Why Are Top-performing Dry Land Pulse Induction Detectors So Frickin' Heavy?

[GB_Amateur]

I think I know the pat answer, but if that's the case I'd like to see it defended.

[dig4gold]

The 6000 isn't heavy.

[phrunt]

The battery is part of it, my GPX 4500 / 5000 batteries weigh 870 grams although using a home made Lipo battery pack significantly improves that so obviously newer models are capable of lightening the weight of the battery using newer battery technology.

It's housing is very robust, it's made of alloy rather than plastic.

One thing about the legacy GPX series is they're built tough, the amount of times I've dropped mine on rocks and bashed it around and it's never once blinked an eye, solid as a rock.  I would not like to treat a newer model the same as it won't survive.

The coils are also quite heavy, they're built tough also though, when do you hear anyone with a GPX complaining about coil ears breaking, even the ones made by Minelab?  The main reason for the coil weight is the amount of wire in them though.

After swinging my GPZ for some time even with my smaller lighter coils to go back and use my GPX 5000 it feels light as a feather, especially now JW gave me a carbon shaft for it 🙂

The Garrett ATX and SDC2300 are heavier than they needed to be simply because of their design, and the waterproofing.

The GPZ has a lot of its weight in the coils, a whole lot of wire to do a DOD design coil over a simple mono for a GPX.

It will be interesting if Nokta can do a lighter PI gold machine while still keeping build quality as tough as they usually do, their VLF detectors are never really lightweights I'm guessing due to their build quality.  Generally I think with light weight comes flimsiness.  I can bulldoze through long grass with my GPZ.....

[MSC]

I have used Doc's battery pack since I have owned my 5000, I do use a bungee cord but I could swing it for hours with out it. The 6000 is very light and needs no bungee. The 7000, is heavy. 

[Valens Legacy]

Why Are Top-performing Dry Land Pulse Induction Detectors So Frickin' Heavy?

 

It has to be one of two reasons,

1st the batteries,

2nd could be because they're made for real men?

Just kidding because I am just a newbie at this.

 

[phrunt]

The 5000 is a pretty light detector really, mainly due to the battery being on your butt as the battery is heavy at 870 grams

It's only approximately 2400 grams with the stock 11" coil fitted, my GPX 5000 is 2312 grams with the 11" Commander fitted due to the full carbon fiber shaft. 

The 6000 is approximately 2100 grams with the 11" stock coil, I don't have one to weigh myself so that's going by Minelabs advertised weight, they seem to round numbers to the nearest 100 grams on the lower side seeing they advertise the GPX 5000 as 2.4 kg / 2400 grams and mine weighed slightly more than that with the stock shaft, and the 6000 at 2.1kg / 2100 grams, so only about 200 grams in it between my 5000 with carbon shaft and the 6000 both with 11" coils, that's next to nothing and I'd not be surprised if a fair bit of that weight difference is the coils, the 6000 coils feels light and have been made with a very light thin plastic.  The 6000 feels nice on the arm though, it feels really light, especially after just putting my GPZ down.  The GPZ is 3.32 kg / 3320 grams so quite a bit heavier than the others.

I'll have to weigh the Lipo battery setup for the 5000 and see what it weighs, it feels like it weighs next to nothing, I just have it attached to the control box. 

It's the GPZ that's a heavy detector by comparison, although I'm not at all bothered by it's weight.

The QED was a light PI detector, my PL3 with the 11" Commander fitted weighed approximately 1800 grams but still heavy compared to say the Equinox at 1350 grams.

Sorry about my lack of Imperial weights, they confuse me 🙂

[PhaseTech]

5000/4500 with a Detech or Minelab 8" Mono is just a joy to swing. Really well balanced, no bungy needed. Even with a 12" Evo I don't use a bungy unless I'm going for a long period without needing to dig up a target. 

The SD2000 was very light, the SD2100 and 2200 were a bit heavier, then the GP series were heavier again. 

GPX series control boxes went on a diet. 

Yep 7000 is a bit of a beast, but it's built tough, internal cable requires thicker shafts, and big power output requires bigger batteries. You can put a 12" NF coil and a CTX3030 battery on and have a much lighter set-up, but the CTX battery is only good for about 2.5 hrs. 

[GB_Amateur]

23 hours ago, phrunt said:

The coils are... quite heavy,...

Let's stop there.  I think that's the driver.  But first let's look at some weights (taken from Steve's Database😞

I've sorted from heaviest to lightest.  Let's cull the first three -- GPZ is unique technology, next two are waterproof which apparently adds quite a bit of weight.  Now we're down to five detectors from three manufacturers, lightest being White's TDI/SL at 3.5 lb with the GPX5000 heaviest at 5.3 lb.  (Note, the White's also has a bit larger coil -- 20% more area which scales naively as weight.)

Now, back to the coil.  Here are a three excerpts from the Geotech book:

on p. 143:  The higher the coil current and the faster it is to shut off, the higher the magnetic field transient dB/dt will be.  (Note: dB/dt is what leads to the eddy current in the target, and the bigger it is the stronger the signal will be.)

on p. 146:  ...The coil should be designed with the greatest number of turns possible for best depth, while still achieving the desired settling speed.

footnote on p 146:  More windings for a given transport current produces a stronger B-field but, in practice, more windings also have a higher series resitance which reduces the trasmit current.  The reality is that a lower inductance trasmit coil produces a stronger B-field for a given drive voltage.  However, the same coil (in the mono case) is also used as a reciever, and a higher turn coil improves the receive sensitivity.  There is no free lunch.

As is often the case, reality isn't simple.  There is a tradeoff in amount of copper in the coil windings and maximum signal.  Not mentioned here is that the diameter of the wire used in the windings also matters, as does the method of winding.  Bottom line, though, is that to optimize signal strength one needs a heavy coil.  (Pretty sure that's the conclusion....)

OK, so now that we have a heavy coil, what about the rest, since the coil is less than half the weight of the detector.  One word answer:  balance.  The battery to drive these currents is heavy, but it can be used for balance, and that is what has been done for most (maybe all) of these detectors.  Yes, a lot of battery charge (typically spec'ed in amp-hrs) is needed to run these, but that can be adjusted by carrying multiple batteries.  Ergonomically, just mount what is needed for balance and put the rest in your backpack.  (Is that what is done now?  IDK.)

The TDI/SL sacrifices signal strength for weight.  But they did a pretty good job at that extreme end of this list.  So does the QED (and I think its 4.0 lb can be improved upon, but then maybe all of these detectors have that option...).  I think the QED is intermediate in signal strength between the TDI/SL and the GPX.  Finally, the recent release GPX6000 has improved upon the weight of its older sibling (GPX5000), with a bit of depth given up for larger nuggets, and fewer features -- features that may not matter to native gold detectorists but do to the (minority) relic and beach detectorists.

Is there room for improvement?  We all can opine in the meantime while we wait for the manufacturers (hopefully) to deliver.  🤞

[phrunt]

You can put a Nugget Finder 8x6" Sadie coil on a stock GPX 5000 and it weigh less than the GPX 6000 with stock 11" coil, of course it's a smaller coil but it does show how much weight is in the coils themselves.  Keep in mind the GPX 5000 battery isn't included in these comparisons as it's not on the detector, it's on a cord hanging off your butt giving it a weight advantage and an ergonomics disadvantage over the 6000 with built in battery.  The 6000 seems so well balanced with the 11" coil to me that even though it's weight is so similar to the GPX 5000 it feels so incredibly light, if you had your eyes shut and someone put it in your hand and you swung it around a bit you'd think you were swinging a VLF, not a high powered PI machine.  I can't find the 11" coil weight anywhere but I think it's part of why the GPX feels so light and well balanced.  Putting the 14" coil on adds another 200 grams and people often say it becomes bungee territory when you add the bigger coils.  The GPX 6000 weight with 14" coil is 2.3kg (2300grams) vs the stock GPX 5000 with 11" coil weight of 2.4kg (2400 grams)

Minelab have done a good job lightening the GPX 6000 coils, it does feel like strength is sacrificed in doing so, although there is no evidence of them being weaker in any way, they just feel weaker because of how thin the plastic is, for example you push on the top of the coil and your finger sinks into it, it has a hollow feel with very thin flexible plastic. 

This is very similar to the Nugget Finder Z-Search 12" for the GPZ which is also a very light coil in terms of GPZ coils at about 950 grams which is about 300 grams lighter than stock 14x13" coil, The Nugget Finder uses similar thin plastic type where you press on it and it is very flexible.  I think this is why a lot of 6000 users are putting a tape or a sticker over their coil where they rub their scoop on it as they're worried they'll wear out the thin plastic from rubbing the scoop on there, it does scratch quite easily but I've still never seen one person wear out the plastic on their coil so its perception more than a problem at this stage.

I hope Nokta doesn't waterproof their gold PI when they make it, sure its nice to have waterproof but the negatives of it for prospecting such as extra weight required for waterproofing a detector and need for custom waterproof coils far outweigh the positives.  I'd be happy with GPX 7000 style rainproof and the use of GPX coils rather than suitable for submersion.

The problem Nokta is going to have is their robust designs are naturally heavier than more flimsy designs so to make a lighter PI detector they're going to have to work hard on cutting weight without sacrificing their well known good build quality.

[Lanny]

This is a very informative thread, and thanks to those that have contributed. Moreover, Simon, you've outdone yourself in explaining things, nicely done!

Heavy PI's/hybrids is one of my main beefs with the technology, not a fan of a heavy detector, though I still swing my 5000 but only when I'm in nasty ground or need to punch super deep. The newer dedicated gold VLF's are better at dealing with mineralization than the old ones, so that lets me operate (even if sometimes with a noisy detector) where I couldn't before.

Someone has to figure it out, the weight issue, and be able to provide a variety of good coils as well, so here's to hoping it happens sooner than later.

All the best,

Lanny