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Fisher F2 Alternative Power Source Question


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I've successfully removed 9V batteries from my Garrett Carrot (which now uses AAA batteries) and I've started on the process and getting rid of 9V batteries in my Fisher F2. 

I've taken the approach if trying to use a single battery to power the F2. A while back, I read from somewhere that the F2 ran off two 9v batteries running in parallel. However, this means that if I use a single battery for the F2, it should work (assuming the single battery has the ability to provide the necessary current). But when I try to use this set up, my battery gets warm. I eventually realized that the Fisher F2 is NOT using a "pure" parallel setup. If it were, it would not be creating a short circuit in my single power source setup. 

So my question is: how exactly is the Fisher F2 power wiring arranged? It's not parallel and it doesn't appear to be in series, either.

Any insight would be appreciated.

Thanks!

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It's a series connection. BUT some of the circuit is powered from one battery only ( likely the audio stage ), so you can't just create an 18V battery and ignore the centre-tap.

You may want to investigate using a negative voltage generator circuit, so you use one 9V battery, and 'create' the other with electronics. Obvious starting points would be a circuit based on the ICL7660 chip, or the many similar devices. Or use an oscillator based around a TLC555 timer IC, and add a diode charge pump circuit - this could create either -9V or +18V . Or use one of those ready-made boost-mode voltage converter modules/boards to generate +18V from +9V.

All of these methods have one big problem: no On/Off control for the power. Remember the F2 uses electronic switching, part of it is always powered up, but drawing only a few micro-amps ( I've never measured it). Any add-on voltage converter won't use that, so you'll have to put the battery in immediately before use, and remove it straight after.
They may also make the supply 'dirty', with AC noise, that may interfere with the detector function.

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2 hours ago, PimentoUK said:

It's a series connection. BUT some of the circuit is powered from one battery only ( likely the audio stage ), so you can't just create an 18V battery and ignore the centre-tap.

That explains a lot, thanks! 

Looks like I have a bit of brainstorming to do...

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  • 2 weeks later...

I wanted to mod mine some years ago, but sold it before I could even try. Plan was to use 1-2 Li-Ions or a powerbank with two step up converters and wire them, as if they were 2 batteries. You can also try to use one 9V source in parallel aka brains / audio each with 9V.

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They do sell 9v lithium rechargeable batteries now. I recently got these and use them on my pinpointer. I also use the aa's in my Tesoro and Makro machines.

https://www.amazon.com/Blackube-Rechargeable-Battery-1-8-Detector-Multimeter/dp/B07VFGC75H/ref=sr_1_54_sspa?dchild=1&keywords=blackcube+9v+lithium&qid=1592481843&sr=8-54-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExMEJXVjMxM1NBOEFaJmVuY3J5cHRlZElkPUEwMjk3MjI1MkdBSzFWSDdFRDM2MSZlbmNyeXB0ZWRBZElkPUEwNzU3NTEyWkQ5QzlTSTEzT1omd2lkZ2V0TmFtZT1zcF9idGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

 

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