Minelab exlpore nimh battery pack mod

[Turboair]

Hello,
I had this battery pack exhausted and would like to modify it, adding some 2700 mah recahrgable AA cells.
I removed the old GP 1600 mah battery pack and temporarily added some contacts (from a White's battery holder) for the incoming new batteries.
I saw that there is a circuit on the front of the battery pack, and would like to know what is for.
Someone told me that is against polarity invertion, but I am not so sure.
So my question is. Will I do a mess, mantaining that circuit and just applying new nimh rechargable batteries (and charge them with the original Minelab charger) or will be better removing it, apply a simple connector to recharge it with a nimh charger with Delta detection?

Please, let me know.

Here are some pictures of the battery holder-:

Battery holder opened


New contact that I have to solder when I will know better


Circuit



New contacts at the holder tail

[Turboair]

Little update:
I have just checked voltage of the Minelab charger on the front contacts and it measures 17,21V.

[Skippy]

What is the circuit for? The IC is a LM317 adjustable voltage regulator. It could be used as a current limiting circuit, over-voltage protection, lots of possibilities. The 7X7 part is a 'polyfuse', probably 1.2 Amps going by the PCB legend.

[Carl-NC]

LM317 is a voltage regulator, so I'd guess that it regulates the applied charging voltage.

[Turboair]

Thank You for reply guys. So, which do You think is the best solution? Considering that has been built for 1600 mah batteries, will it be enough strong to charge some 2700 mah ones (and it has not any detection of fully charge). Or will be better to remove it and connect only a female plug and let the job to a smart charger with delta peak detection?
Again thank U.

[Skippy]

If the charger has been designed to slow-charge 1600 cells, it will likely charge at about 160mA. Putting a higher capacity pack on will just mean a longer charging time (70%+ longer). You should be able to measure the charging current with a multimeter.

[Turboair]

Hi Skippy.
I did measured charging current, maybe my method is wrong but this is what I got.
I put on 4 AA cell and in series, following the current flow, I put the meter sensors.
Multimeter was setted on 200m and it measures 0.9 only...
Here are some shots






This is the charger that I would like to use

[Skippy]

Your multimeter probes are in the 10A sockets, not the 200mA one. And you should charge 8 cells not 4 if you want a realistic test.

[Turboair]

Skippy I tried to change socket but it reads 0,0. With the early setup and 8 AA cells on charge it reads a range from 114 to 116.

[Altra]

Skippy is right the circuit board is a 100mA current limiter with fuse protection. If you wish to charge it at 500mA,
you need to bypass the circuit board. I use to make a fast charger for that battery and
we connected the charger to the external contacts which connect directly to the cells.

Since you have it apart

A simple jumper from the positive pole on the connector to the positive lead on the batteries
will bypass the current limit

[Turboair]

I decided to remove the circuit and make some contacts to connect a mini female plug. I always hate the unsmart Minelab charger.
Here are some shots.





After a check that any connection is correct I placed it on charge, and no "boom" occurred till now...take your finger crossed

[Altra]

Here's a photo

[Altra]

We posted at the same time. good job

[Turboair]

Thanx!!

[Turboair]

Just the last question. In the next furure I would like to add a micro fuse. Do You think that this one could be the right one?
250 ma