alternator problem?

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This is a regular flooded battery.

My headlights are actually already on a relayed harness. That was one of the first upgrades I did when I bought it 5 years ago, since it is a common issue with Cherokees to have weak headlight wiring. I upgraded the ground cables as well when I did the cable upgrade. My main power, ground, and alternator cables are all upgraded.

Today I actually swapped out the 150A alternator for a used stock one from a local junkyard. The alternator turned out to be a Napa rebuild alternator from 2007 judging by the sticker on it. This seems to help a tad bit. I still get a big voltage drop with the high beams on at idle, or when the fan kicks on at idle, but it seems to be a little better than the other alternator.

I'm wondering if my battery just can't handle the load at idle, and maybe I need to get a deep cycle battery, which is what I had before (Optima).
 
That load tester, were you able to set it to 400 amps, 1/2 the CCA rating of the battery?

If the tester can be believed it is still a 800 CCA battery.

I wonder how much that radiator fan is pulling. If it is worn it might be really pulling more amperage.

My alternator is a reman too. It seems to be weak at low rpms as well, but I still have a mechanical fan.

True deep cycle 12v flooded batteries are a rare breed, and quite expensive, and would not be a good application for this 'issue' My group 31 USbattery only has 620CCA.

A marine battery would handle being cycled better than a starting battery, but will have lower CCA than a starting battery, as it is a compromise. While flooded marine batteries say deep cycle on them, a true deep cycle battery is built with much thicker plates and weighs more too.

If you want highest CCA, go for a rectangular AGM like Odyssey or Northstar. They also have 25% more capacity than an Optima, and have not yet cashed in on their reputation and sold out.

See how big of a battery you can shoehorn into the stock location. A group 31 northstar or Odyssey has 1150 CCA

I have a group 27 Northstar at 930CCA and 90 AH capacity, and it cranks my starter motor so fast it is impressive. Cranks it faster than two group 27 marine batteries in parallel could.
 
btw, the standard size battery is group 34 (for xj). some stores will sell you the smaller group 58?. I would verify you have the proper size battery
 
Originally Posted By: jeepman3071
Originally Posted By: wrcsixeight
If the low beams and the fans coming on drop the battery voltage to 12.0 volts nearly instantly, the battery is on its way out, or extremely undercharged.

If it is extremely undercharged, then it will be on its way out in short order.
Are these the radiator fans?
Do you know anybody with a DC clamp on ammeter?

What is the battery resting voltage in the morning before you start it?


The fan is the factory aux. radiator fan that clicks on when the coolant reaches a certain temperature. I wired it to a switch to demonstrate in the video.

One thing I have noticed is that the Jeep will turn over really slow after sitting over night. This is more apparent in the colder weather, but it has been happening for a couple months. If the engine has been running recently (like going into a store) it will crank right up fairly quickly.

I used my battery load tester to test the voltage.

This is what it reads after sitting over night, the Jeep is stone cold. It shows about 12.5 volts.

photo_1.jpg



This is with the load switch on the tester in the "on" position. The battery is testing borderline weak on the gauge. This is an 800 CCA battery. I have done this test after it has been run for a bit and the battery will test a little higher, but still closer to the weak range.

photo_2.jpg


This is the voltage reading after completing the load test.

photo_3.jpg



Charge via AC charger and retest.
 
The battery is the correct group 34 size. I'm not sure how many cranking amps the tester pulls, since it is just a simple on/off switch. I couldn't find any info on the labels.

What is the difference between the Sears Diehard Platinum, which is an Odyssey AGM battery, and the Sears Diehard Advanced Gold, which is also listed as being an AGM battery?
 
Die hard gold is a rebadged east penn/Deka intimidator.

http://www.dekabatteries.com/assets/base/1737.pdf



It has 775 CCA

The Odyssey group 34 has 850 CCA

A proper battery tester is configurable to set the CCA of the battery and sets the load for half that rating.
While it is the only real measurement of cranking power it is not the end all be all.


My 930 CCA Northstar battery cranks my engine faster than two marine batteries in parallel at 1440 CCA. Which surprised the heck out of me.

http://batteryuniversity.com/learn/article/how_to_measure_cca_cold_cranking_amp

Perhaps there is something to Odyssey's "pulse' crank amps figures
 
i had a 2003 jeep gc with the 4.0L, and i had the service manual for it so i know the following,
the alternator used does not have an internal voltage regulator, it is located within the engine pcm. why jeep decided to be different i don't know. the problem with this is voltage regulation (i.e. alternator output) is controlled by the amount of field current going to the rotor in the alternator.
in case you don't remember/know alternators, they all work by a spinning magnet (rotor) and that spinning magnetic field induces a current & voltage to the copper wiring surrounding it (stator). the stronger the magnetic field and/or the faster it spins, the more power the alternator can output. the magnet in the rotor is an electromagnetic, a piece of iron with copper wiring around it, so the way you increase the magnetic field is by putting more current around those rotor windings to increase the electromagnetic strength, which is known as [magnetic] field current [of the rotor]. because your problem is at idle... a fixed rpm then the speed part of the problem your stuck with... you have to look at increasing rotor magnetic field strength. OR.. with being stuck at a given rpm you can increase the size of everything however that doesn't work either because the alternator still has to fit on the engine... so you should never get your hopes up about a replacement "high-output" alternator if it's the same or nearly the same size and weight as your existing.

when you buy a high output alternator with the voltage regulator being within the alternator then all that stuff is taken care of and it works for the most part. because you put a high output alternator on your jeep and your voltage regulator is inside your pcm, that is going by oem programming and doesn't know to output more field current... hence you are most likely getting the same or nearly the same field current to your high output alternator at idle, and the same output. the more field current sent out by the voltage regulator, like with everything the hotter it gets. and the heat whether it's in the voltage regulator circuit or the rectifier circuit is what kills alternators. on a normal vehicle that has the voltage regulator internal to the alternator, you just replace the alternator not a big deal. be aware if you blow the regulator on your jeep, that's inside the pcm and expensive.
 
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Thanks for the info so far guys, it is helping me understand what is going on with this thing.

So I did some more testing today. My buddy also has a 2000 Jeep Cherokee, so it helps to have a vehicle to swap known good parts with.

We swapped his Optima Yellow top battery over to my Jeep and had the same voltage drop as I did with my Duralast battery. That tells me the problem is not the battery, and I'm thinking it isn't the alternator since I have used 3 different ones. Tomorrow night I will swap alternators with him since his is a known good factory one and test that.

I have a feeling it is the voltage regular in the PCM or the battery cables causing these issues.

When I first installed my beefier battery cables (which go to grounds, starter, and main fuse box), I took the Jeep for a test drive to the hardware store. When I came out from the store, it didn't want to start and acted dead with the first turn of the key. I then turned the key again and it slowly turned over and started. I went home and re-checked all my connections and everything was tight and clean. I haven't had it turn over anywhere near that slow since, but the cables could be the problem. They are significantly larger both in wire gauge and connector size, so I might not be making a perfect connection even though they are tight.
 
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I recently replaced that alternator with a "high output 150 amp" alternator from eBay. It is basically a stock alternator that has been rebuilt to put out 150A


like i said, because i know the high output alternator u got fits, it's gotta be the same size. Iron is iron so there is nothing special happening with the electromagnetic with the rotor... some one will probably read this in the high output alternator biz and start claiming that "their" high output alternator has some special iron or rare-earth magnetic in their rotor allowing for high output.... i digress,
the other problem is it's ebay, so don't get your hopes up,
the way they take any stock alternator and modify it to output 150A vs 120 or whatever the stock rated safe output was, is to put a different voltage regular IC chip in it to allow for max field current to be sent to the rotor based on the voltage regulator IC (integrated circuit). problem with this is heat, and while it will work for the first 5 minutes or so the alternator is used, if the extra heat is not accounted for then the alternator will fail sooner than later. also that increased 150 amp rating is dubious, alternator ratings are based on max output but they don't give alternator pulley rpm.
it's like comparing the torque of one engine vs the torque of another without measuring rpm. so that 150A rated output of your high amp alt. is at some speed, certainly much higher than idle rpm. the truth is no one rarely ever has a problem with stock alternators of 100 amp when they are spun fast enough, the real problem has always been at idle when the alternator is spinning slow.
 
Originally Posted By: 1 FMF
Quote:
I recently replaced that alternator with a "high output 150 amp" alternator from eBay. It is basically a stock alternator that has been rebuilt to put out 150A


like i said, because i know the high output alternator u got fits, it's gotta be the same size. Iron is iron so there is nothing special happening with the electromagnetic with the rotor... some one will probably read this in the high output alternator biz and start claiming that "their" high output alternator has some special iron or rare-earth magnetic in their rotor allowing for high output.... i digress,
the other problem is it's ebay, so don't get your hopes up,
the way they take any stock alternator and modify it to output 150A vs 120 or whatever the stock rated safe output was, is to put a different voltage regular IC chip in it to allow for max field current to be sent to the rotor based on the voltage regulator IC (integrated circuit). problem with this is heat, and while it will work for the first 5 minutes or so the alternator is used, if the extra heat is not accounted for then the alternator will fail sooner than later. also that increased 150 amp rating is dubious, alternator ratings are based on max output but they don't give alternator pulley rpm.
it's like comparing the torque of one engine vs the torque of another without measuring rpm. so that 150A rated output of your high amp alt. is at some speed, certainly much higher than idle rpm. the truth is no one rarely ever has a problem with stock alternators of 100 amp when they are spun fast enough, the real problem has always been at idle when the alternator is spinning slow.



That makes sense. I actually swapped back to a stock output alternator from a salvage yard a few posts up. So the high output 150A alternator is no longer part of the equation, and after tonight's test (noted in the post above) I'm thinking the battery isn't the problem either. I'm wondering if it is my battery cables or the PCM voltage regulator. I see that alternatorparts.com makes a special bypass kit for when the PCM regulator stops working.

http://store.alternatorparts.com/hd-external-voltage-regulator-conversion-field-replacement-kit.aspx

It seems like the way he is describing it that the alternator stops charging altogether. Mine still charges. At idle with no lights on I get 14.1 volts. If I apply a load such as the high beams or the electric fan, that is when the charging can't keep up.
 
saying get a smaller pulley is often easier said than done,
and then you may need to find a smaller serpentine belt so that fits which is also easier said than done,
and depending on the current size of the alternator pulley because they are not big to begin with going smaller may also cause the belt to slip or not spin the alternator under load. you need to measure the size of your existing pulley then do the math to see how much smaller you need to increase alternator rpm an adequate amount.

i would say that field replacement module in your link from alternator parts dot com is the way to go other than buying a new vehicle, it solves the problem i was describing of your VR being in your engine computer. with that aftermarket FRM which is an external voltage regulator, it can send more current to the alternator rotor at low rpm so the alternator maintains an output of 14 volts rather than dropping to 12v and below when all your electrical accessories are turned on. the one thing i would be worried about with this aftermarket FRM (voltage regulator) is not interfacing and fooling your engine computer and either causing your check engine light to always be on (best case) or frying your engine computer (worst case). the FRM is external and has a heat sink on it so that is unlikely to overheat, however what happens is it puts too much current to the alternator rotor and burns out the alternator.
 
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LOL i just looked further at the website. That FRM - field replacement module they call it, is nothing more than a power resistor. i wonder if they patented that.
all they are doing is putting a constant resistance in the field current wiring coming from the engine computer going to the alternator to fool the engine computer. rather than the computer seeing an alternator, it's seeing the constant resistance of the resistor. if your VR in your engine computer is good, then it would seem a simple resistance value will fool the computer and keep the check engine light off and not hurt the computer.

fyi- power resistor is nothing more than a resistor having a high power dissipation rating and they are in a metal case to dissipate heat, and you mount them on to a large metal surface so the heat is carried away. i have a bunch laying around ranging from 1-20 ohm and 10-40+ watts of power. their "FRM" is $20, you can buy power resistors for ~$5.
 
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It sounds like you're full fielding your alt. I wonder if your computer data stream will report this. In other words it's producing all it can. Remember an alt only makes around 40 amps at idle.

No different controllers will help with this. The mopar workaround is to use an old external voltage regulator, like from a dodge dart. As brilliantly as this will work, the computer will probably throw a code complaining that it's not in charge. (pardon the pun.)

You could try "hacking" the battery temperature sensor so it reports -25'F all the time, but that would just cause overcharging when you don't want it, and won't help with your full field issue.

You'd need a bigger crank pulley, smaller alt pulley, higher idle RPM, or a second alternator (used to be on RVs, cop cars and ambulances.)

Take a digital voltmeter and measure between the alt + post and other + posts, particularly in the fusebox, PCM power feeds etc and see if there's more than a coupel 1/10s volt difference. Same with grounds.

There's a "no mans land" with batteries where they're neither charging nor discharging, approx 14.1 volts down to 12.4 or so. If you start using just a couple more amps than the alt can produce the system voltage will drop quickly until the battery starts discharging to supply this. You're seeing this.
 
You can't get more output from an alternator by changing the way the regulator works. The MOST that the regulator can do is "full field" the alternator, ie apply full battery voltage to the alternator rotor. The nameplate amperage rating of the alternator ASSUMES full-field.

In the case of your Jeep, the regulator is built into the PCM, but you can bypass it and install a standard Chrysler stand-alone regulator from the 1970s/80s era if it fails. One other thing that can go wrong with the factory regulation setup in your XJ is the battery temperature sensor (located in the bottom of the battery tray) can fail, or its wire connections can corrode. That makes the regulator assume that the battery is either fully warmed up or fully cold, and will skew the charge voltage accordingly. The stand-alone regulators have an ambient temp sensor inside the regulator, so if you can mount it near the battery that's the best option.

The last thing on earth you would ever want is an internally-regulated "One-Wire" alternator. Those things are a kludge intended for hot-rod applications where minimal wiring is wanted. They have circuitry to shut down the field current when the alternator stops turning (ie when you turn the engine off), and about half the time it doesn't work and they drain the battery. The other half the time, they refuse to turn back on and start charging until you practically redline the engine. No manufacturer actually uses a "one-wire" alternator from the factory. GM and others used to put the regulator inside the case on some alternators, but they still had an ignition-switched signal wire to insure that the alternator field/regulator circuit would turn off and on correctly.
 
Originally Posted By: Donald
Less un-necessary accessories.


While normally I would agree that my accessories are to blame, this voltage drop happens when I have just the low beams on, and the factory electric aux. fan clicks on. The high beams + off road lights show the same symptoms, but my main concern is just with the low beams and electric fan. Those should both be able to be on with no problems, as they have been in the past.
 
Originally Posted By: 440Magnum
You can't get more output from an alternator by changing the way the regulator works. The MOST that the regulator can do is "full field" the alternator, ie apply full battery voltage to the alternator rotor. The nameplate amperage rating of the alternator ASSUMES full-field.

In the case of your Jeep, the regulator is built into the PCM, but you can bypass it and install a standard Chrysler stand-alone regulator from the 1970s/80s era if it fails. One other thing that can go wrong with the factory regulation setup in your XJ is the battery temperature sensor (located in the bottom of the battery tray) can fail, or its wire connections can corrode. That makes the regulator assume that the battery is either fully warmed up or fully cold, and will skew the charge voltage accordingly. The stand-alone regulators have an ambient temp sensor inside the regulator, so if you can mount it near the battery that's the best option.

The last thing on earth you would ever want is an internally-regulated "One-Wire" alternator. Those things are a kludge intended for hot-rod applications where minimal wiring is wanted. They have circuitry to shut down the field current when the alternator stops turning (ie when you turn the engine off), and about half the time it doesn't work and they drain the battery. The other half the time, they refuse to turn back on and start charging until you practically redline the engine. No manufacturer actually uses a "one-wire" alternator from the factory. GM and others used to put the regulator inside the case on some alternators, but they still had an ignition-switched signal wire to insure that the alternator field/regulator circuit would turn off and on correctly.



So does it sound like my regulator in the PCM is working correctly? I'm thinking about buying one of those larger case alternators that produces more power at idle. I believe Powermaster makes one, but I don't want to grind down the alt bracket and timing cover if that isn't the problem.
 
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