Diy DD coil for MPP Beach Rev-E calibration?

[tomatos666]

Hello,
I'm a absolutely beginner with metal detector.
I have the REV-E and it works at the moment with a monocoil.
Now I want to make a DD coil for a higher detection rate. So i have made 2 coil's with around 450uH and 10ohm. The housing for the coil's i have just printed.
Now i need to connect the coil's with the REV-E. But i want secure that i don't damage something. What i have to control before i powe it hon. And how i make the calibration of the dump resistor? Are some tutorial where I see where i should measure?
The problem is that i don't speak well English so please have patience with me. Thanks!

[waltr]

Hello,
I'm a absolutely beginner with metal detector.
I have the REV-E and it works at the moment with a monocoil.
Now I want to make a DD coil for a higher detection rate. So i have made 2 coil's with around 450uH and 10ohm. The housing for the coil's i have just printed.
Now i need to connect the coil's with the REV-E. But i want secure that i don't damage something. What i have to control before i powe it hon. And how i make the calibration of the dump resistor? Are some tutorial where I see where i should measure?
The problem is that i don't speak well English so please have patience with me. Thanks!

First, try reading many of the other MPP threads for discussion of building and using DD coils.

Connect both coils with the separation on the PCB. Monitor TX coil with O'scope, being aware of the high kick-back Voltage so may need resistivity divider to protect O'scope input. Adjust TX Damping R.

Connect O'scope to Pre-amp output and adjust the overlap of the TX/RX coils for a null. Fix coils into place.
Now adjust RX Damping R.

[tomatos666]

Thanks for your answer.
I have now a other problem and i dont whant do open a othe Thread.
I have at moment connect a coil with ~400?H and the damping R are the orginal (470ohm)
When i measure on the coil i have only 150-200V kick-back Voltage.
It shoult have arount 350V.
It?s because the damping R are wrong? Are there some how to for the adjustment?

[green]

Thanks for your answer.
I have now a other problem and i dont whant do open a othe Thread.
I have at moment connect a coil with ~400?H and the damping R are the orginal (470ohm)
When i measure on the coil i have only 150-200V kick-back Voltage.
It shoult have arount 350V.
It?s because the damping R are wrong? Are there some how to for the adjustment?

Kick-back volts=resistance across coil(Rd parallel with 1k input resistor) times coil current at Tx off. Coil and lead capacitance can lower it some. Rd should be adjusted for critical damping.

[waltr]

Thanks for your answer.
I have now a other problem and i dont whant do open a othe Thread.
I have at moment connect a coil with ~400?H and the damping R are the orginal (470ohm)
When i measure on the coil i have only 150-200V kick-back Voltage.
It shoult have arount 350V.
It?s because the damping R are wrong? Are there some how to for the adjustment?

Hard to say what kick-back Voltage should be.
What is the coil's resistance? Higher resistance will create lower kick-back Voltage since it is dependent on peak coil current.

You can try removing the damping R and re-measure.

Hint: If you plan to switch between different coils it is best to only install a nominal damping R (~1-2K Ohm) on PCB then add the R needed (in parallel to PCB R) to critically damp the coil in side the coil's connector.

[tomatos666]

Hello,
i have measure now between Coil TX and TP5 and i have ajust the Dumping resistor.
It?s this curve corect?
The value of the damping resistor are 424ohm...

[tomatos666]

Now i have measurte between TP5 and TP3 and i have now this Signal.
The Damping resistor i have mountet now on the coil directly and have 424ohm.
Bud this signal are not how im expectet. What i have worng?
The coil are 380?H and have ~10ohm

[tomatos666]

Sorry it was my fail.
I dont know why. But the right value are 320ohm.
It?s the signal now right or?

[mushaba]

Try use something like this to achieve critical damping

[tomatos666]

I have used a 220ohm and a pots in line du setting up the damping resistor. My question is if the signal what I have made with the oscilloscope looks ok?

[waltr]

O'scope trace look ok.
How is it on detecting objects?

[tomatos666]

O'scope trace look ok.
How is it on detecting objects?

Not realy good.
It detects a 2 euro coin with a distance about ca 25cm ~10"
Work better if a user a thicker wire to make the coil? Or what coil are recommended for the MPP Rev-E?

[waltr]

What distance does a Same diameter Mono detect a 2 euro coin?

[tomatos666]

I think my coil have a to hight resistanz and so i cant bring enough power in the coil. I have user 0,2mm wire. And the coil have about 10ohm.So i have made a other coil with 310uH and a resistanz of 0.1ohm.
Very interesting what happent.
First i have controllet the schematic and i have see that the are the R10 with 3,3ohm to protect the IRF840.
I have in my Hobby room WS2812 LED strippe. They beginn to flickering when i switch the MPP on. The flyback voltage are about 650V.
The coil are working but the R10, D7 and IRF840 beginns to ged warm.
So what resistanze are recomandet for the coil? Can i use a resistor in line with the coil to incrase the resistanz and protect the componets from the MPP?

[waltr]

Yes, some series resistance with the coil will decrease the fly-back Voltage.
You must experiment to find an optional value.