Vallon VMH3CS Mine Detector

[Ferric Toes]

Hello Eric,

In regards to your question about he Copper disc and did it give a descending tone then YES it did in both Normal and Sensitive timing.

Btw the Aluminum and Brass discs also gave a descending tone in both timings however the Lead disc gave a rising tone in both timings.

The Ferrous disc gave a rising tone in both timings.

Just for the record both timings also gave a rising tone on US 5c and Australian 5c coins.

However when testing on an Australian 1923 Threepence which contains 92.5% Silver, 7.5% Copper it gave a descending tone in both timings.
But when testing an Australian 1956 Threepence which contains 50% Silver, 40% Copper, 5% Zinc, 5% Nickel then Normal timing gave a rising tone and Sensitive timing gave a descending tone.

Maybe of further interesting when testing the same detector with the 8" mono coil on Gold nuggets of these weights 0.16 gram, 0.44 gram, 1.60 gram, and a 6.76 gram then the Normal timing gave a descending tone on all of them whereas the Sensitive timing gave a rising tone on all of them.

Gary

All very confusing. With my detectors that have ground cancellation, any target (usually small or low conductivity) that has a faster decay than the ground minerals, will give a rising tone. Any target that has a longer decay than the ground will have a falling tone. This is for a fixed time relationship between all pulses, but any change in that relationship i.e. normal to sensitive can upset that situation and reverse the tones. The SD2100 and 2200 had fixed timing and avoided this confusion.
Copper is used as a standard for conductivity (IACS) at 100% Silver is more at about 108%, with pure gold being about 70%. All other metals and alloys are below that.

Eric.

[Ferric Toes]

Made my own coiled cable from Belden "Tesoro search head cable".

Wrap it tightly around a 12.5mm copper pipe and bake it at 140 degrees C for 30 mins then remove and place directly in the freezer wait a hour. BINGO coiled cable.

Hi Sean,
I tried this on some RG58 coax in a temperature controlled electric fan oven with a timer; then into the freezer and out came BINGO coiled cable. It looked very neat except that the coils were all welded together and impossible to separate without tearing. Into the BIN it GO.
I tried another run and dropped the temperature to 90C but it still was too hot. You could separate the coils when cooled but it needed a little help from the end of a screwdriver. Cable now springy but very hard when back to room temperature. Next tried 80C and that seemed OK. Could you have meant 140 deg F.? Or perhaps the Tesoro cable had a different higher temperature material as the outer sheath.

Eric.

[Ferric Toes]

Coiled Coax

I think I have found the answer. I was rummaging around in a box of mixed cables and found this unused coiled electric guitar cable with a mono jack on each end. Having a Fender Strat I was a bit reluctant to cut off the jack and find it was no good; but I did and what I found looks good. Stranded inner, polythene core insulation, lap wound shield and a substantial outer cover. Coils are 15mm mean diameter so nice and neat and very flexible. I worked out the length which came to 4m and measured capacitance 410pf. So 102pf/m. Not bad at all. All that remains is to try it, but I have high hopes.

Eric.

[Ferric Toes]

More on the guitar cable

O.D. is 4mm; Total resistance forward and back is 0.8 ohms for 4m or 0.2 ohms/m. Notice the good thickness of outer insulation. The centre conductor is 7 strands of 0.15mm copper wire



Eric.

[Ferric Toes]

Li-ion Batteries

Here is the latest news on the rebuilt Vallon VMH3CS.

I'm really hooked on the use of Lithium Ion batteries now. When you compare the size and weight of three alkaline D cells that the original detector uses with the two 18650 size Li-ion batteries it is almost no contest. The three D cells weigh 15oz (425gm) total while the two Li-ion cells in the holder weigh just 2.35oz (66.8gm).

These two are Chinese and are 6000mAh making 12000 in total. If they really are that capacity, then they will exceed the life of alkaline D cells, which are reputed to last 30 hours of operation. The two cells came with the charger which gives 1A per cell up to 4.2 volts. Red LED when charging; green when charged. With the battery holder and inline T connectors, the total outlay was £14.00, which I thought was pretty good. Yes, and the batteries have inbuilt protection circuit, which is just as well as the battery holder is embossed with battery symbols for series connection, although wired by the manufacturer for parallel cells.




It's good that the Vallon electronics operates with no change in performance at battery voltages between 3V and 4.5V, thanks to its onboard converter. As the voltage drops below 3V the detector gives a continuous alarm and all even numbered LEDs light up.

The next stage in my Vallon program is to package the electronics in a Pelican Micro case; either a 1050 or a 1060 size. Using these Li-ion batteries make this a very viable project. Just one control knob and the small push button/display unit is easily made fully sealed. In fact it is done on the unit in the picture with an O ring between the box and the display module.

Eric.

[Skippy]

Oh dear Eric. Sorry to be the bearer of bad news, but you should've done a bit of research into Li cells before purchasing.
Those Chinese '6000' mAh cells are absolute junk, probably less than 1500 mAh. The BEST cells available in 18650 size are 3400 mAh, made by Panasonic (specifically PANASONIC NCR18650B Li-Ion). Anything with a figure above that is a fraud. Anything with xxxxFIRE in the name is to be avoided.
There are some online comparison tests, this one is good:
http://lygte-info.dk/review/batterie...mary%20UK.html

Li cells are good in general, they certainly do have good (energy content / weight) figures. But they are not as robust as good old NiCads of old, and even with correct charging, and over-discharge protection etc, they can still go faulty, dead, high internal resistance, etc.

[Ferric Toes]

I have of course 8 Li-ion cells from the Whites TDi battery pack which show a rating of 4800mAH, so I am not reliant on the Chinese ones. I don't know the source of the Whites batteries, but I would assume they bought from a reputable manufacturer. They are heavier, with the holder plus two cells weighing in at 110gms instead of 67gms for the Chinese ones. I will run the detector tomorrow and see how many hours I get to run the cells down to 3V. Then I will compare them with the Whites cells. That will be my bit of research.

Thanks for the comparison charts, they are very useful and I shall no doubt end up eventually buying Panasonic. In the meantime, even 8 hours of continuous operation is more than enough for my requirements.

Eric.

[Chet]

I have of course 8 Li-ion cells from the Whites TDi battery pack which show a rating of 4800mAH, so I am not reliant on the Chinese ones. I don't know the source of the Whites batteries, but I would assume they bought from a reputable manufacturer. They are heavier, with the holder plus two cells weighing in at 110gms instead of 67gms for the Chinese ones. I will run the detector tomorrow and see how many hours I get to run the cells down to 3V. Then I will compare them with the Whites cells. That will be my bit of research.

Thanks for the comparison charts, they are very useful and I shall no doubt end up eventually buying Panasonic. In the meantime, even 8 hours of continuous operation is more than enough for my requirements.

Eric.

Hi Eric
I think the TDI battery is rated at 4800 mAH because it has four 2400 mAH series cells wired in parallel with another four 2400 mAH series cells. This puts each individual cell at 2400 mAH which is in line with many of the batteries in the market.
Have you tried your ferrite core probe out on the beach yet?
Have a good day,
Chet

[darkfibre]

..........
These two are Chinese and are 6000mAh making 12000 in total.........
[ATTACH]36695[/ATTACH]
[ATTACH]36696[/ATTACH]
[ATTACH]36697[/ATTACH]

I have spent some time playing with quite a few 18650 batteries.
I have a MC3000 charger that can cycle and analyse (graphs voltage, current and temp)

The best 18650 battery capacity that I have found are Sanyo 3500mh cell made in Japan.

The 5000mh and 6000mh chinese cells I tested were about 2000mh which is no better than a good AA rechargable.

[daverave]

Here is the latest news on the rebuilt Vallon VMH3CS.

I'm really hooked on the use of Lithium Ion batteries now. When you compare the size and weight of three alkaline D cells that the original detector uses with the two 18650 size Li-ion batteries it is almost no contest. The three D cells weigh 15oz (425gm) total while the two Li-ion cells in the holder weigh just 2.35oz (66.8gm).

These two are Chinese and are 6000mAh making 12000 in total. If they really are that capacity, then they will exceed the life of alkaline D cells, which are reputed to last 30 hours of operation. The two cells came with the charger which gives 1A per cell up to 4.2 volts. Red LED when charging; green when charged. With the battery holder and inline T connectors, the total outlay was £14.00, which I thought was pretty good. Yes, and the batteries have inbuilt protection circuit, which is just as well as the battery holder is embossed with battery symbols for series connection, although wired by the manufacturer for parallel cells.
[ATTACH]36695[/ATTACH]
[ATTACH]36696[/ATTACH]
[ATTACH]36697[/ATTACH]

It's good that the Vallon electronics operates with no change in performance at battery voltages between 3V and 4.5V, thanks to its onboard converter. As the voltage drops below 3V the detector gives a continuous alarm and all even numbered LEDs light up.

The next stage in my Vallon program is to package the electronics in a Pelican Micro case; either a 1050 or a 1060 size. Using these Li-ion batteries make this a very viable project. Just one control knob and the small push button/display unit is easily made fully sealed. In fact it is done on the unit in the picture with an O ring between the box and the display module.

Eric.

Hi Eric....never trust li-ion batteries from china...i bought some of them rated at 6000 mah and when i ran a test on them using a capacity meter they were only 800 mah...many chinese batteries are fake !!! also the fake ones are much lighter in weight than the true capacity ones...from what i read 18650 3.7v li-ion batteries are only availiable max capacity at 3400 mah.

[Ferric Toes]

Hi Eric
I think the TDI battery is rated at 4800 mAH because it has four 2400 mAH series cells wired in parallel with another four 2400 mAH series cells. This puts each individual cell at 2400 mAH which is in line with many of the batteries in the market.
Have you tried your ferrite core probe out on the beach yet?
Have a good day,
Chet

Hi Chet,
You are absolutely correct. It was a silly mistake to make as I had recently stated on another forum that the TDi cells were 2400mAh each and paired up to give 14.4V. Put it down to late night posting when the brain is signing off.

I have the Chinese batteries running since 6am this morning, so we will see how they fair over the next day or two. I am measuring the voltage every hour or so.

I have taken a couple of probes to the beach. One worked well but the other appeared to have an EF effect. I have noticed this before on some ferrites and came to the conclusion that orientation in the earth's field changed the permiability slightly, much like a fluxgate sensor. The other probe with a different core is absolutely fine. Finding the best way of shielding for the core is also tricky and I am working on that. Obviously you do not want a spurious response when the end of the probe touches wet sand or water. I am grounding the core itself with a drain wire and making the low potential end of the winding to be nearest the working tip. Do I need an outer shield at all? At the moment I don't really know. There is a plastic bung on the end of the core to seal it and prevent actual contact with the rod. This is a 3in rod of a material that I know to work well.


The was a great article in all the newspapers yesterday about a local detectorist who found a £10,000 diamond ring lost by a woman who went to Majorca on holiday and dropped it while in the sea. On returning to England she contacted various detector clubs and paid for George Edmunds, a retired diver, to try and find it. It took him just under a hour to find. Google 'George Edmunds, diver' for story.

Just taken the photo attached here at 08:45 and checked the Vallon with the Chinese batteries that was switched on fully charged at 06:00. Guess what; they had expired!!!!!! Both batteries 1.5V!!! I will charge once more and try them, then it's back to the retailer for a full refund.

Eric.

[Mechanic]

Hi Eric,

One thing to watch with coils and most likely probes as well is that the signal from the coil, shielding and or ferrite settles before the start of the first sample. If the rx signal is not flat before the first sample starts, or even worse, still on the rail, this will have a big effect of EF cancellation. It's a pity you have no way to test where/when the first sample is being taken on the vallon. I think it is really important that when making coils etc, that you are able to check (scope)what the rx signal is doing when the first sample is being taken. Otherwise it is like a blind man trying to make really clear glass!! some of it might be alright.

Cheers Mick

[Skippy]

I suppose it's worth pointing out that the charger you got with these Li cells might not be the finest either. It's perhaps wise to not use it to charge any better-quality replacement cells you get. Maybe return it, along with the cells?

[Ferric Toes]

Hi Eric....never trust li-ion batteries from china...i bought some of them rated at 6000 mah and when i ran a test on them using a capacity meter they were only 800 mah...many chinese batteries are fake !!! also the fake ones are much lighter in weight than the true capacity ones...from what i read 18650 3.7v li-ion batteries are only availiable max capacity at 3400 mah.

I recharged my Chinese batteries and put one in the Vallon to see how long it lasted, which was exactly 1 hour. The mean current drawn by the detector is 350mA, so in this application they are 350mAh not 6000. Lesson learned.

Eric.

[Geo]

I recharged my Chinese batteries and put one in the Vallon to see how long it lasted, which was exactly 1 hour. The mean current drawn by the detector is 350mA, so in this application they are 350mAh not 6000. Lesson learned.

Eric.

Even for you ????