Muddz

~14.5 isn't considered to be too high and uncommon.

If you're at 15 volts at idle rpms then that seems a little high. My ZJ 4.0L with new battery has been around 14.5 to just under 15. After the jeep runs for a while voltage usually drops down to around ~14.2 (gauge on instrument cluster). I haven't had the ZJ that long and don't remember it ever being under 14 volts usually somewhere over 14 to just a hair under 15 (the marker after the 14 volt marker) don't recall ever being at 15 or higher just a hair under 15. The instr. cluster gauge doesn't provide that accurate of a voltage measurement as would an OBD2 scanner with liver readout. On the instru. cluster gauge the 15 volts marker isn't in the Red. The gauge shows red where voltage is considered to be too low or too high.

Where are you getting your voltage measurements from? Myself if trying to obtain accurate live battery voltage measurement I connect an OBD2 scanner with live readout. Also perhaps connect a DMM to the battery or directly to the alternator's output, while the engine is running.

The Denso alternator in Jeeps the PCM has an EVR (electronic voltage regulator) that controls the field terminal voltages which controls the alternators output. The EVR controls the field terminals not by sending a regulated voltage to the field terminals. What it does is grounds one of the field terminal many times per second (at a frequency I believe in Khz) which increases and decreases field terminal voltage and alternator output charging voltage.

It uses the temperature sensor under the battery for a battery temperature plus it monitors battery and alternator output voltages to control the alternator output.

I found understanding how battery chargers work such as ac/dc and solar provides a better understanding of what the alternator is trying to achieve.

Three and four stage battery chargers many come with a battery temperature probe installed directly to the battery post to help determine battery charging voltage.

However many battery chargers now a days don't use a constant DC voltage but uses something like PWM (pulse width modulation) which is capable of more efficient charging. PWM works by pulsing the battery "charge" (many times a second) with a higher charging voltage such as 16 - 17 volts.

Charging voltages for flooded, AGM and GEL batteries differ.

My solar charger has a battery temperature probe and uses PWM.

1. Bulk Charging: In this stage, the battery will accept all the current provided by the solar system.
2. PWM Absorption: When the battery reaches the regulation voltage, the PWM begins to hold the voltage constant. This is to avoid over-heating and over-gasing the battery. The current will taper down to safe levels as the battery becomes more fully charged.
3. Equalization: Many batteries benefit from a periodic boost charge to stir the electrolyte, level the cell voltages, and complete the chemical reactions. The green LED will blink rapidly 2-3 times per second.
4. Float: When the battery is fully recharged, the charging voltage is reduced to prevent further heating or gasing of the battery.

Chargers for flooded batteries with an equalization charge will produce up to a 15.3 volt charge during equalization.

Typical charging voltage for three stage chargers.

14.4 Volts (Boost Mode) – Returned the battery to 90% of full charge in approximately 8 hours. The battery reached full charge in approximately 11 hours.
13.6 Volts (Normal Mode) – Required 40 hours to return the battery to 90% of full charge and 78 hours to reach full charge.
13.2 Volts (Storage Mode) – Required 60 hours to return the battery to 90% of full charge and 100 hours to reach full charge.

My Truecharge 10 doesn't have a temperature sensor but has three settings for Cold, Warm and Hot

Flooded - Cold 14.8/13.9, Warm 14.4/13.5, Hot 14.0/13.1
GEL - Cold - 14.6/14.2, Warm - 14.2/13.8, Hot - 13.8/13.4

So when cold it will charge up to 14.8 volts which is only .2 volts below 15.

The Xantrex Truecharge 10 is similar to my other chargers which will charge at nearly 15 volts when temperatures are cold.

XJNBREWS

dave1123

It may be you have a ground that's not quite clean and is giving the PCM wrong voltage information and causing it to charge at a higher rate. Check the connections on the alternator for being loose. Extreme cold makes metal shrink. Even staked on terminals can be loose inside.

Muddz

Sure you can just take voltage measurement using a dmm directly from the battery (with engine off and running) or take Voltage measurements directly from the alternators B+ output which may be a hair more accurate as there's battery cables running from the B+ to the battery and fuse box with usually a fuse link or fuse to protect the alternator.

My OBD2 scanners I've used have allowed me to record live data saving all or some of the live data measurements of my choosing while the engine is at idle and while driving around. Then I'm able to compare changes to voltage measurement to other live data such as rpms, mph, coolant temperature, etc.

Or if your Jeep is 96+ OBD2 you can get one of those elm327 models for as little as $5.00 with Bluetooth or wifi and observe live data on your cell phone using an app. No need to purchase a scanner. There's some good obd2 apps where you can observe live data while at idle, driving around, under various driving and terrain conditions and also should be able to record and save a history of the live data including voltage measurements.

My 95 ZJ is OBD1 which other than error codes provides no live data for most consumer OBD1/OBD2 scanners.

However I have an old Snap-On MT2500 with modules and adapters which allows me to get live data from most obd1 and pre-obd1 vehicle (such as Renix Jeep) Also works with OBD2 vehicles up to certain years depending on the module. One of the better investments I've made, cost for a used on is similar or even less than most obd1/obd2 scanners on the market.

Here's a video: 89 Cherokee Reading Sensor Data with a Snap On Scanner (MT2500)


Also for those more technically minded, found this snap-on pdf with about snap-on adapters and data parameters. https://www.snapon.com/display/3791/...Parameters.pdf