A question for Eric Foster or Mr. Bill

[Terry SoCal]

I use 2000 mAh Nickel Metal-Hydride rechargeable batteries in all my detectors. Will the Goldquest SS or Aquasearch V.2. operate with rechargeable batteries? I know that some detectors will automatically shut down at a preset voltage. I am not concerned about frequent battery changes, but I am concerned about the minimum operating voltage for the above detectors. Comments from anyone that used or use

 

[Tony]

Terry,

I have been using Sanyo 2100Mah NImh rechargeables in my Goldquest SS with 100% performance. There is no difference(performance) to using alkalines and I can get a good 20 hours of detecting time on the NiMH's.

I did some extensive depth/sensitivity tests with the rechargeables and alkalines as soon as I got the detector (3 years ago now) and I was completely satisfied that I wasn't disadvantaging myself by using the rechargeables.

Hope this helps,
Tony.

PS The low battery alert ("pip") will still kick in at about 8.6v, just as it would with alkalines. Just be aware that when NImh's are discharged, it happens very quickly whereas Nicads deplete/discharge on a more regular rate.

 

[Terry SoCal]

n/t

 

[thinkin2]

Hi, Tony. Could you please tell me where you got the batteries and how much they cost? Thanks, looks like a good setup.
Jerry

 

[Tony]

Jerry,

I'm in Australia but I did buy the batteries at "BatteryWorld".
These same batteries can now be bought at about 2500Mah capacity as I've had these batteries for 3 years now.

These are high quality Japanese made batteries. The previous NiMH batteries I used were from China and I found them to be inferior to the Sanyo's because....

1. They got much hotter when charging
2. They didn't hold their charge as long
3. They didn't provide as long detecting time (even though they were of the same capacity)

I also got a great Smartcharger that charges 10 NiMH or Nicad AA/AAA batteries at once...

Hope this helps,
Tony.

 

[Tony]

n/t

 

[Scott_B]

Here is a good place for rechargeable batteries.
These are some good 2500 mha AA batteries.
http://www.thomas-distributing.com/maha_2500_rechargeable_batteries.php
Here is a link to the Sanyo batteries.
http://www.thomas-distributing.com/sanyo-2500-aa-rechargeable-batteries.htm

 

[Kev]

Hi Terry,
I modified my Goldquest to accept 10 x NiMH. It gives a slightly stronger signal on deeper stuff, and seems more responsive over all.

But, as Tony has said, the endpoint warning sounds at around 8.6 Volts, which is way too low for 10 cells, so the trimmer needs to be
adjusted to sound off around 10.5 Volts to avoid polarity reversal of the weakest cells.

Cheers
Kev.

 

[Tony]

Kev,

Does the clear lid (the one with the captive screws), close okay ?

I wanted to go with with 10 NiMH's but couldn't squeeze them in.

Thanks,
Tony.

 

[Kev]

Hi Tony,
I had to remove the aluminium plate and replace it with one made of 1mm polycarbonate. It screws down onto the standoffs the same and allows the lid to fasten down nicely.

I'll post a better pic tomorrow. I recommend doing it as it really does liven the GQ up quite a bit, especially on those deeper rings you're seeking.

Cheers
Kev.

 

[Tony]

Thanks Kev,

I'm a bit confused about the low battery alarm threshold.

Using 10 NiMH equates to using 8 alkaline cells (both have a nominal voltage of 12V)....is there a need to raise the low battery alarm when using the NiMH's ?? I don't have the best electronic background in the world...please educate me

All the best,
Tony

 

[Kev]

Hi Tony,
You are correct on both accounts. The absolute minimum voltage that a 1.2 Volt nickel cadmium, or nickel metal hydride battery should be discharged to, is 1 (one) Volt. With a battery pack made up of 10 unmatched batteries, it is not wise to discharge the pack down to 10 Volts, it is necessary to leave a little leeway for the weakest cell in the bunch, so between 10.3 and 11 Volts is suggested.

When manufacturers of battery packs make up a gang, they select batteries with the most identical charge/discharge characteristics, so that they all behave similar and the endpoint is reached where the maximum available current is supplied, but we can't achieve this same performance using loose cells.

There is a formula that cell manufacturers suggest using if one is going to assemble assorted cells into a pack.

End Of Discharge Voltage = [(MPV-150mV)(n-1)]-200mV
where MVP is the single-cell mid-point voltage at the given discharge rate and n is the number of cells in the battery.

for 10 NiMH cells it works out to be about 10.24 V
but I made my alarm blip sound off at 10.4 V for a little more margin. The amount of current gained from the last 160mV on the end of the discharge curve is not worth the risk if it means stuffing a battery or batteries.

So attach a variable DC power source, select your desired endpoint voltage, I recommend 10.5 V, connect this to your GQ terminals, Watch polarity, and then turn your trimmer until the blip just begins to sound. This will not allow you to get maximum current from 8 alkaline though, you are now forced to always use 10 rechargeables.

That brings me to another point you raised. The 8 alkaline and 10 rechargeables both add up to 12 Volts. But the performance of the 2 chemistries is not equal. Fresh alkalines make the GQ pretty responsive, but it soon tapers off. If you look at the discharge curve of an alkaline you will see that the voltage drops off quite rapidly so that you soon have the equivalent response of 8 NiMH cells, but with 10 NiMH or even better NiCads the voltage drops very slowly through 75% of the discharge cycle. Voltage means pressure, and pressure means current, and current means flux, and flux means goodies, anyway I've waffled on enough.

For others doing this make sure your unit is out of warranty before you do any mods, or Eric may not be very happy with you if you fry anything.
Keep the polycarbonate away from the IC and transistor pins.

Don

 

[Tony]

n/t

 

[Kev]

Hi Tony,
You will also need to cut a small square section out of the polycarbonate where it meets the Threshold pot.

Cheers
Kev.