GS5C questions

[allan.au]

Reg, Eric or others,
I have recently bought a gs5c, a lovely piece of work, and i have a few questions.
It has been modded in oz with the three position tone switch. i am slowly getting the hang of it, and the sounds, though i have a long way to go to master it.
The unit has a lithium battery that only lasts for about half an hour....so the battery is probably past its use-by date.
I am planning to make up a 14.4v nimh battery pack for it. what are the max and dropout voltages of the detector.?
12 x 2700mah AA cells should go for at least a few hours at the 370ma load i measured... or is a new lithium battery the way to go.
Am i right in guessing that the lithium battery setup didnt charge up in the detector box is because of the risk of a battery meltdown destroying everything.?
So is it ok to charge an nimh battery pack in the detector, like in the earlier versions.? either with a separate socket, or via the headphone socket with the appropriate circuit changes.
If i make a dd or other type of tx/rx coil, what is a ballpark rx damping resistor value ??
what sort of range of inductances will work for an rx coil.?
I can fire up the cro if neccessary, if it still works.
cheers,
al

 

[Reg]

Hi Al,

You have asked a lot of questions and some need more info to answer fully. First, the GS 5C came with a NiMh battery pack originally. So, if your unit has a Li Ion setup, it is home made. The original charging circuit built in was made for a NiMh pack that was rated about 3600ma if I remember correctly.

As for the GS 5, it usually draws more like 500ma to 600 ma which is more than what you measured. With this in mind you can see that 4 hours would be about max with a AA battery pack. There are a few tricks one can do to extend this life, however. There is an internal 10v regulator that needs at least a little over 12v to regulate properly. So, 12 pack of AA's probably work fine until they are depleted to the point they should be charged anyway.

One thing about your current draw, some GS 5's had a current limiter and that might reduce the average current draw, but I don't know for sure. I don't have one that has that circuit.

Now, the design of a DD coil can be about anything but would depend upon what you want to hunt. If small gold is what you want to look for, then keep the transmit about 300 uh and the receive coil should be between 300 uh and maybe 450 uh. The damping resistor for the receive winding should be something between 1K and maybe 1.5K to try initially.

You might want to measure the inductance of the coil you have since Eric did make some units with coils with less inductance to keep the delay down to 10 usec. If you make a mono coil with 300 uh and your unit came with a coil with 250 uh, the coil will work fine but may not work right at the minimum delay.

A DD coil would more than likely work fine with the inductance range I mentioned.

If you are looking for larger objects or maybe coins, then both the transmit and receive can be increased but the coil may not work at the minimum delay.

I am assuming you are in OZ, is that correct?

Reg

 

[allan.au]

Reg, thanks for all that info, you are a wealth of knowledge on things PI.
Yes i am in OZ, in Gympie, the town that saved Queensland from bankruptsy in 1867. The goldfield (5 miles x 1 mile) produced about 4 million ounces from the surface alluvials and hard rock mining to depths of about 2400 feet.
I measured the gs5c current on a digital meter which may have had trouble with the spikey load....I assume the fet coil drive is unregulated, is that correct ?.
I will have to make a shunt for my ancient moving coil meter, which only reads to 250ma, to accurately measure the load.
The unit appears to be from feb 2008, 531, the instructions mention the Li-ion battery.....The gs5c was a work in progress it seems, and a credit to it's creator.
I appreciate the old school use of components that i can identify and replace without needing a microscope......modern surface mount stuff challenges my eyes, my mind, and my tools.
i will visit a mate with an inductance bridge to measure the coil.
I appreciate all your help Reg.
cheers,
al

 

[verylazybeachbum]

I purchased a GS5C about 1 1/2 years ago from Mr. Bill of Surfscanner Detectors. The US Distributor of PulsePower Detectors. My unit was new, but had been the shop display model. It came with the following Li-ion Battery:

http://www.batteryspace.com/polymerli-ionbattery148v4250mah6290whwithpcm.aspx

It also came with a charger that is very similar to the one recommended at the bottom of that page.

I have earlier High Powered Pulse Power detectors, and they did have the NIMH battery. I believe you can still buy those here:

http://www.strikalite.co.uk/prodcat_type/20/Metal_detectors/0/Specialist_Battery_Packs.html

The earliest cells were 3600 mah, now they are 3800. However, I found the same size cells available in a 4000 mah version, and these are sanyos from Japan. I bought mine as individual cells from the following seller, and put my packs together with a jig (it is a very tight fit for some detectors).

http://www.batterystation.com/nicads.htm

Scroll down to HR-4/3AU SALE! These have the tabs but pull right off with pliers if you want to use stronger bars. Great Deal!
Note I only use these packs with the earlier Detectors (Aquastar, Deepstar 3), and still use the Li-ion pack with my GS5C (still works like new).

If you try to make a pack out of just AAs it won't last nearly as long as one of these options. Just make sure if you get other 4/3 A or 4/3AU (the AU seems to be what sanyo calls them), that it does NOT have an F in it, like 4/3 AF. The F means FAT and it will be 1mm thicker diameter, and it will be too big to fit. Check the data sheet for the exact measurements, because some did not say F, but they were in fact the thicker measurement.

I charge my NIMH batteries with the Turnigy Accucell-6 charger (however I might have been better off with the Accucell-8 or other charger for discharging/cycling this many cells), and on some of my detectors I changed the battery connector to a Deans Ultra plug (made for RC hobbies), which is more reliable. Critterhunter on the Excal/Sovereign Forums has some great posts on how to use the Accucell-6.

I plan on posting more detailed information about making the NIMH packs in the near future.

Good Luck,

verylazybeachbum

 

[allan.au]

verylazybb, thanks for the input and links about batteries...lithium has a better power to weight ratio etc, and i tolerate them in my mobile phone and camera, but in my detector in the bush i want a battery that i am in charge of, no pun intended.
A poly li-on battery is an inherently dangerous battery with inflamable electrolyte protected by a brain, that can, in its wisdom to prevent a fire risk, shut down and prevent me from using it.
Nimh is cheap, safe and easily charged at any rate with a series resistor and a biological brain in control.
I can readily get reliable nimh AA's at trade price ($30 for 12), so that is my initial prefered option......i can carry a spare pack if i need to hunt for more than a few hours.... i can bend up another bit of aluminium to get a little bit more depth in the battery compartment.
I would like to know the brand of the waterproof case used for gs5c as i would like to get another clear lid....i want to put some thin solar cells that i have under the label area to keep the batteries topped up., and i dont really want to destroy erics original label.
cheers,
al