PB140/145/160 charging issues with rebuild battery pack

[nvdeynde]

I've recelled several battery packs with 5x Panasonic HHR380A 4/3 Nimh Cells of 3800 Mah each.

The issue I'm having with my PB140,145,145B,160 is that the powerbook stops charging after exactly 2 hours ( original 2A  recapped PSU calibrated at 7.5volts )
It's impossible that the batteries are fully charged. They don't last long too: battery power, everything on, gives me 1.5 hours at most.

The charging system of these powerbooks appears to be based on constant voltage ( tested with current meter on DC input ): it even never draws more than 1.1Amps from the PSU and during the 2 hours of charging it decreases to 0.5 Amps and then charging stops.

The original Apple battery pack was build with Nicad batteries  ( 2400 mah capacity )

Maybe the system is not designed for charging Nimh batteries properly ?

I'm wondering if other members here have similar issues.

What capacity of cells did you use and how long does the powerbook charge them until the battery indicator says they are full ? 
How much running time do you get with everything on after fully charged ?

 

[nvdeynde]

Nobody has this issue with Powerbooks 140, 145, 160 ?

 

[Rajel]

I've built a custom pack using NiMH AAs, but I don't charge in-system, I pull the AA cells out and charge them seperately.
The 1xx series charger is designed for NiCd though, and the charge method for the two are different enough that NiMH cells don't charge properly, and possibly even dangerously.

 

[nvdeynde]

I doubt it will be dangerously as all the after market PB100 battery packs that have been offered in the last years are all based on Nimh cells.

Now you don't find these anymore, but I have several of them an they contained 2/3A Nimh cells, 10 of them ( 2x 5 in series ).
So I guess it isn't dangerous since so many of these were sold.

The original Apple battery packs based on Nicad where only available for a few years after the production of the PB100 series ended. 

The charger is not the issue, Nimh cells can be charged with constant voltage, but I guess the charging system of the powerbooks stops charging too soon. 

 

[Rajel]

You'd have to add extra circuitry in the battery to properly charge NiMH, as well as protection.
Just swapping the cells isn't quite enough to realize the potential. Proper charging methods are quite different between NiCd and NiMH, NiMH packs would usually have components to handle the charge from the Powerbook properly - at the very *least* it needs a thermal shutoff.
Also, it seems the M5545/M5654 batteries have a 4200mAh capacity, your pack may not be equivalent? That could explain the difference.

 

[nvdeynde]

Of course I included a thermal sensor, rated at 57 °C. 
Anyway, I couldn't find the exact specs of the Apple M5545/M5654 batteries anymore but these were Nicad batteries and definitely not 4200 Mah. Such a huge capacity can only be obtained with modern Nimh cells or large Nicad's Sub-C ( or larger cells ) that don't fit in this battery pack.

I have several after market packs, about 7 to 10 years old, for the PB100 series and have taken them apart.
They have all Nimh cells, only with thermal protection, no additional circuitry and are indeed between 3800 to 4200 Mah, way over the specs of the original Nicad packs. 

I know the charging methods for Nicad and Nimh are different. There's 1 big question left: why are all the after market packs Nimh without any extra circuitry ? I have 3 different brands and other than a thermal shutoff, there's nothing else.

 

[Rajel]

They apparently don't care about anything more than thermal protection.
If not this, then I don't know. I'd point to the difference in charging methods causing the powerbook to stop charging short of a full NiMH charge.