Why does running 5 khz drain the battery faster than 14 or 20?

I'm very curious as to what frequency has to do with battery drain.



Edited 1 time(s). Last edit at 04/30/2017 12:25AM by Dan(NM).

I know it goes deeper and only one program I think uses it. It may also have some extra software programed into the freq that doesn't show on the display??? So it takes more power...NASA Tom will know for sure...Hey for Tom to include this impact into the detectors he takes on hunts is saying a lot. It didn't sway me to want the machine and I was privileged to be a tester but Tom goes by science and his tests are beyond my understanding of how I test. But that really says something for this machine..

LowBoy

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I posted this in another thread 5 weeks ago:


If you keep the same inductor (transmit coil) for all 3 operating frequencies, and just vary the tuning capacitor (to suit the frequency choice) and the damping resistor (to maintain a constant Q tuning factor), you will find that the power you have to put into the coil will be more at the lowest frequency.
A quick calculation gives coil power = 20 mWatt at 20kHz, and 80 mWatt at 5kHz.
And these would likely equate to 30mW and 120 mW drawn from the battery, allowing for inefficiencies, possibly more.

Having said that, the coil is not the big power-consumer, over 500 mWatt is taken by the electronics - amplifiers, comparators, analogue-to-digital converter, microprocessor, LCD display, voltage regulators, audio amplifier, wireless transmitter, etc etc.

From what I've been reading about battery drain on the Impact hadn't been very positive for months now!

It's a major deciding factor to many users who ask 2 Questions:
How deep will it go?
What's it like on batteries?

We know BBS & FBS & FBS2 are high drain devices especially when GPS is turned on in the CTX

But, ask yourself a few questions:
Do I 'have to' use my GPS a lot of the time? The answer is no. Turn it off. And turn off other 'features' that you don't need like 'Target Trace' for example.

So the Impact is 'high drain' used in Low kHz
Ask yourself 'do I have to use 5kHz when 14 or 20 might be [ just as good? ]

Then, analyse what else can cause high drain?

Am I using the 'best battery' for the job? I've often read posts from users who are pleased they got [ a great buy on dollar store batteries ] These won't last long at all in a power hungry detector like the Impact

Am I detecting with friends? Is their detector causing [ audible interference ] = drain

Is there additional EMI in some locations?

Is my Iron Disc [ set too low ] and I'm hearing the iron? Well, use higher Disc and eliminate the extraneous ferrous signals you don't need to hear? = drain

All the above can cause higher drain on your batteries.

I'm certain that 'some users' may be reluctant to use the 5kHz Low frequency especially if their cells are reading low on the indicator, don't have back up batteries, are deep in the woods and far from the spares in the vehicle. Hunts might be cut short because of it?
I've often [ thought I had packed my spare batteries ] but when they're needed have found them sitting on the kitchen table when I got home!

Another thing that 'scared me' is the Deus coil battery! What if it goes down deep in the woods?

I've recently tested the "Rutus Alter" and even utilising selectable 'low frequencies', e.g. 4.4, 5.8 etc I've been more than pleased to have gotten around 30 hrs on average from 6 AA's

?Maybe, just maybe the power circuitry of the Impact is too weak?
Maybe it should have used 8 x AA's (or 6 at least)

Why all the fuss about batteries? Buy 2 sets of rechargeables. I have a $20 inverter in my truck, plugs into my cigar lighter, I can plug in any 110 v device.
I keep a set of alkalines for back up.

I am hoping, that maybe it is somewhat adjusted in the future so that the 5khz is more usable. I remember the 2.5khz had a huge drain on the battery as well, but multi frequency at the same time doesn't. I might be able to come up with some work arounds, if i can find the time.

possum mo Wrote:
-------------------------------------------------------
> Why all the fuss about batteries? Buy 2 sets of
> rechargeables. I have a $20 inverter in my truck,
> plugs into my cigar lighter, I can plug in any 110
> v device.
> I keep a set of alkalines for back up.


I don't really care about the fact that it drains batteries, I just wanted to know what it was that was causing it, simply curiosity.

I charge my GPZ 7000 every night. My cell phone also for that matter. Once you get used to using something by day and charging by night it becomes a non-issue.

This thread may provide a clue as to why the power consumption on the Impact increases at 5 kHz:

[www.metaldetectingforum.co.uk]

Nokta may be boosting the power at 5 kHz for reasons noted in that thread.

I do believe this quote also is true in the concept if not the actual figures:

"If you keep the same inductor (transmit coil) for all 3 operating frequencies, and just vary the tuning capacitor (to suit the frequency choice) and the damping resistor (to maintain a constant Q tuning factor), you will find that the power you have to put into the coil will be more at the lowest frequency. A quick calculation gives coil power = 20 mWatt at 20kHz, and 80 mWatt at 5kHz. And these would likely equate to 30mW and 120 mW drawn from the battery, allowing for inefficiencies, possibly more. Having said that, the coil is not the big power-consumer, over 500 mWatt is taken by the electronics - amplifiers, comparators, analogue-to-digital converter, microprocessor, LCD display, voltage regulators, audio amplifier, wireless transmitter, etc etc."

White's V3i will consume more power in 2.5 kHz mode than 22.5 kHz mode.



Edited 2 time(s). Last edit at 05/02/2017 03:07PM by Steve Herschbach.

Dan(NM) Wrote:
-------------------------------------------------------
> possum mo Wrote:
> --------------------------------------------------
> -----
> > Why all the fuss about batteries? Buy 2 sets of
> > rechargeables. I have a $20 inverter in my truc
> k,
> > plugs into my cigar lighter, I can plug in any 1
> 10
> > v device.
> > I keep a set of alkalines for back up.
>
>
> I don't really care about the fact that it drains
> batteries, I just wanted to know what it was that
> was causing it, simply curiosity.

I was trying to show some things that we do not take into consideration and Steve H provided some physics.
(someone had already posted the quote in another thread)
Another factor I didn't highlight was headphones or the non use of same therefore relying on the speaker!
And then there's the 'newness' of it and lots of time air/bench testing, experimenting and just plain using it a lot!!!

Maybe Alper will chime in..

I can only speculate that on 5Khz the Impact is Upping the gain to compensate for the inherent loss of Spark/Zip/Hyper feel that 5khz usually exhibits...

In other words MAYBE it's amped up on 5Khz to get that SPARK feel of the higher freqs...???

With that being said though...an Omega on 8 Khz Vs a G2 on 19khz has better battery drain SO WHo KNows the Omega is Sparky and amped on that low freq..

Guess I don't know ...LOL..

Bet Alper Does though

Keith

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla

OK, here's a realistic worked example to show the mathematics. (if I had some photo-host, I'd throw in a drawing...)

Make you search-coil have Inductance, L = 633 microhenry, and Resistance, R = 1.0 Ohms. [these are perfectly reasonable, not too far from a F75/T2 spec].
Put a capacitor, C = 100nF across the coil.
You now have a system tuned to 20KHz, but with inappropriately high Q-factor.

For '5KHz' operation, switch in a capacitor across the coil of C = 1.5 microfarad. It's now tuned to 5KHz, has a Q = 20.

For '14KHz' operation, switch in a capacitor of 100nF and a damping resistor of 1750 Ohms across the coil.
It's now tuned to 14.1KHz, and has a Q = 20.

For '20KHz' operation, switch in a damping resistor across the coil of R = 1590 Ohms. You have 20 kHz operation, with the Q dropped down to Q = 20.

These 3 scenarios present differing equivalent loads to the oscillator circuit: 395 Ohms, 1122 Ohms and 1588 Ohms for 5/14/20 KHz.
The lower the resistance, the more power is lost. So clearly here, 5KHz is worst.

To assess how much power, assume a realistic voltage across the coil of 7 Volts RMS.
Then power loss for 5/14/20 KHz calculates as 127 / 45 / 31 milliwatts respectively.

Switching in these extra R and C components is simply done with two magnetically-latching relays, much like the Deus does.

Pimento Wrote:
-------------------------------------------------------
> OK, here's a realistic worked example to show the
> mathematics. (if I had some photo-host, I'd throw
> in a drawing...)
>
> Make you search-coil have Inductance, L = 633 micr
> ohenry, and Resistance, R = 1.0 Ohms. [these are p
> erfectly reasonable, not too far from a F75/T2 spe
> c].
> Put a capacitor, C = 100nF across the coil.
> You now have a system tuned to 20KHz, but with ina
> ppropriately high Q-factor.
>
> For '5KHz' operation, switch in a capacitor across
> the coil of C = 1.5 microfarad. It's now tuned to
> 5KHz, has a Q = 20.
>
> For '14KHz' operation, switch in a capacitor of 10
> 0nF and a damping resistor of 1750 Ohms across the
> coil.
> It's now tuned to 14.1KHz, and has a Q = 20.
>
> For '20KHz' operation, switch in a damping resisto
> r across the coil of R = 1590 Ohms. You have 20 kH
> z operation, with the Q dropped down to Q = 20.
>
> These 3 scenarios present differing equivalent loa
> ds to the oscillator circuit: 395 Ohms, 1122 Ohms
> and 1588 Ohms for 5/14/20 KHz.
> The lower the resistance, the more power is lost.
> So clearly here, 5KHz is worst.
>
> To assess how much power, assume a realistic volta
> ge across the coil of 7 Volts RMS.
> Then power loss for 5/14/20 KHz calculates as 127
> / 45 / 31 milliwatts respectively.
>
> Switching in these extra R and C components is sim
> ply done with two magnetically-latching relays, mu
> ch like the Deus does.

I'm surprised at myself, but this actually made sense to me. That electronics book I've been studying and messing around with an oscilloscope I bought off of craigslist is actually paying off. LOL
HH
John

Pimento Wrote:
-------------------------------------------------------
> OK, here's a realistic worked example to show the
> mathematics. (if I had some photo-host, I'd throw
> in a drawing...)
>
> Make you search-coil have Inductance, L = 633 micr
> ohenry, and Resistance, R = 1.0 Ohms. [these are p
> erfectly reasonable, not too far from a F75/T2 spe
> c].
> Put a capacitor, C = 100nF across the coil.
> You now have a system tuned to 20KHz, but with ina
> ppropriately high Q-factor.
>
> For '5KHz' operation, switch in a capacitor across
> the coil of C = 1.5 microfarad. It's now tuned to
> 5KHz, has a Q = 20.
>
> For '14KHz' operation, switch in a capacitor of 10
> 0nF and a damping resistor of 1750 Ohms across the
> coil.
> It's now tuned to 14.1KHz, and has a Q = 20.
>
> For '20KHz' operation, switch in a damping resisto
> r across the coil of R = 1590 Ohms. You have 20 kH
> z operation, with the Q dropped down to Q = 20.
>
> These 3 scenarios present differing equivalent loa
> ds to the oscillator circuit: 395 Ohms, 1122 Ohms
> and 1588 Ohms for 5/14/20 KHz.
> The lower the resistance, the more power is lost.
> So clearly here, 5KHz is worst.
>
> To assess how much power, assume a realistic volta
> ge across the coil of 7 Volts RMS.
> Then power loss for 5/14/20 KHz calculates as 127
> / 45 / 31 milliwatts respectively.
>
> Switching in these extra R and C components is sim
> ply done with two magnetically-latching relays, mu
> ch like the Deus does.

dang Pimento, you're good....I appreciate your explanation, and having an EE helps (got it decades ago, lol)

Dang, this is an intelligent thread!

Hmm. Having spotted a small error in that post, I thought I'd correct it. And I can't, I just get this:

"You don't have permission to access /discussions/posting.php on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request."

Maybe because it's been quoted I'm barred?

But for completeness sakes, it should read:

For '20KHz' operation, switch in a damping resistor across the coil of R = 2100 Ohms. You have 20 kHz operation, with the Q dropped down to Q = 20

but you all spotted that one, anyway....

I understand the relays can be heard clicking in the control-box area of the Impact. Whereas in the Deus, they are inside the coil, for obvious reasons...

This thread caused me to question the crap battery life in my 2yr old iPhone 6

So I did a bit of research and found one interesting post advising 'turn off everything including locator'
and am happy to report it's now a bit better.
Looking like it's back to possibly 2 days in a charge instead of one????

A good deal of the battery drain comes from disc which affects fireing up those speaker in the headphones too. More beeps...... the more battery used.

Dew

Most SF-VLF transmitters run sinusoids (I don't know about Impact or Altus) and most resonate the coil with a parallel cap. I don't know of anyone who adds a damping resistor as all it will do is reduce efficiency.

Let's take Pimento's scenario: L=633uH, fL=5kHz, fH=20kHz. Furthermore, assume the transmitter is powered from 5 volts.

For resonance we have to use 2 different caps. For the question at hand, it doesn't matter what their values are. What matters is the series resistance of the coil, which creates a power loss.

At 5kHz, the coil has a reactance of about 20 ohms, so the peak current is 5v/20 = 250mA.
At 20kHz, the coil has a reactance of about 80 ohms, so the peak current is 5v/80 = 62.5mA.

The power loss in the coil's series resistance (only 1 ohm!) is

5kHz: P = R*Irms^2 = 1*(250/sqrt(2))^2 = 32mW
20kHz: P = R*Irms^2 = 1*(62.5/sqrt(2))^2 = 2mW

The resonant capacitor recycles all of the coil energy except for this power loss, and the power loss has to be made up for by the battery. Note that a 4:1 frequency ratio results in a 16:1 power efficiency. This is a very simplified example and there are other ohmic losses besides the coil resistance, so it only gets worse. But this is the reason why low frequency transmitters are less fuel efficient.

MF-VLF detectors (BBS/FBS, CZ, White's) don't use sinusoids, they use triangle waves and are unresonated. Some of them get energy recycling in a slightly different way, but are still subject to ohmic losses at low frequency.

--Carl

Now we're cooking with peanut oil!

HH
Mike



Edited 1 time(s). Last edit at 05/02/2017 02:27PM by Mike Hillis.

and I've always explained it as "just because". I appreciate everyone's effort in trying to explain it to those of us that just put new batteries in more often.

Carl: I guess you saw that someone posted a couple of months ago a schematic for the Makro Racer on your Geotech1 forum.
jpg:
[s26.postimg.org]
It had a T2-like centre-tapped TX coil, a tuning capacitor across the hot ends, and was driven from a 5 Volt supply with two transistors, alternating. This is where I took my 20 Volt pk-pk (7 V RMS) figure from. The guy who posted it suggested the Impact would share the same basic drive method.
My choice of 633uH was based on a 'reasonable' figure for the middle 14KHz operating freq [eg. Fisher F75, L = 695uH for 13KHz], the low series resistance of 1 Ohm was just in order to get the Q up to 20 when run at the low 5KHz freq. It would be a 'fat' coil winding, that's true.



Edited 1 time(s). Last edit at 05/02/2017 03:33PM by Pimento.