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mh9162013

Using A Garrett Pro-Pointer AT ( Carrot ) Without A 9v Battery

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A while ago, I posted about a using a Minelab Pro-Find 35 without a 9V battery. You can read more about it here: 

But I wanted to run the modification with NiMH batteries. However, due to space constraints in the Pro-Find, this was not possible without modifying the internal battery compartment (which I didn't want to do b/c it would void the warranty, I'm sure). So instead, the Pro-Find runs off of a LiPo cell.

Well, I got a hold of a Garrett Carrot (Pro-Pointer AT) and given the extra space for the battery, I was able to run the 9V booster off of 3 LSD NiMH AAA cells. Works like a charm! The advantage is that I don't have to worry about "babying" the LiPo cell and worry about storing it with too little charge or anything like that.

Not much else to say, except show you the pictures.

 

 

 

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Interesting mission, and you did follow through with what you said you wanted to do, that's dedication 🙂

What's the battery life like and is it comparable to the 9v? Have you compared the difference in performance between the 1.5 volt mod and the original 9v battery with depth on targets and so on?  It should be similar but I've found using a 9.6v Powerex battery appears to give my Carrot better performance than using a standard 9v rechargeable, maybe it's a placebo but I feel it goes deeper using them.

Did you use a boost regulator like this in it? https://www.pololu.com/product/791

 

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I think you'll find it's the Placebo effect, Simon. The beeper and vibe motor are likely to be driven 'directly' from the 9 volt supply, and not from a regulated 5 volt rail, so it's going to beep louder and shake more with one of those batteries, maybe fooling you. I've not seen any reverse-engineering on the 'carrot', only the original model. But in that, nearly everything is powered from a 5 volt linear regulated supply. So you would be better off with a 7-cell "8.4V" NiMH battery, as they have a greater capacity than the 8-cell "9.6V" type.

I'm also curious as to which specific boost regulator was used. Pointers take a hefty current draw when vibe-motor / beeper activate, eg. the turn-on routine. I imagine many of these modules would keel over as soon as you switched on the pointer.
It seems odd that you have no power switch between the NiMH cells and the boost regulator. Isn't this going to flatten the battery, even with the pointer turned off ?

I've played around with similar modules for driving high-power LED's. I have some GU10 5 watt lights, that are 5 x 1 Watt LED's in series, so would need about 16 volts to drive them. I used a boost regulator module, modified for current feedback, so it regulates the output at 280mA. Input power is likely to be two 18650 Li cells in series ( laptop battery salvages ).
I had some similar cunning plans to re-use some LED backlight strips from a defunct LCD television.

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Phrunt,

This is the voltage booster I'm using: https://www.pololu.com/product/2116

As for battery life, I haven't done real world testing, because there's no point given how I'm not able to metal detect as often as I'd like and how inconsistent and qualitative the observations would be. I could create some sort of "lab" set up to measure how long the pinpointer beeps and vibrates or something, but I'm not going to waste my time with that because using simple math should give a good enough ballpark estimate, which I predict will be about 50-60% of the run time you would get with an alkaline battery. I discuss how I get this number in my blog post concerning this set up in a Minelab Pro-Find 35. That LiPo cell has roughly the same capacity as these AAA NiMH cells. In that blog post I also mentioned a very slight performance increase in sensitivity (about 1-3 mm of extra range).

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1 hour ago, PimentoUK said:

...

I'm also curious as to which specific boost regulator was used. Pointers take a hefty current draw when vibe-motor / beeper activate, eg. the turn-on routine. I imagine many of these modules would keel over as soon as you switched on the pointer.
It seems odd that you have no power switch between the NiMH cells and the boost regulator. Isn't this going to flatten the battery, even with the pointer turned off ?

...

I'm not worried about current draw; the voltage booster I'm using can provide up to 1.4 amps, well in excess of what a standard 9V alkaline can reasonably provide.

And no, I have no power switch between the NiMH cells and the booster. Do I need one? Maybe. I'm letting my setup sit in my Garrett Carrot right now and I'll test it every few days to see how long it "lasts" in storage before I need to recharge the battery pack. Assuming the booster draws noticeable current, a switch would be useful, but I doubt it'll be worth the trouble as it would just be easier to unplug the battery pack from the booster if I was going to store my pinpointer for an extended period of time. I may also look for some smaller high efficiency battery plugs, too...

And don't forget, even if my setup has plenty of drawbacks, it still has a HUGE advantage: NO MORE 9V BATTERIES!

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It's a shame it's pretty tricky to modify the pointer so the power switch controls the boost regulator input. You would have to remove the switch from the PCB, then re-fit it on its own isolated board. This would then require the button shaft to be trimmed in length, due to the height increase. It would be easier to do on the original black propointer.

I don't share your dislike of 9V batteries in quite the same way. I don't like NiMH 9V's in high-drain applications, like pinpointers. The cells are rather small, and the heavy current draw causes problems, usually high internal resistance failure. And with 7 cells in series, they have poor reliability and life, as when one cell fails, so does the whole battery, of course.

I'm looking at Lithium 9V batteries at the moment ( for pinpointer use ), the EBL ones specifically. They only have two cells, and they are pretty large cells, so they can easily handle the power requirements.

What is intriguing is how they are charged. Only the two main terminals are brought out, there's no obvious 'hidden' third terminal ( for the internal connection of the cells ). Yet they can be charged at 600 mA in the dedicated charger. There must be some 'clever electronics' inside the battery, to take care of charge-balancing somehow.

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Would you recommend this over my 9.6v batteries?

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I do like this brand, they're solid performers and what they say they are is what they are.  I've been using them for a couple of years now and my original battery seems to work as well now as it did when I first got it.  I've only got the 9.6v versions though.

You may well be right the performance difference might be a placebo and the difference I'm noticing is with volume/more vibration which would make the Carrot feel more powerful. 

 

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It's not so much 'recommend', you already have the 9.6V ones, so there's no point changing or buying more. It's just that the 9.6V ones don't offer any obvious advantage in a pinpointer. You probably take the battery out and recharge it after nearly every session anyway, so it never gets near flat, and so the lower capacity is not relevant.
I usually carry a spare 9V with me, in case the one in the pointer dies [or I leave it at home in the charger ..]. My spare is typically an alkaline non-rechargeable, due to the shelf life.

( and I recharge my non-rechargeable 9V batteries too. If you do it with a low current, it seems to work )

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11 hours ago, PimentoUK said:

...
I don't share your dislike of 9V batteries in quite the same way. I don't like NiMH 9V's in high-drain applications, like pinpointers. The cells are rather small, and the heavy current draw causes problems, usually high internal resistance failure. And with 7 cells in series, they have poor reliability and life, as when one cell fails, so does the whole battery, of course.

...

A NiMH 9V battery? No thank you. The solution to getting rid of heavy duty or alkaline 9V batteries isn't to replace it with a NiMH 9V battery. It's to get rid of the 9V battery.

 

 

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10 hours ago, PimentoUK said:

...
( and I recharge my non-rechargeable 9V batteries too. If you do it with a low current, it seems to work )

What?!

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