Building larger VLF coils

[Unregistered]

I was interested in building a larger DD coil for a motion VLF detector I have. I have a 10.5" DD coil and was wanting to build a 18"x14" DD coil. Does the larger coil need to read the same amount of inductance & resistance as the smaller coil? Will I need the same size wire for both coils, Just a different amount of turns. Anyone who can point me in the right direction, I would be very appreciative. Thanks, Mark L

[Geo]

I was interested in building a larger DD coil for a motion VLF detector I have. I have a 10.5" DD coil and was wanting to build a 18"x14" DD coil. Does the larger coil need to read the same amount of inductance & resistance as the smaller coil? Will I need the same size wire for both coils, Just a different amount of turns. Anyone who can point me in the right direction, I would be very appreciative. Thanks, Mark L

At least you need the same inductance, with about the same dc resistance.

[Carl-NC]

Yes, the inductance is more important than resistance. Some coils are tuned with internal caps, so you need to determine this as well.

[Sean_Goddard]

For what machine are you planning to build this please?

[Esteban]

For example, if you use 90 turns for 10.5", for 18X14" you will use 54-60 turns, mantaining the same gauge of wire. You wind this coil and measure the inductance. Don't cut the wire of the roll. If you need more you must continue winding. In opposite case, if inductance is more high, you quite half or 1 turn and measure. If inductance continue superior than original coil, you quite other half or 1 turn, etc. Measurements must be made with the same instrument (inductimeter).

[Max]

For example, if you use 90 turns for 10.5", for 18X14" you will use 54-60 turns, mantaining the same gauge of wire. You wind this coil and measure the inductance. Don't cut the wire of the roll. If you need more you must continue winding. In opposite case, if inductance is more high, you quite half or 1 turn and measure. If inductance continue superior than original coil, you quite other half or 1 turn, etc. Measurements must be made with the same instrument (inductimeter).

Hi,
yes, it's the way I do also when need to match inductance and don't have enough informations. Just you forget maybe to say that he needs just scraping a bit the enamel on wire for measures , that could be done safely with very thin emery paper (like e.g. the ones used in static model aircrafts and similar... with very small grains on paper).

Just scrap the enamel , measure and if need more wire continue winding on former.

Sure... that way is not the best for complex coils like ML ones.... e.g. RH coil is painful to match and get oscillations if e.g. dc resistance is wrong... but for maybe 95% of VLF coils that way is nice and also saves lot of wire.

Kind regards,
Max

[Esteban]

Hi,
yes, it's the way I do also when need to match inductance and don't have enough informations. Just you forget maybe to say that he needs just scraping a bit the enamel on wire for measures , that could be done safely with very thin emery paper (like e.g. the ones used in static model aircrafts and similar... with very small grains on paper).

Just scrap the enamel , measure and if need more wire continue winding on former.

Sure... that way is not the best for complex coils like ML ones.... e.g. RH coil is painful to match and get oscillations if e.g. dc resistance is wrong... but for maybe 95% of VLF coils that way is nice and also saves lot of wire.

Kind regards,
Max

Ok, yes, this is the way. Patience you need here. Without patient, nothing can you do!

Regards

Esteban

[Unregistered]

Thanks for all the info!

Trying to build coil for a Minelab Exterra 70

[ivconic]

I checked several coils for Musketeer and Relic Hawk recently; 18cm, 32cm, 36cm, 39cm and 45cm coils. All coils have same inductances: close to 1mH for TX and close to 15mH for RX. Resistances are also almost the same but not exact the same...from 2 to 3 ohms for TX and from 37 to 40 ohms for RX. So this just justify previous posts of our fellas here. Pay attention on incustances but also try not to drift to much from resistances too.
But...this is not enough, not success guarantee. Last but most important thing is ; how to balance those coils? Zero balance or not? What residual voltage is most proper from case to case?
So ... firstly try somehow to measure residual voltage on RX. Than respect inductances and resistances...

[Unregistered]

All the X-terra coils have a microcontroller inside. Major time and effort to reproduce or experiment. Its not a good beginners project. If you want to try coil making pick another brand or model.

Regards Mark

[Unregistered]

Wouldnt it be possible to take an existing coil apart-

cut the board out so you could get an accurate reading for both the transmit & recieve coils. Then wind the new larger coils for the same inductance & resistance and put the original board in this new coil?

[jamal]

hi ivconic & hi men
you are speak for VLF .
I have same this detector (VLF443),
but exist some problems in it and no do .
important this problems - disconnected in wiring between bc board and switch panel .
I connected all cables but not doing , I need your help if you have information about it
note - I draw (BC ) board in my self
-- attached file type (auto cad convert to BDF )file.
pleas provide me wiring connected between bc board and switch panel .


Kind regards
jamal