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garikfox

Bigger Coil, More Energy?

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I was wondering why I haven't seen this question anywhere. Does a bigger coil use more power?

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I guess it depends what you mean by use more power. Certainly resistance varies with different coils. In general the detector puts out a regulated amount of power, and a larger coil disperses that power into a larger but weaker detection field. Small coils pump the same power into a more concentrated, more powerful electromagnetic field. This is why small coils react better to small targets, and why it takes larger gold to set large coils off, but at greater depths. Some detectors allow you to change the transmit power via a control, often labeled TX power. Others may vary that setting via programs or “timings”.

Or were you simply asking whether different coils can drain the battery faster? Yes. Though most people will never notice the difference.

Coil Basics by Carl Moreland

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I was thinking the bigger coil the bigger field so thus increasing power usage.

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From a technical perspective a metal detector in perfect tune detecting no targets is in a state of electrical balance and uses no power. Different coil sizes are all tuned to reach this “null” state so in theory coil size makes no difference. These are not antennas transmitting power but more like an alternator circuit creating a magnetic field. A conductive item has current induced into it, causing a power drain. The ground itself is a huge target so simply engaging the coil with the ground uses power, and larger coils “see” more ground. So it is the engagement with a detectable target of some sort that uses the power, not so much the coil by itself. A lot of the battery power actually goes to creating an amplified audio signal which is why headphone use can dramatically save battery power.

My first post is more the view from a layman user perspective, the above closer to reality, but I admit to not being a detector designer or tech wizard, so somebody else can probably get closer to the true correct technical aspects.

Coil Basics by Carl Moreland

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This dovetails into a thought I had this morning while on the beach.  

I was increasing the sensitivity on my 800 to the max.  It was a little noisy but very good anyway.  Was I giving more power to the transmit or receive?  What actually happens when you give it maximum power?  (I found a brass pendant for my deepest object ever at 20 inches!)

Next thought came to me of JW using the Xcoil at maximum power with the Z.  What happens there?  (transmit or receive power)  He says it still stays smooth so why not 'over amp' the power or 'modify' like the GB2 or some version of that to get more out of the same unit?

I know it is more than just pure 'power' being added but can a normal unit be amped or do you just make an amplifier circuit louder and don't change the electronics of transmit/response.

Mitchel

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Thanks i think i understand. So a piece of "metal" in the ground completes the circuit sorta speak.

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37 minutes ago, mn90403 said:

I was increasing the sensitivity on my 800 to the max.  It was a little noisy but very good anyway.  Was I giving more power to the transmit or receive

Sensitivity controls are almost always simply audio amplification controls on the receiving RX end. TX sensitivity/boost is a separate control. Adding more power can hurt as much as help so it is not a magic solution. However, the main difference I am seeing in modern detector models is they are running at higher transmit power levels out of the box than older models as manufacturers squeeze all the performance possible out of units. Detectors in general now are more powerful but less stable, more noisy than older units.

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Most detectors have simplified control sets that combine several controls into one or leave other controls out entirely. The White’s V3i offers more granular control of the detector at every level possible and so it’s manuals are a lesson in how detectors work. One main reason I own a V3i is because we will never see another detector again with this level of control.

From the White’s V3i Advanced User Manual:

Sensitivity

Once you select a basic program you may need to adjust the sensitivity settings. Most of the V3i programs are set up with nominal sensitivities, but some (notably the ‘Pro’ programs) are set up a little hotter.

Most users believe sensitivity should be run as high as possible. In some cases this is true, but if you find the detector is noisy and falses a lot you probably need to turn it down. There are three primary sensitivity settings, plus a boost mode.

Rx Gain

Rx Gain (sometimes called preamp gain) sets the gain of the receiver’s input amplifier. In most cases, you want to set this as high as possible and still maintain stable operation.

Three things can limit the maximum gain setting. The first is external noise, such as electro-magnetic interference (EMI) including 50/ 60Hz mains and RF. EMI typically shows up as erratic operation and noisy audio. Secondly, in highly mineralized ground excessive gain can cause the input amplifier to overload or operate at close to overload due to the large ground signal, limiting the available range for target detection. Finally, the quality of the loop null can also push the input amplifier toward overload. White’s V-compatible loops are designed to minimize null limitations, but third-party loops typically have wide variances in the quality of the null which can require a lower Rx Gain.

EMI affects the lower end of the signal range, which more directly impacts target sensitivity. Both ground signal and loop null affect the upper end of the signal response range, which usually results in a quicker overload. Ground signal and loop null affect target sensitivity only so far as the Rx Gain must be reduced to prevent overload.

All-Metal Sensitivity

All-Metal Sensitivity (sometimes called DC sensitivity) determines the responsiveness of the all-metal channel. Only target signals above the threshold cause an all-metal response, and a higher all-metal sensitivity setting will increase the all-metal audio response rate to targets. This setting affects all-metal modes including pinpoint and mixed-mode, but does not affect normal discrimination mode. Setting this too high will make the all-metal audio chatter.

Discrimination Sensitivity

Discrimination Sensitivity (sometimes called AC sensitivity) determines the responsiveness of the discrimination channel. This is a threshold level, so only target signals above the threshold cause a discrimination response. Setting this too high will cause noise and falsing in the discrimination audio.

Tx Boost

Tx Boost is transmit boost. When enabled, it triples the transmit voltage applied to the loop (from 10V to 30V) and increases the depth. Using this feature has two major drawbacks: it can overload some loops (reduce the Rx Gain), and it quickly drains the battery.

There are two common uses for Tx Boost. One is when hunting an unusually “clean” area where most targets have been cleaned out, and only deep targets remain. TX Boost typically gives about a 1” depth increase. The other is when EMI noise is severe. Reducing the Rx Gain reduces EMI but also reduces target signal strength. Applying Tx Boost increases target signal strength but does not increase EMI noise, so Tx Boost can be used to improve signal-to-noise.

2AD39ADC-D776-426D-AD7B-2933B6D48999.jpeg

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There must be some serious electronics inside a GPX-5000, wow!

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Assuming you're referring to VLF machines:
The power consumed by a coil does not vary at all with size. If the designers have done their job correctly, the electrical resistance should be the same, and in operation, the voltage applied to the coil should remain constant, too. "Ohms Law" fills in the missing info - the current must be unchanged, too. Hence power is unchanged.
Even if there was, say a 10% variation with a particular coil, you would be hard pressed to observe it's effect on the total detector power draw. Take the frugal Teknetics T2: approximate power put into the coil is 20 milliwatts. Total power draw of the whole machine is about 300 milliwatts.

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