Introduction into Batteries and Charging Systems

[darksidecustoms]

Thanks for spending the time to put this together Deez. One quick note, AFAIK all Aussie XJs from 94 to 98/99 have the 90A alternator. I believe the 117A was introduced for '00 model year.

[Doctor W]

The Australian delivery ZG (ZJ) Grand Cherokees (1996-9 Limiteds were fitted with 136 Amp Alternators and I believe the Laredos had lower power output (117 Amp)

[Doctor W]

I have found that splicing a 40K Ohm 1 Watt resistor into the Battery sensor wiring harness prior to its plug connection to the wire harness will boost output voltage to 14.4V at ambient temps of about 25 degrees Celsius and still give 13.9V at about 45 oC, whilst allowing current and voltage to otherwise be controlled normally by the PCM.

This works especially well with Optima Yellow Tops and Blue Tops.

[kj69]

Originally Posted by Doctor W

I have found that splicing a 40K Ohm 1 Watt resistor into the Battery sensor wiring harness prior to its plug connection to the wire harness will boost output voltage to 14.4V at ambient temps of about 25 degrees Celsius and still give 13.8V at about 35 oC, whilst allowing current and voltage to otherwise be controlled normally by the PCM.

This works especially well with Optima Yellow Tops and Blue Tops.

which wire in the harness are you talking about Doctor ? is it the battery temp sensor wire ?

[Deezelweazel]

Be careful with that.
Underhood temperatures are different from 'ambient' temperatures.
You can find the temperature/resistor comparison chart for the battery sensor in the FSM.

If you have trouble with the output voltage I would check the ground system of your Jeep. If you look closer there are sometimes just standard sheet metal screws being used to ground cables. Add this with 10 years of corrosion and think again where your voltage is gone...

I cleaned and replaced all rotten screws into proper stainless bolts and nuts along with some washers.
Sure, not the best conductor, but much better than the previous rusted screws.

Äahem, the PCM regulator does only control voltage, the battery itself controls current...

[layback40]

Originally Posted by darksidecustoms

Thanks for spending the time to put this together Deez. One quick note, AFAIK all Aussie XJs from 94 to 98/99 have the 90A alternator. I believe the 117A was introduced for '00 model year.

& then the diesels are different as well. The 00/01 diesels have an internal vac pump in the engine, the pre 00 ones had a vac pump on the alt. Only a guess but I suspect the 00/01 diesels had a bigger capacity alt.
Normally diesels have bigger alts anyway. not sure about jeeps though.

[Doctor W]

A couple of clarifications:

Splice the resistor into one one the pair of leads within (say) 6"/150mm of the Battery Temp Sensor sitting in the battery tray under the battery. Remove it and solder in the resistor (keep holding the wires on the side nearer the resistor with pliers to stop excess heat travelling up to resistor or sensor).

By "ambient" I meant ambient to/around the area of the Battery Temp Sensor/ battery tray/battery.

I checked/replaced all the main Grounds/Earth returns with Stainless hardware and used copper grease as well.

This modification has been working for me with sucess for about two years..... charging the batteries at a more appropriate/suitable voltage whilst current flow characteristics is not changed (from factory).