Looking to build a Lithium Battery pack for Minelab SD2100v2

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	Looking to build a Lithium Battery pack for Minelab SD2100v2 « on: April 18, 2011, 12:12:02 am »

Yes I know there are some available but for $300.00 I'd like to try making one myself.

Since I'm only going to use it for a SD and not a GP I don't need the dual voltage as in the Coiltek unit.

My plan is to start with 2 sets of 7.2v Lithium Battery packs and 2 matching Chargers. One charger will be gutted for the battery mount and interface components. From what I've learned the Minelab SD's like 7.3 volts but nothing over 8 volts, and as the 7.2v packs may have a max charge of just over 8 volts I may need to lower the voltage by using a Zener Diode and using a on/off micro switch if necessary to prevent tripping the battery overload circuit.

Another option is to use a 3 way on/off/on switch using one for the Zener Diode circuit while the Batteries are over 7.3 volts and flipping the switch over to the other circuit, which will run straight thru to get the most time with 7.3 volts.

I have the Cable Connection and Headphone Plug components from an old 6v battery, just need to make a short cable from the Control Box to the Battery. Am I missing something? It seems pretty straight forward, but I'm no electronics expert.

Any help would be great, Miles

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #1 on: April 18, 2011, 01:30:35 am »

First of all, an unloaded voltage of 8v on a fully charged 7.2v battery will drop immediately to the rated voltage as soon as you add a load. You don't need to add a resistor and zener diode (NEVER add only a zener because that will burn it out instantly) or anything else to the 7.2v pack. Next, you do need to separate the two when charging them. This is an absolute. Be sure you get the right charger for the job and remove the battery from the load circuit during charging.

Overall, it should be lighter and have a greater capacity once you finish your project.

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #2 on: April 18, 2011, 08:43:30 pm »

GD....Thanks for the information, I'm glad it will be easier than I was thinking.

So all I need is the on/off switch? I'm only asking because the Coiltek unit states that the SD when turned on pulls so much current that it trips the fuse in the Battery Packs, requiring them to be reset. Apparently the use of a on/off switch at the Battery Pack prevents this.

I'll due a photo writeup when I start building it, may be a few weeks till I get all the parts together.

Again thanks

Miles

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #3 on: April 18, 2011, 10:07:33 pm »

If the switch can isolate each pack and disconnect it from the detector while charging, that's what you need. Mind your current rating. Be sure you exceed the rating of the stock batteries. In other words, a 900mah battery needs a 1000mah battery or greater with the same voltage.

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #4 on: April 19, 2011, 11:00:43 am »

I'll only be using one battery at a time, only mentioned two because I bought two sets for the chargers. I'll strip out one charger to use for the mounting base to the detector. Basically duplicating the setup that everyone else is using, even got the same batteries that Coiltek uses in their power pack.

I'll post a picture when they come in and work up a rough diagram.

Miles

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #5 on: May 22, 2011, 09:42:32 pm »

Pic #1…….Okay so I finally got most of the parts to start this build. I was intending to mimic the Coiltek Pocket Rocket but didn't like the bulk and since this is just for my SD2100v2 I didn't need all the frills.

Pic #2-5…….I took the guts out of the Charger and put them into my own box with a 4pin connector. Each battery has a 4pin for the power and headphone jack, each with their own leads. Still waiting on the headphone pigtails but used a standard plug for the tests. Power leads are soldered directly to the battery.

Pic #6…….8.36 volts fresh off the charger.

Pic #7…….8.32 volts after sitting idle for 2 days.

Pic #8…….Had to take out the overload circuit, because it kept tripping, so I could run the battery without an on/off switch.

Will heat shrink wrap each battery, add the headphone lead and make a holder. Also I will be making a dual charging station and making 2 more batteries, so I can charge 2 batteries at a time while using the other 2 batteries. Total cost for this 4 battery system with dual charger will have cost me about $150.00 but it's not just the cost savings I really enjoyed making these.

Now for the tests, even thou I didn't do a scientific study, I can say that my detector seems to be running a little smoother and has increased detection depth based on one small target I've been playing with in my yard. A real field test away from power lines will have to run later.

I'll post pictures of the final results when I can.

Miles

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #6 on: May 25, 2011, 06:23:21 pm »

	Quote:	Posted by GoldDigger1950
First of all, an unloaded voltage of 8v on a fully charged 7.2v battery will drop immediately to the rated voltage as soon as you add a load. You don't need to add a resistor and zener diode (NEVER add only a zener because that will burn it out instantly) or anything else to the 7.2v pack. Next, you do need to separate the two when charging them. This is an absolute. Be sure you get the right charger for the job and remove the battery from the load circuit during charging. Overall, it should be lighter and have a greater capacity once you finish your project.

!!! be careful!!! Lithium batteries (and every battery which has very low internal resistance )
will maintain this "full voltage" for some time! A good quality lithium can do this even at heavy loads.
A fully charged lithium battery has a voltage of 4.23 and the discharge rate is allmost linear down to 2.75 Volt (empty). The 3.6 volt rated voltage is just a average voltage.
So using 2 lithium you will get 8.4 Volt . You can lower this voltage by 0.7 V, with the addition of a common silicon diode (better to be a high current to prevent some overheating). Using a switch you can bypass this diode every time you want,usually at lower voltages.
Another solution is to use a low drop out- high current adjustable voltage regulator.
You can try the KA278RA05 for example.

Posted on: May 25, 2011, 06:17:21 PM

ooops, just now i saw your recent post!

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #7 on: June 12, 2011, 10:13:03 pm »

Finally got the last of the parts for the charging station and got it built. I added a mini volt meter so I don't have to find my meter to test my batteries before going out.

Pic #1 The guts.
Pic #2 The volt meter
Pic #3 The finished system 4 Batteries and Dual Charger.

Will order another mini volt meter and make a smaller field meter so I can keep track of the battery voltage while detecting. Also need to make a cover for my detector and battery holders, I'll post them in a separate post when I'm done.

Miles

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	Re: Looking to build a Lithium Battery pack for Minelab SD2100v2 « Reply #8 on: June 13, 2011, 05:12:59 pm »

In an earlier post you mentioned that you disabled the overload circuit because it kept tripping. I missed that until today. I'd advise you to leave your battery door open during charging so you can keep it cooler. The overload circuit may have been tripping due to an overcurrent situation which could either destroy your battery before its time or allow it to catch fire. This is something LiPo batteries are famous for doing.

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