high voltage P.I. !!!

[Funfinder]

do you need extra privilege allowance for posting @
Eric Foster's PI Technology Forum
????

Well, you can add this to me if you want to move this topic there so I can answer, otherwise please leave it here.

However - I had a new fantastic idea:

Most of you know the high-voltage wires around a meadow with cows.
The source is from a stationary battery pack and the pulse is around 1/2 Hz.
(1 beat per 2 seconds).

Next very important:

Usual PI uses 10-30 volts power source giving flyback voltage up to 1000v.
the more voltage the better penetration power - that's for shure!

We must use 10 times stronger voltage for REAL depth results.
Everything else is childsplay! Especially 'cause the larger the coil the
weaker the strenght for small objects we wanna find, too!

I hope here are some persons who have personal experience with
high-voltage technology. Is it possible to built a coil that doesn't create "sparks"?
Would we need special thick isolated wires? There are alot new questions
what could be the limitations using high voltage. Any good input is appreciated.

[goldfinder]

pulse transformer give very high voltage

A really high voltage can be achieved with a pulse transformer. The PI high voltage is gotten from the rapid di/dt of the built up energy in the search coil. The energy is dumped into a low resistance and the consequent voltage rise gives the 600 to 1000 volts.

In a pulse transformer, like in a stun gun, a charged capacitor is dumped across the pulse transformer. Output of the transformer give the very high voltage. This is well known giving voltages in the hundreds of thousands of volts.

So how much voltage do you want and is that what you really are after. It seems in a PI detector the big magnetic field of the coil produced by the rapid decay of current in coil is what is inducing the desired eddy current in the metal the detectorist is search for.

I don't pretend to be an expert here on detectors so maybe Carl or one of you gurus can chime in here.

Goldfinder

[taliesin]

nice idea

it'll draw a lot more current ok if you don't mind lugging big batteries around.then you'd have to stop that voltage peak quick in order to sample the decay .coil material would be pricey.

[Götz von Berlichingen]

As far as i know, the Magnetic Field Strenght is proportional to the Current and Number of Windings, not Flyback Voltage.
I see the high Flyback Voltage as an unwanted Side Effect.
A PI Detector starts sampling the Signal when the Flyback Voltage is down to ~0.6 Volts or even less.

[Funfinder]

@ Götz von Berlichingen
I haven't tested this yet what creates more eddy currents:
high voltage or high ampere. However 10x more power should work.

btw. if you want to use modern corrected translatable german change your signature to: (...) ihrer kaiserlichen (...) (Vor Ihro Kaiserliche Majestät) but perhaps your spelling was orignal medieval - some guys spoke and wrote at that time as they wanted or knew it or simply all kinds of crazy dialects!

@ taliesin
Big batteries are a must!

@ goldfinder
thx for the fast answer - very interesting info. We'd need a guy with PI AND high voltage experience. Yeah, the most power is done in a transformer if the electricity is "off" but how much power is possible?! The coil wires shouldn't melt and there shouldn't occure any spark-shortcuts.

I have already personal experience with highly charged capacitors - those can pierce (= branding) nice spots into your fingers. But as long as everything is inside a plastic-coil- etc. housing it should be save. Perhaps a usual old TV circuit can be used. It consists already of high voltage parts. Only the recognition circuit must be changed.


btw. now this sounds completly crazy but doesn't like flashes to hit metal targets - perhaps even if those are under ground? It depends how detectable this power is. There must exists some measurable amount of 'electrostatic flash light attracation' like a magnet starts to move if iron or second magnet comes nearer.

[DOOLEY]

hello all,

if your thinking of a voltage multiplier and storage , then the limit is the highest capacitor you can find,,,,,,but......

amperage use will be same as voltage increace +25%
at a reasonable efficiency of 75% ,

so 12V boosted to 24V with 1A drain would need 12V @ 2.5A

12V boosted to 100V with 1A drain would need 12V @ 10.4A

current useage may get a little silly

modern inverters may be the answer , comercialy made 240V ac units as a starting point , think there in the 90% efficient area.

OR car ignition systems , 60,000V is the norm these days , and HT cable will keep it in , coils are goint to be a little heavy and bulky as wire is aprox 8mm dia.

the older car ignitions used to be around 20,000V , and ive seen wire with 4mm dia that holds this.

gas cooker igniter coil , similar 15 to 20 KV with "thin" 4mm wire a posibility.

NOW FOR CRAZY TALK :

how about a peizo electric generator , gas lighter ignition element , on a cam , on a small motor , 6000 rpm would get you 100 ppm @ 10 to 20 KV

i can think of a problem , if you go into production , detectorists may be dropping like fly's in the field when it rains !!!!!

[Carl-NC]

Yeah, you want high current, and there are better ways to get higher current. Ferinstance, use a single-turn TX coil of large-gauge wire, and a super-low R switch.

[DOOLEY]

i used to think voltage and lots of it , thinking the higher flyback was the key to it all.

but , thinking in terms of watts , in order to get a stronger magnetic field to "kick the target" we can either raise the voltage OR the amperage to get the same result. so rather than waisting energy converting to HV simply apply more amperage.

as carls says , low resistance single turn coil , and fire lots of amps into it.

was reading an article on emp weapons , similar thing , 8mm thick conductor , in a single loop , with low voltage , high amperage stored pulse is applied , and magnetic field is so strong all electrical equiptment nearby get's fried.

after alot of reading here and elsewhere , people quote di/dt alot,

the sudden change of CURRENT , the faster the better , voltage doesnt seem that important , more of a by product that happens in the process.

[taliesin]

single turn cool

what about the hv cap across the coil ?

[taliesin]

just an idea

could use one of them giant thyristor's they use to stop electric rollercoaster's

[mikebg]

could use one of them giant thyristor's they use to stop electric rollercoaster's

Taliesin, keep thinking and you will reinvent the pulser.
See this:
http://en.wikipedia.org/wiki/Artific...nsmission_line

http://en.wikipedia.org/wiki/Pulse_forming_network

http://www.nessengr.com/techdata/pfn/pfn.html

http://namcub.accela-labs.com/pdf/30...ein_Pulser.pdf

Search web for "artificial transmission line", "pulse forming network", "Blumlein pulse generator"

The original inventor is Alan Dower Blumlein

http://www.alanturing.net/turing_arc...es/blumlein/#2

[Tinkerer]

What generates the most eddy currents, is a high rate of change of a strong magnetic field.
We can produce the same strength magnetic field with a one turn 100A coil as with a 100 turn 1A coil.
A 100A cable is heavy to lug around.

The next important factor is the fast switching, to get a high di/dt or fast rate of change in the magnetic field or current.

Switching 100A is a bit of a problem. 1A is much easier.

At switch OFF, a 3uH coil with 100A and a 10 Ohm damping resistor will build a 1000V Flyback

A 300uH coil with 1A and 1k Ohm resistor will also build 1000V Flyback.

The decay time of both coils is essentially the same.

Nowadays there are new Mosfets available with up to 4000V Flyback capability.

How about using these? We need to have a close look at cables connectors and PCB layout, dust and humidity if we want to work with such a voltage. We might get sparks all over the place.

Tinkerer

[taliesin]

ouch

Taliesin, keep thinking and you will reinvent the pulser.
See this:
http://en.wikipedia.org/wiki/Artific...nsmission_line

http://en.wikipedia.org/wiki/Pulse_forming_network

http://www.nessengr.com/techdata/pfn/pfn.html

http://namcub.accela-labs.com/pdf/30...ein_Pulser.pdf

Search web for "artificial transmission line", "pulse forming network", "Blumlein pulse generator"

The original inventor is Alan Dower Blumlein

http://www.alanturing.net/turing_arc...es/blumlein/#2

i need a bigger shack i think.

[kt315]

Usual PI uses 10-30 volts power source giving flyback voltage up to 1000v.
the more voltage the better penetration power - that's for shure!

seems you are absoliutely out of the subject. last (new) detectors of Eric Foster are not HV ones. the coils have more turns, more hight resistanse. mosfets are low voltage too.

[Tinkerer]

We could get a bit more specific and enter into the nitty-gritty of the problem.

Let's see if we can design a powerful pulse, that delivers a magnetic field of 5 Gauss and a di/dt of 2A/usec.

Just 2 amperes of rate of change within 1 micro second. Can we do it?

For the more clever ones, a little additional challenge: how can we sustain this rate of change during 3us?

What are the power requirements?

How can we fit all that into the limits and parameters of available components?

At first sight it may seem not worth the trouble of going through this academic exercise. However, this would produce a very powerful PI.

Is anybody up to the challenge?

Tinkerer