PI max current

[efret]

Been researching PI metal detectors recently and haven't been able to find what the peak current through the transmit coil of <insert brand here> metal detectors. The number I've seen for kits is 2-3 Amps. Does industry stay around there or do they obliterate those numbers?

Thanks,

Efret

 

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[Rob in KS]

I have a homebuilt Hammer Head PI. The coil peaks at about 2 amps. That's on a 3 ft square coil. Of course, it's only on for a few milliseconds

Just checked my notes 185 mS coil on time

 

[efret]

185 mS.. Your coil must have some huge inductance. Around 1 Henry if your using a 12 V battery. How well does it work?

 

[Rob in KS]

185 mS.. Your coil must have some huge inductance. Around 1 Henry if your using a 12 V battery. How well does it work?

My inductance meter says 572uH

 

[efret]

what's the resistance?

 

[Rob in KS]

I didn't measure the coil itself. It has a 770ohm damping resistor in parallel with the coil.
The hammerhead is from the Geotech forum

 

[efret]

No worries, just wanted to rerun the numbers for my own amusement.

So, how well does the hammerhead work? I've looked over the pdf for it and I'm thinking about trying to make my own simply PI machine.

 

[Rob in KS]

It works pretty well. I have a standard set of targets I swing over the coil. I throw a rope over a tree branch so the target does a flat arc. Distance in inches.

It has developed a problem, probably needs to be tuned up to compensate for aging caps.
The nozzle is brass, the pliers are old and larger, the beer can is smashed flat

[TABLE="width: 265"]
[TR]
[TD]1.5" Washer[/TD]
[TD="align: right"]17.5[/TD]
[/TR]
[TR]
[TD]Nozzle
[/TD]
[TD="align: right"]26.5[/TD]
[/TR]
[TR]
[TD]Horse Shoe[/TD]
[TD="align: right"]32[/TD]
[/TR]
[TR]
[TD]Pliers[/TD]
[TD="align: right"]40[/TD]
[/TR]
[TR]
[TD]Beercan[/TD]
[TD="align: right"]47[/TD]
[/TR]
[TR]
[TD]Dutch Oven[/TD]
[TD="align: right"]60[/TD]
[/TR]
[/TABLE]

 

[Reg]

efret,

The range of peak current can be all over the place, but the numbers you mention are about par. Check the resistance of the coils and wiring and most have a limit of 2 to 3 amps. The exception is ML which has a potential of close to 8 amps when on the long pulse.

Current draw of a typical ML SD is about 700ma. Current of a typical TDI is 600ma plus.

I also suspect that Rob's current on time is in usec and not msec. So, most likely it is 185 microseconds and not milliseconds. People often use msec to mean microseconds but it is normally used to indicate milliseconds.

Reg

 

[Rob in KS]

I had to go and look at my notes. You're right it is uSec. It's been about 6 years since I built it.
I shouldn't try to go from memory at my age

 

[efret]

Thanks for the info Reg. Does the high current on the ML give it more depth?

efret