Big Batteries

[Adrian SS]

Everybody is going on about big battery powered detectors being more powerful than the dry cell powered units,
The fact is that big batteries enable the detector to operate longer between charges and that's about all.
Hand held metal detectors are restricted by law to a particular max power output at the transmit coil and all of the top brand PIs are operating at max output already, so if you use a big battery the detectors ccts will only draw the current that they are designed to draw. If you use a higher voltage battery then the rest of the ccts will have to be altered to keep the output power to the legal limit so very little if any advantage is gained as far as detecting depth is concerned.
The Minelab units are not more powerful than the Infinium or whatever, they simply operate in a different manner which gives them a slight edge on small targets and as a result they are more noisy in hot ground.

Adrian SS

 

[Reg]

Hi Adrian,

Actually, the higher powered units do energize the coil with a stronger field and this can result in more depth. Just how much of an increase is the big question since there are so many other variables that enter into the picture. As an example, there may not be any difference on smaller nuggets but show up more on the bigger stuff. Then there is the ground problems that can affect all detectors and just may have a greater impact on higher powered units. I am not sure anyone knows for sure.

ML does increase the gain dramatically and this can result in greater depth capabilities also but normally do so at the expense of having to deal with more noise, so there are always tradeoffs. Sometimes a detector that is quieter is also the one that works better. Again, it is one of those factors that normally isn't taken into account.

People owning a lower powered PI shouldn't worry about any differences. The fact is most gold (both jewelry and nuggets) found is that gold within the normal range of both low powered and high powered PI's. So, over a period of time a user of a low powered PI will be or can be as successful as an owner of a high powered unit. Keep in mind that the over all success rate depends a whole lot upon the time spent looking plus the luck factor. The success rate is also compounded by the knowledge of the detector also.

Now, most gold in nugget form found here in the US is smaller gold so it does help to have an advantage if possible. Using a smaller coil will strengthen the signal from small gold, but the more important factor is the minimum delay of the detector. Sweep speed plays an important part on many detectors, so knowing the best sweep speed can make all the difference in the world also. Another important issue is the operation of the coil height while searching.

A lot of people claim they can do better with a mono coil versus a DD type. Is that really true? Well, it takes a lot of testing to be sure and then one should test using different size nuggets. It is just quite possible that the DD might be more sensitive in many instances.

So, there are a lot of key issues besides the power issue that can make a big difference in just how successful a person might be. One of my favorite stories is about my finding a nice 7 grain nugget with a low powered PI in an area that had been pounded hard by people using high powered PI's for several days before. If I had to guess, I would say that nugget had been passed over maybe 50 times before I found it. Why was I successful? Well, I attribute my success to sweep speed and the fact I had the coil closer to the ground. Later comparisons of my low powered PI and a high powered unit that both could detect the same nugget at almost the same distance. I just happened to be the one that took the time to keep the coil as close to the ground as possible.

I personally own both low powered and high powered PI's, and I don't worry in the least that someone with a high powered PI will do better when I use one of my low powered PI's. I find that my sloppy techniques are generally the reason others may be more successful. So, I am always trying to correct that condition.

Reg

 

[Monolith]

Hi Reg,
Having some experience with PI metal detectors, I understand when you talk about high power or low power in the field. I don't like to dig 3 foot deep holes because I can dig many 10" holes in the time it takes to dig just on deep one. The rest is law of averages. About 5 digs in one hundred produce a valuable target.
However, I do not really know what the definition of high power or low power in a PI means. Does high power mean the watts consumed by the machine? Is a PI with 100 PPS and 2 amps coil current of higher power than a machine with 1000 PPS and 200mA coil current, considering equal TX time and coil inductance?
If a machine runs 8 hours on a set of batteries, how many Amp hours of battery does a low power machine use? From how many Amp hours upwards would it be considered a high power machine?
The battery problem is changing a lot nowadays. LI-Ion polymer batteries are lightweight and a lot of power can be carried around, but the cost is considerable.
So the question of how much power a machine uses is still important.

Sorry for the many questions.

Monolith

 

[Reg]

Hi monolith,

Don't underestimate the ability of the low powered PI's. They work exceptionally well and don't give up that much on depth on coin size objects.

Now, there isn't any general rule that I know of that separates a high powered PI from a low powered one. So, there can easily be PI's that fall in the middle. Given that, one can look at Eric's detectors and compare them to get an idea of what I call a high powered PI versus a low powered one.

The Goldquest is a low powered PI. To reduce the current, there is a current limiting resistor in series with the coil to keep the coil current low. As such, the detector will only draw about 80 ma of current. Now, the high powered one Eric sells is the GS 5C and that unit limits the coil current but only to the point to avoid damage. On this unit, the coil peak current is about 2 amps and the unit draws an average of maybe close to 300 to 500 ma. So, when one compares the two, it is obvious that one needs much larger batteries. The Goldquest can operate easily on smaller batteries including AA's or even AAA's if necessary. I have even used smaller LI ion batteries that don't weigh much to try to reduce the weight of the detector. On the GS 5, a much heavier battery is required to assure a longer run time between charges.

Here is something interesting, the high powered unit draws maybe 4 to 6 times the current of the low powered one. So, the initial thought would be there would be a dramatic difference in depth capabilities, right? Well, that really isn't true. Yes, there is a depth difference, but no where near the difference there is in current draw.

My experience is on a coin size object, there may be an 1" difference to maybe a little more, depending upon the metal when using something like a standard 11" coil. Because Eric's low powered PI is designed to detect low conductive objects best, the advantage is less on nickels, gold, etc. The advantage increases when testing copper and silver objects. This is because of the pulse length as well as the lower current draw.

Lower powered PI's work better with standard size and smaller coils. High powered units can use larger coils much better and this does extend the depth difference between the two types of PI's.

Which is best? That depends upon the operator and the ultimate use. I have used both with great success and will continue to do so. The lower powered units have a tendency to be much lighter and that is a real advantage to someone who doesn't desire to carry the extra weight. On the other hand, one who doesn't mind the weight and wants that extra depth is perfectly willing to use the high powered one to obtain all the advantage they can.

So, this concept of low versus high powered PI is more relative than anything. There is a difference but that difference isn't that dramatic on many of the objects we have a tendency to hunt for.

Finally, to try to answer your question about current usage and pulse rates, the answer is quite complex and depends upon several factors. Pulse length and current limiting of that pulse are usually more important, than the pulse rate. This becomes more important when searching for high conductors objects also. So, there isn't a simple answer to your question.

Reg

 

[Monolith]

Reg,

thank you for taking the time to explain in detail.
So if I understand right, a PI detector that draws around 100mA can be considered a low power unit. How does this compare to a VLF detector in power and in detecting depth?

Monolith

 

[Reg]

Hi Monolith,

Please keep in mind that what I call high power and what I call low power are relative terms. In other words, there is no precise definition regarding what constitutes a high power unit or what might be called a low powered PI as far as I know.

Now, as for how well a PI does that draws about 100 ma, that depends upon the design as much as anything. So, it is impossible to say just how well a generic PI might do in terms of depth of detection.

A well designed PI operating at a particular delay will come quite close to obtaining the depth that might be obtained with a higher powered PI. By close I mean that maybe a low powered PI may detect a buried nickel at a foot to 14" inches while a high powered PI might detect the same object at 14" to as much as 18" or so using the same size coil. Now, on my units, if I measure both at the same time on the same coin size or smaller target, I usually do not see a several inch difference, but may see an inch or two difference and even that only occurs if I have carefully adjusted the two detectors. In other words, I can adjust my lower powered PI properly and not adjusted my high powered unit for the least amount of noise and have the low powered PI appear to go as deep or deeper than the high powered one.

Usually, the depth capabilities of a low powered PI or a high powered PI will exceed those of a VLF, especially in bad ground. At least, the PI's I own exhibit this feature. Once again, just how well they do depends upon how well they are adjusted also.

So, there will usually be a depth advantage if one uses a high powered PI. Once again, all of this depends upon a lot of issues including the design, the location, the noise level, etc. Again, keep in mind that issues such as external noise can make a big difference in just how well a PI works. Some PI's work much better than others in noisy environments. So, it is possible for a well engineered low powered PI to go deeper than a high powered one under the right conditions and the right detectors. This is what makes it so difficult to provide a solid answer to your question.

What most people do not realize is just how critical the adjustments are when it comes to trying to obtain maximum depth. Yes, the delay and pulse width are important, but the noise level can make a tremendous difference if the detector isn't adjusted to minimize the effects of the noise.

As I mentioned in a previous response, I have what I call low powered PI's and high powered PI's and use them both. My high powered units usually get more use because they have more features such as a form of discrimination. Also, many of the lower powered PI's do not have any ground balance features, which I prefer for most of my hunting. So, I look at all aspects of a PI when making a choice and determine whether it will suit my needs based upon several issues and not just the power it consumes.

Reg

 

[Monolith]

Thanks Reg, for taking the time to explain.

All the best
Monolith