wasn't aware that a DD coil needed a balancing winding. Am I missing something here?

[Ferric Toes]

Hi Sean,

The way Minelab make them, you do. The two coils are mounted in grooves in a rigid styrofoam former. They are epoxied in and can only be approximately balanced in this way. A few turns on the end of the RX winding is positioned to give a good balance, then that is epoxied. I have one open, and can see that this is what is showing on the radiograph.

Ferric Toes

[Gosho]

Some ML mashines have 3th coil (1uH) just for adjustment (38sm-DD) and correction of the phase

[Siliquae_Sid]

So, let me clear this up...the large THICK winding at the top is the Tx and the thin weedy one at the bottom is the Rx?

I heard Minelab used very low resisitance Tx coil to stretch out the current rise time, and switched off the Tx pulse whilst the current was still rising. :confused:

[Ferric Toes]

Correct on all three counts

[Siliquae_Sid]

WOW, maybe I'm not a stupid as I look...

[gadgetmaker]

Super Gold Search the same?

Hi,

I have a Super Gold Search 11" coil for the SD series and one winding measures out as 0.6 ohms and 300 uh and the second winding is 16.5 ohms and 450 uh. Does this seem close to the one you have??

I want to use it to build the hammer head PI from Carl.

Thanks in advance for any help.

Karl

[Ferric Toes]

I have a Super Goldsearch ML coil and it measures the same. Should work OK with the Hammerhead design but the low resistance of the TX coil will make the power fet run hot. Make sure you have adequate heatsinking. You can put some series resistance in the fet drain circuit which improves the current waveform and takes some stress off the transistor. Say, a 2 ohm 7W non inductive resistor for starters.

Ferric.

[gadgetmaker]

11 inch ML coil

Ferric,

Thanks for the info, I think I will try a fet with a lower Rds on to minimize the drop and run a larger battery supply. Also I think I will experiment with different voltage levels to the coil by using high voltage with a very efficient variable switching supply.

Just got a GP extreme 11 inch coil also.

Will let you know how things go.

Karl

[Ferric Toes]

Hi Karl,


OK, you should be able to pulse some serious current levels through the Minelab coil using a low resistance fet. The problem then is getting rid of the energy when the pulse is switched off. Whichever way you do it, something has to get hot, unless you find a way of returning the energy to the power supply for the next pulse.

Ferric.

[gadgetmaker]

Inductive Spike

Ferric,

Well I have used transorbs , free wheeling diodes and large RC snubbers before to deal with the spike. It would be great to use some sort of regenerative process like back emf from a motor to charge a battery. Have also used quinching capacitors to try to hold down the spike but it usually end up resorting to some sort of resistive load.

Will try a few different things.

Many thanks,

Karl in Arizona

[ivconic]

Of course!


I always claimed that Minelab detectors are probably the best on market.
Why? Simply,it is my personal experience.Minelab Relic Hawk is probably the best ever coinshooter, i have been seen. Jackdetect claims that Troy Shadow machines are well to for coins.I do not have any experiences yet. I guess that their top model X5 can do a job as well as Relic Hawk.We will see in future...
About coil, well that's Minelab.....no wonder!
Regards!