sirhcman

Started the Jeep up tonight to go home from work and the battery charge light popped on. Got home and noticed the fog lamps were also not working with the Jeep running. Turned off the Jeep and turned the key to power only and the fog lamps worked. It sounded like there was an odd "whine" sound coming from the engine after starting up the Jeep. Did a little research but couldn't find a definitive answer of what the problem might be? Alternator going out, blown fuse, loose cable?

Battery is an Exide Orbital ORB75DT-108 (installed in April 2012)

Where should I start to troubleshoot this?

Thanks in advance!

gunbo75

Start the Jeep and Disconnect positive side of the battery cable if the Jeep keeps running the alternator is working if it dies the alternator is not charging

MSmitty

That is the funniest title I have ever seen.

Lorrel

I would never disconnect the cable while the vehicle is running, nor give advice to do this.
With newer vehicles the battery does more than just starts the vehicle. It also provides the impedance for the alternator and acts to prevent electrical spikes that the alternator could produce. Spiking the electronic components of the vehicle is not a good thing . It could also spike the diodes in the alternator resulting in shorted or open diodes.
To test an alternator simply use a voltmeter or multimeter. Place the meter in the DC mode and put the leads on the battery terminals. With the vehicle running the meter should read between 14 to 15 volts DC this indicates the alternator is working properly. To test the battery turn the vehicle off, and place the leads on the battery terminals. The meter should read between 12.5 to 12.75 volts DC.

ronjenx

↑ This is sound advice. More people should be made aware of it.
Things aren't like they used to be.

Other JK owners have said the JK will shut off when you disconnect the battery while it's running. It's probably for protection of the other systems.

Another point to consider. Whenever you want to disconnect the battery, always disconnect the negative terminal. It's safer than working on the positive when the negative is still connected.

Macman1138

Could be a lose belt, alternator going out or both. Sounds like you have a new battery, but I don't know if it is a good one.
When this one plays out, I strongly suggest you get a DieHard. Never a problem with them.

carolinajk

also remember your alternator could be putting out correct voltage but with not enough amps , if you have access to a clamp on ammeter clip it on the positive cable with the arrow pointing away from the alt , place a load on the system by turning on lights , blower etc and rev engine to 2k rpm if the amps arent at least 90 percent of rated then consider the alternator bad

ronjenx

Wouldn't you have to know, and add up, what each item draws?
Otherwise, you don't know how many amps to look for on the readout.

sirhcman

Guys thanks for all the help! I ran a multimeter on the battery (only pulling 12 volts) and while running it started around 13.96 and kept going down (to 13.5 volts). The alternator began to really make a "whine" noise so I got it up to my local shop today for them to check it out.

I'll report back with what they tell me

Thanks again!

Lorrel

I think it could be stated that if there is voltage present and a resistance to that voltage such as a load of some type and we have a complete path from and back to the source, than there is current flow. If this is not correct, Georg Simon Ohm got it wrong a long time ago.
The question should rather be, when talking about a vehicles alternator, just how much current is flowing, and is it enough to do the job.
How much current is flowing is a mathamaticle equation depending on the voltage present and the resistance in the circuit.
The alternator is rated by it's maxium output, and once that output is reached, it can produce nothing higer. If it is a 160 amp alternator, then it can only produce 160 amps and nothing more. But it is not designed to produce that output all the time. If it is asked to do so, it will burn out in a very short period.
By adding accessories we are adding more resistance to the circuit, and each of those components require a potential difference of the electromotive force or voltage to operate correctly. This means that while those components are in use, current is flowing. If we add to much resistance, the demand on the alternator could excede its capacity and current flow would be limited for each accessory, including re-charging the battery. The battery would then begin to output to try to maintain the demand. Once this happens the entire system would become so overtaxed, that the alternator could not produce enough power to re-charge the battery to its proper level of charge, and just like the batteries in a flashlight that is left on for long periods, would discharge. Once the battery discharges to below 12 VDC, it would no longer be capable of starting the vehicle when required.
Since the battery has only so many discharge cycles, once that number is reached it will no longer hold a charge, capable of it's entended purpase which is to start the vehicle.