Questions on Sniffer XR-71 build

[kt315]

https://www.youtube.com/watch?v=Ur3vPwELd_c

[Gunslinger44]

Machine is working fine with 8 AA batteries, as shown, however the red "low battery" light is on continuously. I tested resistance of coil, supposed to be 3-5 ohm range for the Sniffer, it is 1.7 ohm. I checked Crazy Tech's site, the coil I bought was suppsed to be 2.1 ohm. This is no trouble, I will make a new coil out of CAT 6 cable easily.
My other question, this machine runs off of 12v, however I am going to make a new battery pack out of 18650 Lithium-ion cells, I was thinking of making 4 of them in series, which would be 14.8 volts, the question is, is this too much power for the machine to take? This is 23% over the intended voltage.

[qute1]

So long as the inductance is in the ball park .4 ohm will have a negligible effect on the xr-71's performance and may even be the percentage error between two different meters, surprisingly i have had up to a full ohm difference across 3 different meters with cheaper multimeter's being particularly awful in this respect!
Also not all aa batteries are equal and variations between different brands voltages are common, quality Alkaline are slightly higher than cheap or zinc carbon and recharge-ables which only give 1.2volts per cell so will only give around 9.6v for 8 cells even when fresh.
Duracell or energizer start out at 1.7v and give circa 13.6v for 8 cells when fresh, it is common for people to use 3 - 4 18650's in these types of devices as all components are rated for minimum of 16volts internally, bear in mind that 4 freshly charged 18650 which are in reality starting out at 4.2v per cell even though they say 3.7v on the can gives you 16.8volts which is really pushing the envelope. Also the battery low should not kick on till around 8.7 volts or lower but may be 9.2 volts is more realistic for the 12volt machines.

[kt315]

you can not use some type of 4066 that have 12V max supply. you do not give us full list of ICs on your board, no pics, luck info, anotherway you must learn datasheets
of 4000s on your board. also you must use not electrolitics 10V in some places with 12V power supply before, you have set more 16V or 25V.

[Tim]

I run 3x18650s through a LV/HV cutoff solar charge controller, but recently my LV LED is also on constantly. Back through the many hundreds of pages here there are several mentioned causes of this, including a faulty/burnt LV diode. But I suspect the second-hand 18650s I fitted are flogged out.

Perhaps Sinko (or others) can chime in here ???

[kt315]

which would be 14.8 volts
---
in last time i see an ambition from people with low cvalification in electronics to get 'more depth' from the detector with
maximal possible depth. they mind primitively - if i encrease the power supply voltage i get more depth.
thats rally me much. they do not want think unconventional, in scale of POWER PULSE WIDTH that DP has 500us in
maximal value. i say again - you must read ITMD, you must read great and perfect magazine article of C. Moreland on Hammerhead
before (BEFORE) you want do change something.

[Gunslinger44]

It states in the Sniffer manual, that low battery light can be due to a coil with too low resistance, and it says optimal is 3-5 ohm, so this is less than half, so I will either put a resistor in series with the coil, or build a new coil out of CAT 6, see what that does. I just bought 4 18650's last night, tested them at 3.82, so that puts me at 15.4 volts output. The reason for 18650's is they give more even power until depletion, also they are rechargeable which is good for obvious reasons. Tesla cars run off of a series of 18650 cells.

[Gunslinger44]

which would be 14.8 volts
---
in last time i see an ambition from people with low cvalification in electronics to get 'more depth' from the detector with
maximal possible depth. they mind primitively - if i encrease the power supply voltage i get more depth.
thats rally me much. they do not want think unconventional, in scale of POWER PULSE WIDTH that DP has 500us in
maximal value. i say again - you must read ITMD, you must read great and perfect magazine article of C. Moreland on Hammerhead
before (BEFORE) you want do change something.

If you were paying attention, I'm not asking about using the 18650's to "increase depth" nowhere did I imply this, ever. I asked because they are rechargeable and keep voltage up longer. I was very clearly asking about the safety of using 14-15 volt supply in a 12v system. Read next time

[kt315]

have to see the snifo working from 14-15V. any news?

[dbanner]

15 volts with 500us pulse width, yikes. MOSFET say adios amigos.

[kt315]

i have to see magic smoke. magic smoke is living in every electronic board, but you do not see because it is unvisible.
but only at onetime he is visible when gone out.

[qute1]

So many times i have let the magic smoke out

[Gunslinger44]

I have new 18650's and 4-cell battery holder, ready to install, some were saying that 4x 18650's (14.8v) is safe for this machine, now you're saying it will smoke the Sniffer? I don't want to come even close to cooking this machine. I will do 4 18650's charged at 3volts each then, this will be safe, correct? These are 2000maH batteries, Westinghouse brand

[6666]

An 18650 at 3 volts is considered flat, a good quality fully charged battery straight out of the charger should be around 4.2 volts
to preserve the long life of the battery and maintain maximum capacity you should stop discharging around 3.5 volts