Vallon VMH3CS Mine Detector

[Ferric Toes]

http://www.geotech1.com/forums/showt...501#post233501

I do not know if it is the same, but the one I see at the moment has a failure not listed in the manual.
Any ideas?

[ATTACH]40194[/ATTACH]

Yes, I have just made an offer which was accepted. The failure is an A/D converter overflow which may, or may not be fixable. The manual says return to manufacturer for this fault. We will see. If I can't fix it, I have a spare electronic unit I can install.
I notice it has a C after the serial number. I wonder if this indicates a different firmware.

Eric.

[chevesne]

Thanks for the reply.

[stefan-s]

Eric,

Did this fabric works good to invoid false signals? And where did you get it from?
http://www.geotech1.com/forums/attac...4&d=1463253506

I have made a 38cm coil for my vmh3cs without shield and i get non-stop false signals. I was looking for copper fabric tape but thats a bain in the butt to get.

Greetings
Stefan

[Ferric Toes]

Eric,

Did this fabric works good to invoid false signals? And where did you get it from?
http://www.geotech1.com/forums/attac...4&d=1463253506

I have made a 38cm coil for my vmh3cs without shield and i get non-stop false signals. I was looking for copper fabric tape but thats a bain in the butt to get.

Greetings
Stefan

Even without shielding the coil should run reasonably quietly as long as the emi level is low. Check your inductance and resistance is close to the stock coil value.

Shielding is necessary outdoors on wet ground or at the beach and it does reduce some emi in the radio frequency band. I initially used Scotch 24 tinned copper wire mesh, which is what Vallon use. There is some on eBay but is high priced. It doesn't show if you do an eBay search for Scotch 24. Instead type tinned copper wire mesh. I see also the 3M are making woven copper fabric tape again at £100 per roll. I am now looking at woven silver fabric tape and will be doing tests shortly.

Eric.

[stefan-s]

I made a 15" coil with 39 turns and 0.5mm wire, this is correct isnt it?

As coil cable im using 6mm copper coax.

Even without shielding the coil should run reasonably quietly as long as the emi level is low. Check your inductance and resistance is close to the stock coil value.

Shielding is necessary outdoors on wet ground or at the beach and it does reduce some emi in the radio frequency band. I initially used Scotch 24 tinned copper wire mesh, which is what Vallon use. There is some on eBay but is high priced. It doesn't show if you do an eBay search for Scotch 24. Instead type tinned copper wire mesh. I see also the 3M are making woven copper fabric tape again at £100 per roll. I am now looking at woven silver fabric tape and will be doing tests shortly.

Eric.

[stefan-s]

I think i find the problem. I made a wrong calculation with 39 turns of 0.5 it comes on 1.831mH
The standard coil is 1.493mH so 35 windings will be better it will make 1.489mH

I made a 15" coil with 39 turns and 0.5mm wire, this is correct isnt it?

As coil cable im using 6mm copper coax.

[stefan-s]

I made a 38cm coil with 35 windings this evening it doesn't make any differences the detector is keep giving non-stop fals signals. Only when i put the sensitivity on 4 max 5 it will be quiet and give me real signals(most of the time).
I also put back on the standard coil (only withe the 6mm coax cable around the shaft this is the only change i made) and with this one i have the problem. And i tried it on a second vmh3cs and this detector is giving the same problems of non-stop signals with both coils. To me it doesn't look normal when it is only possible to search on sensitivity 4/5 ? I tried it in both settings normal and mineral

[Ferric Toes]

It is difficult to know what to suggest next. I had problems, and still have, getting coils to work properly first time. Only yesterday I made a probe which had the correct inductance and resistance, but was very noisey. The only quick thing I could think of was to put some extra resistance in series, although that seemed counter intuitive. Anyway 1 ohm was put in series and now the probe is quiet as a mouse and detects coins to around 30cm. Very strange. With normal coils, I always try to get the resonant frequency the same as the stock coil, and that includes having a shield on and also a similar length of coax. Generally they work first time.

Eric.

[Ferric Toes]

Here is the probe that has been added to my re-boxed Vallon. The toggle switch changes from main coil to probe, and it works without the detector going through its start up sequence again. It is a 2 pole changeover switch as you need a 1k damping resistor across either coil when it is not used. This is to prevent ringing being induced.

The other change is that the batteries are now in an additional rear box which makes them easy to change. The space vacated by the batteries in the main box now incorporates a speaker, and phones are now from a 1/4in jack on the battery box. The speaker is muted when phones are plugged in.

Eric.

[Funfinder]

Maybe this interests you:
http://www.geotech1.com/forums/showt...021#post234021

[stefan-s]

Ok Erik, Yes its really strange special when your are looking ad the fact that i have the problems also with the original coil.
Witch sensitivity level are you searching with? I cant get higher than 4/5

Maybe do you know whats the lenght of the original cable? I allready cut my cabel in pices i can try if this is making any diference. I also ordered some double shielded cable to try it.

It is difficult to know what to suggest next. I had problems, and still have, getting coils to work properly first time. Only yesterday I made a probe which had the correct inductance and resistance, but was very noisey. The only quick thing I could think of was to put some extra resistance in series, although that seemed counter intuitive. Anyway 1 ohm was put in series and now the probe is quiet as a mouse and detects coins to around 30cm. Very strange. With normal coils, I always try to get the resonant frequency the same as the stock coil, and that includes having a shield on and also a similar length of coax. Generally they work first time.

Eric.

[Ferric Toes]

Ok Erik, Yes its really strange special when your are looking ad the fact that i have the problems also with the original coil.
Witch sensitivity level are you searching with? I cant get higher than 4/5

Maybe do you know whats the lenght of the original cable? I allready cut my cabel in pices i can try if this is making any diference. I also ordered some double shielded cable to try it.

Hi Stefan,

I have just wound a 28cm coil but not shielded it. It has 44 turns of 0.53mm enamelled wire (solderable); a measured inductance of 1.51uH and a resistance of 3.2 ohms. I connected it to a VMH3CS as in the pictures, so there is an additional 0.6 ohms in the coiled cable in the top shaft. It worked perfectly at the default sensitivity(12), with only an occasional flash from the No.1 LED and very rarely the No.2 LED. The illuminated LED is the confidence one. The channel that the detector is set to is 4/13. I will shield it tomorrow and am reasonably confident all will be OK. I am going to try silver fabric tape this time.

Eric.

[ionut_mtb]

Hi Eric, regarding the probe, i made something similar used with surfmaster pi but have so many false signals, i used a scope to get the right dumping resistor. I use spiral wire not shielded, coil not shielded. from what i remember inductance 300uh, 0.33 CuEm, 10mm ferite. any advice? thanks

Here is the probe that has been added to my re-boxed Vallon. The toggle switch changes from main coil to probe, and it works without the detector going through its start up sequence again. It is a 2 pole changeover switch as you need a 1k damping resistor across either coil when it is not used. This is to prevent ringing being induced.

The other change is that the batteries are now in an additional rear box which makes them easy to change. The space vacated by the batteries in the main box now incorporates a speaker, and phones are now from a 1/4in jack on the battery box. The speaker is muted when phones are plugged in.

Eric.

[ATTACH]40256[/ATTACH] [ATTACH]40257[/ATTACH]

[stefan-s]

Erik,

Thanks for your reply, i measured the two original coils i have they are both 3.9Ohm straight measured on the soldering points for the cable. I also measured it on the end of the cable also 3.9Ohm You are telling your detector is set on channel 4/13 how did you o that maybe my problem is there.

As you can see in the video i switch my detector in normal mode and it is going crazy, when i lower the sens to 4/5 its quiet and is working normal.

Hi Stefan,

I have just wound a 28cm coil but not shielded it. It has 44 turns of 0.53mm enamelled wire (solderable); a measured inductance of 1.51uH and a resistance of 3.2 ohms. I connected it to a VMH3CS as in the pictures, so there is an additional 0.6 ohms in the coiled cable in the top shaft. It worked perfectly at the default sensitivity(12), with only an occasional flash from the No.1 LED and very rarely the No.2 LED. The illuminated LED is the confidence one. The channel that the detector is set to is 4/13. I will shield it tomorrow and am reasonably confident all will be OK. I am going to try silver fabric tape this time.

Eric.

[ATTACH]40273[/ATTACH] [ATTACH]40274[/ATTACH]

[kingswood]

Hi Stefan, when you switch to mineralized mode and ground balance does it still do what it did in the video?