Computer Interfacing
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Enquiry about depth range vs. battery life


 

       Computer Interfacing Forum Index -> Pulse Induction metal detector
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Joop
New User



Joined: 18 Feb 2009
Posts: 2


Feb 18, 2009 3:00 pm

Hi Lammert,

as you may know, depth range of the PI design is dependend on the capacity of the power source used. The larger the current we can make, the higher the amplitude of the pulse, which gives a better depth range. However, large pulses may drain the battery quickly.

The common solution for this is to provide a large battery pack, which makes the detector very heavy. A modern PI detector may weigh a couple of kilo's and some of these detectors require a special harness to carry them around.

Have you looked into this? Can you tell us something about battery life and depth range of your design?

Thanks,
Joop
lammert
Site Admin



Joined: 13 Mar 2007
Posts: 145
Location: Netherlands and Kazakhstan

Feb 21, 2009 1:08 pm

Battery life is not primarily dependent on depth in the design. The depth is mainly dependent on the size of the search coil. By having a nearly constant inductance between the different coil designs of about 400ÁH and resistance of 2Ohm, charge time and peak current are about the same independent of the coil model and search depth.

The charge time is at maximum 250Ás and depending on the duty cycle the average current drawn from the battery pack will be around 0.5A in normal mode to 200 mA in current saving mode. In the latter mode there are less pulses generated per second which reduces resolution in the horizontal plane, but not the maximum depth.

The other energy consumer in the design is the processor with peripherals. These will draw around 300mA, dependent on the type display type etc. This causes the complete detector to draw between 500 and 800mA. For a nine hour search session, batteries with a capacity between 5Ah to 8Ah are needed. This is one larger 12V lead acid battery of 2.5 kg, or two packs of 8x1.2Volt NiNH penlights which weigh approximately 300 grams per pack.

I can go down in current consumption by reducing the duty cycle of the coil without losing depth. I only lose horizontal resolution in that case. But the current draw of the digital part of the circuit cannot be easily reduced.
colin324
Guest







Mar 13, 2009 12:39 pm

If you can email me the schematics, I may be able to offer emthods for reducing the power consumption. I used to design fire detectors and ancilliary devices, which normally drew only microamps of current in their quiescent state. I can suggest possible changes that could help.

Colin
colin324
New User



Joined: 13 Mar 2009
Posts: 2
Location: Gillingham, Kent

Mar 13, 2009 12:42 pm

Sorry, forgot to log in first - oops. Send to my hotmail account - colin324 at hotmail dot com

Colin.
Guest








Aug 13, 2012 12:10 am

I recently saw an idea that was genius !!!
I saw a man who had a home made detector, that required 12v to operate. Instead of lugging around a heavy car battery, or a large battery pack, he used a 12v battery powered drill and charger. He removed the drill works and hooked it up the the battery terminals within the drill. Now he has a way to change out the battery on the fly !! You can use LI Ion Batteries and get extended battery life. I definately want to try this idea.

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