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post #1 of 16 Old 07-19-2014, 02:21 AM Thread Starter
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Question Alternator Question?

I used my air compressor VIAR 400P to pump up my neighbors small inflatable pool today. The compressor ran for about 5 minutes, the jeep was running the entire time and about five minutes afterwards. An hour or so later, I was going to drive my wife to work and the jeep would not turn over, the battery was dead. I had my neighbor give me a jump and let it idle for about 30 minutes.

After the idle period I attempted to drive to on-base auto repair shop. I have to go off base to get to it but it is only about four miles away. As I was driving the brake and ABS warning lights were going off. When I attempted to drive up a hill, the traction control light came on as well as the downhill assist and the jeep sounded like it was misfiring. I did not have any electrical components running only the engine. I only made it about a mile before I turned around and went back home.

My research shows that the JK stock alternator is a fairly good alternator. Should it be able to power the engine under these conditions or should I look at purchasing a new factory or aftermarket alternator?

I got a ride to the repair shop and had my old battery tested, it was bad so I replaced it. With most vehicles I have had in the past when I got a jump I could usually make it to a repair shop running on the alternator. Is this normal for a JK? Based on the symptoms what do you think?

BTW, I know I need to get a multimeter so I can post the readings which would probably be more helpful than just listing the symptoms. BTW, I am in Korea so dealing with the local repair shops can be a challenge.

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post #2 of 16 Old 07-19-2014, 06:09 AM
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I don't remember the threshold for volts, but if the battery falls below that threshold it will do all kind of strange things on a JK. The alternator has nothing to do with it unless it's bad also.

If I'm wrong, someone please correct me.

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post #3 of 16 Old 07-21-2014, 06:03 AM Thread Starter
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Thanks
I got the new battery installed after some work with the Dremel tool to make it fit, it is working fine now.

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post #4 of 16 Old 07-21-2014, 10:20 PM
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re: Alternator Question?

Quote:
Originally Posted by warcop View Post
Thanks
I got the new battery installed after some work with the Dremel tool to make it fit, it is working fine now.
Glad you got it back where it needs to be battery-wise; care if I inquire as-to precisely what you needed the old Dremel for to install a new battery? Just curious.....


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post #5 of 16 Old 07-21-2014, 10:43 PM
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A common misconception with vehicle charging systems is that once the battery is charged, the alternator runs the systems. That is incorrect. Back in the days of automotive generators, that was for the most part true. Which is why it was common to test a generator by disconnecting the positive cable from the battery while the vehicle was running. With the modern alternator equipped vehicles, they rely on the battery as the source of current and the alternator supplies current to recharge as needed. If the battery drops a plate or loses a cell, the vehicle typically acts weird because of the low voltage condition. A 12vdc battery has 6 cells, that are good for 2.10 volts per cell in a perfect state, so dropping a single cell will put you at around 10.5vdc which is near the threshold for most electronics designed for 9-18vdc. Which you experienced today with your JK. I know that most modern vehicles can run with the battery disconnected, but for the sake of the alternator and voltage regulator, I wouldn't do that more than once.

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post #6 of 16 Old 07-21-2014, 11:10 PM
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Quote:
Originally Posted by warcop View Post
I used my air compressor VIAR 400P to pump up my neighbors small inflatable pool today. The compressor ran for about 5 minutes, the jeep was running the entire time and about five minutes afterwards.
If your alternator is working properly, the compressor use should have nothing to do with it. Pure coincidence.

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Originally Posted by warcop View Post
My research shows that the JK stock alternator is a fairly good alternator. Should it be able to power the engine under these conditions or should I look at purchasing a new factory or aftermarket alternator?
If your alternator is working properly, it should be plenty of alternator. Most likely, you only had a battery issue. Did you test the alternator?

Quote:
Originally Posted by warcop View Post
With most vehicles I have had in the past when I got a jump I could usually make it to a repair shop running on the alternator. Is this normal for a JK? Based on the symptoms what do you think?
One possibility is an internal short in the battery. Sediment buildup on an older battery, or random piece of crap in a poorly made newer battery, can bridge across the plates and create a draw in addition to killing one of the cells. It could easily not be this, but that's one straw I'm grasping at . . .

Quote:
Originally Posted by warcop View Post
BTW, I know I need to get a multimeter so I can post the readings which would probably be more helpful than just listing the symptoms. BTW, I am in Korea so dealing with the local repair shops can be a charrenge.
What he said ^^^

Quote:
Originally Posted by warcop View Post
I got the new battery installed after some work with the Dremel tool to make it fit, it is working fine now.
Dremel modification required to install larger group size battery? Pleeze 'splain.
Quote:
Originally Posted by j3ff3ry_j33p View Post
Glad you got it back where it needs to be battery-wise; care if I inquire as-to precisely what you needed the old Dremel for to install a new battery? Just curious.....
What he said ^^^

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post #7 of 16 Old 07-21-2014, 11:33 PM
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Hey Wrench, do you know the charging threshold on our alternators? I.e., at what RPM they will produce enough current to overcome the demand of the system under normal conditions? I know that sometimes a battery drain condition can result from a high load situation such as winching (some programmers allow for an idle up function for this very purpose). I understand his compressor wouldn't be anywhere near the load of a winch, and I agree that this was probably a fluke coincidence. Just asking for information's sake.

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post #8 of 16 Old 07-21-2014, 11:38 PM
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I believe the ProCal sets the wiper stalk to a speed of 2000 RPM. The RPM range has some effect on the output. Obviously if the armature is moving too slow the output will naturally be limited, but past a certain speed the regulator is what determines charge value, not armature speed. Not to say that you are actually hitting maximum rated capacity at a lower RPM, alternators don't need to be spinning at high speed make their rated output.

I want to clarify - the whole point of an alternator with an internal regulator is to be able to charge at near rated capacity at idle speed, unlike generators. That is why most modern cars have them.

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post #9 of 16 Old 07-22-2014, 05:09 AM Thread Starter
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Quote:
Originally Posted by j3ff3ry_j33p View Post
Glad you got it back where it needs to be battery-wise; care if I inquire as-to precisely what you needed the old Dremel for to install a new battery? Just curious.....
The raised edges on the bottom of the battery (lower angled mounting edges) did not seat in the battery tray well. When I sat it in the tray it sat at an angle and did not fit in the grooves that secure it. This was the only battery that had that had at least 600 CCA. I had to dremel a bit off the raised plastic edges on two sides of the battery to make it fit in the tray using the factory brackets. It took a while because I shaved a little at a time as to keep the integrity of the lower part of the battery strong. I can post a couple of pics if you are interested. The battery I purchased was also the only name brand I have heard of out of the ones they had.

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post #10 of 16 Old 07-22-2014, 05:13 AM Thread Starter
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Quote:
Originally Posted by JKCTAZ View Post
A common misconception with vehicle charging systems is that once the battery is charged, the alternator runs the systems. That is incorrect. Back in the days of automotive generators, that was for the most part true. Which is why it was common to test a generator by disconnecting the positive cable from the battery while the vehicle was running. With the modern alternator equipped vehicles, they rely on the battery as the source of current and the alternator supplies current to recharge as needed. If the battery drops a plate or loses a cell, the vehicle typically acts weird because of the low voltage condition. A 12vdc battery has 6 cells, that are good for 2.10 volts per cell in a perfect state, so dropping a single cell will put you at around 10.5vdc which is near the threshold for most electronics designed for 9-18vdc. Which you experienced today with your JK. I know that most modern vehicles can run with the battery disconnected, but for the sake of the alternator and voltage regulator, I wouldn't do that more than once.
Thanks for your reply, this was a one time overseas emergency to get the Jeep going. The US repair shop is close but there are several hills between here and there and the Jeep could not take the hills with a weak battery.

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post #11 of 16 Old 07-22-2014, 05:18 AM Thread Starter
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Quote:
Originally Posted by ExWrench View Post
If your alternator is working properly, the compressor use should have nothing to do with it. Pure coincidence.


If your alternator is working properly, it should be plenty of alternator. Most likely, you only had a battery issue. Did you test the alternator?


One possibility is an internal short in the battery. Sediment buildup on an older battery, or random piece of crap in a poorly made newer battery, can bridge across the plates and create a draw in addition to killing one of the cells. It could easily not be this, but that's one straw I'm grasping at . . .

What he said ^^^


Dremel modification required to install larger group size battery? Pleeze 'splain.

What he said ^^^
Wrench,

Dremel modifications were to make the larger battery fit. I am sure the battery got weak/died due to harsh conditions. The JK doesn't get driven far. It gets driven maybe once or twice a week for less than a mile. We live in Seoul, I can walk or take the subway to get to most places much faster than I can drive there.

BTW, I also used a cut inner tube to pad it, but that is another story.

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post #12 of 16 Old 07-22-2014, 05:34 AM Thread Starter
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I think it was a combination of a 2 year old stock battery, sort trips and Korean weather conditions that assisted in the failure of the battery. When I installed the new battery, I wired the compressor to my SPOD so hopefully it will detect low voltage situations and prevent this from happening again.

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post #13 of 16 Old 07-22-2014, 05:31 PM
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Let me toss in two cents...
the 3.6 engine has a horrible alternator for some reason, in the past month, I have seen 6 different vehicles (1 was a wrangler) with generators failed.... I am not sure what is causing it, but all of them at 100% duty cycle of the system but only putting out 11 volts.... now the part numbers are different from vehicle to vehicle, but the result is still failed parts...
I SUSPECT it has to do with batteries failing and sending the system into 100% duty cycle for extended periods of time, but I could be wrong, im not an engineer, but I slept at a holiday inn once (well, I didn't really sleep... but that's another story)
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post #14 of 16 Old 07-25-2014, 10:01 PM
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Biggest alternator killer is a bad battery. Alternators are not designed to recharge a battery, That's what a generators job is.
Think of the battery/alternator in a car like the well pump/tank at your home(city water doesn't apply here). The tank(battery) supplies the juice while the pump(alternator) fills the tank. Lose all the water and you have to prime the pump, (use a battery charger)

Most alternator problems I see now relate to the one-way clutch used on most, Chrysler uses the shit out of them, VW lots too. Noisy, binding, free wheeling etc.

All it takes id one bump to short a battery or lose a cell, like a light bulb at home.... Worked last time you used it but flip switch and boom... out

Short trips and sitting absolutely kills vehicles. Think about a GOOD trickle charger to offset the parasitic losses in Jeep and battery... Yes Virginia batteries self discharge.

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post #15 of 16 Old 07-25-2014, 10:37 PM
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I charge mine between uses because my Jeep sits a lot. I am going on three + years with the OE battery and it still fires right up. That was what I was trying to explain, but I got a little too technical.

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post #16 of 16 Old 07-28-2014, 03:08 PM
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The JK alternator can run the electrical system without a battery however the electronics may not like the sudden power drops the system gets when high current draw items like the rad fan switch on. The battery is in there for starting the engine, provide power while the engine is off, as a buffer if current exceeds alternator output and as a capacitor to smooth out sudden drops. High underhood temperature on the JK is a big problem as it tends to shorten battery life. Another issue that seems to be a common battery killer on the JK is bad ground connections causing overcharged batteries.


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