Battery pack/charger question...

[rjwpavo]

I have a pair of Motorola walkabout T5500 radios and the battery packs in them have gone bad. I took one of the packs and tore off the plastic wrapper. It appears to be 3 AA in series that have 600mah rating @ 1.2 volts each. You can also use regular alkaline AA's and it works fine. I figured I could buy 6 new rechargable cells, reassemble the packs, and use a smart charger for them. One of the "charging strips" on the packs also has a resistor going to the "+" terminal. I'm assuming its to reduce the charging voltage from 9v as the transformer output is 9V @ 200ma. There is also another "chip" in the pack, but I don't know what it is. I'll try and take a pic when I get home. Sound like something that can be done? My overall idea is to upgrade the packs for longer life(runtime as well as battery pack life) and use the original charging base minus transformer with a different charger... What do yall think??

Edit: here are the existing packs....

 

[rjwpavo]

Added pics.... You can see the components of the pack. Any ideas?? Do I just need to unsolder these batts and resolder newer higher capacity ones?

 

[Norm]

Your resistor is a diode sorry can't help with the other component.
Norm

 

[rjwpavo]

Thanks Norm! When I first took it apart, I just saw the familiar shape, didn't look at the lack of colored bands.... OK, how about this question then...How or can I charge 3 AA Nimh in series with a smart charger? Is there a way to reliable charge each cell equally? And at what charge rate assuming I used eneloops?

 

[SilverFox]

Hello Rjwpavo,

I appears that some of the charging circuit controls are incorporated into the battery pack. When you change out the batteries, you will need to be careful to make sure your charger is working properly with the new cells.

When you build a battery pack, or put one into service that has been in storage, your first charge is designed to balance the cells in the pack. You use a timed charge for this. The charge rate is 0.1C and the duration is 16 hours. At the end of that time, your cells will be fully charged and balanced with each other.

Eneloop cells have a capacity of 2000 mAh, so a 0.1C charge rate would be 200 mA.

Now that the cells in the pack are balanced, you can hook up your smart charger and charge them normally. The smart charger will terminate the charge on a slight drop in voltage at the end of the charge, and with the cells balanced, there should be no problems observing that. You can check your cells at the end of the charge, and they should all be equally warm. If you find one cell warmer than the others, you pack is getting out of balance and you need to repeat the 16 hour charge at 0.1C.

Depending on how smart your charger is, you can also keep the cells in you pack in balance by using an extended top off after the main charge. The Schulze charger, for example, has a setting that allows you to balance your cells after the main charge. Care must be taken during this phase of charging because overcharging can damage your cells.

Tom

 

[rjwpavo]

Thanks Tom! I assume I could charge them initially individually on a MH-C800S first, then assemble them in series? Once assembled, I would be looking for a charger that charges @ 3.6 or so volts, right?

 

[SilverFox]

Hello Rjwpavo,

Right.

Tom